From 3c3bb0580be0027a1c7187b78c747af74dcfa884 Mon Sep 17 00:00:00 2001 From: Andrew Burgess Date: Fri, 13 Jul 2018 12:01:16 +0100 Subject: [PATCH] gdb: Add switch to disable DWARF stack unwinders Add a maintenance command to disable the DWARF stack unwinders. Normal users would not need this feature, but it is useful to allow extended testing of fallback stack unwinding strategies, for example, prologue scanners. This is a partial implementation of the idea discussed in pr gdb/8434, which talks about a generic ability to disable any frame unwinder. Being able to arbitrarily disable any frame unwinder would be a more complex patch, and I was unsure how useful such a feature would really be, however, I can see (and have) a real need to disable DWARF unwinders. That's why this patch only targets that specific set of unwinders. If in the future we find ourselves adding more switches to disable different unwinders, then we should probably move to a more generic solution, and remove this patch. gdb/ChangeLog: * dwarf2-frame-tailcall.c (tailcall_frame_sniffer): Exit early if DWARF unwinders are disabled. * dwarf2-frame.c: Add dwarf2read.h include. (dwarf2_frame_sniffer): Exit early if DWARF unwinders are disabled. (dwarf2_frame_unwinders_enabled_p): Define. (show_dwarf_unwinders_enabled_p): New function. (_initialize_dwarf2_frame): Register switch to control DWARF unwinder use. * dwarf2-frame.h (dwarf2_frame_unwinders_enabled_p): Declare. * dwarf2read.c (set_dwarf_cmdlist): Remove static keyword. (show_dwarf_cmdlist): Remove static keyword. * dwarf2read.h (set_dwarf_cmdlist): Declare. (show_dwarf_cmdlist): Declare. * NEWS: Document new feature. gdb/doc/ChangeLog: * gdb.texinfo (Maintenance Commands): Add description of maintenance command to control dwarf unwinders. gdb/testsuite/ChangeLog: * gdb.base/maint.exp: Add check that dwarf unwinders control flag is visible. --- gdb/ChangeLog | 18 ++++++++++++++++++ gdb/NEWS | 4 ++++ gdb/doc/ChangeLog | 5 +++++ gdb/doc/gdb.texinfo | 24 ++++++++++++++++++++++++ gdb/dwarf2-frame-tailcall.c | 3 +++ gdb/dwarf2-frame.c | 31 +++++++++++++++++++++++++++++++ gdb/dwarf2-frame.h | 6 ++++++ gdb/dwarf2read.c | 4 ++-- gdb/dwarf2read.h | 4 ++++ gdb/testsuite/ChangeLog | 5 +++++ gdb/testsuite/gdb.base/maint.exp | 4 ++++ 11 files changed, 106 insertions(+), 2 deletions(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 605aeef603b..26c1fd4cb81 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,21 @@ +2018-07-26 Andrew Burgess + + * dwarf2-frame-tailcall.c (tailcall_frame_sniffer): Exit early if + DWARF unwinders are disabled. + * dwarf2-frame.c: Add dwarf2read.h include. + (dwarf2_frame_sniffer): Exit early if DWARF unwinders are + disabled. + (dwarf2_frame_unwinders_enabled_p): Define. + (show_dwarf_unwinders_enabled_p): New function. + (_initialize_dwarf2_frame): Register switch to control DWARF + unwinder use. + * dwarf2-frame.h (dwarf2_frame_unwinders_enabled_p): Declare. + * dwarf2read.c (set_dwarf_cmdlist): Remove static keyword. + (show_dwarf_cmdlist): Remove static keyword. + * dwarf2read.h (set_dwarf_cmdlist): Declare. + (show_dwarf_cmdlist): Declare. + * NEWS: Document new feature. + 2018-07-26 Tom de Vries PR breakpoints/23366 diff --git a/gdb/NEWS b/gdb/NEWS index 76b963e2bc1..669ed2d0ebd 100644 --- a/gdb/NEWS +++ b/gdb/NEWS @@ -27,6 +27,10 @@ tfaas COMMAND output). Shortcut for 'thread apply all -s frame apply all -s COMMAND'. +maint set dwarf unwinders (on|off) +maint show dwarf unwinders + Control whether DWARF unwinders can be used. + * Changed commands thread apply [all | COUNT | -COUNT] [FLAG]... COMMAND diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog index d2bd3831aef..1bcf9dfc167 100644 --- a/gdb/doc/ChangeLog +++ b/gdb/doc/ChangeLog @@ -1,3 +1,8 @@ +2018-07-26 Andrew Burgess + + * gdb.texinfo (Maintenance Commands): Add description of + maintenance command to control dwarf unwinders. + 2018-07-12 Philippe Waroquiers * gdb.texinfo (Debugging Programs with Multiple Threads): diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo index b36a39b5b4c..b95c2b4f49a 100644 --- a/gdb/doc/gdb.texinfo +++ b/gdb/doc/gdb.texinfo @@ -35986,6 +35986,30 @@ compilation units will be stored in memory longer, and more total memory will be used. Setting it to zero disables caching, which will slow down @value{GDBN} startup, but reduce memory consumption. +@kindex maint set dwarf unwinders +@kindex maint show dwarf unwinders +@item maint set dwarf unwinders +@itemx maint show dwarf unwinders +Control use of the DWARF frame unwinders. + +@cindex DWARF frame unwinders +Many targets that support DWARF debugging use @value{GDBN}'s DWARF +frame unwinders to build the backtrace. Many of these targets will +also have a second mechanism for building the backtrace for use in +cases where DWARF information is not available, this second mechanism +is often an analysis of a function's prologue. + +In order to extend testing coverage of the second level stack +unwinding mechanisms it is helpful to be able to disable the DWARF +stack unwinders, this can be done with this switch. + +In normal use of @value{GDBN} disabling the DWARF unwinders is not +advisable, there are cases that are better handled through DWARF than +prologue analysis, and the debug experience is likely to be better +with the DWARF frame unwinders enabled. + +If DWARF frame unwinders are not supported for a particular target +architecture, then enabling this flag does not cause them to be used. @kindex maint set profile @kindex maint show profile @cindex profiling GDB diff --git a/gdb/dwarf2-frame-tailcall.c b/gdb/dwarf2-frame-tailcall.c index 1d3e1f445bb..f565a2eecc8 100644 --- a/gdb/dwarf2-frame-tailcall.c +++ b/gdb/dwarf2-frame-tailcall.c @@ -318,6 +318,9 @@ tailcall_frame_sniffer (const struct frame_unwind *self, int next_levels; struct tailcall_cache *cache; + if (!dwarf2_frame_unwinders_enabled_p) + return 0; + /* Inner tail call element does not make sense for a sentinel frame. */ next_frame = get_next_frame (this_frame); if (next_frame == NULL) diff --git a/gdb/dwarf2-frame.c b/gdb/dwarf2-frame.c index 91e16cf024e..58f1ba4f2fc 100644 --- a/gdb/dwarf2-frame.c +++ b/gdb/dwarf2-frame.c @@ -35,6 +35,7 @@ #include "complaints.h" #include "dwarf2-frame.h" +#include "dwarf2read.h" #include "ax.h" #include "dwarf2loc.h" #include "dwarf2-frame-tailcall.h" @@ -169,6 +170,9 @@ static CORE_ADDR read_encoded_value (struct comp_unit *unit, gdb_byte encoding, CORE_ADDR func_base); +/* See dwarf2-frame.h. */ +int dwarf2_frame_unwinders_enabled_p = 1; + /* Store the length the expression for the CFA in the `cfa_reg' field, which is unused in that case. */ #define cfa_exp_len cfa_reg @@ -1326,6 +1330,9 @@ static int dwarf2_frame_sniffer (const struct frame_unwind *self, struct frame_info *this_frame, void **this_cache) { + if (!dwarf2_frame_unwinders_enabled_p) + return 0; + /* Grab an address that is guarenteed to reside somewhere within the function. get_frame_pc(), with a no-return next function, can end up returning something past the end of this function's body. @@ -2394,12 +2401,36 @@ dwarf2_build_frame_info (struct objfile *objfile) set_objfile_data (objfile, dwarf2_frame_objfile_data, fde_table2); } +/* Handle 'maintenance show dwarf unwinders'. */ + +static void +show_dwarf_unwinders_enabled_p (struct ui_file *file, int from_tty, + struct cmd_list_element *c, + const char *value) +{ + fprintf_filtered (file, + _("The DWARF stack unwinders are currently %s.