powerpc: update ppc_save_regs to save current r1 in pt_regs

ppc_save_regs() skips one stack frame while saving the CPU register states.
Instead of saving current R1, it pulls the previous stack frame pointer.

When vmcores caused by direct panic call (such as `echo c >
/proc/sysrq-trigger`), are debugged with gdb, gdb fails to show the
backtrace correctly. On further analysis, it was found that it was because
of mismatch between r1 and NIP.

GDB uses NIP to get current function symbol and uses corresponding debug
info of that function to unwind previous frames, but due to the
mismatching r1 and NIP, the unwinding does not work, and it fails to
unwind to the 2nd frame and hence does not show the backtrace.

GDB backtrace with vmcore of kernel without this patch:

---------
(gdb) bt
#0 0xc0000000002a53e8 in crash_setup_regs (oldregs=<optimized out>,
newregs=0xc000000004f8f8d8) at ./arch/powerpc/include/asm/kexec.h:69
#1 __crash_kexec (regs=<optimized out>) at kernel/kexec_core.c:974
#2 0x0000000000000063 in ?? ()
#3 0xc000000003579320 in ?? ()
---------

Further analysis revealed that the mismatch occurred because
"ppc_save_regs" was saving the previous stack's SP instead of the current
r1. This patch fixes this by storing current r1 in the saved pt_regs.

GDB backtrace with vmcore of patched kernel:

--------
(gdb) bt
#0 0xc0000000002a53e8 in crash_setup_regs (oldregs=0x0, newregs=0xc00000000670b8d8)
at ./arch/powerpc/include/asm/kexec.h:69
#1 __crash_kexec (regs=regs@entry=0x0) at kernel/kexec_core.c:974
#2 0xc000000000168918 in panic (fmt=fmt@entry=0xc000000001654a60 "sysrq triggered crash\n")
at kernel/panic.c:358
#3 0xc000000000b735f8 in sysrq_handle_crash (key=<optimized out>) at drivers/tty/sysrq.c:155
#4 0xc000000000b742cc in __handle_sysrq (key=key@entry=99, check_mask=check_mask@entry=false)
at drivers/tty/sysrq.c:602
#5 0xc000000000b7506c in write_sysrq_trigger (file=<optimized out>, buf=<optimized out>,
count=2, ppos=<optimized out>) at drivers/tty/sysrq.c:1163
#6 0xc00000000069a7bc in pde_write (ppos=<optimized out>, count=<optimized out>,
buf=<optimized out>, file=<optimized out>, pde=0xc00000000362cb40) at fs/proc/inode.c:340
#7 proc_reg_write (file=<optimized out>, buf=<optimized out>, count=<optimized out>,
ppos=<optimized out>) at fs/proc/inode.c:352
#8 0xc0000000005b3bbc in vfs_write (file=file@entry=0xc000000006aa6b00,
buf=buf@entry=0x61f498b4f60 <error: Cannot access memory at address 0x61f498b4f60>,
count=count@entry=2, pos=pos@entry=0xc00000000670bda0) at fs/read_write.c:582
#9 0xc0000000005b4264 in ksys_write (fd=<optimized out>,
buf=0x61f498b4f60 <error: Cannot access memory at address 0x61f498b4f60>, count=2)
at fs/read_write.c:637
#10 0xc00000000002ea2c in system_call_exception (regs=0xc00000000670be80, r0=<optimized out>)
at arch/powerpc/kernel/syscall.c:171
#11 0xc00000000000c270 in system_call_vectored_common ()
at arch/powerpc/kernel/interrupt_64.S:192
--------

Nick adds:
So this now saves regs as though it was an interrupt taken in the
caller, at the instruction after the call to ppc_save_regs, whereas
previously the NIP was there, but R1 came from the caller's caller and
that mismatch is what causes gdb's dwarf unwinder to go haywire.

Signed-off-by: Aditya Gupta <adityag@linux.ibm.com>
Fixes: d16a58f8854b1 ("powerpc: Improve ppc_save_regs()")
Reivewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230615091047.90433-1-adityag@linux.ibm.com

powerpc: add definition for pt_regs offset within an interrupt frame

This is a common offset that currently uses the overloaded
STACK_FRAME_OVERHEAD constant. It's easier to read and more
flexible to use a specific regs offset for this.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221127124942.1665522-8-npiggin@gmail.com

powerpc: simplify ppc_save_regs

Adjust the pt_regs pointer so the interrupt frame offsets can be used
to save registers.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221127124942.1665522-7-npiggin@gmail.com

powerpc: Improve ppc_save_regs()

Make ppc_save_regs() a bit more useful:
- Set NIP to our caller rather rather than the caller's
caller (which is what we save to LR in the stack frame).
- Set SOFTE to the current irq soft-mask state rather than
uninitialised.
- Zero CFAR rather than leave it uninitialised.

In qemu, injecting a nmi to an idle CPU gives a nicer stack
trace (note NIP, IRQMASK, CFAR).

