src/start_root.c

/*
 * Copyright 2019, 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 <sel4/sel4.h>
#include <sel4runtime/start.h>
#include <sel4runtime/stdint.h>
#include <sel4runtime/stddef.h>

/*
 * As this file is only included when we are running a root server,
 * these symbols must exist and be provided for this file to function
 * properly.
 *
 * This will generate a link time error if this function is used outside
 * of a root server.
 */

extern unsigned int _tdata_start[];
extern unsigned int _tdata_end[];
extern unsigned int _tbss_end[];

long sel4_vsyscall(long sysnum, ...);

/*
 * The entrypoint into a root task is somewhat different to the
 * entrypoint into a regular process. The kernel does not provide a
 * stack to the root task nor does it conform to System-V ABI; instead
 * it simply starts execution at the entrypoint with the first argument
 * being the pointer to the seL4_BootInfo.
 *
 * This is invoked by _sel4_start, which simply sets up a static stack
 * and passes the argument to us.
 */
void __sel4_start_root(seL4_BootInfo *boot_info)
{
    sel4runtime_uintptr_t tdata_start = (sel4runtime_uintptr_t) &_tdata_start[0];
    sel4runtime_uintptr_t tdata_end = (sel4runtime_uintptr_t) &_tdata_end[0];
    sel4runtime_uintptr_t tbss_end = (sel4runtime_uintptr_t) &_tbss_end[0];

    Elf_Phdr tls_header = {
        .p_type   = PT_TLS,
        .p_offset = 0,
        .p_vaddr  = (Elf_Addr) tdata_start,
        .p_paddr  = 0,
        .p_filesz = tdata_end - tdata_start,
        .p_memsz  = tbss_end - tdata_start,
        .p_align = sizeof(seL4_Word),
    };

    auxv_t auxv[] = {
        {
            .a_type = AT_PHENT,
            .a_un.a_val = sizeof(Elf32_Phdr),
        }, {
            .a_type = AT_PHNUM,
            .a_un.a_val = 1,
        }, {
            .a_type = AT_PHDR,
            .a_un.a_ptr = &tls_header,
        }, {
            .a_type = AT_SYSINFO,
            .a_un.a_ptr = &sel4_vsyscall,
        }, {
            .a_type = AT_SEL4_BOOT_INFO,
            .a_un.a_ptr = boot_info,
        }, {
            .a_type = AT_SEL4_TCB,
            .a_un.a_val = seL4_CapInitThreadTCB,
        }, {
            // Null terminating entry
            .a_type = AT_NULL,
            .a_un.a_val = 0
        },
    };

    char const *const envp[] = {
        "seL4=1",
        SEL4RUNTIME_NULL,
    };

    char const *const argv[] = {
        "rootserver",
        SEL4RUNTIME_NULL,
    };

    __sel4runtime_start_main(main, ARRAY_LENGTH(argv), argv, envp, auxv);
}