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

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

[Ramin Moussavi]

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 lets a handler store its
incoming register arguments into [r1+4]..[r1+28]; since r1 points at
struct rt_sigframe on entry, those stores land in siginfo/ucontext and
corrupt the signal state.  An eight-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) now pass.  checkpatch --strict is clean and both apply to
current linux-next.

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

 arch/microblaze/kernel/signal.c             | 7 +++++++
 arch/microblaze/kernel/syscalls/syscall.tbl | 2 +-
 2 files changed, 8 insertions(+), 1 deletion(-)

-- 
2.53.0

[PATCH 1/2] microblaze: wire up sigaltstack

[Ramin Moussavi]

sigaltstack is wired to sys_ni_syscall - microblaze is the only
architecture without it - although the microblaze signal delivery code
fully supports the alternate signal stack: get_sigframe() picks the
stack via sigsp(), setup_rt_frame() saves it with __save_altstack() and
sys_rt_sigreturn() calls restore_altstack().

Wire it up to sys_sigaltstack.

Tested on qemu petalogix-s3adsp1800 (microblazeel) with the uClibc-ng
test suite: the five sigaltstack-dependent NPTL tests (tst-cancel20/21,
tst-cancelx20/21, tst-signal6) pass; before this change sigaltstack()
returned ENOSYS.

Signed-off-by: Ramin Moussavi <ramin.moussavi@yacoub.de>
---
 arch/microblaze/kernel/syscalls/syscall.tbl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
index 223d26303..b4ce48e8a 100644
--- a/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl
@@ -193,7 +193,7 @@
 183	common	getcwd				sys_getcwd
 184	common	capget				sys_capget
 185	common	capset				sys_capset
-186	common	sigaltstack			sys_ni_syscall
+186	common	sigaltstack			sys_sigaltstack
 187	common	sendfile			sys_sendfile
 188	common	getpmsg				sys_ni_syscall
 189	common	putpmsg				sys_ni_syscall
-- 
2.53.0

[PATCH 2/2] microblaze: reserve the ABI argument-home area in the signal frame

[Ramin Moussavi]

The MicroBlaze procedure call standard lets a callee store its incoming
register arguments r5..r10 into the caller-provided home slots at
[r1+4]..[r1+28].  When the kernel enters a signal handler it sets r1 to
point at struct rt_sigframe, whose leading members are the siginfo and
ucontext prepared for the handler.  A handler that homes its arguments -
which an unoptimised (-O0) build always does - therefore overwrites the
start of siginfo/ucontext, corrupting the signal state that the handler
and sys_rt_sigreturn() depend on.

Reserve the home area by making an eight-word gap the first member of
struct rt_sigframe, so the handler's argument stores land in scratch space
instead of clobbering siginfo.

Tested on qemu-system-microblazeel (petalogix-s3adsp1800) with the
uClibc-ng NPTL test suite: tst-timer4, tst-timer5, tst-mqueue5 and
tst-signal6 pass; before this change they failed because the handler
clobbered the signal frame.

Signed-off-by: Ramin Moussavi <ramin.moussavi@yacoub.de>
---
 arch/microblaze/kernel/signal.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/microblaze/kernel/signal.c b/arch/microblaze/kernel/signal.c
index c78a0ff48..df9c07d77 100644
--- a/arch/microblaze/kernel/signal.c
+++ b/arch/microblaze/kernel/signal.c
@@ -49,6 +49,13 @@ struct sigframe {
 };
 
 struct rt_sigframe {
+	/*
+	 * Home area for the handler's register arguments: the MicroBlaze
+	 * ABI lets the callee store r5..r10 at [r1+4]..[r1+28], and r1
+	 * points at this frame when the handler is entered.  Without the
+	 * gap those stores corrupt info/uc.
+	 */
+	unsigned long abi_gap[8];
 	struct siginfo info;
 	struct ucontext uc;
 	unsigned long tramp[2];	/* signal trampoline */
-- 
2.53.0