libsel4utils/src/elf.c - 3p/sel4/sel4_libs - Git at Google

 /*
  * Copyright 2017, Data61
  * Commonwealth Scientific and Industrial Research Organisation (CSIRO)
  * ABN 41 687 119 230.
  *
  * This software may be distributed and modified according to the terms of
  * the BSD 2-Clause license. Note that NO WARRANTY is provided.
  * See "LICENSE_BSD2.txt" for details.
  *
  * @TAG(DATA61_BSD)
  */
 #include <autoconf.h>

 #include <string.h>
 #include <sel4/sel4.h>
 #include <elf/elf.h>
 #include <cpio/cpio.h>
 #include <vka/capops.h>
 #include <sel4utils/thread.h>
 #include <sel4utils/util.h>
 #include <sel4utils/mapping.h>
 #include <sel4utils/elf.h>

 /* This library works with our cpio set up in the build system */
 extern char _cpio_archive[];

 /*
  * Convert ELF permissions into seL4 permissions.
  *
  * @param permissions elf permissions
  * @return seL4 permissions
  */
 static inline seL4_CapRights_t
 rights_from_elf(unsigned long permissions)
 {
     bool canRead = permissions & PF_R || permissions & PF_X;
     bool canWrite = permissions & PF_W;

     return seL4_CapRights_new(false, canRead, canWrite);
 }

 static int
 load_segment(vspace_t *loadee_vspace, vspace_t *loader_vspace,
              vka_t *loadee_vka, vka_t *loader_vka,
              char *src, size_t file_size, int num_regions,
              sel4utils_elf_region_t regions[num_regions], int region_index)
 {
     int error = seL4_NoError;
     sel4utils_elf_region_t region = regions[region_index];
     size_t segment_size = region.size;
     uintptr_t dst = (uintptr_t) region.elf_vstart;
     if (file_size > segment_size) {
         ZF_LOGE("Error, file_size %zu > segment_size %zu", file_size, segment_size);
         return seL4_InvalidArgument;
     }

     /* create a slot to map a page into the loader address space */
     seL4_CPtr loader_slot;
     cspacepath_t loader_frame_cap;

     error = vka_cspace_alloc(loader_vka, &loader_slot);
     if (error) {
         ZF_LOGE("Failed to allocate cslot by loader vka: %d", error);
         return error;
     }
     vka_cspace_make_path(loader_vka, loader_slot, &loader_frame_cap);

     /* We work a page at a time */
     unsigned int pos = 0;
     while (pos < segment_size && error == seL4_NoError) {
         void *loader_vaddr = 0;
         void *loadee_vaddr = (void *) ((seL4_Word)ROUND_DOWN(dst, PAGE_SIZE_4K));

         /* Find the reservation that this frame belongs to.
          * The reservation may belong to an adjacent region */
         reservation_t reservation;
         if (loadee_vaddr < region.reservation_vstart) {
             //  Have to use reservation from adjacent region
             if ((region_index - 1) < 0) {
                 ZF_LOGE("Invalid regions: bad elf file.");
                 return 1;
             }
             reservation = regions[region_index-1].reservation;
         } else if (loadee_vaddr + (MIN(segment_size - pos, PAGE_SIZE_4K)) >
             (region.reservation_vstart + region.reservation_size)) {
             if ((region_index + 1) >= num_regions) {
                 ZF_LOGE("Invalid regions: bad elf file.");
                 return 1;
             }
             reservation = regions[region_index+1].reservation;
         } else {
             reservation = region.reservation;
         }

         /* We need to check if the frame has already been mapped by another region.
          * Currently this check is done on every frame because it is assumed to be cheap. */
         seL4_CPtr cap = vspace_get_cap(loadee_vspace, loadee_vaddr);
         if (cap == seL4_CapNull) {
             error = vspace_new_pages_at_vaddr(loadee_vspace, loadee_vaddr, 1, seL4_PageBits, reservation);
         }

         if (error != seL4_NoError) {
             ZF_LOGE("ERROR: failed to allocate frame by loadee vka: %d", error);
             continue;
         }

         /* copy the frame cap to map into the loader address space */
         cspacepath_t loadee_frame_cap;

         vka_cspace_make_path(loadee_vka, vspace_get_cap(loadee_vspace, loadee_vaddr),
                              &loadee_frame_cap);
         error = vka_cnode_copy(&loader_frame_cap, &loadee_frame_cap, seL4_AllRights);
         if (error != seL4_NoError) {
             ZF_LOGE("ERROR: failed to copy frame cap into loader cspace: %d", error);
             continue;
         }

         /* map the frame into the loader address space */
         loader_vaddr = vspace_map_pages(loader_vspace, &loader_frame_cap.capPtr, NULL, seL4_AllRights,
                                         1, seL4_PageBits, 1);
         if (loader_vaddr == NULL) {
             ZF_LOGE("failed to map frame into loader vspace.");
             error = -1;
             continue;
         }

         /* finally copy the data */
         int nbytes = PAGE_SIZE_4K - (dst & PAGE_MASK_4K);
         if (pos < file_size) {
             memcpy(loader_vaddr + (dst % PAGE_SIZE_4K), (void*)src, MIN(nbytes, file_size - pos));
         }
         /* Note that we don't need to explicitly zero frames as seL4 gives us zero'd frames */

 #ifdef CONFIG_ARCH_ARM
         /* Flush the caches */
         seL4_ARM_Page_Unify_Instruction(loader_frame_cap.capPtr, 0, PAGE_SIZE_4K);
         seL4_ARM_Page_Unify_Instruction(loadee_frame_cap.capPtr, 0, PAGE_SIZE_4K);
 #endif /* CONFIG_ARCH_ARM */

