sh4: Unsupported syscall: 186

[John Paul Adrian Glaubitz]

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

[John Paul Adrian Glaubitz (glaubitz)]

I have enabled this syscall in the source code now and performing a test build and run and will report back.

Furthermore, looking at the kernel sources, both the 32-bit and 64-bit Linux SH-specific code defines "sigaltstack" as syscall 186:

> https://github.com/torvalds/linux/blob/master/arch/sh/kernel/syscalls_32.S#L205
> https://github.com/torvalds/linux/blob/master/arch/sh/kernel/syscalls_64.S#L209

The whole syscall also doesn't appear to be architecture-specific after reading the manpage for sigaltstack. Is it?

Will report back after further testing.

Thanks,
Adrian

[John Paul Adrian Glaubitz (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

[John Paul Adrian Glaubitz (glaubitz)]

Ping. Any chance to get this merged?

I don't think this patch could have any particular bad impact on qemu as it affects the sh4 emulation only and so far my tests with building packages on qemu-sh4 have shown no regressions. But with the patch, sigaltstack now works fine on sh4 which the above testcase also positively has proven.

Having this bug and #1254824 fixed would help the sh4 porters in Debian quite a lot as qemu-sh4 can be used to set up a virtual buildd for this architecture.

Adrian

> [1] https://bugs.launchpad.net/ubuntu/+source/qemu-linaro/+bug/1254824

[Peter Maydell (pmaydell)]

Looks like we fixed this in commit c0d35736323e5b in December, which was released as part of QEMU 2.6.