Messages in this thread Patch in this message | | | From | Song Shuai <> | Date | Tue, 22 Nov 2022 09:11:34 +0000 | Subject | Re: [PATCH] riscv/ftrace: fix ftrace_modify_call bug |
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Guo Ren <guoren@kernel.org> 于2022年11月22日周二 08:57写道: > > On Tue, Nov 22, 2022 at 3:54 PM Song Shuai <suagrfillet@gmail.com> wrote: > > > > 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. > Thank you, it's my fault, but I think the problem is: > > Before (riscv: ftrace: Reduce the detour code size to half) > 0: REG_S ra, -SZREG(sp) > 4: auipc ra, ? <- We need "rec->ip + 4" here > 8: jalr ?(ra) > 12: REG_L ra, -SZREG(sp) > > After (riscv: ftrace: Reduce the detour code size to half) > 0: auipc t0, ? <- We needn't "rec->ip + 4" anymore > 4: jalr t0, ?(t0) > > I copied rec->ip + 4 blindly, then caused the bug. Right? > Yes, you're right.
Here's my simple test case for your convenience. ``` echo kernel_read > set_ftrace_filter echo function > current_tracer echo 'p:myp kernel_read' > kprobe_events echo 1 > events/kprobes/myp/enable # ftrace bug ``` > > > > 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@gmail.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 > > > > > -- > Best Regards > Guo Ren Thanks, Song
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