HW breakpoints events stopped working correctly with kgdb as a result of commit: 018cbffe6819f6f8db20a0a3acd9bab9bfd667e4 (Merge commit 'v2.6.33' into perf/core), later commit: ba773f7c510c0b252145933926c636c439889207 (x86,kgdb: Fix hw breakpoint regression) allowed breakpoints to propagate to the debugger core but did not completely address the original regression in functionality found in 2.6.35. When the DR_STEP flag is set in dr6 along with any of the DR_TRAP bits, the kgdb exception handler will enter once from the hw_breakpoint API call back and again from the die notifier for do_debug(), which causes the debugger to stop twice and also for the kgdb regression tests to fail running under kvm with: echo V2I1 > /sys/module/kgdbts/parameters/kgdbts To address the problem, the kgdb overflow handler needs to implement the same logic as the ptrace overflow handler call back with respect to updating the virtual copy of dr6. This will allow the kgdb do_debug() die notifier to properly handle the exception and the attached debugger, or kgdb test suite, will only receive a single notification.
Unified · Split
| @@ -621,7 +621,12 @@ int kgdb_arch_init(void) · 620 unmodified lines | ||
| 621 | 621 | static void kgdb_hw_overflow_handler(struct perf_event *event, int nmi, |
| 622 | 622 | struct perf_sample_data *data, struct pt_regs *regs) |
| 623 | 623 | { |
| 624 | − kgdb_ll_trap(DIE_DEBUG, "debug", regs, 0, 0, SIGTRAP); | |
| 624 | + struct task_struct *tsk = current; | |
| 625 | + int i; | |
| 626 | + | |
| 627 | + for (i = 0; i < 4; i++) | |
| 628 | + if (breakinfo[i].enabled) | |
| 629 | + tsk->thread.debugreg6 |= (DR_TRAP0 << i); | |
| 625 | 630 | } |
| 626 | 631 | |
| 627 | 632 | void kgdb_arch_late(void) |