linux-kernel - [RFC] tools/nolibc: x86_64: Make it compile with -pie

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Message-Id: <20230820181900.3786107-1-vt@altlinux.org>
Date:   Sun, 20 Aug 2023 21:19:00 +0300
From:   Vitaly Chikunov <vt@...linux.org>
To:     Willy Tarreau <w@....eu>, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: [RFC] tools/nolibc: x86_64: Make it compile with -pie

Use RIP-relative addressing when setting `environ` and `_auxv` in
startup code.

Some toolchains have `-pie` enabled by default. On them or when -pie is
specified manually gcc produces error like this:

  ld: /tmp/cci0uPcR.o: relocation R_X86_64_32S against symbol `environ' can not be used when making a PIE object; recompile with -fPIE
  ld: failed to set dynamic section sizes: bad value

This is because asm() startup code accesses there pointers with absolute
addressing.

This may inspire others to fix the problem for other architectures too.

Signed-off-by: Vitaly Chikunov <vt@...linux.org>
---
 tools/include/nolibc/arch-x86_64.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/include/nolibc/arch-x86_64.h b/tools/include/nolibc/arch-x86_64.h
index 6fc4d8392742..a6be44b333ce 100644
--- a/tools/include/nolibc/arch-x86_64.h
+++ b/tools/include/nolibc/arch-x86_64.h
@@ -199,14 +199,14 @@ void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) __no_stack_pr
 		"pop %rdi\n"                /* argc   (first arg, %rdi)                            */
 		"mov %rsp, %rsi\n"          /* argv[] (second arg, %rsi)                           */
 		"lea 8(%rsi,%rdi,8),%rdx\n" /* then a NULL then envp (third arg, %rdx)             */
-		"mov %rdx, environ\n"       /* save environ                                        */
+		"mov %rdx, environ(%rip)\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                                  */
+		"mov %rax, _auxv(%rip)\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)                         */
-- 
2.33.8