From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 806 invoked by alias); 25 Jul 2018 15:18:51 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 797 invoked by uid 89); 25 Jul 2018 15:18:51 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-26.3 required=5.0 tests=AWL,BAYES_00,GIT_PATCH_0,GIT_PATCH_1,GIT_PATCH_2,GIT_PATCH_3,RCVD_IN_DNSWL_NONE,SPF_PASS autolearn=ham version=3.3.2 spammy=globally, Maintenance, consumption, Changed X-HELO: mail-wm0-f51.google.com Received: from mail-wm0-f51.google.com (HELO mail-wm0-f51.google.com) (74.125.82.51) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Wed, 25 Jul 2018 15:18:48 +0000 Received: by mail-wm0-f51.google.com with SMTP id o11-v6so6437749wmh.2 for ; Wed, 25 Jul 2018 08:18:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=embecosm.com; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=FqSaOvY+vi3uWYRJ4Ifqw/OjxAw4kHlfmC1oBTutaUI=; b=e+EwDcUHY29VVgDN1JLryiSBzLUSicQDdBCiRRFv3SRW2R03oNN2xaTZYivOWoHqa6 ukjt2TxTUUFfluG9cLEhtbQSn7bCHIv9/k/FQfXqo2QFqOEtvTjQBSN2spDNi4wRm/5R 9X8x+pKOPVly1+qlcbJG1aW9CxeNgUIqVB1lJUN1cOHWpeyPWW5RssjoO1QozYz9RQkw wQ+W5sqiP1sGSy05nZim2MELjwZWrU9gBTmC3ivRZc6Yx8CqpyDonqluUd35PiJWp+Xw E+WU7J/HqHMEXUQFBw1Ac0avf5E5rzNAf0euVaevSPVx/D9y3AnlMJOZp8U05/w27Vl9 MVJQ== Return-Path: Received: from localhost (host86-162-243-217.range86-162.btcentralplus.com. [86.162.243.217]) by smtp.gmail.com with ESMTPSA id h14-v6sm11577938wro.15.2018.07.25.08.18.44 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 25 Jul 2018 08:18:45 -0700 (PDT) From: Andrew Burgess To: gdb-patches@sourceware.org Cc: Andrew Burgess , Simon Marchi , Tom Tromey Subject: [PATCHv2] gdb: Add switch to disable DWARF stack unwinders Date: Wed, 25 Jul 2018 15:18:00 -0000 Message-Id: <20180725151842.6443-1-andrew.burgess@embecosm.com> In-Reply-To: <20180713134629.27011-1-andrew.burgess@embecosm.com> References: <20180713134629.27011-1-andrew.burgess@embecosm.com> X-IsSubscribed: yes X-SW-Source: 2018-07/txt/msg00692.txt.bz2 This revision addresses the review feedback: - Minor doc change suggested by Eli. - DWARF unwinders start globally enabled. - Minor comment typo fixes - New maintenance command is now registered in dwarf2-frame.c The commit message now mentions pr 8434, which is about being able to enable or disable any/all unwinders. After the discussions on the mailing list, and on IRC I'm still proposing that this patch only allow control of DWARF unwinders. The thinking is that, this is only a maintenance command, so we can change the UI later if we wish, and allowing full unwinder control would be a much bigger, more invasive change, and it's unclear how useful that feature would actually be. Being able to switch of DWARF unwinders is useful, so that's all I'm proposing right now. -- 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/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/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 @@ 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..2e1110bbe8b 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 45280fec410..8455d948412 100644 --- a/gdb/dwarf2read.c +++ b/gdb/dwarf2read.c @@ -25330,8 +25330,8 @@ 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/gdb.base/maint.exp b/gdb/testsuite/gdb.base/maint.exp index 92086eec862..6125b6ec6f2 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"} { -- 2.14.4