Re: [Qemu-devel] Armv5 target

[Paul Brook <paul@codesourcery.com>]

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On Wednesday 02 February 2005 12:01, Lennert Buytenhek wrote:
> On Wed, Feb 02, 2005 at 01:26:37AM +0000, Paul Brook wrote:
> > > > +    /* XXX: locking issue */
> > > > +    if (is_write && page_unprotect(address, pc, puc)) {
> > > > +        return 1;
> > > > +    }
> > > >      /* XXX: do more */
> > > >      return 0;
> > > >  }
> > >
> > > Sort of. Self-modifying code (e.g. stack trampolines) are still broken,
> > > and the patch above should work.
> > >
> > > However I just tested it and it doesn't seem to work any more. It seems
> > > that the SEGV handler is being passed an address of 0, rather than the
> > > actual faulting location.
> > >
> > > This may be a host kernel/libc bug.
> >
> > I just tried on a few different machines, and this is a host kernel bug
> > specific to one particular kernel (custom 2.6.9).
>
> Do you have some example code that demonstrates this?

I've attached two programs. segv-test.c tests for the kernel bug. nest_test.c 
tests stack trampolines, which exposes the bug then run inside qemu-user.

Note that the proper fix for arm is to remove the ||1 hack on the 
TARGET_HAS_SMC tests in exec.c. Comments indicate this hack is to work around 
bugs in the PPC emulation.

Paul

[-- Attachment #2: segv_test.c --]
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/* Test that gatching SIGSEGV gives the correct fault address.  */
#include <stdio.h>
#include <signal.h>
#include <sys/mman.h>
#include <stdio.h>

void * volatile p = NULL;
void * volatile block;

void foo(int n, siginfo_t *info, void *data)
{
  p = info->si_addr;
  printf ("%p\n", block);
  mprotect(block, sizeof(int), PROT_READ | PROT_WRITE);
}

int main()
{
  struct sigaction sa;

  p = &sa;
  memset (&sa, 0, sizeof(sa));
  sa.sa_sigaction = foo;
  sa.sa_flags = SA_SIGINFO;
  sigaction (SIGSEGV, &sa, NULL);
  block = mmap(NULL, sizeof(int), PROT_READ, MAP_SHARED|MAP_ANONYMOUS, 0, 0);
  if (block == MAP_FAILED)
    {
      printf ("mmap failed\n");
      return 1;
    }
  *(volatile int *) block = 42;
  sleep(1);
  if (p != block)
    printf ("FAIL: expected %p, got %p\n",  block, p);
  else
    printf ("OK\n");
  
  return 0;
}


[-- Attachment #3: nest_test.c --]
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/* Test stack trampolines (nested functions).  */
/* Should print "Hello nested world". */
#include <stdio.h>

void bar(void (*)())
{
  f();
}
int main()
{
  void f()
    {
      printf ("nested ");
    }
  printf ("Hello ");
  bar(f);
  printf ("world\n");
  return 0;
}