[Crash-utility] [PATCH] ARM: Fix idle task stack unwinding on Thumb-2 kernels

[Dave Anderson]

----- Original Message -----
> ARM kernels built with the Thumb-2 instruction need R7 instead of FP for
> unwinding stacks using the DWARF unwinder.
> 
> On a Thumb-2 kernel:
> 
> Before:
> crash> bt 1
> PID: 1      TASK: ee7e0000  CPU: 1   COMMAND: "systemd-shutdow"
> 
> After:
> crash> bt 1
> PID: 1      TASK: ee7e0000  CPU: 1   COMMAND: "systemd-shutdow"
>  #0 [<805587a1>] (__schedule) from [<80558d2b>]
>  #1 [<80558d2b>] (schedule) from [<8055c8bb>]
>  #2 [<8055c8bb>] (schedule_hrtimeout_range_clock) from [<8055c937>]
>  #3 [<8055c937>] (schedule_hrtimeout_range) from [<8012cbdf>]
>  #4 [<8012cbdf>] (sys_rt_sigtimedwait) from [<80107259>]

Queued for crash-7.2.6:

  https://github.com/crash-utility/crash/commit/8e21aa3fa5c255396e9dce49786eae595f0371c1

Thanks,
  Dave


> 
> Change-Id: Iec0c3a3ab089441d0ebf0002343790d65fe6ca78
> ---
>  arm.c        | 15 +++++++++++----
>  defs.h       |  1 +
>  symbols.c    |  2 ++
>  unwind_arm.c | 14 ++++++++++----
>  4 files changed, 24 insertions(+), 8 deletions(-)
> 
> diff --git a/arm.c b/arm.c
> index 9652361..b05b0b3 100644
> --- a/arm.c
> +++ b/arm.c
> @@ -301,6 +301,8 @@ arm_init(int when)
>  		 * thread_info.cpu_context.
>  		 */
>  		STRUCT_SIZE_INIT(cpu_context_save, "cpu_context_save");
> +		MEMBER_OFFSET_INIT(cpu_context_save_r7,
> +			"cpu_context_save", "r7");
>  		MEMBER_OFFSET_INIT(cpu_context_save_fp,
>  			"cpu_context_save", "fp");
>  		MEMBER_OFFSET_INIT(cpu_context_save_sp,
> @@ -1313,13 +1315,18 @@ arm_get_frame(struct bt_info *bt, ulong *pcp, ulong
> *spp)
>  	cpu_context = tt->thread_info + OFFSET(thread_info_cpu_context);
>  
>  #define GET_REG(ptr, cp, off) ((*ptr) = (*((ulong *)((cp) + OFFSET(off)))))
> -	/*
> -	 * Unwinding code needs FP value also so we pass it with bt.
> -	 */
> -	GET_REG(&bt->frameptr, cpu_context, cpu_context_save_fp);
>  	GET_REG(spp, cpu_context, cpu_context_save_sp);
>  	GET_REG(pcp, cpu_context, cpu_context_save_pc);
>  
> +	/*
> +	 * Unwinding code needs FP (R7 for Thumb code) value also so we pass it
> +	 * with bt.
> +	 */
> +	if (*pcp & 1)
> +		GET_REG(&bt->frameptr, cpu_context, cpu_context_save_r7);
> +	else
> +		GET_REG(&bt->frameptr, cpu_context, cpu_context_save_fp);
> +
>  	return TRUE;
>  }
>  
> diff --git a/defs.h b/defs.h
> index 5841b1f..b4f6372 100644
> --- a/defs.h
> +++ b/defs.h
> @@ -2066,6 +2066,7 @@ struct offset_table {                    /* stash of
> commonly-used offsets */
>  	long xa_node_shift;
>  	long hd_struct_dkstats;
>  	long disk_stats_in_flight;
> +	long cpu_context_save_r7;
>  };
>  