         /* now unmap the page in the loader address space */
         vspace_unmap_pages(loader_vspace, (void *) loader_vaddr, 1, seL4_PageBits, VSPACE_PRESERVE);
         vka_cnode_delete(&loader_frame_cap);

         pos += nbytes;
         dst += nbytes;
         src += nbytes;
     }

     /* clear the cslot */
     vka_cspace_free(loader_vka, loader_frame_cap.capPtr);

     return error;
 }

 /**
  * Load an array of regions into a vspace.
  *
  * The region array passed in won't be mutated by this function or functions it calls.
  * State in the vspaces and vkas will be mutated to track resources used.
  * If this function fails, any allocated and mapped frames will not be freed.
  *
  * @param loadee_vspace target vspace to map frames into.
  * @param loader_vspace vspace of the caller.  Frames are temporarily mapped into this to init with
  *                      elf data from elf file.
  * @param loadee_vka target vka
  * @param loader_vka caller vka
  * @param elf_file pointer to elf object
  * @param num_regions total number of segments/regions to load.
  * @param regions region array containing segment info.
  *
  * @return 0 on success.
  */
 static int
 load_segments(vspace_t *loadee_vspace, vspace_t *loader_vspace,
              vka_t *loadee_vka, vka_t *loader_vka, char *elf_file,
              int num_regions, sel4utils_elf_region_t regions[num_regions]) {
     for (int i = 0; i < num_regions; i++) {
         int segment_index = regions[i].segment_index;
         char *source_addr = elf_file + elf_getProgramHeaderOffset(elf_file, segment_index);
         size_t file_size = elf_getProgramHeaderFileSize(elf_file, segment_index);

         int error = load_segment(loadee_vspace, loader_vspace, loadee_vka, loader_vka,
             source_addr, file_size, num_regions, regions, i);
         if (error) {
             return error;
         }
     }
     return 0;
 }

 static bool is_loadable_section(char* elf_file, int index) {
     return elf_getProgramHeaderType(elf_file, index) == PT_LOAD;
 }

 static int
 count_loadable_regions(char* elf_file) {
     int num_headers = elf_getNumProgramHeaders(elf_file);
     int loadable_headers = 0;

     for (int i = 0; i < num_headers; i++) {
         /* Skip non-loadable segments (such as debugging data). */
         if (is_loadable_section(elf_file, i)) {
             loadable_headers++;
         }
     }
     return loadable_headers;
 }

 int
 sel4utils_elf_num_regions(const char *image_name)
 {
     unsigned long elf_size;
     assert(image_name);
     char *elf_file = cpio_get_file(_cpio_archive, image_name, &elf_size);
     if (elf_file == NULL) {
         ZF_LOGE("ERROR: failed to load elf file %s", image_name);
         return 0;
     }
     return count_loadable_regions(elf_file);
 }

 /**
  * Create reservations for regions in a target vspace.
  *
  * The region position and size fields should have already been calculated by prepare_reservations.
  *
  * @param loadee the vspace to load into.
  * @param total_regions the size of the regions array
  * @param regions the array of regions.
  * @param anywhere some legacy parameter that throws away the vspace address.  It is supposedly to support
                    loading a segment for inspection rather than execution.
  *
  * @return 0 on success.
  */
 static int
 create_reservations(vspace_t *loadee, size_t total_regions, sel4utils_elf_region_t regions[total_regions], int anywhere) {
     for (int i = 0; i < total_regions; i++) {
         if (regions[i].reservation_size == 0) {
             ZF_LOGD("Empty reservation detected. This should indicate that this segments"
                 "data is entirely stored in other section reservations.");
             continue;
         }
         if (anywhere) {
             regions[i].reservation = vspace_reserve_range(loadee, regions[i].reservation_size,
                 regions[i].rights, regions[i].cacheable, (void**)&regions[i].reservation_vstart);
         } else {
             regions[i].reservation = vspace_reserve_range_at(loadee,
                                                           regions[i].reservation_vstart,
                                                           regions[i].reservation_size,
                                                           regions[i].rights,
                                                           regions[i].cacheable);
         }
         if (regions[i].reservation.res == NULL) {
             ZF_LOGE("Failed to make reservation: %p, %zd", regions[i].reservation_vstart, regions[i].reservation_size);
             return -1;
         }
     }
     return 0;

 }

 /**
  * Function for deciding whether a frame needs to be moved to a different reservation.
  *
  * Mapping permissions are set for a whole reservation.  With adjacent segments of different
  * permissions, we need to give the shared frame mapping to the reservation with the more permissive
  * permissions.  Currently this assumes that every region will have read permissions, and the frame
  * only needs to be moved if the lower region doesn't have write permissions and the upper one does.
  *
  * @param a CapRights for reservation a.
  * @param b CapRights for reservation b.
  * @param result whether the frame should be moved.
  *
  * @return 0 on success.
  */
 static int
 cap_writes_check_move_frame(seL4_CapRights_t a, seL4_CapRights_t b, bool *result) {
     if (!seL4_CapRights_get_capAllowRead(a) || !seL4_CapRights_get_capAllowRead(b)) {
         ZF_LOGE("Regions do not have read rights.");
         return -1;
     }
     if (!seL4_CapRights_get_capAllowWrite(a) && seL4_CapRights_get_capAllowWrite(b)) {
         *result = true;
         return 0;
     }
     *result = false;
     return 0;
 }

