Re: [PATCH v2] powerpc/ptrace: remove BUG_ON when full register set not available

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Wed, 2011-03-16 at 08:37 -0500, Michael Wolf wrote:
> In some cases during a threaded core dump not all 
> the threads will have a full register set.  This
> will cause problems when the sigkill is sent to
> the thread.  To solve this problem a poison value
> (0xdeadbeef) will be placed in the buffer in place 
> of the actual register values.  This will affect
> gpr14 to gpr31.
> 
> Signed-off-by: Mike Wolf <mjw@linux.vnet.ibm.com>

Patch is busted on ppc32 (you add  #define's in the middle of a
multi-line macro) and of doubtful stylistic value :-) I'll merge
a slightly reworked variant that includes a new cset comment
with Paulus explanation in it.

Cheers,
Ben.

> ----------
> --- linux-2.6.32-71.el6.ppc64.orig/arch/powerpc/include/asm/ptrace.h	2010-08-31 23:56:50.000000000 -0500
> +++ linux-2.6.32-71.el6.ppc64/arch/powerpc/include/asm/ptrace.h	2011-03-14 11:43:33.176667099 -0500
> @@ -123,8 +123,14 @@ extern int ptrace_put_reg(struct task_st
>  #define TRAP(regs)		((regs)->trap & ~0xF)
>  #ifdef __powerpc64__
>  #define CHECK_FULL_REGS(regs)	BUG_ON(regs->trap & 1)
> +#define PARTIAL_REG_FILL	0xdeadbeefdeadbeefUL
> +#define PARTIAL_REG_START	14
> +#define PARTIAL_REG_END		31
>  #else
>  #define CHECK_FULL_REGS(regs)						      \
> +#define PARTIAL_REG_FILL	0xdeadbeef
> +#define PARTIAL_REG_START	14
> +#define PARTIAL_REG_END		31
>  do {									      \
>  	if ((regs)->trap & 1)						      \
>  		printk(KERN_CRIT "%s: partial register set\n", __func__); \
> --- linux-2.6.32-71.el6.ppc64.orig/arch/powerpc/kernel/ptrace.c	2009-12-02 21:51:21.000000000 -0600
> +++ linux-2.6.32-71.el6.ppc64/arch/powerpc/kernel/ptrace.c	2011-03-14 13:01:51.955586126 -0500
> @@ -125,11 +125,16 @@ static int gpr_get(struct task_struct *t
>  		   void *kbuf, void __user *ubuf)
>  {
>  	int ret;
> +	int partial_reg;
>  
>  	if (target->thread.regs == NULL)
>  		return -EIO;
>  
> -	CHECK_FULL_REGS(target->thread.regs);
> +	if (!FULL_REGS(target->thread.regs))
> +	   /* We have a partial register set.  Fill 14-31 with bogus values */
> +	   for(partial_reg=PARTIAL_REG_START;partial_reg <= PARTIAL_REG_END;
> +		partial_reg++)
> +           	target->thread.regs->gpr[partial_reg] = PARTIAL_REG_FILL; 
>  
>  	ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf,
>  				  target->thread.regs,
> @@ -536,11 +541,16 @@ static int gpr32_get(struct task_struct 
>  	compat_ulong_t *k = kbuf;
>  	compat_ulong_t __user *u = ubuf;
>  	compat_ulong_t reg;
> +	int partial_reg;
>  
>  	if (target->thread.regs == NULL)
>  		return -EIO;
>  
> -	CHECK_FULL_REGS(target->thread.regs);
> +	if (!FULL_REGS(target->thread.regs))
> +	   /* We have a partial register set.  Fill 14-31 with bogus values */
> +	   for(partial_reg=PARTIAL_REG_START;partial_reg <= PARTIAL_REG_END;
> +		partial_reg++)
> +           	target->thread.regs->gpr[partial_reg] = PARTIAL_REG_FILL; 
>  
>  	pos /= sizeof(reg);
>  	count /= sizeof(reg);
> 
> 
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