Re: [PATCH 21/23] arm64: ilp32: introduce ilp32-specific handlers for sigframe and ucontext

[Yury Norov]

Hi Bamvor,

Sorry, I missed this patch.

On Sat, Jun 04, 2016 at 07:34:32PM +0800, Zhangjian (Bamvor) wrote:
> Hi,
> 
> I found an issue of unwind with the following code. The correct backtrace
> should be:
> (gdb) where
> #0 0x004004d0 in my_sig (sig=11) at test_force3.c:16
> #1 <signal handler called>
> #2 func2 (num=0) at test_force3.c:22
> #3 0x00400540 in func1 (num=1) at test_force3.c:28
> #4 0x00400574 in main (argc=1, argv=0xffd7bc04) at test_force3.c:33
> 
> Without my patch, the backtrace is:
> (gdb) where
> #0 0x00400490 in my_sig (sig=11) at test_force3.c:16
> #1 <signal handler called>
> #2 0x004004e4 in main (argc=1, argv=0xffe6f8f4) at test_force3.c:33
> 
> With my patch which fix the wrong frame pointer(setup_return calculate the offset
> of fp through ilp32_sigframe instead of sigfreame), the backtrace is:
> (gdb) where
> #0 0x00400490 in my_sig (sig=11) at test_force3.c:16
> #1 <signal handler called>
> #2 func1 () at test_force3.c:28
> #3 0x004004e4 in main (argc=1, argv=0xffe6f8f4) at test_force3.c:33
> 
> I am not sure there is still some issue in kernel. But it seem that the gdb of ilp32
> does not work correctly when unwind without framepointer.
> 
> The test code is:
> 
> From 7e364a765097f57aed2d73f94c1688c2e7343e79 Mon Sep 17 00:00:00 2001
> From: Bamvor Jian Zhang <bamvor.zhangjian@xxxxxxxxxx>
> Date: Sat, 4 Jun 2016 14:30:05 +0800
> Subject: [PATCH] arm64: ilp32: fix for wrong fp offset when calculate the
>  new fp
> 
> ILP32 define its own sigframe(ilp32_sigframe) because of the
> difference uc_context. setup_return do not use ilp32 specific
> sigframe to calculate the new offset of fp which lead to wrong
> fp in signal handler. At this circumstance, gdb backtrace will miss
> one item:
> (gdb) where
> 
> It should be:
> (gdb) where
> 
> The test code is as follows:
> 
> void my_sig(int sig)
> {
>         printf("sig=%d\n", sig);
>         *(int *)0 = 0x0;
> }
> 
> void func2(int num)
> {
>         printf("%s: %d\n", __FUNCTION__, num);
>         *(int *)0 = 0x0;
>         func2(num-1);
> }
> 
> void func1(int num)
> {
>         printf("%s\n", __FUNCTION__);
>         func2(num - 1);
> }
> 
> int main(int argc, char **argv)
> {
>         signal(11, my_sig);
>         func1(argc);
>         return 0;
> }
> 
> This patch fix this by passing the correct offset of fp to
> setup_return.
> Test pass on both ILP32 and LP64 in aarch64 EE.
> 
> Signed-off-by: Bamvor Jian Zhang <bamvor.zhangjian@xxxxxxxxxx>
> ---
>  arch/arm64/include/asm/signal_common.h | 3 ++-
>  arch/arm64/kernel/signal.c             | 9 +++++----
>  arch/arm64/kernel/signal_ilp32.c       | 4 ++--
>  3 files changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/signal_common.h b/arch/arm64/include/asm/signal_common.h
> index de93c71..a5d7b63 100644
> --- a/arch/arm64/include/asm/signal_common.h
> +++ b/arch/arm64/include/asm/signal_common.h
> @@ -29,6 +29,7 @@ int setup_sigcontex(struct sigcontext __user *uc_mcontext,
>  		    struct pt_regs *regs);
>  int restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sf);
>  void setup_return(struct pt_regs *regs, struct k_sigaction *ka,
> -			void __user *frame, off_t sigframe_off, int usig);
> +			void __user *frame, off_t sigframe_off, off_t fp_off,
> +			int usig); 
> 
>  #endif /* __ASM_SIGNAL_COMMON_H */
> diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
> index 038bebe..e66a6e9 100644
> --- a/arch/arm64/kernel/signal.c
> +++ b/arch/arm64/kernel/signal.c
> @@ -256,14 +256,14 @@ static struct rt_sigframe __user *get_sigframe(struct ksignal *ksig,
>  }
> 
>  void setup_return(struct pt_regs *regs, struct k_sigaction *ka,
> -			 void __user *frame, off_t sigframe_off, int usig)
> +			 void __user *frame, off_t sigframe_off, off_t fp_off,
> +			 int usig)
>  {
>  	__sigrestore_t sigtramp;
> 
>  	regs->regs[0] = usig;
>  	regs->sp = (unsigned long)frame;
> -	regs->regs[29] = regs->sp + sigframe_off +
> -		offsetof(struct sigframe, fp);
> +	regs->regs[29] = regs->sp + sigframe_off + fp_off;