Oops: System Reset, sig: 6 [#1]
LE PAGE_SIZE=64K MMU=Hash PREEMPT SMP NR_CPUS=2048 NUMA PowerNV
Modules linked in:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.6.0-rc2-00429-ga76e38fd80bf #1277
NIP: c0000000000b6e5c LR: c0000000000b6e5c CTR: c000000000b06270
REGS: c00000000173fb08 TRAP: 0100 Not tainted
MSR: 9000000000001033 <SF,HV,ME,IR,DR,RI,LE> CR: 28000224 XER: 00000000
CFAR: c0000000016a2128 IRQMASK: c00000000173fc80
GPR00: c0000000000b6e5c c00000000173fc80 c000000001743400 c00000000173fb08
GPR04: 0000000000000000 0000000000000000 0000000000000008 0000000000000001
GPR08: 00000001fea80000 0000000000000000 0000000000000000 ffffffffffffffff
GPR12: c000000000b06270 c000000001930000 00000000300026c0 0000000000000000
GPR16: 0000000000000000 0000000000000000 0000000000000003 c0000000016a2128
GPR20: c0000001ffc97148 0000000000000001 c000000000f289a8 0000000000080000
GPR24: c0000000016e1480 000000011dc870ba 0000000000000000 0000000000000003
GPR28: c0000000016a2128 c0000001ffc97148 c0000000016a2260 0000000000000003
NIP [c0000000000b6e5c] power9_idle_type+0x5c/0x70
LR [c0000000000b6e5c] power9_idle_type+0x5c/0x70
Call Trace:
[c00000000173fc80] [c0000000000b6e5c] power9_idle_type+0x5c/0x70 (unreliable)
[c00000000173fcb0] [c000000000b062b0] stop_loop+0x40/0x60
[c00000000173fce0] [c000000000b022d8] cpuidle_enter_state+0xa8/0x660
[c00000000173fd60] [c000000000b0292c] cpuidle_enter+0x4c/0x70
[c00000000173fda0] [c00000000017624c] call_cpuidle+0x4c/0x90
[c00000000173fdc0] [c000000000176768] do_idle+0x338/0x460
[c00000000173fe60] [c000000000176b3c] cpu_startup_entry+0x3c/0x40
[c00000000173fe90] [c0000000000126b4] rest_init+0x124/0x140
[c00000000173fed0] [c0000000010948d4] start_kernel+0x938/0x988
[c00000000173ff90] [c00000000000cdcc] start_here_common+0x1c/0x20

Oops: System Reset, sig: 6 [#1]
LE PAGE_SIZE=64K MMU=Hash PREEMPT SMP NR_CPUS=2048 NUMA PowerNV
Modules linked in:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.6.0-rc2-00430-gddce91b8712f #1278
NIP: c00000000001d150 LR: c0000000000b6e5c CTR: c000000000b06270
REGS: c00000000173fb08 TRAP: 0100 Not tainted
MSR: 9000000000001033 <SF,HV,ME,IR,DR,RI,LE> CR: 28000224 XER: 00000000
CFAR: 0000000000000000 IRQMASK: 1
GPR00: c0000000000b6e5c c00000000173fc80 c000000001743400 c00000000173fb08
GPR04: 0000000000000000 0000000000000000 0000000000000008 0000000000000001
GPR08: 00000001fea80000 0000000000000000 0000000000000000 ffffffffffffffff
GPR12: c000000000b06270 c000000001930000 00000000300026c0 0000000000000000
GPR16: 0000000000000000 0000000000000000 0000000000000003 c0000000016a2128
GPR20: c0000001ffc97148 0000000000000001 c000000000f289a8 0000000000080000
GPR24: c0000000016e1480 00000000b68db8ce 0000000000000000 0000000000000003
GPR28: c0000000016a2128 c0000001ffc97148 c0000000016a2260 0000000000000003
NIP [c00000000001d150] replay_system_reset+0x30/0xa0
LR [c0000000000b6e5c] power9_idle_type+0x5c/0x70
Call Trace:
[c00000000173fc80] [c0000000000b6e5c] power9_idle_type+0x5c/0x70 (unreliable)
[c00000000173fcb0] [c000000000b062b0] stop_loop+0x40/0x60
[c00000000173fce0] [c000000000b022d8] cpuidle_enter_state+0xa8/0x660
[c00000000173fd60] [c000000000b0292c] cpuidle_enter+0x4c/0x70
[c00000000173fda0] [c00000000017624c] call_cpuidle+0x4c/0x90
[c00000000173fdc0] [c000000000176768] do_idle+0x338/0x460
[c00000000173fe60] [c000000000176b38] cpu_startup_entry+0x38/0x40
[c00000000173fe90] [c0000000000126b4] rest_init+0x124/0x140
[c00000000173fed0] [c0000000010948d4] start_kernel+0x938/0x988
[c00000000173ff90] [c00000000000cdcc] start_here_common+0x1c/0x20

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200403131006.123243-1-npiggin@gmail.com

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152

Based on 1 normalized pattern(s):

this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version

extracted by the scancode license scanner the SPDX license identifier

GPL-2.0-or-later

has been chosen to replace the boilerplate/reference in 3029 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190527070032.746973796@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

powerpc: move ASM_CONST and stringify_in_c() into asm-const.h

This patch moves ASM_CONST() and stringify_in_c() into
dedicated asm-const.h, then cleans all related inclusions.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
[mpe: asm-compat.h should include asm-const.h]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

powerpc/32: Use stmw/lmw for registers save/restore in asm

arch/powerpc/Makefile activates -mmultiple on BE PPC32 configs
in order to use multiple word instructions in functions entry/exit.

The patch does the same for the asm parts, for consistency.

On processors like the 8xx on which insn fetching is pretty slow,
this speeds up registers save/restore.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
[mpe: PPC32 is BE only, so drop the endian checks]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>

powerpc: Remove second definition of STACK_FRAME_OVERHEAD

Since STACK_FRAME_OVERHEAD is defined in asm/ptrace.h and that
is ASSEMBER safe, we can just include that instead of going via
asm-offsets.h.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

powerpc: Prepare xmon_save_regs for use with kdump

Today the arch/powerpc/xmon/setjmp.S file contains only the
xmon_save_regs function. We want to use it for kdump purposes, so
let's move the file into arch/powerpc/kernel/ and give the function a
more generic name (ppc_save_regs).

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>