 /**
  * Prepares a list of regions to have reservations reserved by a vspace.
  *
  * Iterates through a region array in ascending order.
  * For each region it tries to place a reservation that contains the segment.
  * Reservations are rounded up to 4k alignments.  This means that the previous reservation
  * may overlap with the start of the current region.  When this occurs, the last frame of the
  * previous reservation may need to be moved to the current reservation.  This is decided based
  * on the reservation permissions by the cap_writes_check_move_frame function.
  * If the frame doesn't need to be moved, then this reservation starts from the first unreserved
  * frame of the segment.  When the segment is eventually loaded, the frames may need to be mapped
  * from from other segment's reservations.
  *
  * @param total_regions total number of regions in array.
  * @param regions array of regions sorted in ascending order.
  *
  * @return 0 on success.
  */
 static int
 prepare_reservations(size_t total_regions, sel4utils_elf_region_t regions[total_regions]) {
     uintptr_t prev_res_start = 0;
     size_t prev_res_size = 0;
     seL4_CapRights_t prev_rights = seL4_CapRights_new(0,0,0);
     for (int i = 0; i < total_regions; i++) {
         uintptr_t current_res_start = PAGE_ALIGN_4K((uintptr_t)regions[i].elf_vstart);
         uintptr_t current_res_top = ROUND_UP((uintptr_t)regions[i].elf_vstart + regions[i].size, PAGE_SIZE_4K);
         size_t current_res_size = current_res_top - current_res_start;
         assert(current_res_size % PAGE_SIZE_4K == 0);
         seL4_CapRights_t current_rights = regions[i].rights;

         if ((prev_res_start + prev_res_size) > current_res_start) {
             /* This segment shares a frame with the previous segment */
             bool should_move;
             int error = cap_writes_check_move_frame(prev_rights, current_rights, &should_move);
             if (error) {
                 /* Comparator function failed. Return error. */
                 return -1;
             }
             if (should_move) {
                 /* Frame needs to be moved from the last reservation into this one */
                 ZF_LOGF_IF(i == 0, "Should not need to adjust first element in list");
                 ZF_LOGF_IF(regions[i-1].reservation_size < PAGE_SIZE_4K, "Invalid previous region");
                 regions[i-1].reservation_size -= PAGE_SIZE_4K;
             } else {
                 /* Frame stays in previous reservation and we update our reservation start address and size */
                 current_res_start = ROUND_UP((prev_res_start + prev_res_size) + 1, PAGE_SIZE_4K);
                 current_res_size = current_res_top - current_res_start;
                 ZF_LOGF_IF(ROUND_UP(regions[i].size, PAGE_SIZE_4K) - current_res_size == PAGE_SIZE_4K,
                     "Regions shouldn't overlap by more than a single 4k frame");
             }
         }
         /* Record this reservation layout */
         regions[i].reservation_size = current_res_size;
         regions[i].reservation_vstart = (void *)current_res_start;
         prev_res_size = current_res_size;
         prev_res_start = current_res_start;
         prev_rights = current_rights;
     }
     return 0;
 }

 /**
  * Reads segment data out of elf file and creates region list.
  *
  * The region array must have the correct size as calculated by count_loadable_regions.
  *
  * @param elf_file pointer to start of elf_file
  * @param total_regions total number of loadable segments.
  * @param regions array of regions.
  *
  * @return 0 on success.
  */
 static int
 read_regions(char* elf_file, size_t total_regions, sel4utils_elf_region_t regions[total_regions]) {
     int num_headers = elf_getNumProgramHeaders(elf_file);
     int region_id = 0;
     for (int i = 0; i < num_headers; i++) {

         /* Skip non-loadable segments (such as debugging data). */
         if (is_loadable_section(elf_file, i)) {
             sel4utils_elf_region_t *region = &regions[region_id];
             /* Fetch information about this segment. */

             region->cacheable = 1;
             region->rights = rights_from_elf(elf_getProgramHeaderFlags(elf_file, i));
             // elf_getProgramHeaderMemorySize should just return `uintptr_t`
             region->elf_vstart = (void*)(uintptr_t)elf_getProgramHeaderVaddr(elf_file, i);
             region->size = elf_getProgramHeaderMemorySize(elf_file, i);
             region->segment_index = i;
             region_id++;
         }
     }
     if (region_id != total_regions) {
         ZF_LOGE("Did not correctly read all regions.");
         return 1;
     }

     return 0;
 }

 /**
  * Compare function for ordering regions. Passed to sglib quick sort.
  *
  * Sort is based on base address.  This assumes segments do not overlap.
  * There is likely a chance that quick sort won't terminate if segments overlap.
  *
  * @param a region a
  * @param b region b
  *
  * @return 1 for a > b, -1 for b > a
  */
 static int
 compare_regions(sel4utils_elf_region_t a, sel4utils_elf_region_t b) {
     if (a.elf_vstart + a.size <= b.elf_vstart) {
         return -1;
     } else if (b.elf_vstart + b.size <= a.elf_vstart) {
         return 1;
     } else {
         ZF_LOGF("Bad elf file: segments overlap");
         return 0;
     }
 }

 /**
  * Parse an elf file and create reservations in a target vspace for all loadable segments.
  *
  * Reads segment layout data out of elf file and stores in elf_region array.
  * Then sorts the array, then plans reservations based on segment layout.
  * Finally creates reservations in vspace.
  *
  * @param loadee vspace to create reservations in.
  * @param elf_file pointer to elf file.
  * @param num_regions number of regions in array as calculated by count_loadable_regions.
  * @param regions region array.
  * @param mapanywhere throw away vspace positioning if set to 1.
  *
  * @return 0 on success.
  */
 static int
 elf_reserve_regions_in_vspace(vspace_t *loadee, char* elf_file,
     int num_regions, sel4utils_elf_region_t regions[num_regions], int mapanywhere) {
     int error = read_regions(elf_file, num_regions, regions);
     if (error) {
         ZF_LOGE("Failed to read regions");
         return error;
     }