I think you are right here. The only nitpick is what for we send 2
offsets just to add one to another inside setup_return()?
We can do like this:

        void setup_return(struct pt_regs *regs, struct k_sigaction *ka,
        			 void __user *frame, off_t fp_off, int usig)
        {
        	__sigrestore_t sigtramp;
        
        	regs->regs[0] = usig;
        	regs->sp = (unsigned long)frame;
        	regs->regs[29] = regs->sp + fp_off;
                [...]
        }

Where fp_off calculation is done by caller. 

	setup_return(regs, &ksig->ka, frame,
		offsetof(struct rt_sigframe, sig) + offsetof(struct sigframe, fp),
                usig);

For me it's more clear to understand what happens with this approach.
I don't think struct rt_sigframe will grow, but we can even introduce
some helper for it:
        #define RT_SIGFRAME_FP_POS (offsetof(struct rt_sigframe, sig) + offsetof(struct sigframe, fp))

If no objections, I'll apply your patch with my fix in next series.

>  	regs->pc = (unsigned long)ka->sa.sa_handler;
> 
>  	if (ka->sa.sa_flags & SA_RESTORER)
> @@ -294,7 +294,8 @@ static int setup_rt_frame(int usig, struct ksignal *ksig, sigset_t *set,
>  	err |= setup_sigframe(&frame->sig, regs, set);
>  	if (err == 0) {
>  		setup_return(regs, &ksig->ka, frame,
> -			offsetof(struct rt_sigframe, sig), usig);
> +			offsetof(struct rt_sigframe, sig),
> +			offsetof(struct sigframe, fp), usig);
>  		if (ksig->ka.sa.sa_flags & SA_SIGINFO) {
>  			err |= copy_siginfo_to_user(&frame->info, &ksig->info);
>  			regs->regs[1] = (unsigned long)&frame->info;
> diff --git a/arch/arm64/kernel/signal_ilp32.c b/arch/arm64/kernel/signal_ilp32.c
> index a8ea73e..9030f14 100644
> --- a/arch/arm64/kernel/signal_ilp32.c
> +++ b/arch/arm64/kernel/signal_ilp32.c
> @@ -147,7 +147,6 @@ static struct ilp32_rt_sigframe __user *ilp32_get_sigframe(struct ksignal *ksig,
>  	struct ilp32_rt_sigframe __user *frame;
> 
>  	sp = sp_top = sigsp(regs->sp, ksig);
> -
>  	sp = (sp - sizeof(struct ilp32_rt_sigframe)) & ~15;
>  	frame = (struct ilp32_rt_sigframe __user *)sp;
> 
> @@ -183,7 +182,8 @@ int ilp32_setup_rt_frame(int usig, struct ksignal *ksig,
>  	err |= setup_ilp32_sigframe(&frame->sig, regs, set);
>  	if (err == 0) {
>  		setup_return(regs, &ksig->ka, frame,
> -			     offsetof(struct ilp32_rt_sigframe, sig), usig);
> +			     offsetof(struct ilp32_rt_sigframe, sig),
> +			     offsetof(struct ilp32_sigframe, fp), usig);
>  		regs->regs[1] = (unsigned long)&frame->info;
>  		regs->regs[2] = (unsigned long)&frame->sig.uc;
>  	}
> -- 
> 1.8.4.5
> 
> Regards
> 
> Bamvor
> 
>