On Mon, 13 Jul 2020 16:39:18 PDT (-0700), guo...@kernel.org wrote:
From: Guo Ren <guo...@linux.alibaba.com>
The "Changing Execution Path" section in the Documentation/kprobes.txt
said:
Since kprobes can probe into a running kernel code, it can change the
register set, including instruction pointer.
Signed-off-by: Guo Ren <guo...@linux.alibaba.com>
Cc: Masami Hiramatsu <mhira...@kernel.org>
Cc: Palmer Dabbelt <palmerdabb...@google.com>
---
arch/riscv/kernel/mcount-dyn.S | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
index 35a6ed7..4b58b54 100644
--- a/arch/riscv/kernel/mcount-dyn.S
+++ b/arch/riscv/kernel/mcount-dyn.S
@@ -123,6 +123,7 @@ ENDPROC(ftrace_caller)
sd ra, (PT_SIZE_ON_STACK+8)(sp)
addi s0, sp, (PT_SIZE_ON_STACK+16)
+ sd ra, PT_EPC(sp)
sd x1, PT_RA(sp)
sd x2, PT_SP(sp)
sd x3, PT_GP(sp)
So that's definately not going to be EPC any more. I'm not sure that field is
sanely named, though, as it's really just the PC when it comes to other ptrace
stuff.
@@ -157,6 +158,7 @@ ENDPROC(ftrace_caller)
.endm
.macro RESTORE_ALL
+ ld ra, PT_EPC(sp)
ld x1, PT_RA(sp)
x1 is ra, so loading it twice doesn't seem reasonable.
ld x2, PT_SP(sp)
ld x3, PT_GP(sp)
@@ -190,7 +192,6 @@ ENDPROC(ftrace_caller)
ld x31, PT_T6(sp)
ld s0, (PT_SIZE_ON_STACK)(sp)
- ld ra, (PT_SIZE_ON_STACK+8)(sp)
addi sp, sp, (PT_SIZE_ON_STACK+16)
.endm
If you're dropping the load you should drop the store above as well. In
general this seems kind of mixed up, both before and after this patch.