     /* Sort region list */
     SGLIB_ARRAY_SINGLE_QUICK_SORT(sel4utils_elf_region_t, regions, num_regions, compare_regions);

     error = prepare_reservations(num_regions, regions);
     if (error) {
         ZF_LOGE("Failed to prepare reservations");
         return error;
     }
     error = create_reservations(loadee, num_regions, regions, mapanywhere);
     if (error) {
         ZF_LOGE("Failed to create reservations");
         return error;
     }
     return 0;
 }

 static void *
 entry_point(char *elf_file) {
     uint64_t entry_point = elf_getEntryPoint(elf_file);
     if ((uint32_t) (entry_point >> 32) != 0) {
         ZF_LOGE("ERROR: this code hasn't been tested for 64bit!");
         return NULL;
     }
     assert(entry_point != 0);
     return (void*)(seL4_Word)entry_point;

 }


 void *
 sel4utils_elf_reserve(vspace_t *loadee, const char *image_name, sel4utils_elf_region_t *regions)
 {
     unsigned long elf_size;
     char *elf_file = cpio_get_file(_cpio_archive, image_name, &elf_size);
     if (elf_file == NULL) {
         ZF_LOGE("ERROR: failed to load elf file %s", image_name);
         return NULL;
     }

     /* Count number of loadable segments */
     int num_regions = count_loadable_regions(elf_file);

     /* Create reservations in vspace using internal functions */
     int error = elf_reserve_regions_in_vspace(loadee, elf_file, num_regions, regions, 0);
     if (error) {
         ZF_LOGE("Failed to reserve regions");
         return NULL;
     }

     /* Return entry point */
     return entry_point(elf_file);
 }

 void *
 sel4utils_elf_load_record_regions(vspace_t *loadee, vspace_t *loader, vka_t *loadee_vka, vka_t *loader_vka, const char *image_name, sel4utils_elf_region_t *regions, int mapanywhere)
 {
     unsigned long elf_size;
     char *elf_file = cpio_get_file(_cpio_archive, image_name, &elf_size);
     if (elf_file == NULL) {
         ZF_LOGE("ERROR: failed to load elf file %s", image_name);
         return NULL;
     }

     /* Calculate number of loadable regions.  Use stack array if one wasn't passed in */
     int num_regions = count_loadable_regions(elf_file);
     bool clear_at_end = false;
     sel4utils_elf_region_t stack_regions[num_regions];
     if (regions == NULL) {
         regions = stack_regions;
         clear_at_end = true;
     }

     /* Create reservations */
     int error = elf_reserve_regions_in_vspace(loadee, elf_file, num_regions, regions, mapanywhere);
     if (error) {
         ZF_LOGE("Failed to reserve regions");
         return NULL;
     }

     /* Load Map reservations and load in elf data */
     error = load_segments(loadee, loader, loadee_vka, loader_vka, elf_file, num_regions, regions);
     if (error) {
         ZF_LOGE("Failed to load segments");
         return NULL;
     }

     /* Clean up reservations if we allocated our own array */
     if (clear_at_end) {
         for (int i = 0; i < num_regions; i++) {
             if (regions[i].reservation_size > 0) {
                 vspace_free_reservation(loadee, regions[i].reservation);
             }
         }
     }

     /* Return entry point */
     return entry_point(elf_file);
 }

 uintptr_t sel4utils_elf_get_vsyscall(const char *image_name)
 {
     uintptr_t* addr = (uintptr_t*)sel4utils_elf_get_section(image_name, "__vsyscall", NULL);
     /* Hope everything is good and just dereference it */
     return *addr;
 }

 uintptr_t sel4utils_elf_get_section(const char *image_name, const char *section_name, uint64_t* section_size)
 {
     unsigned long elf_size;
     char *elf_file = cpio_get_file(_cpio_archive, image_name, &elf_size);
     if (elf_file == NULL) {
         ZF_LOGE("ERROR: failed to lookup elf file %s", image_name);
         return 0;
     }
     /* See if we can find the section */
     int section_id;
     void *addr = elf_getSectionNamed(elf_file, section_name, &section_id);
     if (addr) {
         if (section_size != NULL) {
             *section_size = elf_getSectionSize(elf_file, section_id);
         }
         return (uintptr_t) addr;
     } else {
         return 0;
     }
 }

 void *
 sel4utils_elf_load(vspace_t *loadee, vspace_t *loader, vka_t *loadee_vka, vka_t *loader_vka, const char *image_name)
 {
     return sel4utils_elf_load_record_regions(loadee, loader, loadee_vka, loader_vka, image_name, NULL, 0);
 }

 uint32_t
 sel4utils_elf_num_phdrs(const char *image_name)
 {
     unsigned long elf_size;
     char *elf_file = cpio_get_file(_cpio_archive, image_name, &elf_size);
     return elf_getNumProgramHeaders(elf_file);
 }

 void
 sel4utils_elf_read_phdrs(const char *image_name, uint32_t max_phdrs, Elf_Phdr *phdrs)
 {
     unsigned long elf_size;
     char *elf_file = cpio_get_file(_cpio_archive, image_name, &elf_size);
     uint32_t num_phdrs = elf_getNumProgramHeaders(elf_file);
     for (uint32_t i = 0; i < num_phdrs && i < max_phdrs; i++) {
         /* cannot take addresses directly from the final struct as the types might
          * be different, so store into locals first */
         uint64_t p_vaddr, p_paddr, p_filesz, p_offset, p_memsz;
         elf_getProgramHeaderInfo(elf_file, i, &p_vaddr, &p_paddr, &p_filesz, &p_offset, &p_memsz);
         phdrs[i] = (Elf_Phdr) {
             .p_type = elf_getProgramHeaderType(elf_file, i),
             .p_offset = p_offset,
             .p_vaddr = p_vaddr,
             .p_paddr = p_paddr,
             .p_filesz = p_filesz,
             .p_memsz = p_memsz,
             .p_flags = elf_getProgramHeaderFlags(elf_file,i),
             .p_align = elf_getProgramHeaderAlign(elf_file, i)
         };
     }
 }
	/*
	* Copyright 2017, Data61
	* Commonwealth Scientific and Industrial Research Organisation (CSIRO)
	* ABN 41 687 119 230.
	*
	* This software may be distributed and modified according to the terms of
	* the BSD 2-Clause license. Note that NO WARRANTY is provided.
	* See "LICENSE_BSD2.txt" for details.
	*
	* @TAG(DATA61_BSD)
	*/
	#include <autoconf.h>

