Here's the (abbreviated) output of strace'ing qemu:
farino ~ # strace -f /usr/bin/qemu-riscv32
/chroot/riscv-ilp32/tmp/wait-test-short
execve("/usr/bin/qemu-riscv32", ["/usr/bin/qemu-riscv32",
"/chroot/riscv-ilp32/tmp/wait-tes"...], 0x7ffd95fb1330 /* 40 vars */) = 0
[...]
[pid 16569] uname({sysname="Linux", nodename="farino", ...}) = 0
[pid 16569] lstat("/chroot", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
[pid 16569] lstat("/chroot/riscv-ilp32", {st_mode=S_IFDIR|S_ISGID|0755,
st_size=4096, ...}) = 0
[pid 16569] lstat("/chroot/riscv-ilp32/tmp", {st_mode=S_IFDIR|S_ISVTX|0777,
st_size=4096, ...}) = 0
[pid 16569] lstat("/chroot/riscv-ilp32/tmp/wait-test-short",
{st_mode=S_IFREG|0755, st_size=445632, ...}) = 0
[pid 16569] mmap(0x413f1000, 135168, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x413f1000
[pid 16569] mprotect(0x413eb000, 8192, PROT_READ) = 0
[pid 16569] rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], NULL, 8) = 0
[pid 16569] clone(child_stack=NULL,
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x1339710)
= 16571
strace: Process 16571 attached
[pid 16571] set_robust_list(0x1339720, 24 <unfinished ...>
[pid 16569] rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], NULL, 8) = 0
[pid 16571] <... set_robust_list resumed>) = 0
[pid 16569] rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
[pid 16571] rt_sigprocmask(SIG_SETMASK, ~[ILL FPE SEGV RTMIN RT_1], ~[KILL STOP
RTMIN RT_1], 8) = 0
[pid 16571] rt_sigprocmask(SIG_BLOCK, ~[], ~[ILL FPE KILL SEGV STOP RTMIN
RT_1], 8) = 0
[pid 16571] clone(child_stack=0x7fe5b73871f0,
flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID,
parent_tid=[16572], tls=0x7fe5b7387640, child_tidptr=0x7fe5b7387910) = 16572
[pid 16571] rt_sigprocmask(SIG_SETMASK, ~[ILL FPE KILL SEGV STOP RTMIN RT_1],
NULL, 8) = 0
[pid 16571] rt_sigprocmask(SIG_SETMASK, ~[KILL STOP RTMIN RT_1], NULL, 8) = 0
[pid 16571] gettid() = 16571
[pid 16571] rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], NULL, 8) = 0
[pid 16571] rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
[pid 16569] waitid(P_ALL, -1, <unfinished ...>
[pid 16571] exit_group(42) = ?
strace: Process 16572 attached
[pid 16572] +++ exited with 42 +++
[pid 16571] +++ exited with 42 +++
[pid 16569] <... waitid resumed>{si_signo=SIGCHLD, si_code=CLD_EXITED,
si_pid=16571, si_uid=0, si_status=42, si_utime=3472328296226648184,
si_stime=3475143045726351408}, WEXITED, NULL) = 0
[pid 16569] --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=16571,
si_uid=0, si_status=42, si_utime=0, si_stime=0} ---
[pid 16569] statx(1, "", AT_STATX_SYNC_AS_STAT|AT_EMPTY_PATH,
STATX_BASIC_STATS, {stx_mask=STATX_BASIC_STATS|STATX_MNT_ID, stx_attributes=0,
stx_mode=S_IFCHR|0600, stx_size=0, ...}) = 0
[pid 16569] write(1, "child wants to return 42 (0x2A),"..., 74child wants to
return 42 (0x2A), parent received 40 (0x28), difference -2
) = 74
[pid 16569] brk(0x13c1000) = 0x13c1000
[pid 16569] brk(0x13c0000) = 0x13c0000
[pid 16569] exit_group(0) = ?
[pid 16570] <... futex resumed>) = ?
[pid 16570] +++ exited with 0 +++
+++ exited with 0 +++
--
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https://bugs.launchpad.net/bugs/1906193
Title:
riscv32 user mode emulation: fork return values broken
Status in QEMU:
New
Bug description:
When running in a chroot with riscv32 (on x86_64; qemu git master as
of today):
The following short program forks; the child immediately returns with
exit(42). The parent checks for the return value - and obtains 40!
gcc-10.2
===============================================
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/wait.h>
main(c, v)
int c;
char **v;
{
pid_t pid, p;
int s, i, n;
s = 0;
pid = fork();
if (pid == 0)
exit(42);
/* wait for the process */
p = wait(&s);
if (p != pid)
exit (255);
if (WIFEXITED(s))
{
int r=WEXITSTATUS(s);
if (r!=42) {
printf("child wants to return %i (0x%X), parent received %i (0x%X),
difference %i\n",42,42,r,r,r-42);
}
}
}
===============================================
(riscv-ilp32 chroot) farino /tmp # ./wait-test-short
child wants to return 42 (0x2A), parent received 40 (0x28), difference -2
===============================================
(riscv-ilp32 chroot) farino /tmp # gcc --version
gcc (Gentoo 10.2.0-r1 p2) 10.2.0
Copyright (C) 2020 Free Software Foundation, Inc.
Dies ist freie Software; die Kopierbedingungen stehen in den Quellen. Es
gibt KEINE Garantie; auch nicht für MARKTGÄNGIGKEIT oder FÜR SPEZIELLE ZWECKE.
(riscv-ilp32 chroot) farino /tmp # ld --version
GNU ld (Gentoo 2.34 p6) 2.34.0
Copyright (C) 2020 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or (at your option) a later version.
This program has absolutely no warranty.
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