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From:   Zhaoyang Huang <huangzhaoyang@gmail.com>
To:     Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Dave Martin <dave.martin@arm.com>,
        Michael Weiser <michael.weiser@gmx.de>,
        Mark Rutland <mark.rutland@arm.com>,
        James Morse <james.morse@arm.com>, linux-kernel@vger.kernel.org
Subject: [PATCH] arch/arm64 : fix error in dump_backtrace
Date:   Tue,  6 Nov 2018 15:19:35 +0800
Message-Id: <1541488775-29610-1-git-send-email-huangzhaoyang@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

From: Zhaoyang Huang <zhaoyang.huang@unisoc.com>

In some cases, the instruction of "bl foo1" will be the last one of the
foo2[1], which will cause the lr be the first instruction of the adjacent
foo3[2]. Hence, the backtrace will show the weird result as bellow[3].
The patch will fix it by miner 4 of the lr when dump_backtrace

[1]
0xffffff80081e6b04 <handle_mm_fault+3996>:      adrp    x0, 0xffffff8008ca8000
0xffffff80081e6b08 <handle_mm_fault+4000>:      add     x0, x0, #0x5a8
0xffffff80081e6b0c <handle_mm_fault+4004>:      bl      0xffffff80081b0ca0 <panic>
0xffffff80081e6b10 <access_remote_vm>:  stp     x29, x30, [sp,#-64]!
0xffffff80081e6b14 <access_remote_vm+4>:        mov     x29, sp

[2]
crash_arm64> rd ffffffc02eec3bd0 2
ffffffc02eec3bd0:  ffffffc02eec3cb0 ffffff80081e6b10

[3]
wrong:
[<ffffff80081b0d90>] panic+0xf0/0x24c
[<ffffff80081e6b10>] access_remote_vm+0x0/0x5c
[<ffffff800809d7b0>] do_page_fault+0x290/0x3b8
[<ffffff8008081570>] do_mem_abort+0x64/0xdc

correct:
[ffffffc02eec3bd0] panic at ffffff80081b0da4
[ffffffc02eec3cb0] handle_mm_fault at ffffff80081e6b0c
[ffffffc02eec3d80] do_page_fault at ffffff800809d7ac
[ffffffc02eec3df0] do_mem_abort at ffffff800808156c

Signed-off-by: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
---
 arch/arm64/kernel/traps.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index d399d45..7a097cc 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -113,7 +113,7 @@ void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
 
 	if (tsk == current) {
 		frame.fp = (unsigned long)__builtin_frame_address(0);
-		frame.pc = (unsigned long)dump_backtrace;
+		frame.pc = (unsigned long)dump_backtrace + 4;
 	} else {
 		/*
 		 * task blocked in __switch_to
@@ -130,7 +130,7 @@ void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
 	do {
 		/* skip until specified stack frame */
 		if (!skip) {
-			dump_backtrace_entry(frame.pc);
+			dump_backtrace_entry(frame.pc - 4);
 		} else if (frame.fp == regs->regs[29]) {
 			skip = 0;
 			/*
-- 
1.9.1