powerpc/ptrace: Remove BUG_ON when full register set not available (a71f5d5d) · Commits · 戴 / test

In some cases during a threaded core dump not all the threads will have a full register set. This happens when the signal causing the core dump races with a thread exiting. The race happens when the exiting thread has entered the kernel for the last time before the signal arrives, but doesn't get far enough through the exit code to avoid being included in the core dump. So we get a thread included in the core dump which is never going to go out to userspace again and only has a partial register set recorded Normally we would catch each thread as it is about to go into userspace and capture the full register set then. However, this exiting thread is never going to go out to userspace again, so we have no way to capture its full register set. It doesn't really matter, though, as this is a thread which is effectively already dead. So instead of hitting a BUG() in this case (a really bad choice of action in the first place), we use a poison value for the register values. [BenH]: Some cosmetic/stylistic changes and fix build on ppc32 Signed-off-by:

Mike Wolf <mjw@linux.vnet.ibm.com> Signed-off-by:

Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/ptrace.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -125,8 +125,10 @@ extern int ptrace_put_reg(struct task_struct *task, int regno,
		#endif /* ! __powerpc64__ */
		#define TRAP(regs) ((regs)->trap & ~0xF)
		#ifdef __powerpc64__
		#define NV_REG_POISON 0xdeadbeefdeadbeefUL
		#define CHECK_FULL_REGS(regs) BUG_ON(regs->trap & 1)
		#else
		#define NV_REG_POISON 0xdeadbeef
		#define CHECK_FULL_REGS(regs) \
		do { \
		if ((regs)->trap & 1) \

arch/powerpc/kernel/ptrace.c

+12 −3

Original line number	Diff line number	Diff line
		@@ -229,12 +229,16 @@ static int gpr_get(struct task_struct target, const struct user_regset regset,
		unsigned int pos, unsigned int count,
		void kbuf, void __user ubuf)
		{
		int ret;
		int i, ret;

		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 (i = 14; i < 32; i++)
		target->thread.regs->gpr[i] = NV_REG_POISON;
		}

		ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf,
		target->thread.regs,
		@@ -641,11 +645,16 @@ static int gpr32_get(struct task_struct *target,
		compat_ulong_t *k = kbuf;
		compat_ulong_t __user *u = ubuf;
		compat_ulong_t reg;
		int i;

		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 (i = 14; i < 32; i++)
		target->thread.regs->gpr[i] = NV_REG_POISON;
		}

		pos /= sizeof(reg);
		count /= sizeof(reg);

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