Many a times, the requested breakpoint length can be less than the fixed breakpoint length i.e. 8 bytes supported by PowerPC BookIII S. This could lead to extraneous interrupts resulting in false breakpoint notifications. The patch below detects and discards such interrupts for non-ptrace requests (we don't want to change ptrace behaviour for fear of breaking compatability).
[Suggestions from Paul Mackerras <[email protected]> to add a new flag in 'struct arch_hw_breakpoint' to identify extraneous interrupts] Signed-off-by: K.Prasad <[email protected]> --- arch/powerpc/include/asm/hw_breakpoint.h | 1 + arch/powerpc/kernel/hw_breakpoint.c | 23 +++++++++++++++++++++-- 2 files changed, 22 insertions(+), 2 deletions(-) Index: linux-2.6.ppc64_test/arch/powerpc/kernel/hw_breakpoint.c =================================================================== --- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/hw_breakpoint.c +++ linux-2.6.ppc64_test/arch/powerpc/kernel/hw_breakpoint.c @@ -202,6 +202,7 @@ int __kprobes hw_breakpoint_handler(stru struct pt_regs *regs = args->regs; int stepped = 1; struct arch_hw_breakpoint *info; + unsigned long dar = regs->dar; /* Disable breakpoints during exception handling */ set_dabr(0); @@ -232,6 +233,22 @@ int __kprobes hw_breakpoint_handler(stru goto out; } + /* + * Verify if dar lies within the address range occupied by the symbol + * being watched to filter extraneous exceptions. + */ + if (!((bp->attr.bp_addr <= dar) && + (dar <= (bp->attr.bp_addr + bp->attr.bp_len)))) { + /* + * This exception is triggered not because of a memory access + * on the monitored variable but in the double-word address + * range in which it is contained. We will consume this + * exception, considering it as 'noise'. + */ + info->extraneous_interrupt = true; + } else + info->extraneous_interrupt = false; + /* Do not emulate user-space instructions, instead single-step them */ if (user_mode(regs)) { bp->ctx->task->thread.last_hit_ubp = bp; @@ -255,7 +272,8 @@ int __kprobes hw_breakpoint_handler(stru * As a policy, the callback is invoked in a 'trigger-after-execute' * fashion */ - perf_bp_event(bp, regs); + if (!info->extraneous_interrupt) + perf_bp_event(bp, regs); set_dabr(info->address | info->type | DABR_TRANSLATION); out: @@ -286,7 +304,8 @@ int __kprobes single_step_dabr_instructi * We shall invoke the user-defined callback function in the single * stepping handler to confirm to 'trigger-after-execute' semantics */ - perf_bp_event(bp, regs); + if (!bp_info->extraneous_interrupt) + perf_bp_event(bp, regs); /* * Do not disable MSR_SE if the process was already in Index: linux-2.6.ppc64_test/arch/powerpc/include/asm/hw_breakpoint.h =================================================================== --- linux-2.6.ppc64_test.orig/arch/powerpc/include/asm/hw_breakpoint.h +++ linux-2.6.ppc64_test/arch/powerpc/include/asm/hw_breakpoint.h @@ -27,6 +27,7 @@ #ifdef CONFIG_HAVE_HW_BREAKPOINT struct arch_hw_breakpoint { + bool extraneous_interrupt; u8 len; /* length of the target data symbol */ int type; unsigned long address; _______________________________________________ Linuxppc-dev mailing list [email protected] https://lists.ozlabs.org/listinfo/linuxppc-dev
