From 358515f9f951e3140adda3795d0d0441db3f7436 Mon Sep 17 00:00:00 2001 From: Onkarnath Date: Tue, 11 Aug 2026 10:52:19 +0100 Subject: [PATCH] ARM: 9490/1: backtrace-clang: fix wrong sp usage for unwinding show_stack() can be called for any task, but c_backtrace is always unwinding frames based on "sp" register. Which leads to printing backtrace of current task instead of required task. Try with normal TC: ================== for_each_process(p){ sched_show_task(p); } [7.433271] task:kthreadd state:S stack:0 pid:2 tgid:2 ppid:0 task_flags:0x208040 flags:0x00000000 [7.433633] Call trace: [7.433640] [<80113418>] (dump_backtrace) from [<80113510>] (show_stack+0x14/0x18) .. [7.433676] [<8016749c>] (sched_show_task) from [<803cb324>] (meminfo_proc_show+0x6c/0x930) [7.434019] r5:8158e300 r4:8b4882d0 [7.434024] [<803cb324>] (meminfo_proc_show) from [<80365788>] (seq_read_iter+0x148/0x4bc) [7.434045] [<80365788>] (seq_read_iter) from [<803c044c>] (proc_reg_read_iter+0xb8/0xc4) [7.434060] [<803c044c>] (proc_reg_read_iter) from [<80377104>] (copy_splice_read+0x228/0x308) It should unwind frame based on passed "fp". (CONFIG_UNWINDER_FRAME_POINTER=y) Extra sp manipulation is needed only when c_backtrace() is called from dump_backtrace() with "frame == fp" i.e. NULL regs and not current task. (Suggested by Ard Biesheuvel) Otherwise passed "fp" should be used to unwind backtraces. With fix: ========= [13.933732] task:kthreadd state:S stack:0 pid:2 tgid:2 ppid:0 task_flags:0x208040 flags:0x00000000 [13.934165] Call trace: [13.934604] [<80afa1a8>] (schedule) from [<8015426c>] (kthreadd+0x124/0x208) [13.934654] r10:8100bbf0 r4:8116f440 [13.934664] [<8015426c>] (kthreadd) from [<8010010c>] (ret_from_fork+0x14/0x28) [13.934691] Exception stack(0xf081df9c to 0xf081dfe4) Suggested-by: Ard Biesheuvel Reviewed-by: Nick Desaulniers Signed-off-by: Onkarnath Signed-off-by: Maninder Singh Signed-off-by: Russell King --- arch/arm/lib/backtrace-clang.S | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/arm/lib/backtrace-clang.S b/arch/arm/lib/backtrace-clang.S index 290c52a60fc6..9a10828992af 100644 --- a/arch/arm/lib/backtrace-clang.S +++ b/arch/arm/lib/backtrace-clang.S @@ -107,8 +107,10 @@ ENDPROC(c_backtrace) /* * Switches the current frame to be the frame for dump_stack. + * (Only in case of current task using current registers) */ - add frame, sp, #24 @ switch to false frame + cmp frame, fp + addeq frame, sp, #24 @ switch to false frame for_each_frame: tst frame, mask @ Check for address exceptions bne no_frame