Date: Sat, 17 Sep 2016 11:43:51 +0000 (UTC) From: Bruce Evans <bde@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r305897 - head/sys/ddb Message-ID: <201609171143.u8HBhpNQ046437@repo.freebsd.org>
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Author: bde Date: Sat Sep 17 11:43:51 2016 New Revision: 305897 URL: https://svnweb.freebsd.org/changeset/base/305897 Log: 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. Modified: head/sys/ddb/db_run.c Modified: head/sys/ddb/db_run.c ============================================================================== --- head/sys/ddb/db_run.c Sat Sep 17 08:10:01 2016 (r305896) +++ head/sys/ddb/db_run.c Sat Sep 17 11:43:51 2016 (r305897) @@ -136,21 +136,29 @@ db_stop_at_pc(int type, int code, bool * *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;
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