commit b15a663ceaf7798e39fcba9909fcc5d8359337cf
author Curtis Millar <curtis.millar@data61.csiro.au> Fri Sep 18 15:41:19 2020 +1000
committer Curtis Millar <curtis.millar@data61.csiro.au> Fri Sep 18 16:22:28 2020 +1000
tree 096a06868fbd5edb823162736d84e4bc25a8687f
parent 0612156b1ba45ebf00f4f00b75ccdbcd358db902

Force stack order for system-V info

The order, spacing and alignment of the argv, envp, and auxv regions are
part of the system-V specification and the init in muslc uses this to
derive the location of auxv from envp.

This uses an anonymous struct to enforce the ordering and spacing of
these items in release builds such that muslc can still initialise libc.

src/start_root.c

diff --git a/src/start_root.c b/src/start_root.c
index 677d5f7..fe6aa39 100644
--- a/src/start_root.c
+++ b/src/start_root.c
@@ -55,41 +55,45 @@
         .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
+    struct {
+        char const *const argv[2];
+        char const *const envp[2];
+        auxv_t auxv[7];
+    } info = {
+        .argv = {
+            "rootserver",
+            SEL4RUNTIME_NULL,
+        },
+        .envp = {
+            "seL4=1",
+            SEL4RUNTIME_NULL,
+        },
+        .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);
+    __sel4runtime_start_main(main, ARRAY_LENGTH(info.argv), info.argv, info.envp, info.auxv);
 }