[Qemu-devel] [Bug 1516408] Re: sh4: Unsupported syscall: 186

[John Paul Adrian Glaubitz]

Hello!

The attached patch enables the sigaltstack syscall in qemu-sh4.

The following minimal test code verifies that sigaltstack works as
expected:

=============================================================

#include <setjmp.h>
#include <signal.h>
#include <stdlib.h>
#include <stdio.h>

jmp_buf exit_jmp;

void handler(int x)
{
  longjmp(exit_jmp, 1);
}

int f(void)
{
  return f();
}

int main(void)
{
  stack_t sigstack;
  sigstack.ss_sp = malloc(1024*1024);
  sigstack.ss_size = 1024*1024;
  sigstack.ss_flags = 0;
  sigaltstack(&sigstack, NULL);
  struct sigaction sa;
  sa.sa_handler = handler;
  sigemptyset(&sa.sa_mask);
  sa.sa_flags = SA_ONSTACK;
  sigaction(SIGSEGV, &sa, NULL);
  if (setjmp(exit_jmp) == 0)
  {
    return f();
  }
  puts("recovered");
  return 0;
}

=============================================================

Without sigaltstack enabled, this code produces a segmentation fault.
With sigaltstack enabled, it prints out "recovered".

Also posted on qemu-devel mailing list:

> http://lists.nongnu.org/archive/html/qemu-devel/2015-11/msg04300.html
> http://lists.nongnu.org/archive/html/qemu-devel/2015-11/msg04301.html

Cheers,
Adrian

** Patch added: "Patch to enable sigaltstack in qemu-sh4"
   
https://bugs.launchpad.net/qemu/+bug/1516408/+attachment/4521728/+files/0001-linux-user-Enable-sigaltstack-syscall-for-sh4.patch

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https://bugs.launchpad.net/bugs/1516408

Title:
  sh4: Unsupported syscall: 186

Status in QEMU:
  New

Bug description:
  Hello!

  I'm currently testing qemu as a possibility to set up a buildd for the
  Debian sh4 port.

  I set up qemu and an sh4 chroot as described in the Debian Wiki [1].
  This seems to be working mostly fine (besides the fact that qemu
  segfaults on an amd64 host while it runs fine on an i386 host, I'll
  file a separate bug report). However, when installing python3.4 in the
  sh4 chroot, qemu repeatedly printed an error message about an
  unimplemented syscall: 186:

  qemu: Unsupported syscall: 186

  From the source code in linux-user/sh4/syscall_nr.h it's apparent that
  186 is defined as

  #define TARGET_NR_sigaltstack   186

  Looking at the implementation part, it becomes obvious that this
  syscall is not enabled for sh4:

  #if defined(TARGET_I386) || defined(TARGET_ARM) || defined(TARGET_MIPS) || \
      defined(TARGET_SPARC) || defined(TARGET_PPC) || defined(TARGET_ALPHA) || \
      defined(TARGET_M68K) || defined(TARGET_S390X) || defined(TARGET_OPENRISC)
          ret = do_sigaltstack(arg1, arg2, get_sp_from_cpustate((CPUArchState 
*)cpu_env));
          break;
  #else
          goto unimplemented;
  #endif

  Is there any particular reason why TARGET_NR_sigaltstack is not
  enabled on sh4? If not, could you enable it?

  Thanks,
  Adrian

  > [1] https://wiki.debian.org/QemuUserEmulation

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