On Sat, Aug 15, 2020 at 6:36 AM Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx> wrote:
>
> On Mon, 13 Jul 2020 16:39:18 PDT (-0700), guoren@xxxxxxxxxx wrote:
> > From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> >
> > 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 <guoren@xxxxxxxxxxxxxxxxx>
> > Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> > Cc: Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx>
> > ---
> > 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.
This is a wrong patch, it should be:
diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
index 35a6ed7..d82b8f0 100644
--- a/arch/riscv/kernel/mcount-dyn.S
+++ b/arch/riscv/kernel/mcount-dyn.S
@@ -120,10 +120,10 @@ ENDPROC(ftrace_caller)
.macro SAVE_ALL
addi sp, sp, -(PT_SIZE_ON_STACK+16)
sd s0, (PT_SIZE_ON_STACK)(sp)
- sd ra, (PT_SIZE_ON_STACK+8)(sp)
addi s0, sp, (PT_SIZE_ON_STACK+16)
- sd x1, PT_RA(sp)
+ sd ra, PT_EPC(sp)
+ sd ra, PT_RA(sp)
sd x2, PT_SP(sp)
sd x3, PT_GP(sp)
sd x4, PT_TP(sp)
@@ -157,7 +157,7 @@ ENDPROC(ftrace_caller)
.endm
.macro RESTORE_ALL
- ld x1, PT_RA(sp)
+ ld ra, PT_EPC(sp)
ld x2, PT_SP(sp)
ld x3, PT_GP(sp)
ld x4, PT_TP(sp)
@@ -190,7 +190,6 @@ 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
Now, I'm developing livepatch and they are so mixed features (kprobe,
livepatch, ftrace, optprobes, STACK_WALK, -fpatchable-function-entry
'no -pg'). I'll test this patch in the next version of the patchset.
Thx for the review.
--
Best Regards
Guo Ren
ML: https://lore.kernel.org/linux-csky/
