| Message ID | 1310209058-20980-16-git-send-email-tixy@yxit.co.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Sat, 9 Jul 2011, Tixy wrote: > From: Jon Medhurst <tixy@yxit.co.uk> > > This patch changes the behavior of kprobes on ARM so that: > > Kprobes on conditional instructions don't trigger when the > condition is false. For conditional branches, this means that > they don't trigger in the branch not taken case. > > Rationale: > > When probes are placed onto conditionally executed instructions in a > Thumb IT block, they may not fire if the condition is not met. This > is because we use invalid instructions for breakpoints and "it is > IMPLEMENTATION DEFINED whether the instruction executes as a NOP or > causes an Undefined Instruction exception". Therefore, for consistency, > we will ignore all probes on any conditional instructions when the > condition is false. Alternative solutions seem to be too complex to > implement or inconsistent. > > This issue was discussed on linux.arm.kernel in the thread titled > "[RFC] kprobes with thumb2 conditional code" See > http://comments.gmane.org/gmane.linux.linaro.devel/2985 > > Signed-off-by: Jon Medhurst <tixy@yxit.co.uk> Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org> > --- > arch/arm/kernel/kprobes.c | 24 +++++++++++++++++++++++- > 1 files changed, 23 insertions(+), 1 deletions(-) > > diff --git a/arch/arm/kernel/kprobes.c b/arch/arm/kernel/kprobes.c > index b8f5b3b..7a9be60 100644 > --- a/arch/arm/kernel/kprobes.c > +++ b/arch/arm/kernel/kprobes.c > @@ -207,6 +207,20 @@ static void __kprobes set_current_kprobe(struct kprobe *p) > __get_cpu_var(current_kprobe) = p; > } > > +static void __kprobes > +singlestep_skip(struct kprobe *p, struct pt_regs *regs) > +{ > +#ifdef CONFIG_THUMB2_KERNEL > + regs->ARM_cpsr = it_advance(regs->ARM_cpsr); > + if (is_wide_instruction(p->opcode)) > + regs->ARM_pc += 4; > + else > + regs->ARM_pc += 2; > +#else > + regs->ARM_pc += 4; > +#endif > +} > + > static void __kprobes singlestep(struct kprobe *p, struct pt_regs *regs, > struct kprobe_ctlblk *kcb) > { > @@ -262,7 +276,8 @@ void __kprobes kprobe_handler(struct pt_regs *regs) > /* impossible cases */ > BUG(); > } > - } else { > + } else if (p->ainsn.insn_check_cc(regs->ARM_cpsr)) { > + /* Probe hit and conditional execution check ok. */ > set_current_kprobe(p); > kcb->kprobe_status = KPROBE_HIT_ACTIVE; > > @@ -282,6 +297,13 @@ void __kprobes kprobe_handler(struct pt_regs *regs) > } > reset_current_kprobe(); > } > + } else { > + /* > + * Probe hit but conditional execution check failed, > + * so just skip the instruction and continue as if > + * nothing had happened. > + */ > + singlestep_skip(p, regs); > } > } else if (cur) { > /* We probably hit a jprobe. Call its break handler. */ > -- > 1.7.2.5 > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >
diff --git a/arch/arm/kernel/kprobes.c b/arch/arm/kernel/kprobes.c index b8f5b3b..7a9be60 100644 --- a/arch/arm/kernel/kprobes.c +++ b/arch/arm/kernel/kprobes.c @@ -207,6 +207,20 @@ static void __kprobes set_current_kprobe(struct kprobe *p) __get_cpu_var(current_kprobe) = p; } +static void __kprobes +singlestep_skip(struct kprobe *p, struct pt_regs *regs) +{ +#ifdef CONFIG_THUMB2_KERNEL + regs->ARM_cpsr = it_advance(regs->ARM_cpsr); + if (is_wide_instruction(p->opcode)) + regs->ARM_pc += 4; + else + regs->ARM_pc += 2; +#else + regs->ARM_pc += 4; +#endif +} + static void __kprobes singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb) { @@ -262,7 +276,8 @@ void __kprobes kprobe_handler(struct pt_regs *regs) /* impossible cases */ BUG(); } - } else { + } else if (p->ainsn.insn_check_cc(regs->ARM_cpsr)) { + /* Probe hit and conditional execution check ok. */ set_current_kprobe(p); kcb->kprobe_status = KPROBE_HIT_ACTIVE; @@ -282,6 +297,13 @@ void __kprobes kprobe_handler(struct pt_regs *regs) } reset_current_kprobe(); } + } else { + /* + * Probe hit but conditional execution check failed, + * so just skip the instruction and continue as if + * nothing had happened. + */ + singlestep_skip(p, regs); } } else if (cur) { /* We probably hit a jprobe. Call its break handler. */