\n"), + value); +} + void _initialize_dwarf2_frame (void) { dwarf2_frame_data = gdbarch_data_register_pre_init (dwarf2_frame_init); dwarf2_frame_objfile_data = register_objfile_data (); + add_setshow_boolean_cmd ("unwinders", class_obscure, + &dwarf2_frame_unwinders_enabled_p , _("\ +Set whether the DWARF stack frame unwinders are used."), _("\ +Show whether the DWARF stack frame unwinders are used."), _("\ +When enabled the DWARF stack frame unwinders can be used for architectures\n\ +that support the DWARF unwinders. Enabling the DWARF unwinders for an\n\ +architecture that doesn't support them will have no effect."), + NULL, + show_dwarf_unwinders_enabled_p, + &set_dwarf_cmdlist, + &show_dwarf_cmdlist); + #if GDB_SELF_TEST selftests::register_test_foreach_arch ("execute_cfa_program", selftests::execute_cfa_program_test); diff --git a/gdb/dwarf2-frame.h b/gdb/dwarf2-frame.h index 471281a2c3f..52316e5e168 100644 --- a/gdb/dwarf2-frame.h +++ b/gdb/dwarf2-frame.h @@ -210,6 +210,12 @@ struct dwarf2_frame_state bool armcc_cfa_offsets_reversed = false; }; +/* When this is true the DWARF frame unwinders can be used if they are + registered with the gdbarch. Not all architectures can or do use the + DWARF unwinders. Setting this to true on a target that does not + otherwise support the DWARF unwinders has no effect. */ +extern int dwarf2_frame_unwinders_enabled_p; + /* Set the architecture-specific register state initialization function for GDBARCH to INIT_REG. */ diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c index de6b9f13a09..d16700fb924 100644 --- a/gdb/dwarf2read.c +++ b/gdb/dwarf2read.c @@ -25345,8 +25345,8 @@ partial_die_eq (const void *item_lhs, const void *item_rhs) return part_die_lhs->sect_off == part_die_rhs->sect_off; } -static struct cmd_list_element *set_dwarf_cmdlist; -static struct cmd_list_element *show_dwarf_cmdlist; +struct cmd_list_element *set_dwarf_cmdlist; +struct cmd_list_element *show_dwarf_cmdlist; static void set_dwarf_cmd (const char *args, int from_tty) diff --git a/gdb/dwarf2read.h b/gdb/dwarf2read.h index 74335d77db0..6e37c5d06f5 100644 --- a/gdb/dwarf2read.h +++ b/gdb/dwarf2read.h @@ -23,6 +23,10 @@ #include "filename-seen-cache.h" #include "gdb_obstack.h" +/* Hold 'maintenance (set|show) dwarf' commands. */ +extern struct cmd_list_element *set_dwarf_cmdlist; +extern struct cmd_list_element *show_dwarf_cmdlist; + typedef struct dwarf2_per_cu_data *dwarf2_per_cu_ptr; DEF_VEC_P (dwarf2_per_cu_ptr); diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog index aa8b06a0723..cdba393ea84 100644 --- a/gdb/testsuite/ChangeLog +++ b/gdb/testsuite/ChangeLog @@ -1,3 +1,8 @@ +2018-07-26 Andrew Burgess + + * gdb.base/maint.exp: Add check that dwarf unwinders control flag + is visible. + 2018-07-26 Tom de Vries PR breakpoints/23366 diff --git a/gdb/testsuite/gdb.base/maint.exp b/gdb/testsuite/gdb.base/maint.exp index 92086eec862..ee0d08927bb 100644 --- a/gdb/testsuite/gdb.base/maint.exp +++ b/gdb/testsuite/gdb.base/maint.exp @@ -526,6 +526,10 @@ gdb_test_no_output "maint info line-table xxx.c" \ set timeout $oldtimeout +# Just check that the DWARF unwinders control flag is visible. +gdb_test "maint show dwarf unwinders" \ + "The DWARF stack unwinders are currently (on|off)\\." + #============test help on maint commands test_prefix_command_help {"maint info" "maintenance info"} { -- 2.30.2