When using GDBserver on Windows XP, GDBserver reports and assertion failure after hitting a hardware watchpoint. The problem was reproduced using the sources from gdb.ada/int_deref, but should probably reproduce with any scenario involving hardware watchpoints. In our scenario, we break on line 5, just before the increment, insert a watchhpoint on it, and then continue: (gdb) b foo.adb:5 Breakpoint 1 at 0x4017c2: file foo.adb, line 5. (gdb) cont Continuing. Breakpoint 1, foo () at foo.adb:5 5 Pck.Watch := Pck.Watch + 1; (gdb) watch watch Hardware watchpoint 2: watch (gdb) c Continuing. Remote communication error. Target disconnected.: Invalid argument. The immediate cause for the communication error is easily explained, gdbserver crashes due to a failed assertion: x86_remove_aligned_watchpoint: Assertion `state->dr_control_mirror == 0' failed.
This is an automated email from the git hooks/post-receive script. It was generated because a ref change was pushed to the repository containing the project "gdb and binutils". The branch, gdb-7.8-branch has been updated via a70c6d64c936f981640b8e3315ddadb141af7aad (commit) from a39611f90c9a8ae50ab08c17e68af0490ab95352 (commit) Those revisions listed above that are new to this repository have not appeared on any other notification email; so we list those revisions in full, below. - Log ----------------------------------------------------------------- https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=a70c6d64c936f981640b8e3315ddadb141af7aad commit a70c6d64c936f981640b8e3315ddadb141af7aad Author: Joel Brobecker <brobecker@adacore.com> Date: Tue Oct 14 23:18:35 2014 +0200 state->dr_control_mirror == 0 failed assertion in gdbserver on Windows XP When using GDBserver on Windows XP, GDBserver reports an assertion failure after hitting a hardware watchpoint. The problem was reproduced using the sources from gdb.ada/int_deref, but should probably reproduce with any scenario involving hardware watchpoints. In our scenario, we break on line 5, just before the increment, insert a watchhpoint on it, and then continue: (gdb) b foo.adb:5 Breakpoint 1 at 0x4017c2: file foo.adb, line 5. (gdb) cont Continuing. Breakpoint 1, foo () at foo.adb:5 5 Pck.Watch := Pck.Watch + 1; (gdb) watch watch Hardware watchpoint 2: watch (gdb) c Continuing. Remote communication error. Target disconnected.: Invalid argument. The immediate cause for the communication error is easily explained, gdbserver crashes due to a failed assertion: x86_remove_aligned_watchpoint: Assertion `state->dr_control_mirror == 0' failed. The assertion occurs because debug_reg_state.dr_control_mirror gets overwritten by the value read from the inferior, when processing the watchpoint event in win32_wait: win32_wait finds that we stopped, calls get_thread_regcache which causes i386_get_thread_context to get called, which then... if (th->tid == current_event->dwThreadId) { /* Copy dr values from the current thread. */ struct x86_debug_reg_state *dr = &debug_reg_state; [...] dr->dr_control_mirror = th->context.Dr7; } Both should be identical, normally making this a no-op, but it turns out that bits 12-11-10 are documented as being fixed and equal to 001. Our handling of dr_control_mirror does not manage those bits, and leaves them as zeros instead. So, when we overwrite the value from the thread's DR7 register, we accidentally set bit 10, causing state->dr_control_mirror to be 0x400 after we've cleared everything internally. This patch fixes the issue by removing the statement setting state->dr_control_mirror to the thread's DR7 register value. gdb/gdbserver/ChangeLog: PR server/17487 * win32-i386-low.c (i386_get_thread_context): Do not set dr->dr_control_mirror. ----------------------------------------------------------------------- Summary of changes: gdb/gdbserver/ChangeLog | 6 ++++++ gdb/gdbserver/win32-i386-low.c | 1 - 2 files changed, 6 insertions(+), 1 deletions(-)
This is an automated email from the git hooks/post-receive script. It was generated because a ref change was pushed to the repository containing the project "gdb and binutils". The branch, master has been updated via a2abc7de6804e7e9882a86375767b24a6c215f28 (commit) from 6979730b1b9378a143b1bea3d0ff7b96c7bf02c5 (commit) Those revisions listed above that are new to this repository have not appeared on any other notification email; so we list those revisions in full, below. - Log ----------------------------------------------------------------- https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=a2abc7de6804e7e9882a86375767b24a6c215f28 commit a2abc7de6804e7e9882a86375767b24a6c215f28 Author: Pedro Alves <palves@redhat.com> Date: Wed Oct 15 19:55:50 2014 +0100 gdbserver/win32: Rewrite debug registers handling Don't use debug_reg_state for both: * "intent" - what we want the debug registers to look like * "reality" - what/which were the contents of the DR registers when the event triggered Reserve it for the former only, like in the GNU/Linux port. Otherwise the core x86 debug registers code can get confused if the inferior itself changes the debug registers since GDB last set them. This is also a requirement for being able to set watchpoints while the target is running, if/when we get to it on Windows. See the big comment in x86_dr_stopped_data_address. Seems to me this may also fixes propagating watchpoints to all threads -- continue_one_thread only calls win32_set_thread_context (what copies the DR registers to the thread), if something already fetched the thread's context before. Something else may be masking this issue, I haven't checked. Smoke tested by running gdbserver under Wine, connecting to it from GNU/Linux, and checking that I could trigger a watchpoint as expected. Joel tested it on x86-windows using AdaCore's testsuite. gdb/gdbserver/ 2014-10-15 Pedro Alves <palves@redhat.com> PR server/17487 * win32-arm-low.c (arm_set_thread_context): Remove current_event parameter. (arm_set_thread_context): Delete. (the_low_target): Adjust. * win32-i386-low.c (debug_registers_changed) (debug_registers_used): Delete. (update_debug_registers_callback): New function. (x86_dr_low_set_addr, x86_dr_low_set_control): Mark all threads as needing to update their debug registers. (win32_get_current_dr): New function. (x86_dr_low_get_addr, x86_dr_low_get_control) (x86_dr_low_get_status): Fetch the debug register from the thread record's context. (i386_initial_stuff): Adjust. (i386_get_thread_context): Remove current_event parameter. Don't clear debug_registers_changed nor copy DR values to debug_reg_state. (i386_set_thread_context): Delete. (i386_prepare_to_resume): New function. (i386_thread_added): Mark the thread as needing to update irs debug registers. (the_low_target): Remove i386_set_thread_context and install i386_prepare_to_resume. * win32-low.c (win32_get_thread_context): Adjust. (win32_set_thread_context): Use SetThreadContext directly. (win32_prepare_to_resume): New function. (win32_require_context): New function, factored out from ... (thread_rec): ... this. (continue_one_thread): Call win32_prepare_to_resume on each thread we're about to continue. (win32_resume): Call win32_prepare_to_resume on the event thread. * win32-low.h (struct win32_thread_info) <debug_registers_changed>: New field. (struct win32_target_ops): Change prototype of set_thread_context, delete set_thread_context and add prepare_to_resume. (win32_require_context): New declaration. ----------------------------------------------------------------------- Summary of changes: gdb/gdbserver/ChangeLog | 41 ++++++++++++ gdb/gdbserver/win32-arm-low.c | 10 +--- gdb/gdbserver/win32-i386-low.c | 137 +++++++++++++++++++++------------------ gdb/gdbserver/win32-low.c | 73 ++++++++++++++------- gdb/gdbserver/win32-low.h | 15 +++-- 5 files changed, 175 insertions(+), 101 deletions(-)
Fixed on the branch and HEAD.