[PATCH v2 0/2] microblaze: fix signal-frame handling for NPTL

[Ramin Moussavi <lordrasmus@gmail.com>]

Two independent fixes to the microblaze signal-delivery path, both found
while bringing the uClibc-ng NPTL test suite up on microblazeel under
qemu-system (petalogix-s3adsp1800).

Patch 1 wires up sigaltstack(), which is currently routed to
sys_ni_syscall even though the signal code fully supports an alternate
stack - microblaze is the only architecture leaving it unimplemented.

Patch 2 reserves the ABI argument-home area at the top of the signal
frame.  The MicroBlaze calling convention reserves [r1+0] for the return
address and lets a handler store its incoming register arguments r5..r10
into [r1+4]..[r1+24]; since r1 points at struct rt_sigframe on entry,
those stores land in siginfo/ucontext and corrupt the signal state.  A
seven-word leading gap moves them into scratch space.

Both were tested with the uClibc-ng NPTL tests; the affected tests
(tst-cancel20/21, tst-cancelx20/21, tst-signal6, tst-timer4/5,
tst-mqueue5) pass.  checkpatch --strict is clean and both apply to
current linux-next.

Changes since v1 [1]:
 - Patch 2: shrink the gap from eight to seven words.  Michal pointed
   out that the home area is exactly seven words (r15 at r1+0, r5..r10
   at r1+4..r1+24); the eighth word was never written by the ABI.
   Retested on qemu - tst-timer4/5, tst-mqueue5, tst-signal6 still pass.
 - Patch 2: fix the offset range in the commit message and the in-code
   comment ([r1+4]..[r1+24], not [r1+28]).
 - Patch 1: unchanged.

[1] https://lore.kernel.org/all/cover.1780587199.git.lordrasmus@gmail.com/

Ramin Moussavi (2):
  microblaze: wire up sigaltstack
  microblaze: reserve the ABI argument-home area in the signal frame

 arch/microblaze/kernel/signal.c             | 8 ++++++++
 arch/microblaze/kernel/syscalls/syscall.tbl | 2 +-
 2 files changed, 9 insertions(+), 1 deletion(-)

-- 
2.53.0