tools/nolibc: add auxiliary vector retrieval for x86_64

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

diff --git a/tools/include/nolibc/arch-x86_64.h b/tools/include/nolibc/arch-x86_64.h
index 683702a16a6103c370cf4459b0c5a1fb4c2e8c68..17f6751208e7e9d93229f1248bf0518c51f48985 100644 (file)
--- a/tools/include/nolibc/arch-x86_64.h
+++ b/tools/include/nolibc/arch-x86_64.h
@@ -179,6 +179,7 @@ struct sys_stat_struct {
 })
 
 char **environ __attribute__((weak));
+const unsigned long *_auxv __attribute__((weak));
 
 /* startup code */
 /*
@@ -195,6 +196,12 @@ void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) _start(void)
                "lea 8(%rsi,%rdi,8),%rdx\n" // then a NULL then envp (third arg, %rdx)
                "mov %rdx, environ\n"       // save environ
                "xor %ebp, %ebp\n"          // zero the stack frame
+               "mov %rdx, %rax\n"          // search for auxv (follows NULL after last env)
+               "0:\n"
+               "add $8, %rax\n"            // search for auxv using rax, it follows the
+               "cmp -8(%rax), %rbp\n"      // ... NULL after last env (rbp is zero here)
+               "jnz 0b\n"
+               "mov %rax, _auxv\n"         // save it into _auxv
                "and $-16, %rsp\n"          // x86 ABI : esp must be 16-byte aligned before call
                "call main\n"               // main() returns the status code, we'll exit with it.
                "mov %eax, %edi\n"          // retrieve exit code (32 bit)