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Message-Id: <20221122075440.1165172-1-suagrfillet@gmail.com>
Date: Tue, 22 Nov 2022 15:54:40 +0800
From: Song Shuai <suagrfillet@...il.com>
To: guoren@...nel.org, rostedt@...dmis.org, mhiramat@...nel.org,
mark.rutland@....com, paul.walmsley@...ive.com, palmer@...belt.com,
aou@...s.berkeley.edu
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
Song Shuai <suagrfillet@...il.com>
Subject: [PATCH] riscv/ftrace: fix ftrace_modify_call bug
With this commit (riscv: ftrace: Reduce the detour code size to half)
patched, ftrace bug occurred When hosting kprobe and function tracer
at the same function.
Obviously, the variable caller in ftrace_modify_call was assigned by
rec->ip with 4 offset failing the code replacing at function entry.
And the caller should be assigned by rec->ip directly to indicate
the function entry.
The following is the ftrace bug log.
```
[ 419.632855] 00000000f8776803: expected (ffe00297 1a4282e7) but got (1a8282e7 f0227179)
[ 419.633390] ------------[ ftrace bug ]------------
[ 419.633553] ftrace failed to modify
[ 419.633569] [<ffffffff802091cc>] kernel_read+0x0/0x52
[ 419.633863] actual: 97:02:e0:ff:e7:82:82:1a
[ 419.634087] Updating ftrace call site to call a different ftrace function
[ 419.634279] ftrace record flags: e0000002
[ 419.634487] (2) R
[ 419.634487] expected tramp: ffffffff800093cc
[ 419.634935] ------------[ cut here ]------------
```
Signed-off-by: Song Shuai <suagrfillet@...il.com>
---
arch/riscv/kernel/ftrace.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index 8c77f236fc71..61b24d767e2e 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -132,7 +132,7 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
unsigned long addr)
{
unsigned int call[2];
- unsigned long caller = rec->ip + 4;
+ unsigned long caller = rec->ip;
int ret;
make_call_t0(caller, old_addr, call);
--
2.20.1
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