tools/nolibc: add auxiliary vector retrieval for arm

In the _start block we now iterate over envp to find the auxiliary
vector after the NULL. The pointer is saved into an _auxv variable
that is marked as weak so that it's accessible from multiple units.

Signed-off-by: Willy Tarreau <w@1wt.eu>
It was tested in arm, thumb1 and thumb2 modes.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/tools/include/nolibc/arch-arm.h b/tools/include/nolibc/arch-arm.h
index 79666b590e87fdfb444bb04e7a7ec1b8d30306d0..42499f23e73c5c583e434d5c579c95104e7d8ff7 100644 (file)
--- a/tools/include/nolibc/arch-arm.h
+++ b/tools/include/nolibc/arch-arm.h
@@ -197,6 +197,7 @@ struct sys_stat_struct {
 })
 
 char **environ __attribute__((weak));
+const unsigned long *_auxv __attribute__((weak));
 
 /* startup code */
 void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) _start(void)
@@ -211,6 +212,16 @@ void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) _start(void)
                "ldr %r3, 1f\n"               // r3 = &environ (see below)
                "str %r2, [r3]\n"             // store envp into environ
 
+               "mov r4, r2\n"                // search for auxv (follows NULL after last env)
+               "0:\n"
+               "mov r5, r4\n"                // r5 = r4
+               "add r4, r4, #4\n"            // r4 += 4
+               "ldr r5,[r5]\n"               // r5 = *r5 = *(r4-4)
+               "cmp r5, #0\n"                // and stop at NULL after last env
+               "bne 0b\n"
+               "ldr %r3, 2f\n"               // r3 = &_auxv (low bits)
+               "str r4, [r3]\n"              // store r4 into _auxv
+
                "mov %r3, $8\n"               // AAPCS : sp must be 8-byte aligned in the
                "neg %r3, %r3\n"              //         callee, and bl doesn't push (lr=pc)
                "and %r3, %r3, %r1\n"         // so we do sp = r1(=sp) & r3(=-8);
@@ -222,6 +233,8 @@ void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) _start(void)
                ".align 2\n"                  // below are the pointers to a few variables
                "1:\n"
                ".word environ\n"
+               "2:\n"
+               ".word _auxv\n"
        );
        __builtin_unreachable();
 }