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Linux native: Use TRAP_BRKPT/TRAP_HWBPT
This patch adjusts the native Linux target backend to tell the core whether a trap was caused by a breakpoint. It teaches the target to get that information out of the si_code of the SIGTRAP siginfo. Tested on x86-64 Fedora 20, s390 RHEL 7, and PPC64 Fedora 18. An earlier version was tested on ARM Fedora 21. gdb/ChangeLog: 2015-03-04 Pedro Alves <palves@redhat.com> * linux-nat.c (save_sigtrap): Check for breakpoints before checking watchpoints. (status_callback) [USE_SIGTRAP_SIGINFO]: Don't check whether a breakpoint is inserted if relying on SIGTRAP's siginfo.si_code. (check_stopped_by_breakpoint) [USE_SIGTRAP_SIGINFO]: Decide whether a breakpoint triggered based on the SIGTRAP's siginfo.si_code. (linux_nat_stopped_by_sw_breakpoint) (linux_nat_supports_stopped_by_sw_breakpoint) (linux_nat_stopped_by_hw_breakpoint) (linux_nat_supports_stopped_by_hw_breakpoint): New functions. (linux_nat_wait_1): Don't re-increment the PC if relying on SIGTRAP's siginfo->si_code. (linux_nat_add_target): Install new target methods. * linux-thread-db.c (check_event): Don't account for breakpoint PC offset if the target already adjusted the PC. * nat/linux-ptrace.h (USE_SIGTRAP_SIGINFO): New. (GDB_ARCH_TRAP_BRKPT): New. (TRAP_HWBKPT): Define if not already defined.
This commit is contained in:
Pedro Alves
parent
f7e6eed528
commit
faf09f0119
@ -1,3 +1,24 @@
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2015-03-04 Pedro Alves <palves@redhat.com>
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* linux-nat.c (save_sigtrap): Check for breakpoints before
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checking watchpoints.
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(status_callback) [USE_SIGTRAP_SIGINFO]: Don't check whether a
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breakpoint is inserted if relying on SIGTRAP's siginfo.si_code.
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(check_stopped_by_breakpoint) [USE_SIGTRAP_SIGINFO]: Decide whether
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a breakpoint triggered based on the SIGTRAP's siginfo.si_code.
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(linux_nat_stopped_by_sw_breakpoint)
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(linux_nat_supports_stopped_by_sw_breakpoint)
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(linux_nat_stopped_by_hw_breakpoint)
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(linux_nat_supports_stopped_by_hw_breakpoint): New functions.
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(linux_nat_wait_1): Don't re-increment the PC if relying on
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SIGTRAP's siginfo->si_code.
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(linux_nat_add_target): Install new target methods.
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* linux-thread-db.c (check_event): Don't account for breakpoint PC
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offset if the target already adjusted the PC.
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* nat/linux-ptrace.h (USE_SIGTRAP_SIGINFO): New.
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(GDB_ARCH_TRAP_BRKPT): New.
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(TRAP_HWBKPT): Define if not already defined.
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2015-03-04 Pedro Alves <palves@redhat.com>
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* NEWS: Mention the new "swbreak" and "hwbreak" stop reasons.
