Hi Vitaly,
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@xxxxxxxxxxxx>
> ---
> 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.
Thomas
