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