From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 2692 invoked by alias); 4 Jul 2009 00:37:55 -0000 Received: (qmail 2684 invoked by uid 22791); 4 Jul 2009 00:37:54 -0000 X-SWARE-Spam-Status: No, hits=-2.4 required=5.0 tests=AWL,BAYES_00 X-Spam-Check-By: sourceware.org Received: from smtp-outbound-2.vmware.com (HELO smtp-outbound-2.vmware.com) (65.115.85.73) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Sat, 04 Jul 2009 00:37:47 +0000 Received: from mailhost4.vmware.com (mailhost4.vmware.com [10.16.67.124]) by smtp-outbound-2.vmware.com (Postfix) with ESMTP id 76CC24B003; Fri, 3 Jul 2009 17:37:45 -0700 (PDT) Received: from [10.20.94.141] (msnyder-server.eng.vmware.com [10.20.94.141]) by mailhost4.vmware.com (Postfix) with ESMTP id 64669C9DAB; Fri, 3 Jul 2009 17:37:45 -0700 (PDT) Message-ID: <4A4EA3B3.9030107@vmware.com> Date: Sat, 04 Jul 2009 00:37:00 -0000 From: Michael Snyder User-Agent: Thunderbird 1.5.0.12 (X11/20080411) MIME-Version: 1.0 To: Michael Snyder CC: "gdb-patches@sourceware.org" , "drow@false.org" , "kettenis@gnu.org" , "teawater@gmail.com" Subject: Re: [RFA] epilogue unwinder for i386 (reverse 1/2) References: <4A4EA0F7.1040004@vmware.com> In-Reply-To: <4A4EA0F7.1040004@vmware.com> Content-Type: multipart/mixed; boundary="------------020905000104060503030105" X-IsSubscribed: yes 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 X-SW-Source: 2009-07/txt/msg00101.txt.bz2 This is a multi-part message in MIME format. --------------020905000104060503030105 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-length: 710 Michael Snyder wrote: > This comes out of a discussion with Daniel, about how gcc > does not generate the right dwarf info to allow correct > frame unwinding in function epilogues, causing frame_unwind > to return bad results. > > It's necessary for reverse-step, which will frequently step > backward to the return instruction of a function. But it also > provides an improvement for forward debugging, in that now, > without this change, if you STEPI until you are at the return > instruction, you will get a bad backtrace. > > The infrun changes that take advantage of this patch will follow > separately. > > Michael Oops, the patch wasn't meant to have that "#if 0" in it... corrected patch below. --------------020905000104060503030105 Content-Type: text/plain; name="epilogue.txt" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="epilogue.txt" Content-length: 3491 2009-07-03 Michael Snyder * i386-tdep.c: Add a frame unwinder for function epilogues. (i386_in_function_epilogue_p): New function. (i386_epilogue_frame_sniffer): New function. (i386_epilogue_frame_cache): New function. (i386_epilogue_frame_this_id): New function. (i386_epilogue_frame_unwind): New struct frame_unwind. (i386_gdbarch_init): Hook the new unwinder. Index: i386-tdep.c =================================================================== RCS file: /cvs/src/src/gdb/i386-tdep.c,v retrieving revision 1.280 diff -u -p -r1.280 i386-tdep.c --- i386-tdep.c 2 Jul 2009 17:25:54 -0000 1.280 +++ i386-tdep.c 4 Jul 2009 00:37:12 -0000 @@ -1487,6 +1487,89 @@ static const struct frame_unwind i386_fr NULL, default_frame_sniffer }; + +/* Normal frames, but in a function epilogue. */ + +/* The epilogue is defined here as the RET instruction, which will + follow any instruction such as LEAVE or POP EBP that destroys the + function's stack frame. */ + +static int +i386_in_function_epilogue_p (struct gdbarch *gdbarch, CORE_ADDR pc) +{ + gdb_byte insn; + + if (target_read_memory (pc, &insn, 1) != 0) + return 0; /* Can't read memory at pc. */ + + if (insn != 0xc3) /* RET */ + return 0; + + return 1; +} + +static int +i386_epilogue_frame_sniffer (const struct frame_unwind *self, + struct frame_info *this_frame, + void **this_prologue_cache) +{ + if (frame_relative_level (this_frame) == 0) + return i386_in_function_epilogue_p (get_frame_arch (this_frame), + get_frame_pc (this_frame)); + else + return 0; +} + +static struct i386_frame_cache * +i386_epilogue_frame_cache (struct frame_info *this_frame, void **this_cache) +{ + struct gdbarch *gdbarch = get_frame_arch (this_frame); + enum bfd_endian byte_order = gdbarch_byte_order (gdbarch); + struct i386_frame_cache *cache; + gdb_byte buf[4]; + + if (*this_cache) + return *this_cache; + + cache = i386_alloc_frame_cache (); + *this_cache = cache; + + /* Cache base will be ESP plus cache->sp_offset (-4). */ + get_frame_register (this_frame, I386_ESP_REGNUM, buf); + cache->base = extract_unsigned_integer (buf, 4, + byte_order) + cache->sp_offset; + + /* Cache pc will be the frame func. */ + cache->pc = get_frame_pc (this_frame); + + /* The saved ESP will be at cache->base plus 8. */ + cache->saved_sp = cache->base + 8; + + /* The saved EIP will be at cache->base plus 4. */ + cache->saved_regs[I386_EIP_REGNUM] = cache->base + 4; + + return cache; +} + +static void +i386_epilogue_frame_this_id (struct frame_info *this_frame, + void **this_cache, + struct frame_id *this_id) +{ + struct i386_frame_cache *cache = i386_epilogue_frame_cache (this_frame, + this_cache); + + (*this_id) = frame_id_build (cache->base + 8, cache->pc); +} + +static const struct frame_unwind i386_epilogue_frame_unwind = +{ + NORMAL_FRAME, + i386_epilogue_frame_this_id, + i386_frame_prev_register, + NULL, + i386_epilogue_frame_sniffer +}; /* Signal trampolines. */ @@ -5328,7 +5411,10 @@ i386_gdbarch_init (struct gdbarch_info i /* Helper for function argument information. */ set_gdbarch_fetch_pointer_argument (gdbarch, i386_fetch_pointer_argument); - +#if 0 + /* Hook the function epilogue frame unwinder. */ + frame_unwind_append_unwinder (gdbarch, &i386_epilogue_frame_unwind); +#endif /* Hook in the DWARF CFI frame unwinder. */ dwarf2_append_unwinders (gdbarch); --------------020905000104060503030105--