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Date: Tue, 19 Jan 2021 16:16:53 -0500
From: Rich Felker <dalias@...c.org>
To: Rasmus Andersson <rasmus@...ion.se>
Cc: musl@...ts.openwall.com
Subject: Re: waitpid (wait4) on Linux 5 returns invalid values
On Tue, Jan 19, 2021 at 12:35:26PM -0800, Rasmus Andersson wrote:
> Relevant parts from disassembly: (objdump --disassemble --source
> --line-numbers a.out)
>
> 0000000000401f61 <__syscall_cp_c>:
> sccp():
> 401f61: 48 89 f8 mov %rdi,%rax
> 401f64: 4d 89 c2 mov %r8,%r10
> 401f67: 48 89 f7 mov %rsi,%rdi
> 401f6a: 4d 89 c8 mov %r9,%r8
> 401f6d: 48 89 d6 mov %rdx,%rsi
> 401f70: 4c 8b 4c 24 08 mov 0x8(%rsp),%r9
> 401f75: 48 89 ca mov %rcx,%rdx
> 401f78: 0f 05 syscall
> 401f7a: c3 retq
>
> 0000000000401f7b <__syscall_cp>:
> __syscall_cp():
> 401f7b: e9 e1 ff ff ff jmpq 401f61 <__syscall_cp_c>
>
> 00000000004004fd <waitpid>:
> waitpid():
> ...
> 40051a: e8 5c 1a 00 00 callq 401f7b <__syscall_cp>
> 40051f: 48 83 c4 18 add $0x18,%rsp
> 400523: c3 retq
This disassembly shows a miscompiled (or compiled with wrong patches)
waitpid. It should be a tail call to __syscall_ret, not a retq.
Rich
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