[Bug 1906193] Re: riscv32 user mode emulation: fork return values broken

["Andreas K. Hüttel" <1906193@bugs.launchpad.net>]

Done (took a while to figure out how...)

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https://bugs.launchpad.net/bugs/1906193

Title:
  riscv32 user mode emulation: fork return values broken

Status in QEMU:
  Confirmed

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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