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tools/nolibc: add auxiliary vector retrieval for x86_64

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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>
This commit is contained in:
Willy Tarreau 2023-01-10 08:24:26 +01:00 committed by Paul E. McKenney
parent 2ab4aa487b
commit 1cce162ab4
1 changed files with 7 additions and 0 deletions
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7
tools/include/nolibc/arch-x86_64.h
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@ -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)