[PATCH] riscv/ftrace: fix ftrace_modify_call bug

[Conor Dooley]

On Tue, Nov 22, 2022 at 03:54:40PM +0800, Song Shuai wrote:
> With this commit (riscv: ftrace: Reduce the detour code size to half)

AFAICT the above patch has not been applied & this patch here should be
folded into the offending patch?
I've marked this one as "Not Applicable" in patchwork as a result, but
let me know if that is an incorrect assumption.

Thanks,
Conor.

> 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 at 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
>