On 05/10/2012 11:50 AM, Benjamin Herrenschmidt wrote: > On Thu, 2011-12-15 at 19:00 +0800, Tiejun Chen wrote: >> We can't emulate stwu since that may corrupt current exception stack. >> So we will have to do real store operation in the exception return code. >> >> Firstly we'll allocate a trampoline exception frame below the kprobed >> function stack and copy the current exception frame to the trampoline. >> Then we can do this real store operation to implement 'stwu', and reroute >> the trampoline frame to r1 to complete this exception migration. >> >> Signed-off-by: Tiejun Chen <tiejun.c...@windriver.com> >> --- >> arch/powerpc/kernel/entry_32.S | 35 +++++++++++++++++++++++++++++++++++ >> 1 files changed, 35 insertions(+), 0 deletions(-) >> >> diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S >> index 56212bc..0cdd27d 100644 >> --- a/arch/powerpc/kernel/entry_32.S >> +++ b/arch/powerpc/kernel/entry_32.S >> @@ -850,6 +850,41 @@ resume_kernel: >> >> /* interrupts are hard-disabled at this point */ >> restore: >> + lwz r3,_MSR(r1) /* Returning to user mode? */ >> + andi. r0,r3,MSR_PR >> + bne 1f > > .../... >
Sorry for this delay response since I can't take time to do this last week :( > Wouldn't it be better to use resume_kernel here ? Agreed :) > > IE. We already have restore_user vs. resume_kernel labels, including > the PR test. In the !PREEMPT case, resume_kernel is empty but it's > there, so you can just "populate" it, ie, something like: > > restore_user: > ... existing dbcr0 stuff ... > b restore > > resume_kernel: <-- removed the ifdef CONFIG_PREEMPT > > ... Do the stack store business here... > > #ifdef CONFIG_PREEMPT > ... move the preempt code here... > #endif > > restore: > ... existing stuff ... > > Also, the added advantage is that the code to calc > the thread info pointer and load the TI_FLAG can be > shared now between your stuff and preempt, ie: > > resume_kernel: > rlwinm r9,r1,0,0,(31-THREAD_SHIFT) > lwz r0,TI_FLAGS(r9) > andis. r0,r0,_TIF_EMULATE_STACK_STORE@h > bne- emulate_stack_store > #ifdef CONFIG_PREEMPT > lwz r8,TI_PREEMPT(r9) <-- note use of r8 instead of r0, > I -think- r8 can be clobbered > here but pls dbl check Its should be safe. > cmpwi 0,r8,0 > bne restore > andi. r0,r0,_TIF_NEED_RESCHED > etc... Please check if next, v3, is fine. > >> + /* check current_thread_info, _TIF_EMULATE_STACK_STORE */ >> + rlwinm r9,r1,0,0,(31-THREAD_SHIFT) >> + lwz r0,TI_FLAGS(r9) >> + andis. r0,r0,_TIF_EMULATE_STACK_STORE@h >> + beq+ 1f >> + >> + addi r9,r1,INT_FRAME_SIZE /* Get the kprobed function entry */ >> + >> + lwz r3,GPR1(r1) >> + subi r3,r3,INT_FRAME_SIZE /* dst: Allocate a trampoline exception >> frame */ >> + mr r4,r1 /* src: current exception frame */ >> + li r5,INT_FRAME_SIZE /* size: INT_FRAME_SIZE */ >> + mr r1,r3 /* Reroute the trampoline frame to r1 */ >> + bl memcpy /* Copy from the original to the >> trampoline */ >> + >> + /* Do real store operation to complete stwu */ >> + lwz r5,GPR1(r1) >> + stw r9,0(r5) > > Ok, I think I -finally- understand your trick of using r1 + > INT_FRAME_SIZE as the value to store :-) It makes sense and it's > actually a nice hack :-) > > I would recommend that in the C code part of the emulation, you > add some sanity checking to make sure we don't overflow the > kernel stack etc... it should come in generally handy especially > if what's your trying to debug with kprobes is a kernel stack > overflow :-) Added. > >> + /* Clear _TIF_EMULATE_STACK_STORE flag */ >> + rlwinm r9,r1,0,0,(31-THREAD_SHIFT) >> + lis r11,_TIF_EMULATE_STACK_STORE@h >> + addi r9,r9,TI_FLAGS >> +0: lwarx r8,0,r9 >> + andc r8,r8,r11 >> +#ifdef CONFIG_IBM405_ERR77 >> + dcbt 0,r9 >> +#endif >> + stwcx. r8,0,r9 >> + bne- 0b >> +1: >> + >> #ifdef CONFIG_44x >> BEGIN_MMU_FTR_SECTION >> b 1f > > BTW. Are you going to do a ppc64 variant of that patch ? I'd like to go ppc64 ASAP once we did on ppc32 is good enough :) Tiejun > > Cheers, > Ben. > > > > _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
