Fix typos, most reported by "codespell arch/arc".  Only touches comments,
no code changes.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Vineet Gupta <vgupta@kernel.org>

THe high level structure of most ARC exception handlers is
 1. save regfile with EXCEPTION_PROLOGUE
 2. setup r0: EFA (not part of pt_regs)
 3. setup r1: pointer to pt_regs (SP)
 4. drop down to pure kernel mode (from exception)
 5. call the Linux "C" handler

Remove the boiler plate code by moving #2, #3, #4 into #1.

The exceptions to most exceptions are syscall Trap and Machine check
which don't do some of above for various reasons, so call a newly
introduced variant EXCEPTION_PROLOGUE_KEEP_AE (same as original
EXCEPTION_PROLOGUE)

Tested-by: Pavel Kozlov <Pavel.Kozlov@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@kernel.org>

Signed-off-by: Vineet Gupta <vgupta@kernel.org>

 - comments update
 - rename syscall_trace_entry
 - use PT_xxx in entry code

Signed-off-by: Vineet Gupta <vgupta@kernel.org>

The motivation is eventual ABI considerations for ARCv3 but even without
it this change us worthwhile as diffstat reduces 100 net lines

r25 is a callee saved register, normally not saved by entry code in
pt_regs. However because of its usage in CONFIG_ARC_CURR_IN_REG it needs
to be. This in turn requires a whole bunch of special casing when we
need to access r25. Then there is distinction between user mode r25 vs.
kernel mode r25 - hence distinct SAVE_CALLEE_SAVED_{USER,KERNEL}

Instead use gp which is a scratch register and thus saved already in entry
code. This cleans things up significantly and much nocer on eyes:

 - SAVE_CALLEE_SAVED_{USER,KERNEL} are now exactly same
 - no special user_r25 slot in pt_reggs

Note that typical global asm registers are callee-saved (r25), but gp is
not callee-saved thus needs additional -ffixed-<reg> toggle

Signed-off-by: Vineet Gupta <vgupta@kernel.org>

Implement all the bits required to support HAVE_SYSCALL_TRACEPOINTS
according to Documentation/trace/ftrace-design.rst.

Signed-off-by: Sergey Matyukevich <sergey.matyukevich@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@kernel.org>

Function syscall_trace_exit expects pointer to pt_regs. However
r0 is also used to keep syscall return value. Restore pointer
to pt_regs before calling syscall_trace_exit.

Cc: <stable@vger.kernel.org>
Signed-off-by: Sergey Matyukevich <sergey.matyukevich@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@kernel.org>

... to avoid polluting shared entry code (across three ISA variants)
with ISA/MMU specific code.

Cc: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@kernel.org>

We have NR_syscall syscalls from [0 .. NR_syscall-1].
However the check for invalid syscall number is "> NR_syscall" as
opposed to >=. This off-by-one error erronesously allows "NR_syscall"
to be treated as valid syscall causeing out-of-bounds access into
syscall-call table ensuing a crash (holes within syscall table have a
invalid-entry handler but this is beyond the array implementing the
table).

This problem showed up on v5.6 kernel when testing glibc 2.33 (v5.10
kernel capable, includng faccessat2 syscall 439). The v5.6 kernel has
NR_syscalls=439 (0 to 438). Due to the bug, 439 passed by glibc was
not handled as -ENOSYS but processed leading to a crash.

Link: https://github.com/foss-for-synopsys-dwc-arc-processors/linux/issues/48
Reported-by: Shahab Vahedi <shahab@synopsys.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

Linux 5.11.rcX was failing to boot on ARC HSDK board. Turns out we have
a couple of issues, this being the first one, and I'm to blame as I
didn't pay attention during review.

TIF_NOTIFY_SIGNAL support requires checking multiple TIF_* bits in
kernel return code path. Old code only needed to check a single bit so
BBIT0 <TIF_SIGPENDING> worked. New code needs to check multiple bits so
AND <bit-mask> instruction. So needs to use bit mask variant _TIF_SIGPENDING

Cc: Jens Axboe <axboe@kernel.dk>
Fixes: 53855e12588743ea128 ("arc: add support for TIF_NOTIFY_SIGNAL")
Link: https://github.com/foss-for-synopsys-dwc-arc-processors/linux/issues/34
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>