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powerpc, hw_breakpoint: Discard extraneous interrupt due to accesses outside symbol length

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Many a times, the requested breakpoint length can be less than the
fixed breakpoint length i.e. 8 bytes supported by PowerPC 64-bit
server (Book III S) processors.  This could lead to extraneous
interrupts resulting in false breakpoint notifications.  This
detects and discards such interrupts for non-ptrace requests.
We don't change ptrace behaviour to avoid breaking compatability.

[Suggestion from Paul Mackerras <paulus@samba.org> to add a new flag in
'struct arch_hw_breakpoint' to identify extraneous interrupts]

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
This commit is contained in:
K.Prasad 2010-06-15 11:36:12 +05:30 committed by Paul Mackerras
parent 06532a6743
commit e3e94084ad
2 changed files with 22 additions and 2 deletions
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1
arch/powerpc/include/asm/hw_breakpoint.h
View file

@ -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;

23
arch/powerpc/kernel/hw_breakpoint.c
View file

@ -204,6 +204,7 @@ int __kprobes hw_breakpoint_handler(struct die_args *args)
int stepped = 1;
struct arch_hw_breakpoint *info;
unsigned int instr;
unsigned long dar = regs->dar;
/* Disable breakpoints during exception handling */
set_dabr(0);
@ -234,6 +235,22 @@ int __kprobes hw_breakpoint_handler(struct die_args *args)
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;
@ -261,7 +278,8 @@ int __kprobes hw_breakpoint_handler(struct die_args *args)
* 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:
@ -292,7 +310,8 @@ int __kprobes single_step_dabr_instruction(struct die_args *args)
* 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