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

Thomas,

On Sun, Aug 20, 2023 at 09:13:51PM +0200, Thomas Weißschuh wrote:

On 2023-08-20 21:19:00+0300, Vitaly Chikunov wrote:

...

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@altlinux.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

nolibc recently switched to startup code that is mostly implemented in C instead of assembly. See the current linux-next tree.

That should make this change unnecessary I guess.

Yes seems so! Zhangjin Wu done a fine job.

Thanks,

Thomas