	#include <string.h>
	#include <sel4/sel4.h>
	#include <elf/elf.h>
	#include <cpio/cpio.h>
	#include <vka/capops.h>
	#include <sel4utils/thread.h>
	#include <sel4utils/util.h>
	#include <sel4utils/mapping.h>
	#include <sel4utils/elf.h>

	/* This library works with our cpio set up in the build system */
	extern char _cpio_archive[];

	/*
	* Convert ELF permissions into seL4 permissions.
	*
	* @param permissions elf permissions
	* @return seL4 permissions
	*/
	static inline seL4_CapRights_t
	rights_from_elf(unsigned long permissions)
	{
	bool canRead = permissions & PF_R \|\| permissions & PF_X;
	bool canWrite = permissions & PF_W;

	return seL4_CapRights_new(false, canRead, canWrite);
	}

	static int
	load_segment(vspace_t loadee_vspace, vspace_t loader_vspace,
	vka_t loadee_vka, vka_t loader_vka,
	char *src, size_t file_size, int num_regions,
	sel4utils_elf_region_t regions[num_regions], int region_index)
	{
	int error = seL4_NoError;
	sel4utils_elf_region_t region = regions[region_index];
	size_t segment_size = region.size;
	uintptr_t dst = (uintptr_t) region.elf_vstart;
	if (file_size > segment_size) {
	ZF_LOGE("Error, file_size %zu > segment_size %zu", file_size, segment_size);
	return seL4_InvalidArgument;
	}

	/* create a slot to map a page into the loader address space */
	seL4_CPtr loader_slot;
	cspacepath_t loader_frame_cap;

	error = vka_cspace_alloc(loader_vka, &loader_slot);
	if (error) {
	ZF_LOGE("Failed to allocate cslot by loader vka: %d", error);
	return error;
	}
	vka_cspace_make_path(loader_vka, loader_slot, &loader_frame_cap);

	/* We work a page at a time */
	unsigned int pos = 0;
	while (pos < segment_size && error == seL4_NoError) {
	void *loader_vaddr = 0;
	void loadee_vaddr = (void ) ((seL4_Word)ROUND_DOWN(dst, PAGE_SIZE_4K));

	/* Find the reservation that this frame belongs to.
	* The reservation may belong to an adjacent region */
	reservation_t reservation;
	if (loadee_vaddr < region.reservation_vstart) {
	// Have to use reservation from adjacent region
	if ((region_index - 1) < 0) {
	ZF_LOGE("Invalid regions: bad elf file.");
	return 1;
	}
	reservation = regions[region_index-1].reservation;
	} else if (loadee_vaddr + (MIN(segment_size - pos, PAGE_SIZE_4K)) >
	(region.reservation_vstart + region.reservation_size)) {
	if ((region_index + 1) >= num_regions) {
	ZF_LOGE("Invalid regions: bad elf file.");
	return 1;
	}
	reservation = regions[region_index+1].reservation;
	} else {
	reservation = region.reservation;
	}

	/* We need to check if the frame has already been mapped by another region.
	* Currently this check is done on every frame because it is assumed to be cheap. */
	seL4_CPtr cap = vspace_get_cap(loadee_vspace, loadee_vaddr);
	if (cap == seL4_CapNull) {
	error = vspace_new_pages_at_vaddr(loadee_vspace, loadee_vaddr, 1, seL4_PageBits, reservation);
	}

	if (error != seL4_NoError) {
	ZF_LOGE("ERROR: failed to allocate frame by loadee vka: %d", error);
	continue;
	}

	/* copy the frame cap to map into the loader address space */
	cspacepath_t loadee_frame_cap;

	vka_cspace_make_path(loadee_vka, vspace_get_cap(loadee_vspace, loadee_vaddr),
	&loadee_frame_cap);
	error = vka_cnode_copy(&loader_frame_cap, &loadee_frame_cap, seL4_AllRights);
	if (error != seL4_NoError) {
	ZF_LOGE("ERROR: failed to copy frame cap into loader cspace: %d", error);
	continue;
	}

	/* map the frame into the loader address space */
	loader_vaddr = vspace_map_pages(loader_vspace, &loader_frame_cap.capPtr, NULL, seL4_AllRights,
	1, seL4_PageBits, 1);
	if (loader_vaddr == NULL) {
	ZF_LOGE("failed to map frame into loader vspace.");
	error = -1;
	continue;
	}

	/* finally copy the data */
	int nbytes = PAGE_SIZE_4K - (dst & PAGE_MASK_4K);
	if (pos < file_size) {
	memcpy(loader_vaddr + (dst % PAGE_SIZE_4K), (void*)src, MIN(nbytes, file_size - pos));
	}
	/* Note that we don't need to explicitly zero frames as seL4 gives us zero'd frames */

	#ifdef CONFIG_ARCH_ARM
	/* Flush the caches */
	seL4_ARM_Page_Unify_Instruction(loader_frame_cap.capPtr, 0, PAGE_SIZE_4K);
	seL4_ARM_Page_Unify_Instruction(loadee_frame_cap.capPtr, 0, PAGE_SIZE_4K);
	#endif /* CONFIG_ARCH_ARM */

