From 45614f153407762d83e8ecaf271b9b6e524c62db Mon Sep 17 00:00:00 2001 From: Yao Qi Date: Fri, 8 May 2015 12:29:13 +0100 Subject: [PATCH] [gdbserver] Disable conditional breakpoints on no-hardware-single-step targets GDBserver steps over breakpoint if the condition is false, but if target doesn't support hardware single step, the step over is very simple, if not incorrect, in linux-arm-low.c: /* We only place breakpoints in empty marker functions, and thread locking is outside of the function. So rather than importing software single-step, we can just run until exit. */ static CORE_ADDR arm_reinsert_addr (void) { struct regcache *regcache = get_thread_regcache (current_thread, 1); unsigned long pc; collect_register_by_name (regcache, "lr", &pc); return pc; } and linux-mips-low.c does the same. GDBserver sets a breakpoint at the return address of the current function, resume and wait the program hits the breakpoint in order to achieve "breakpoint step over". What if program hits other user breakponits during this "step over"? It is worse if the arm/thumb interworking is considered. Nowadays, GDBserver arm backend unconditionally inserts arm breakpoint, /* Define an ARM-mode breakpoint; we only set breakpoints in the C library, which is most likely to be ARM. If the kernel supports clone events, we will never insert a breakpoint, so even a Thumb C library will work; so will mixing EABI/non-EABI gdbserver and application. */ (const unsigned char *) &arm_breakpoint, (const unsigned char *) &arm_eabi_breakpoint, note that the comments are no longer valid as C library can be compiled in thumb mode. When GDBserver steps over a breakpoint in arm mode function, which returns to thumb mode, GDBserver will insert arm mode breakpoint by mistake and the program will crash. GDBserver alone is unable to determine the arm/thumb mode given a PC address. See how GDB does it in arm-tdep.c:arm_pc_is_thumb. After thinking about how to teach GDBserver inserting right breakpoint (arm or thumb) for a while, I reconsider it from a different direction that it may be unreasonable to run target-side conditional breakpoint for targets without hardware single step. Pedro also pointed this out here https://sourceware.org/ml/gdb-patches/2015-04/msg00337.html This patch is to add a new target_ops hook supports_conditional_breakpoints, and only reply ";ConditionalBreakpoints+" if it is true. On linux targets, supports_conditional_breakpoints returns true if target has hardware single step, on other targets, (win32, lynx, nto, spu), set it to NULL, because conditional breakpoint is a linux-specific feature. gdb/gdbserver: 2015-05-08 Yao Qi * linux-low.c (linux_supports_conditional_breakpoints): New function. (linux_target_ops): Install new target method. * lynx-low.c (lynx_target_ops): Install NULL hook for supports_conditional_breakpoints. * nto-low.c (nto_target_ops): Likewise. * spu-low.c (spu_target_ops): Likewise. * win32-low.c (win32_target_ops): Likewise. * server.c (handle_query): Check target_supports_conditional_breakpoints. * target.h (struct target_ops) : New field. (target_supports_conditional_breakpoints): New macro. --- gdb/gdbserver/ChangeLog | 16 ++++++++++++++++ gdb/gdbserver/linux-low.c | 14 ++++++++++++++ gdb/gdbserver/lynx-low.c | 4 ++++ gdb/gdbserver/nto-low.c | 4 ++++ gdb/gdbserver/server.c | 3 ++- gdb/gdbserver/spu-low.c | 1 + gdb/gdbserver/target.h | 8 ++++++++ gdb/gdbserver/win32-low.c | 4 ++++ 8 files changed, 53 insertions(+), 1 deletion(-) diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog index c5312d02181..191c90e8b02 100644 --- a/gdb/gdbserver/ChangeLog +++ b/gdb/gdbserver/ChangeLog @@ -1,3 +1,19 @@ +2015-05-08 Yao Qi + + * linux-low.c (linux_supports_conditional_breakpoints): New + function. + (linux_target_ops): Install new target method. + * lynx-low.c (lynx_target_ops): Install NULL hook for + supports_conditional_breakpoints. + * nto-low.c (nto_target_ops): Likewise. + * spu-low.c (spu_target_ops): Likewise. + * win32-low.c (win32_target_ops): Likewise. + * server.c (handle_query): Check + target_supports_conditional_breakpoints. + * target.h (struct target_ops) : + New field. + (target_supports_conditional_breakpoints): New macro. + 2015-05-06 Pedro Alves PR server/18081 diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c index 1c4c2d73bd3..bc76ffc1266 100644 --- a/gdb/gdbserver/linux-low.c +++ b/gdb/gdbserver/linux-low.c @@ -5177,6 +5177,19 @@ linux_supports_stopped_by_hw_breakpoint (void) return USE_SIGTRAP_SIGINFO; } +/* Implement the supports_conditional_breakpoints target_ops + method. */ + +static int +linux_supports_conditional_breakpoints (void) +{ + /* GDBserver needs to step over the breakpoint if the condition is + false. GDBserver software single step is too simple, so disable + conditional breakpoints if the target doesn't have hardware single + step. */ + return can_hardware_single_step (); +} + static int linux_stopped_by_watchpoint (void) { @@ -6375,6 +6388,7 @@ static struct target_ops linux_target_ops = { linux_supports_stopped_by_sw_breakpoint, linux_stopped_by_hw_breakpoint, linux_supports_stopped_by_hw_breakpoint, + linux_supports_conditional_breakpoints, linux_stopped_by_watchpoint, linux_stopped_data_address, #if defined(__UCLIBC__) && defined(HAS_NOMMU) \ diff --git a/gdb/gdbserver/lynx-low.c b/gdb/gdbserver/lynx-low.c index 2f858297d0b..364c79f363c 100644 --- a/gdb/gdbserver/lynx-low.c +++ b/gdb/gdbserver/lynx-low.c @@ -746,6 +746,10 @@ static struct target_ops lynx_target_ops = { NULL, /* supports_stopped_by_sw_breakpoint */ NULL, /* stopped_by_hw_breakpoint */ NULL, /* supports_stopped_by_hw_breakpoint */ + /* Although lynx has hardware single step, still disable this + feature for lynx, because it is implemented in linux-low.c instead + of in generic code. */ + NULL, /* supports_conditional_breakpoints */ NULL, /* stopped_by_watchpoint */ NULL, /* stopped_data_address */ NULL, /* read_offsets */ diff --git a/gdb/gdbserver/nto-low.c b/gdb/gdbserver/nto-low.c index 801d76a7c44..92767362043 100644 --- a/gdb/gdbserver/nto-low.c +++ b/gdb/gdbserver/nto-low.c @@ -949,6 +949,10 @@ static struct target_ops nto_target_ops = { NULL, /* supports_stopped_by_sw_breakpoint */ NULL, /* stopped_by_hw_breakpoint */ NULL, /* supports_stopped_by_hw_breakpoint */ + /* Although nto has hardware single step, still disable this + feature for not, because it is implemented in linux-low.c instead + of in generic code. */ + NULL, /* supports_conditional_breakpoints */ nto_stopped_by_watchpoint, nto_stopped_data_address, NULL, /* nto_read_offsets */ diff --git a/gdb/gdbserver/server.c b/gdb/gdbserver/server.c index 62287d47573..3f9bb8938d6 100644 --- a/gdb/gdbserver/server.c +++ b/gdb/gdbserver/server.c @@ -2107,7 +2107,8 @@ handle_query (char *own_buf, int packet_len, int *new_packet_len_p) } /* Support target-side breakpoint conditions and commands. */ - strcat (own_buf, ";ConditionalBreakpoints+"); + if (target_supports_conditional_breakpoints ()) + strcat (own_buf, ";ConditionalBreakpoints+"); strcat (own_buf, ";BreakpointCommands+"); if (target_supports_agent ()) diff --git a/gdb/gdbserver/spu-low.c b/gdb/gdbserver/spu-low.c index 73f17860807..a56a8893c4a 100644 --- a/gdb/gdbserver/spu-low.c +++ b/gdb/gdbserver/spu-low.c @@ -662,6 +662,7 @@ static struct target_ops spu_target_ops = { NULL, /* supports_stopped_by_sw_breakpoint */ NULL, /* stopped_by_hw_breakpoint */ NULL, /* supports_stopped_by_hw_breakpoint */ + NULL, /* supports_conditional_breakpoints */ NULL, NULL, NULL, diff --git a/gdb/gdbserver/target.h b/gdb/gdbserver/target.h index 6280c267377..b3d08cddd1a 100644 --- a/gdb/gdbserver/target.h +++ b/gdb/gdbserver/target.h @@ -222,6 +222,10 @@ struct target_ops HW breakpoint triggering. */ int (*supports_stopped_by_hw_breakpoint) (void); + /* Returns true if the target can evaluate conditions of + breakpoints. */ + int (*supports_conditional_breakpoints) (void); + /* Returns 1 if target was stopped due to a watchpoint hit, 0 otherwise. */ int (*stopped_by_watchpoint) (void); @@ -550,6 +554,10 @@ int kill_inferior (int); (the_target->supports_stopped_by_hw_breakpoint ? \ (*the_target->supports_stopped_by_hw_breakpoint) () : 0) +#define target_supports_conditional_breakpoints() \ + (the_target->supports_conditional_breakpoints ? \ + (*the_target->supports_conditional_breakpoints) () : 0) + #define target_stopped_by_hw_breakpoint() \ (the_target->stopped_by_hw_breakpoint ? \ (*the_target->stopped_by_hw_breakpoint) () : 0) diff --git a/gdb/gdbserver/win32-low.c b/gdb/gdbserver/win32-low.c index 6c86765b2db..6cf56bd54d3 100644 --- a/gdb/gdbserver/win32-low.c +++ b/gdb/gdbserver/win32-low.c @@ -1811,6 +1811,10 @@ static struct target_ops win32_target_ops = { NULL, /* supports_stopped_by_sw_breakpoint */ NULL, /* stopped_by_hw_breakpoint */ NULL, /* supports_stopped_by_hw_breakpoint */ + /* Although win32-i386 has hardware single step, still disable this + feature for win32, because it is implemented in linux-low.c instead + of in generic code. */ + NULL, /* supports_conditional_breakpoints */ win32_stopped_by_watchpoint, win32_stopped_data_address, NULL, /* read_offsets */ -- 2.30.2