From: Matthew Bystrin <dev.mbstr@gmail.com>
To: linux-riscv@lists.infradead.org
Subject: [PATCH] riscv: stacktrace: fixed walk_stackframe()
Date: Fri, 26 Apr 2024 10:24:11 +0300 [thread overview]
Message-ID: <20240426072701.6463-1-dev.mbstr@gmail.com> (raw)
If the load access fault occures in a function without callee
(CONFIG_FRAME_POINTER=y), when wrong stack trace will be displayed:
[<ffffffff804853c2>] regmap_mmio_read32le+0xe/0x1c
---[ end trace 0000000000000000 ]---
Registers dump:
ra 0xffffffff80485758 <regmap_mmio_read+36>
sp 0xffffffc80200b9a0
fp 0xffffffc80200b9b0
pc 0xffffffff804853ba <regmap_mmio_read32le+6>
Stack dump:
0xffffffc80200b9a0: 0xffffffc80200b9e0 0xffffffc80200b9e0
0xffffffc80200b9b0: 0xffffffff8116d7e8 0x0000000000000100
0xffffffc80200b9c0: 0xffffffd8055b9400 0xffffffd8055b9400
0xffffffc80200b9d0: 0xffffffc80200b9f0 0xffffffff8047c526
0xffffffc80200b9e0: 0xffffffc80200ba30 0xffffffff8047fe9a
The assembler dump of the function preambula:
add sp,sp,-16
sd s0,8(sp)
add s0,sp,16
In the fist stack frame, where ra is not stored on the stack we can
observe:
0(sp) 8(sp)
.---------------------------------------------.
sp->| frame->fp | frame->ra (saved fp) |
|---------------------------------------------|
fp->| .... | .... |
|---------------------------------------------|
| | |
and in the code check is performed:
if (regs && (regs->epc == pc) && (frame->fp & 0x7))
I see no reason to check frame->fp value at all, because it is can be
uninitialized value on the stack, so removed it. After the stacktrace
shows as expect:
[<ffffffff804853c2>] regmap_mmio_read32le+0xe/0x1c
[<ffffffff80485758>] regmap_mmio_read+0x24/0x52
[<ffffffff8047c526>] _regmap_bus_reg_read+0x1a/0x22
[<ffffffff8047fe9a>] _regmap_read+0x5c/0xea
[<ffffffff80480376>] _regmap_update_bits+0x76/0xc0
...
---[ end trace 0000000000000000 ]---
Fixes: f766f77a74f5 ("riscv/stacktrace: Fix stack output without ra on the stack top")
Signed-off-by: Matthew Bystrin <dev.mbstr@gmail.com>
---
I've catched this bug on v6.1 with gcc 12.2.0 (Debian 12.2.0-13). Different
compiler versions generate the same assembler code. So I think this is not a
compiler issue.
arch/riscv/kernel/stacktrace.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
index 64a9c093aef9..8138c68270c9 100644
--- a/arch/riscv/kernel/stacktrace.c
+++ b/arch/riscv/kernel/stacktrace.c
@@ -55,7 +55,7 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
/* Unwind stack frame */
frame = (struct stackframe *)fp - 1;
sp = fp;
- if (regs && (regs->epc == pc) && (frame->fp & 0x7)) {
+ if (regs && regs->epc == pc) {
fp = frame->ra;
pc = regs->ra;
} else {
--
2.43.0
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next reply other threads:[~2024-04-26 7:27 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-26 7:24 Matthew Bystrin [this message]
2024-05-08 15:51 ` [PATCH] riscv: stacktrace: fixed walk_stackframe() Samuel Holland
2024-05-08 17:05 ` Palmer Dabbelt
2024-05-09 22:13 ` Matthew Bystrin
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