selftests/powerpc: Fix and enhance TM signal context tests

selftests/powerpc: Fix and enhance TM signal context tests

Currently TM signal context tests for GPR, FPR, VMX, and VSX registers
print wrong register numbers (wrongly starting from register 0 instead
of the first register in the non-volatile subset). Besides it the
output when a mismatch happens is poor giving not much information
about which context and which register mismatches, because it prints
both contexts at the same time and not a comparison between the value
that mismatches and the value expected and, moreover, it stops
printing on the first mismatch, but it's important to know if there
are other mismatches happening beyond the first one.

For instance, this is the current output when a mismatch happens:

  test: tm_signal_context_chk_gpr
  tags: git_version:v5.2-8249-g02e970fae465-dirty
  Failed on 0 GPR 1 or 18446744073709551615
  failure: tm_signal_context_chk_gpr

  test: tm_signal_context_chk_fpu
  tags: git_version:v5.2-8248-g09c289e3ef80
  Failed on 0 FP -1 or -1
  failure: tm_signal_context_chk_fpu

  test: tm_signal_context_chk_vmx
  tags: git_version:v5.2-8248-g09c289e3ef80
  Failed on 0 vmx 0xfffffffffffffffefffffffdfffffffc vs 0xfffffffffffffffefffffffdfffffffc
  failure: tm_signal_context_chk_vmx

  test: tm_signal_context_chk_vsx
  tags: git_version:v5.2-8248-g09c289e3ef80
  Failed on 0 vsx 0xfffffffffefffffffdfffffffcffffff vs 0xfffffffffefffffffdfffffffcffffff
  failure: tm_signal_context_chk_vsx

This commit fixes the register numbers printed and enhances the error
output by providing a full list of mismatching registers separated by
the context (non-speculative or speculative context), for example:

  test: tm_signal_context_chk_gpr
  tags: git_version:v5.2-8249-g02e970fae465-dirty
  GPR14 (1st context) == 1 instead of -1 (expected)
  GPR15 (1st context) == 2 instead of -2 (expected)
  GPR14 (2nd context) == 0 instead of 18446744073709551615 (expected)
  GPR15 (2nd context) == 0 instead of 18446744073709551614 (expected)
  failure: tm_signal_context_chk_gpr

  test: tm_signal_context_chk_fpu
  tags: git_version:v5.2-8249-g02e970fae465-dirty
  FPR14 (1st context) == -1 instead of 1 (expected)
  FPR15 (1st context) == -2 instead of 2 (expected)
  failure: tm_signal_context_chk_fpu

  test: tm_signal_context_chk_vmx
  tags: git_version:v5.2-8249-g02e970fae465-dirty
  VMX20 (1st context) == 0xfffffffffffffffefffffffdfffffffc instead of 0x00000001000000020000000300000004 (expected)
  VMX21 (1st context) == 0xfffffffbfffffffafffffff9fffffff8 instead of 0x00000005000000060000000700000008 (expected)
  failure: tm_signal_context_chk_vmx

  test: tm_signal_context_chk_vsx
  tags: git_version:v5.2-8249-g02e970fae465-dirty
  VSX20 (1st context) == 0xfffffffffefffffffdfffffffcffffff instead of 0x00000001000000020000000300000004 (expected)
  VSX21 (1st context) == 0xfbfffffffafffffff9fffffff8ffffff instead of 0x00000005000000060000000700000008 (expected)
  failure: tm_signal_context_chk_vsx

Finally, this commit adds comments to the tests in the hope that it
will help people not so familiar with TM understand the tests.

Signed-off-by: Gustavo Romero <gromero@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190814205211.24840-1-gromero@linux.ibm.com