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Sat, 11 Jan 2025 16:01:46 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id QCz6AeqVgmdkdwAAD6G6ig (envelope-from ); Sat, 11 Jan 2025 16:01:46 +0000 Message-ID: <28934663-54a6-47cf-8d30-dace9cde8d20@suse.de> Date: Sat, 11 Jan 2025 17:01:37 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] GDB: Use gdb::array_view for buffers used in register reading and unwinding To: Thiago Jung Bauermann Cc: Simon Marchi , gdb-patches@sourceware.org, "Aktemur, Tankut Baris" , "Maciej W. Rozycki" References: <20250110164430.3376697-1-thiago.bauermann@linaro.org> <20250110164430.3376697-3-thiago.bauermann@linaro.org> <321e71e0-43de-4604-bb7e-34f6f64b83bf@simark.ca> <871pxa9udr.fsf@linaro.org> <347ca2f6-aa4a-4f08-8675-a8f0bce65e93@suse.de> <87ikql8ibi.fsf@linaro.org> Content-Language: en-US From: Tom de Vries In-Reply-To: <87ikql8ibi.fsf@linaro.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-0.995]; MIME_GOOD(-0.10)[text/plain]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_FIVE(0.00)[5]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,suse.de:mid] X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: gdb-patches-bounces~public-inbox=simark.ca@sourceware.org On 1/11/25 16:46, Thiago Jung Bauermann wrote: > > Hello Tom, > > Tom de Vries writes: > >> On 1/10/25 23:28, Thiago Jung Bauermann wrote: >>> + gdb_assert (buffer.size () >= value->type ()->length ()); >>> + >> >> This causes a regression on s390x-linux for test-case gdb.base/return.exp: >> ... >> (gdb) PASS: gdb.base/return.exp: continue to return of -5 >> return 5^M >> Make func2 return now? (y or n) y^M >> /home/vries/gdb/src/gdb/frame.c:1207: internal-error: frame_register_unwind: Assertion >> `buffer.size () >= value->type ()->length ()' failed.^M >> A problem internal to GDB has been detected,^M >> further debugging may prove unreliable.^M >> ----- Backtrace -----^M >> FAIL: gdb.base/return.exp: return value 5 (GDB internal error) >> ... >> >> Before the commit, the test-case produces a fail, but doesn't assert: >> ... >> (gdb) PASS: gdb.base/return.exp: continue to return of -5 >> return 5^M >> Make func2 return now? (y or n) y^M >> value has been optimized out^M >> (gdb) FAIL: gdb.base/return.exp: return value 5 >> ... >> >> Concretely, we're trying to read machine register r11, which according to the CFI is saved >> in dwarf register 16: >> ... >> DW_CFA_register: r11 in r16 (f0) >> ... >> >> Dwarf register 16 corresponds to f0 / v0 according to the ABI, and since v0 is available, >> v0 is picked by s390_dwarf_reg_to_regnum. >> >> The assert then fails because the buffer that should hold the value of 8 byte register >> r11: >> ... >> (gdb) p buffer.size () >> $1 = 8 >> ... >> is smaller than the size of register v0: >> ... >> (gdb) p value->type ()->length () >> $2 = 16 >> ... >> >> Removing the assert reverts back to previous behaviour. > > Thank you for debugging the issue! So memcpy was overflowing the > buffer. Nice to see the assert in action. :) > Hi Thiago, thanks for the quick review. Not the memcpy, but the memset, because the optimized out branch was activated, but buffer overflow indeed. >> Properly fixing this requires us to only look at the part that is relevant, copying the >> value from there, and checking for optimized out and unavailable only there. >> >> This worked for s390x-linux: >> ... >> diff --git a/gdb/frame.c b/gdb/frame.c >> index 10a32dcd896..02583857019 100644 >> --- a/gdb/frame.c >> +++ b/gdb/frame.c >> @@ -1193,8 +1193,14 @@ frame_register_unwind (const frame_info_ptr &next_frame, int >> regnum, >> >> gdb_assert (value != NULL); >> >> - *optimizedp = value->optimized_out (); >> - *unavailablep = !value->entirely_available (); >> + if (value->lazy ()) >> + value->fetch_lazy (); >> + >> + *optimizedp >> + = value->bits_any_optimized_out (value->offset () * 8, >> + buffer.size () * 8); >> + *unavailablep >> + = !value->bytes_available (value->offset (), buffer.size ()); >> *lvalp = value->lval (); >> *addrp = value->address (); >> if (*lvalp == lval_register) >> @@ -1204,13 +1210,17 @@ frame_register_unwind (const frame_info_ptr &next_frame, int >> regnum, >> >> if (!buffer.empty ()) >> { >> - gdb_assert (buffer.size () >= value->type ()->length ()); >> + gdb_assert (buffer.size () >> + <= value->type ()->length () - value->offset ()); > > It should be '>=' above. > That doesn't work unfortunately: - buffer.size () is 8 - value->type ()->length () is 16 - value->offset () == 0 So we'd have gdb_assert (8 >= 16). FWIW, I've tried out a less intrusive fix which also works: ... diff --git a/gdb/frame.c b/gdb/frame.c index 10a32dcd896..96e0752888f 100644 --- a/gdb/frame.c +++ b/gdb/frame.c @@ -1191,6 +1191,19 @@ frame_register_unwind (const frame_info_ptr &next_frame, int regnum, value = frame_unwind_register_value (next_frame, regnum); + frame_info_ptr this_frame = get_prev_frame (next_frame); + struct gdbarch *gdbarch = frame_unwind_arch (this_frame); + size_t reg_size = register_size (gdbarch, regnum); + + if (value->type ()->length () > reg_size) + { + struct value *part_val + = value::allocate_register (this_frame, regnum); + value->contents_copy (part_val, 0, value->offset (), reg_size); + release_value (value); + value = part_val; + } + gdb_assert (value != NULL); *optimizedp = value->optimized_out (); ... but I have doubts whether reg_size is correct in case gdbarch changes between frames and register sizes are different. Thanks, - Tom >> if (!*optimizedp && !*unavailablep) >> - memcpy (buffer.data (), value->contents_all ().data (), >> - value->type ()->length ()); >> + { >> + auto value_part >> + = value->contents_all ().slice (value->offset (), buffer.size ()); >> + memcpy (buffer.data (), value_part.data (), buffer.size ()); >> + } >> else >> - memset (buffer.data (), 0, value->type ()->length ()); >> + memset (buffer.data (), 0, buffer.size ()); >> } >> >> /* Dispose of the new value. This prevents watchpoints from >> ... > > Thank you for the patch! With the fix in the assert comparison: > > Reviewed-by: Thiago Jung Bauermann > > -- > Thiago