[PATCH] selftests/powerpc: New TM signal self test

[Michael Ellerman]

Breno Leitao <leitao at debian.org> writes:

> A new self test that forces MSR[TS] to be set without calling any TM
> instruction. This test also tries to cause a page fault at a signal
> handler, exactly between MSR[TS] set and tm_recheckpoint(), forcing
> thread->texasr to be rewritten with TEXASR[FS] = 0, which will cause a BUG
> when tm_recheckpoint() is called.
>
> This test is not deterministic since it is hard to guarantee that the page
> access will cause a page fault. Tests have shown that the bug could be
> exposed with few interactions in a buggy kernel. This test is configured to
> loop 5000x, having a good chance to hit the kernel issue in just one run.
> This self test takes less than two seconds to run.
>
> This test uses set/getcontext because the kernel will recheckpoint
> zeroed structures, causing the test to segfault, which is undesired because
> the test needs to rerun, so, there is a signal handler for SIGSEGV which
> will restart the test.

Hi Breno,

Thanks for the test, some of these TM tests are getting pretty advanced! :)

Unfortunately it doesn't build in a few configurations.

On Ubuntu 18.10 built with powerpc-linux-gnu-gcc I get:

  tm-signal-force-msr.c: In function 'trap_signal_handler':
  tm-signal-force-msr.c:42:19: error: 'union uc_regs_ptr' has no member named 'gp_regs'; did you mean 'uc_regs'?
    ucp->uc_mcontext.gp_regs[PT_MSR] |= MSR_TS_S;
                     ^~~~~~~
                     uc_regs
  tm-signal-force-msr.c:17:29: error: left shift count >= width of type [-Werror=shift-count-overflow]
   #define __MASK(X)       (1UL<<(X))
                               ^~
  tm-signal-force-msr.c:20:25: note: in expansion of macro '__MASK'
   #define MSR_TS_S        __MASK(MSR_TS_S_LG) /* Transaction Suspended */
                           ^~~~~~
  tm-signal-force-msr.c:42:38: note: in expansion of macro 'MSR_TS_S'
    ucp->uc_mcontext.gp_regs[PT_MSR] |= MSR_TS_S;
                                        ^~~~~~~~

And using powerpc64le-linux-gnu-gcc I get:

  In file included from /usr/powerpc64le-linux-gnu/include/string.h:494,
                   from tm-signal-force-msr.c:10:
  In function 'memcpy',
      inlined from 'trap_signal_handler' at tm-signal-force-msr.c:39:2:
  /usr/powerpc64le-linux-gnu/include/bits/string_fortified.h:34:10: error: '__builtin_memcpy' accessing 1272 bytes at offsets 8 and 168 overlaps 1112 bytes at offset 168 [-Werror=restrict]
     return __builtin___memcpy_chk (__dest, __src, __len, __bos0 (__dest));
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

cheers