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109
gdb/linux-nat.c
109
gdb/linux-nat.c
@ -2399,11 +2399,19 @@ save_sigtrap (struct lwp_info *lp)
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gdb_assert (lp->stop_reason == TARGET_STOPPED_BY_NO_REASON);
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gdb_assert (lp->status != 0);
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if (check_stopped_by_watchpoint (lp))
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return;
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/* Check first if this was a SW/HW breakpoint before checking
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watchpoints, because at least s390 can't tell the data address of
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hardware watchpoint hits, and the kernel returns
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stopped-by-watchpoint as long as there's a watchpoint set. */
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if (linux_nat_status_is_event (lp->status))
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check_stopped_by_breakpoint (lp);
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/* Note that TRAP_HWBKPT can indicate either a hardware breakpoint
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or hardware watchpoint. Check which is which if we got
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TARGET_STOPPED_BY_HW_BREAKPOINT. */
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if (lp->stop_reason == TARGET_STOPPED_BY_NO_REASON
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|| lp->stop_reason == TARGET_STOPPED_BY_HW_BREAKPOINT)
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check_stopped_by_watchpoint (lp);
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}
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/* Returns true if the LWP had stopped for a watchpoint. */
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@ -2557,6 +2565,8 @@ status_callback (struct lwp_info *lp, void *data)
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paddress (target_gdbarch (), pc));
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discard = 1;
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}
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#if !USE_SIGTRAP_SIGINFO
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else if (!breakpoint_inserted_here_p (get_regcache_aspace (regcache), pc))
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{
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if (debug_linux_nat)
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@ -2567,6 +2577,7 @@ status_callback (struct lwp_info *lp, void *data)
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discard = 1;
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}
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#endif
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if (discard)
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{
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@ -2669,10 +2680,49 @@ check_stopped_by_breakpoint (struct lwp_info *lp)
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struct gdbarch *gdbarch = get_regcache_arch (regcache);
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CORE_ADDR pc;
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CORE_ADDR sw_bp_pc;
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#if USE_SIGTRAP_SIGINFO
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siginfo_t siginfo;
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#endif
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pc = regcache_read_pc (regcache);
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sw_bp_pc = pc - target_decr_pc_after_break (gdbarch);
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#if USE_SIGTRAP_SIGINFO
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if (linux_nat_get_siginfo (lp->ptid, &siginfo))
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{
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if (siginfo.si_signo == SIGTRAP)
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{
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if (siginfo.si_code == GDB_ARCH_TRAP_BRKPT)
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{
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if (debug_linux_nat)
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fprintf_unfiltered (gdb_stdlog,
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"CSBB: Push back software "
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"breakpoint for %s\n",
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target_pid_to_str (lp->ptid));
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/* Back up the PC if necessary. */
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if (pc != sw_bp_pc)
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regcache_write_pc (regcache, sw_bp_pc);
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lp->stop_pc = sw_bp_pc;
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lp->stop_reason = TARGET_STOPPED_BY_SW_BREAKPOINT;
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return 1;
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}
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else if (siginfo.si_code == TRAP_HWBKPT)
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{
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if (debug_linux_nat)
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fprintf_unfiltered (gdb_stdlog,
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"CSBB: Push back hardware "
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"breakpoint/watchpoint for %s\n",
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target_pid_to_str (lp->ptid));
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lp->stop_pc = pc;
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lp->stop_reason = TARGET_STOPPED_BY_HW_BREAKPOINT;
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return 1;
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}
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}
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}
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#else
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if ((!lp->step || lp->stop_pc == sw_bp_pc)
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&& software_breakpoint_inserted_here_p (get_regcache_aspace (regcache),
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sw_bp_pc))
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@ -2704,10 +2754,53 @@ check_stopped_by_breakpoint (struct lwp_info *lp)
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lp->stop_reason = TARGET_STOPPED_BY_HW_BREAKPOINT;
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return 1;
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}
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#endif
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return 0;
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}
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/* Returns true if the LWP had stopped for a software breakpoint. */
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static int
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linux_nat_stopped_by_sw_breakpoint (struct target_ops *ops)
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{
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struct lwp_info *lp = find_lwp_pid (inferior_ptid);
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gdb_assert (lp != NULL);
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return lp->stop_reason == TARGET_STOPPED_BY_SW_BREAKPOINT;
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}
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/* Implement the supports_stopped_by_sw_breakpoint method. */
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static int
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linux_nat_supports_stopped_by_sw_breakpoint (struct target_ops *ops)
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{
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return USE_SIGTRAP_SIGINFO;
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}
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/* Returns true if the LWP had stopped for a hardware
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breakpoint/watchpoint. */
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static int
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linux_nat_stopped_by_hw_breakpoint (struct target_ops *ops)
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{
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struct lwp_info *lp = find_lwp_pid (inferior_ptid);
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gdb_assert (lp != NULL);
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return lp->stop_reason == TARGET_STOPPED_BY_HW_BREAKPOINT;
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}
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/* Implement the supports_stopped_by_hw_breakpoint method. */