	/* now unmap the page in the loader address space */
	vspace_unmap_pages(loader_vspace, (void *) loader_vaddr, 1, seL4_PageBits, VSPACE_PRESERVE);
	vka_cnode_delete(&loader_frame_cap);

	pos += nbytes;
	dst += nbytes;
	src += nbytes;
	}

	/* clear the cslot */
	vka_cspace_free(loader_vka, loader_frame_cap.capPtr);

	return error;
	}

	/**
	* Load an array of regions into a vspace.
	*
	* The region array passed in won't be mutated by this function or functions it calls.
	* State in the vspaces and vkas will be mutated to track resources used.
	* If this function fails, any allocated and mapped frames will not be freed.
	*
	* @param loadee_vspace target vspace to map frames into.
	* @param loader_vspace vspace of the caller. Frames are temporarily mapped into this to init with
	* elf data from elf file.
	* @param loadee_vka target vka
	* @param loader_vka caller vka
	* @param elf_file pointer to elf object
	* @param num_regions total number of segments/regions to load.
	* @param regions region array containing segment info.
	*
	* @return 0 on success.
	*/
	static int
	load_segments(vspace_t loadee_vspace, vspace_t loader_vspace,
	vka_t loadee_vka, vka_t loader_vka, char *elf_file,
	int num_regions, sel4utils_elf_region_t regions[num_regions]) {
	for (int i = 0; i < num_regions; i++) {
	int segment_index = regions[i].segment_index;
	char *source_addr = elf_file + elf_getProgramHeaderOffset(elf_file, segment_index);
	size_t file_size = elf_getProgramHeaderFileSize(elf_file, segment_index);

	int error = load_segment(loadee_vspace, loader_vspace, loadee_vka, loader_vka,
	source_addr, file_size, num_regions, regions, i);
	if (error) {
	return error;
	}
	}
	return 0;
	}

	static bool is_loadable_section(char* elf_file, int index) {
	return elf_getProgramHeaderType(elf_file, index) == PT_LOAD;
	}

	static int
	count_loadable_regions(char* elf_file) {
	int num_headers = elf_getNumProgramHeaders(elf_file);
	int loadable_headers = 0;

	for (int i = 0; i < num_headers; i++) {
	/* Skip non-loadable segments (such as debugging data). */
	if (is_loadable_section(elf_file, i)) {
	loadable_headers++;
	}
	}
	return loadable_headers;
	}

	int
	sel4utils_elf_num_regions(const char *image_name)
	{
	unsigned long elf_size;
	assert(image_name);
	char *elf_file = cpio_get_file(_cpio_archive, image_name, &elf_size);
	if (elf_file == NULL) {
	ZF_LOGE("ERROR: failed to load elf file %s", image_name);
	return 0;
	}
	return count_loadable_regions(elf_file);
	}

	/**
	* Create reservations for regions in a target vspace.
	*
	* The region position and size fields should have already been calculated by prepare_reservations.
	*
	* @param loadee the vspace to load into.
	* @param total_regions the size of the regions array
	* @param regions the array of regions.
	* @param anywhere some legacy parameter that throws away the vspace address. It is supposedly to support
	loading a segment for inspection rather than execution.
	*
	* @return 0 on success.
	*/
	static int
	create_reservations(vspace_t *loadee, size_t total_regions, sel4utils_elf_region_t regions[total_regions], int anywhere) {
	for (int i = 0; i < total_regions; i++) {
	if (regions[i].reservation_size == 0) {
	ZF_LOGD("Empty reservation detected. This should indicate that this segments"
	"data is entirely stored in other section reservations.");
	continue;
	}
	if (anywhere) {
	regions[i].reservation = vspace_reserve_range(loadee, regions[i].reservation_size,
	regions[i].rights, regions[i].cacheable, (void**)&regions[i].reservation_vstart);
	} else {
	regions[i].reservation = vspace_reserve_range_at(loadee,
	regions[i].reservation_vstart,
	regions[i].reservation_size,
	regions[i].rights,
	regions[i].cacheable);
	}
	if (regions[i].reservation.res == NULL) {
	ZF_LOGE("Failed to make reservation: %p, %zd", regions[i].reservation_vstart, regions[i].reservation_size);
	return -1;
	}
	}
	return 0;

	}

	/**
	* Function for deciding whether a frame needs to be moved to a different reservation.
	*
	* Mapping permissions are set for a whole reservation. With adjacent segments of different
	* permissions, we need to give the shared frame mapping to the reservation with the more permissive
	* permissions. Currently this assumes that every region will have read permissions, and the frame
	* only needs to be moved if the lower region doesn't have write permissions and the upper one does.
	*
	* @param a CapRights for reservation a.
	* @param b CapRights for reservation b.
	* @param result whether the frame should be moved.
	*
	* @return 0 on success.
	*/
	static int
	cap_writes_check_move_frame(seL4_CapRights_t a, seL4_CapRights_t b, bool *result) {
	if (!seL4_CapRights_get_capAllowRead(a) \|\| !seL4_CapRights_get_capAllowRead(b)) {
	ZF_LOGE("Regions do not have read rights.");
	return -1;
	}
	if (!seL4_CapRights_get_capAllowWrite(a) && seL4_CapRights_get_capAllowWrite(b)) {
	*result = true;
	return 0;
	}
	*result = false;
	return 0;
	}

