c74837292d
commit b684c09f09e7a6af3794d4233ef785819e72db79 upstream. 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 Cc: stable@vger.kernel.org Signed-off-by: Aditya Gupta <adityag@linux.ibm.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
80 lines
2 KiB
ArmAsm
Executable file
80 lines
2 KiB
ArmAsm
Executable file
/* SPDX-License-Identifier: GPL-2.0-or-later */
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/*
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* Copyright (C) 1996 Paul Mackerras.
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*
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* NOTE: assert(sizeof(buf) > 23 * sizeof(long))
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*/
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#include <asm/processor.h>
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#include <asm/ppc_asm.h>
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#include <asm/asm-offsets.h>
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#include <asm/ptrace.h>
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#include <asm/asm-compat.h>
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/*
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* Grab the register values as they are now.
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* This won't do a particularly good job because we really
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* want our caller's caller's registers, and our caller has
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* already executed its prologue.
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* ToDo: We could reach back into the caller's save area to do
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* a better job of representing the caller's state (note that
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* that will be different for 32-bit and 64-bit, because of the
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* different ABIs, though).
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*/
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_GLOBAL(ppc_save_regs)
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PPC_STL r0,0*SZL(r3)
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#ifdef CONFIG_PPC32
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stmw r2, 2*SZL(r3)
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#else
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PPC_STL r2,2*SZL(r3)
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PPC_STL r3,3*SZL(r3)
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PPC_STL r4,4*SZL(r3)
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PPC_STL r5,5*SZL(r3)
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PPC_STL r6,6*SZL(r3)
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PPC_STL r7,7*SZL(r3)
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PPC_STL r8,8*SZL(r3)
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PPC_STL r9,9*SZL(r3)
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PPC_STL r10,10*SZL(r3)
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PPC_STL r11,11*SZL(r3)
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PPC_STL r12,12*SZL(r3)
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PPC_STL r13,13*SZL(r3)
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PPC_STL r14,14*SZL(r3)
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PPC_STL r15,15*SZL(r3)
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PPC_STL r16,16*SZL(r3)
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PPC_STL r17,17*SZL(r3)
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PPC_STL r18,18*SZL(r3)
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PPC_STL r19,19*SZL(r3)
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PPC_STL r20,20*SZL(r3)
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PPC_STL r21,21*SZL(r3)
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PPC_STL r22,22*SZL(r3)
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PPC_STL r23,23*SZL(r3)
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PPC_STL r24,24*SZL(r3)
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PPC_STL r25,25*SZL(r3)
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PPC_STL r26,26*SZL(r3)
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PPC_STL r27,27*SZL(r3)
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PPC_STL r28,28*SZL(r3)
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PPC_STL r29,29*SZL(r3)
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PPC_STL r30,30*SZL(r3)
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PPC_STL r31,31*SZL(r3)
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lbz r0,PACAIRQSOFTMASK(r13)
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PPC_STL r0,SOFTE-STACK_FRAME_OVERHEAD(r3)
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#endif
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/* store current SP */
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PPC_STL r1,1*SZL(r3)
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/* get caller's LR */
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PPC_LL r4,0(r1)
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PPC_LL r0,LRSAVE(r4)
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PPC_STL r0,_LINK-STACK_FRAME_OVERHEAD(r3)
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mflr r0
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PPC_STL r0,_NIP-STACK_FRAME_OVERHEAD(r3)
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mfmsr r0
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PPC_STL r0,_MSR-STACK_FRAME_OVERHEAD(r3)
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mfctr r0
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PPC_STL r0,_CTR-STACK_FRAME_OVERHEAD(r3)
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mfxer r0
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PPC_STL r0,_XER-STACK_FRAME_OVERHEAD(r3)
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mfcr r0
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PPC_STL r0,_CCR-STACK_FRAME_OVERHEAD(r3)
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li r0,0
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PPC_STL r0,_TRAP-STACK_FRAME_OVERHEAD(r3)
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PPC_STL r0,ORIG_GPR3-STACK_FRAME_OVERHEAD(r3)
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blr
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