>  struct size_table {         /* stash of commonly-used sizes */
> diff --git a/symbols.c b/symbols.c
> index e73e735..31a4d7b 100644
> --- a/symbols.c
> +++ b/symbols.c
> @@ -10047,6 +10047,8 @@ dump_offset_table(char *spec, ulong makestruct)
>  	fprintf(fp, "          s390_stack_frame_r14: %ld\n",
>  		OFFSET(s390_stack_frame_r14));
>  
> +	fprintf(fp, "           cpu_context_save_r7: %ld\n",
> +		OFFSET(cpu_context_save_r7));
>  	fprintf(fp, "           cpu_context_save_fp: %ld\n",
>  		OFFSET(cpu_context_save_fp));
>  	fprintf(fp, "           cpu_context_save_sp: %ld\n",
> diff --git a/unwind_arm.c b/unwind_arm.c
> index 8667d3c..1a8f51e 100644
> --- a/unwind_arm.c
> +++ b/unwind_arm.c
> @@ -87,6 +87,7 @@ struct stackframe {
>  };
>  
>  enum regs {
> +	R7 = 7,
>  	FP = 11,
>  	SP = 13,
>  	LR = 14,
> @@ -615,6 +616,7 @@ unwind_frame(struct stackframe *frame, ulong stacktop)
>  	struct unwind_ctrl_block ctrl;
>  	struct unwind_idx *idx;
>  	ulong low, high;
> +	int fpindex = FP;
>  
>  	low = frame->sp;
>  	high = stacktop;
> @@ -622,6 +624,10 @@ unwind_frame(struct stackframe *frame, ulong stacktop)
>  	if (!is_kernel_text(frame->pc))
>  		return FALSE;
>  
> +	/* Thumb needs R7 instead of FP */
> +	if (frame->pc & 1)
> +		fpindex = R7;
> +
>  	tbl = search_table(frame->pc);
>  	if (!tbl) {
>  		error(WARNING, "UNWIND: cannot find unwind table for %lx\n",
> @@ -630,13 +636,13 @@ unwind_frame(struct stackframe *frame, ulong stacktop)
>  	}
>  	idx = search_index(tbl, frame->pc);
>  
> -	ctrl.vrs[FP] = frame->fp;
> +	ctrl.vrs[fpindex] = frame->fp;
>  	ctrl.vrs[SP] = frame->sp;
>  	ctrl.vrs[LR] = frame->lr;
>  	ctrl.vrs[PC] = 0;
>  
>  	if (CRASHDEBUG(5)) {
> -		fprintf(fp, "UNWIND: >frame: FP=%lx\n", ctrl.vrs[FP]);
> +		fprintf(fp, "UNWIND: >frame: FP=%lx\n", ctrl.vrs[fpindex]);
>  		fprintf(fp, "UNWIND: >frame: SP=%lx\n", ctrl.vrs[SP]);
>  		fprintf(fp, "UNWIND: >frame: LR=%lx\n", ctrl.vrs[LR]);
>  		fprintf(fp, "UNWIND: >frame: PC=%lx\n", ctrl.vrs[PC]);
> @@ -706,13 +712,13 @@ unwind_frame(struct stackframe *frame, ulong stacktop)
>  	if (frame->pc == ctrl.vrs[PC])
>  		return FALSE;
>  
> -	frame->fp = ctrl.vrs[FP];
> +	frame->fp = ctrl.vrs[fpindex];
>  	frame->sp = ctrl.vrs[SP];
>  	frame->lr = ctrl.vrs[LR];
>  	frame->pc = ctrl.vrs[PC];
>  
>  	if (CRASHDEBUG(5)) {
> -		fprintf(fp, "UNWIND: <frame: FP=%lx\n", ctrl.vrs[FP]);
> +		fprintf(fp, "UNWIND: <frame: FP=%lx\n", ctrl.vrs[fpindex]);
>  		fprintf(fp, "UNWIND: <frame: SP=%lx\n", ctrl.vrs[SP]);
>  		fprintf(fp, "UNWIND: <frame: LR=%lx\n", ctrl.vrs[LR]);
>  		fprintf(fp, "UNWIND: <frame: PC=%lx\n", ctrl.vrs[PC]);
> --
> 2.20.0
> 
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