	/**
	* Prepares a list of regions to have reservations reserved by a vspace.
	*
	* Iterates through a region array in ascending order.
	* For each region it tries to place a reservation that contains the segment.
	* Reservations are rounded up to 4k alignments. This means that the previous reservation
	* may overlap with the start of the current region. When this occurs, the last frame of the
	* previous reservation may need to be moved to the current reservation. This is decided based
	* on the reservation permissions by the cap_writes_check_move_frame function.
	* If the frame doesn't need to be moved, then this reservation starts from the first unreserved
	* frame of the segment. When the segment is eventually loaded, the frames may need to be mapped
	* from from other segment's reservations.
	*
	* @param total_regions total number of regions in array.
	* @param regions array of regions sorted in ascending order.
	*
	* @return 0 on success.
	*/
	static int
	prepare_reservations(size_t total_regions, sel4utils_elf_region_t regions[total_regions]) {
	uintptr_t prev_res_start = 0;
	size_t prev_res_size = 0;
	seL4_CapRights_t prev_rights = seL4_CapRights_new(0,0,0);
	for (int i = 0; i < total_regions; i++) {
	uintptr_t current_res_start = PAGE_ALIGN_4K((uintptr_t)regions[i].elf_vstart);
	uintptr_t current_res_top = ROUND_UP((uintptr_t)regions[i].elf_vstart + regions[i].size, PAGE_SIZE_4K);
	size_t current_res_size = current_res_top - current_res_start;
	assert(current_res_size % PAGE_SIZE_4K == 0);
	seL4_CapRights_t current_rights = regions[i].rights;

	if ((prev_res_start + prev_res_size) > current_res_start) {
	/* This segment shares a frame with the previous segment */
	bool should_move;
	int error = cap_writes_check_move_frame(prev_rights, current_rights, &should_move);
	if (error) {
	/* Comparator function failed. Return error. */
	return -1;
	}
	if (should_move) {
	/* Frame needs to be moved from the last reservation into this one */
	ZF_LOGF_IF(i == 0, "Should not need to adjust first element in list");
	ZF_LOGF_IF(regions[i-1].reservation_size < PAGE_SIZE_4K, "Invalid previous region");
	regions[i-1].reservation_size -= PAGE_SIZE_4K;
	} else {
	/* Frame stays in previous reservation and we update our reservation start address and size */
	current_res_start = ROUND_UP((prev_res_start + prev_res_size) + 1, PAGE_SIZE_4K);
	current_res_size = current_res_top - current_res_start;
	ZF_LOGF_IF(ROUND_UP(regions[i].size, PAGE_SIZE_4K) - current_res_size == PAGE_SIZE_4K,
	"Regions shouldn't overlap by more than a single 4k frame");
	}
	}
	/* Record this reservation layout */
	regions[i].reservation_size = current_res_size;
	regions[i].reservation_vstart = (void *)current_res_start;
	prev_res_size = current_res_size;
	prev_res_start = current_res_start;
	prev_rights = current_rights;
	}
	return 0;
	}

	/**
	* Reads segment data out of elf file and creates region list.
	*
	* The region array must have the correct size as calculated by count_loadable_regions.
	*
	* @param elf_file pointer to start of elf_file
	* @param total_regions total number of loadable segments.
	* @param regions array of regions.
	*
	* @return 0 on success.
	*/
	static int
	read_regions(char* elf_file, size_t total_regions, sel4utils_elf_region_t regions[total_regions]) {
	int num_headers = elf_getNumProgramHeaders(elf_file);
	int region_id = 0;
	for (int i = 0; i < num_headers; i++) {

	/* Skip non-loadable segments (such as debugging data). */
	if (is_loadable_section(elf_file, i)) {
	sel4utils_elf_region_t *region = &regions[region_id];
	/* Fetch information about this segment. */

	region->cacheable = 1;
	region->rights = rights_from_elf(elf_getProgramHeaderFlags(elf_file, i));
	// elf_getProgramHeaderMemorySize should just return `uintptr_t`
	region->elf_vstart = (void*)(uintptr_t)elf_getProgramHeaderVaddr(elf_file, i);
	region->size = elf_getProgramHeaderMemorySize(elf_file, i);
	region->segment_index = i;
	region_id++;
	}
	}
	if (region_id != total_regions) {
	ZF_LOGE("Did not correctly read all regions.");
	return 1;
	}

	return 0;
	}

	/**
	* Compare function for ordering regions. Passed to sglib quick sort.
	*
	* Sort is based on base address. This assumes segments do not overlap.
	* There is likely a chance that quick sort won't terminate if segments overlap.
	*
	* @param a region a
	* @param b region b
	*
	* @return 1 for a > b, -1 for b > a
	*/
	static int
	compare_regions(sel4utils_elf_region_t a, sel4utils_elf_region_t b) {
	if (a.elf_vstart + a.size <= b.elf_vstart) {
	return -1;
	} else if (b.elf_vstart + b.size <= a.elf_vstart) {
	return 1;
	} else {
	ZF_LOGF("Bad elf file: segments overlap");
	return 0;
	}
	}

	/**
	* Parse an elf file and create reservations in a target vspace for all loadable segments.
	*
	* Reads segment layout data out of elf file and stores in elf_region array.
	* Then sorts the array, then plans reservations based on segment layout.
	* Finally creates reservations in vspace.
	*
	* @param loadee vspace to create reservations in.
	* @param elf_file pointer to elf file.
	* @param num_regions number of regions in array as calculated by count_loadable_regions.
	* @param regions region array.
	* @param mapanywhere throw away vspace positioning if set to 1.
	*
	* @return 0 on success.
	*/
	static int
	elf_reserve_regions_in_vspace(vspace_t loadee, char elf_file,
	int num_regions, sel4utils_elf_region_t regions[num_regions], int mapanywhere) {
	int error = read_regions(elf_file, num_regions, regions);
	if (error) {
	ZF_LOGE("Failed to read regions");
	return error;
	}

