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Date: Tue, 19 Jan 2021 14:02:50 -0800
From: Rasmus Andersson <rasmus@...ion.se>
To: Rich Felker <dalias@...c.org>
Cc: musl@...ts.openwall.com
Subject: Re: waitpid (wait4) on Linux 5 returns invalid values
The program compiles correctly with
https://more.musl.cc/9/x86_64-linux-musl/x86_64-linux-musl-native.tgz
(The GCC 9 version) Perhaps an issue with GCC 10?
On Tue, Jan 19, 2021 at 2:00 PM Rasmus Andersson <rasmus@...ion.se> wrote:
>
> That was compiled using
> https://more.musl.cc/10/x86_64-linux-musl/x86_64-linux-musl-native.tgz
> on Alpine Linux in a docker container (alpine:3.12)
>
> Full repro:
> $ wget https://more.musl.cc/10/x86_64-linux-musl/x86_64-linux-musl-native.tgz
> $ tar -xf x86_64-linux-musl-native.tgz
> $ cat << EOF > a.c
> #include <sys/wait.h>
> #include <stdio.h>
> #include <errno.h>
> #include <string.h>
> int main(int argc, char **argv) {
> int wstat = 0;
> pid_t child = waitpid(-1, &wstat, WNOHANG);
> printf("waitpid returned %d, wstat=%d, errno=%d (%s)\n", child,
> wstat, errno, strerror(errno));
> return 0;
> }
> EOF
> $ x86_64-linux-musl-native/bin/gcc -static a.c
> $ ./a.out
> waitpid returned -10, wstat=0, errno=0 (No error information)
>
> On Tue, Jan 19, 2021 at 1:16 PM Rich Felker <dalias@...c.org> wrote:
> >
> > 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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