From e1e554a382c4d213323b27f1609d4a19c5ba7472 Mon Sep 17 00:00:00 2001 From: Bruce Evans Date: Sat, 17 Sep 2016 11:43:51 +0000 Subject: [PATCH] Silently ignore unexpected single-step traps (except for turning off single-stepping). Only do this on arches (only x86 so far) which classify single-step traps unambiguously. This allows other parts of the kernel to be intentionally and unintentionally sloppy about generating single-step traps. On x86, at least the following places were unintentionally sloppy: - all operations that context-switched [er]flags. Especially spinlock_enter()/exit() and cpu_switch(). When single-stepped, saving the flags leaves PSL_T set in the saved flags, so restoring gives a trap that is spurious if it occurs after single-step mode has been left. Switching contexts away from a low priority thread gives especially long-lived saved copies. - the vm86 emulation allows user mode to set PSL_T. This was correct until vm86 bios call mode was unintentionally given access to kdb handling its single-step traps. Now these places are intentionally sloppy, but unexpected debugger traps still cause panics if no debugger that handles the trap is attached when the trap is delivered. --- sys/ddb/db_run.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) diff --git a/sys/ddb/db_run.c b/sys/ddb/db_run.c index 8cfcfc7fdfc..4ffba48583b 100644 --- a/sys/ddb/db_run.c +++ b/sys/ddb/db_run.c @@ -136,21 +136,29 @@ db_stop_at_pc(int type, int code, bool *is_breakpoint, bool *is_watchpoint) *is_breakpoint = false; /* might be a breakpoint, but not ours */ /* + * If not stepping, then silently ignore single-step traps + * (except for clearing the single-step-flag above). + * * If stepping, then abort if the trap type is unexpected. * Breakpoints owned by us are expected and were handled above. * Single-steps are expected and are handled below. All others * are unexpected. * - * If the MD layer doesn't tell us when it is stepping, use the - * bad historical default that all unexepected traps. + * Only do either of these if the MD layer claims to classify + * single-step traps unambiguously (by defining IS_SSTEP_TRAP). + * Otherwise, fall through to the bad historical behaviour + * given by turning unexpected traps into expected traps: if not + * stepping, then expect only breakpoints and stop, and if + * stepping, then expect only single-steps and step. */ -#ifndef IS_SSTEP_TRAP -#define IS_SSTEP_TRAP(type, code) true -#endif +#ifdef IS_SSTEP_TRAP + if (db_run_mode == STEP_CONTINUE && IS_SSTEP_TRAP(type, code)) + return (false); if (db_run_mode != STEP_CONTINUE && !IS_SSTEP_TRAP(type, code)) { printf("Stepping aborted\n"); return (true); } +#endif if (db_run_mode == STEP_INVISIBLE) { db_run_mode = STEP_CONTINUE;