	/* Sort region list */
	SGLIB_ARRAY_SINGLE_QUICK_SORT(sel4utils_elf_region_t, regions, num_regions, compare_regions);

	error = prepare_reservations(num_regions, regions);
	if (error) {
	ZF_LOGE("Failed to prepare reservations");
	return error;
	}
	error = create_reservations(loadee, num_regions, regions, mapanywhere);
	if (error) {
	ZF_LOGE("Failed to create reservations");
	return error;
	}
	return 0;
	}

	static void *
	entry_point(char *elf_file) {
	uint64_t entry_point = elf_getEntryPoint(elf_file);
	if ((uint32_t) (entry_point >> 32) != 0) {
	ZF_LOGE("ERROR: this code hasn't been tested for 64bit!");
	return NULL;
	}
	assert(entry_point != 0);
	return (void*)(seL4_Word)entry_point;

	}


	void *
	sel4utils_elf_reserve(vspace_t loadee, const char image_name, sel4utils_elf_region_t *regions)
	{
	unsigned long elf_size;
	char *elf_file = cpio_get_file(_cpio_archive, image_name, &elf_size);
	if (elf_file == NULL) {
	ZF_LOGE("ERROR: failed to load elf file %s", image_name);
	return NULL;
	}

	/* Count number of loadable segments */
	int num_regions = count_loadable_regions(elf_file);

	/* Create reservations in vspace using internal functions */
	int error = elf_reserve_regions_in_vspace(loadee, elf_file, num_regions, regions, 0);
	if (error) {
	ZF_LOGE("Failed to reserve regions");
	return NULL;
	}

	/* Return entry point */
	return entry_point(elf_file);
	}

	void *
	sel4utils_elf_load_record_regions(vspace_t loadee, vspace_t loader, vka_t loadee_vka, vka_t loader_vka, const char image_name, sel4utils_elf_region_t regions, int mapanywhere)
	{
	unsigned long elf_size;
	char *elf_file = cpio_get_file(_cpio_archive, image_name, &elf_size);
	if (elf_file == NULL) {
	ZF_LOGE("ERROR: failed to load elf file %s", image_name);
	return NULL;
	}

	/* Calculate number of loadable regions. Use stack array if one wasn't passed in */
	int num_regions = count_loadable_regions(elf_file);
	bool clear_at_end = false;
	sel4utils_elf_region_t stack_regions[num_regions];
	if (regions == NULL) {
	regions = stack_regions;
	clear_at_end = true;
	}

	/* Create reservations */
	int error = elf_reserve_regions_in_vspace(loadee, elf_file, num_regions, regions, mapanywhere);
	if (error) {
	ZF_LOGE("Failed to reserve regions");
	return NULL;
	}

	/* Load Map reservations and load in elf data */
	error = load_segments(loadee, loader, loadee_vka, loader_vka, elf_file, num_regions, regions);
	if (error) {
	ZF_LOGE("Failed to load segments");
	return NULL;
	}

	/* Clean up reservations if we allocated our own array */
	if (clear_at_end) {
	for (int i = 0; i < num_regions; i++) {
	if (regions[i].reservation_size > 0) {
	vspace_free_reservation(loadee, regions[i].reservation);
	}
	}
	}

	/* Return entry point */
	return entry_point(elf_file);
	}

	uintptr_t sel4utils_elf_get_vsyscall(const char *image_name)
	{
	uintptr_t* addr = (uintptr_t*)sel4utils_elf_get_section(image_name, "__vsyscall", NULL);
	/* Hope everything is good and just dereference it */
	return *addr;
	}

	uintptr_t sel4utils_elf_get_section(const char image_name, const char section_name, uint64_t* section_size)
	{
	unsigned long elf_size;
	char *elf_file = cpio_get_file(_cpio_archive, image_name, &elf_size);
	if (elf_file == NULL) {
	ZF_LOGE("ERROR: failed to lookup elf file %s", image_name);
	return 0;
	}
	/* See if we can find the section */
	int section_id;
	void *addr = elf_getSectionNamed(elf_file, section_name, &section_id);
	if (addr) {
	if (section_size != NULL) {
	*section_size = elf_getSectionSize(elf_file, section_id);
	}
	return (uintptr_t) addr;
	} else {
	return 0;
	}
	}

	void *
	sel4utils_elf_load(vspace_t loadee, vspace_t loader, vka_t loadee_vka, vka_t loader_vka, const char *image_name)
	{
	return sel4utils_elf_load_record_regions(loadee, loader, loadee_vka, loader_vka, image_name, NULL, 0);
	}

	uint32_t
	sel4utils_elf_num_phdrs(const char *image_name)
	{
	unsigned long elf_size;
	char *elf_file = cpio_get_file(_cpio_archive, image_name, &elf_size);
	return elf_getNumProgramHeaders(elf_file);
	}

	void
	sel4utils_elf_read_phdrs(const char image_name, uint32_t max_phdrs, Elf_Phdr phdrs)
	{
	unsigned long elf_size;
	char *elf_file = cpio_get_file(_cpio_archive, image_name, &elf_size);
	uint32_t num_phdrs = elf_getNumProgramHeaders(elf_file);
	for (uint32_t i = 0; i < num_phdrs && i < max_phdrs; i++) {
	/* cannot take addresses directly from the final struct as the types might
	* be different, so store into locals first */
	uint64_t p_vaddr, p_paddr, p_filesz, p_offset, p_memsz;
	elf_getProgramHeaderInfo(elf_file, i, &p_vaddr, &p_paddr, &p_filesz, &p_offset, &p_memsz);
	phdrs[i] = (Elf_Phdr) {
	.p_type = elf_getProgramHeaderType(elf_file, i),
	.p_offset = p_offset,
	.p_vaddr = p_vaddr,
	.p_paddr = p_paddr,
	.p_filesz = p_filesz,
	.p_memsz = p_memsz,
	.p_flags = elf_getProgramHeaderFlags(elf_file,i),
	.p_align = elf_getProgramHeaderAlign(elf_file, i)
	};
	}
	}