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static int
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linux_nat_supports_stopped_by_hw_breakpoint (struct target_ops *ops)
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{
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return USE_SIGTRAP_SIGINFO;
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}
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/* Select one LWP out of those that have events pending. */
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static void
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@ -3360,8 +3453,10 @@ linux_nat_wait_1 (struct target_ops *ops,
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gdb_assert (lp != NULL);
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/* Now that we've selected our final event LWP, un-adjust its PC if
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it was a software breakpoint. */
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if (lp->stop_reason == TARGET_STOPPED_BY_SW_BREAKPOINT)
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it was a software breakpoint, and we can't reliably support the
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"stopped by software breakpoint" stop reason. */
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if (lp->stop_reason == TARGET_STOPPED_BY_SW_BREAKPOINT
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&& !USE_SIGTRAP_SIGINFO)
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{
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struct regcache *regcache = get_thread_regcache (lp->ptid);
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struct gdbarch *gdbarch = get_regcache_arch (regcache);
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@ -4651,6 +4746,10 @@ linux_nat_add_target (struct target_ops *t)
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t->to_thread_address_space = linux_nat_thread_address_space;
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t->to_stopped_by_watchpoint = linux_nat_stopped_by_watchpoint;
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t->to_stopped_data_address = linux_nat_stopped_data_address;
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t->to_stopped_by_sw_breakpoint = linux_nat_stopped_by_sw_breakpoint;
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t->to_supports_stopped_by_sw_breakpoint = linux_nat_supports_stopped_by_sw_breakpoint;
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t->to_stopped_by_hw_breakpoint = linux_nat_stopped_by_hw_breakpoint;
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t->to_supports_stopped_by_hw_breakpoint = linux_nat_supports_stopped_by_hw_breakpoint;
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t->to_can_async_p = linux_nat_can_async_p;
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t->to_is_async_p = linux_nat_is_async_p;
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@ -1437,8 +1437,10 @@ check_event (ptid_t ptid)
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info = get_thread_db_info (ptid_get_pid (ptid));
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/* Bail out early if we're not at a thread event breakpoint. */
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stop_pc = regcache_read_pc (regcache)
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- target_decr_pc_after_break (gdbarch);
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stop_pc = regcache_read_pc (regcache);
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if (!target_supports_stopped_by_sw_breakpoint ())
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stop_pc -= target_decr_pc_after_break (gdbarch);
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if (stop_pc != info->td_create_bp_addr
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&& stop_pc != info->td_death_bp_addr)
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return;
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@ -88,6 +88,57 @@ struct buffer;
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#define __WALL 0x40000000 /* Wait for any child. */
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#endif
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/* True if whether a breakpoint/watchpoint triggered can be determined
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from the si_code of SIGTRAP's siginfo_t (TRAP_BRKPT/TRAP_HWBKPT).
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That is, if the kernel can tell us whether the thread executed a
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software breakpoint, we trust it. The kernel will be determining
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that from the hardware (e.g., from which exception was raised in
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the CPU). Relying on whether a breakpoint is planted in memory at
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the time the SIGTRAP is processed to determine whether the thread
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stopped for a software breakpoint can be too late. E.g., the
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breakpoint could have been removed since. Or the thread could have
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stepped an instruction the size of a breakpoint instruction, and
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before the stop is processed a breakpoint is inserted at its
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address. Getting these wrong is disastrous on decr_pc_after_break
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architectures. The moribund location mechanism helps with that
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somewhat but it is an heuristic, and can well fail. Getting that
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information out of the kernel and ultimately out of the CPU is the
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way to go. That said, some architecture may get the si_code wrong,
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and as such we're leaving fallback code in place. We'll remove
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this after a while if no problem is reported. */
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#define USE_SIGTRAP_SIGINFO 1
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/* The x86 kernel gets some of the si_code values backwards, like
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this:
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| what | si_code |
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|------------------------------------------+------------|
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| software breakpoints (int3) | SI_KERNEL |
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| single-steps | TRAP_TRACE |
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| single-stepping a syscall | TRAP_BRKPT |
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| user sent SIGTRAP | 0 |
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| exec SIGTRAP (when no PTRACE_EVENT_EXEC) | 0 |
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| hardware breakpoints/watchpoints | TRAP_HWBPT |
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That is, it reports SI_KERNEL for software breakpoints (and only
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for those), and TRAP_BRKPT for single-stepping a syscall... If the
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kernel is ever fixed, we'll just have to detect it like we detect
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optional ptrace features: by forking and debugging ourselves,
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running to a breakpoint and checking what comes out of
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siginfo->si_code.
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The generic Linux target code should use GDB_ARCH_TRAP_BRKPT
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instead of TRAP_BRKPT to abstract out this x86 peculiarity. */
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#if defined __i386__ || defined __x86_64__
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# define GDB_ARCH_TRAP_BRKPT SI_KERNEL
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#else
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# define GDB_ARCH_TRAP_BRKPT TRAP_BRKPT
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#endif
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#ifndef TRAP_HWBKPT
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# define TRAP_HWBKPT 4
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#endif
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extern void linux_ptrace_attach_fail_reason (pid_t pid, struct buffer *buffer);
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/* Find all possible reasons we could have failed to attach to PTID
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