From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 22242 invoked by alias); 15 Jan 2014 18:39:22 -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 22143 invoked by uid 89); 15 Jan 2014 18:39:21 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=0.8 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_LOW,SPF_PASS autolearn=ham version=3.3.2 X-HELO: mail-ob0-f171.google.com Received: from mail-ob0-f171.google.com (HELO mail-ob0-f171.google.com) (209.85.214.171) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES128-SHA encrypted) ESMTPS; Wed, 15 Jan 2014 18:39:19 +0000 Received: by mail-ob0-f171.google.com with SMTP id wm4so1590335obc.2 for ; Wed, 15 Jan 2014 10:39:17 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc:content-type; bh=ovV2st4KF58z7WkrIPcHS1KqkLJKncQq24fI47vqgGc=; b=javHl5rcTAMvuvcdCU4Pz5hI2UedTx0t+hZ+vYPlyfGTMaOdLb2/LVJGDeje5fxTTq KJJES8mxKbrbvOC6BEqx44pfKDxYc/2qYnzN530vWY0+UQ6siw7umlW1x4moDKR5Lt5x eHC4BD8RHqkYC4F0cTXClenxvqv1cwrVWLlb17yTz6cTFZ6sDxwxvb6hQZ6D8srZ7ajb hh+Zpz9PuFynZubt2ooVCb5Q1Mh0Q7jM7T148DjJHy0YCb8emzINiLyH5JeTJ2w5WU/4 9jTgBXtk2UMI5GTvDdacUJ6fkFL0qcmw4nuBeWwtOJHKofBkscDdPBLhybYCzkgCPE/h M+nQ== X-Gm-Message-State: ALoCoQnUXBhOh6Mj8sFDA2JQkguH9Sg3HvSw/zHpTosXt2AnzCRf09Y31zvVe/KOxzguXeXBbei9 X-Received: by 10.182.213.166 with SMTP id nt6mr3005479obc.53.1389811157477; Wed, 15 Jan 2014 10:39:17 -0800 (PST) MIME-Version: 1.0 Received: by 10.182.137.135 with HTTP; Wed, 15 Jan 2014 10:38:57 -0800 (PST) In-Reply-To: <529CF8B3.60906@linaro.org> References: <51F7DDF0.8090605@redhat.com> <523B1DDE.2060002@redhat.com> <524AEB9A.8090303@redhat.com> <529CF8B3.60906@linaro.org> From: Omair Javaid Date: Wed, 15 Jan 2014 18:39:00 -0000 Message-ID: Subject: Re: [PATCH] testsuite/gdb.dwarf2: Fix for dw2-dos-drive failure on ARM To: Pedro Alves Cc: "gdb-patches@sourceware.org" Content-Type: text/plain; charset=ISO-8859-1 X-IsSubscribed: yes X-SW-Source: 2014-01/txt/msg00537.txt.bz2 On 3 December 2013 02:16, Omair Javaid wrote: > > On 10/01/2013 08:34 PM, Pedro Alves wrote: >> On 10/01/2013 09:32 AM, Omair Javaid wrote: >>> On 19 September 2013 20:53, Pedro Alves wrote: >>>> Please don't top post. >>>> >>>> On 09/19/2013 04:23 PM, Omair Javaid wrote: >>>>> Thanks everyone for the feedback. >>>>> >>>>> I am getting following problem with 1byte text section in the dw2-dos-drive.exp >>>>> >>>>> (gdb) PASS: gdb.dwarf2/dw2-dos-drive.exp: set breakpoint pending off >>>>> break 'z:file.c':func >>>>> Cannot access memory at address 0x0 >>>>> >>>>> When I change this to 4bytes the problem gets fixed. That is why I >>>>> thought this could be an unaligned illegal memory access but I accept >>>>> that the above comments verify that its not a alignment issue. >>>>> >>>>> Can anyone help me figure out what could be the cause of this problem? >>>> >>>> Breakpoint instructions on ARM are 4-byte wide. It sounds like >>>> GDB is trying to read the memory at the breakpoint's address, and >>>> that fails (that error message comes from GDB, not the program). >>>> AFAICS, the test doesn't execute the compiled object's code, so >>>> GDB will try to read memory from the binary's sections. As the >>>> section is only 1 byte long, and probably no other section is allocated >>>> contiguously, that'll fail... To confirm, debug GDB under GDB, >>>> and put a break on throw_it or some such. Then work up the stack >>>> to see where that is thrown, and why. >>>> >>>> -- >>>> Pedro Alves >>>> >>> >>> I have verified the error is being thrown by gdb while its unable to >>> read the 4byte breakpoint address. >>> Heres the call stack: >>> Thread [1] (Suspended: Breakpoint hit.) >>> 38 throw_error() exceptions.c:444 0x0016728c >>> 37 memory_error() corefile.c:204 0x001d1fcc >>> 36 read_memory() corefile.c:223 0x001d201a >>> 35 read_memory_unsigned_integer() corefile.c:312 0x001d2166 >>> 34 arm_skip_prologue() arm-tdep.c:1452 0x00054270 >> >> Right, though this is actually parsing the prologue: >> >> static CORE_ADDR >> arm_skip_prologue (struct gdbarch *gdbarch, CORE_ADDR pc) >> { >> ... >> for (skip_pc = pc; skip_pc < limit_pc; skip_pc += 4) >> { >> inst = read_memory_unsigned_integer (skip_pc, 4, byte_order_for_code); >> >> Some ports detect errors and instead return the PC as far >> as it was managed to be skip. >> E.g. rs6000-tdep.c:skip_prologue (rs6000==PowerPC): >> >> /* Fetch the instruction and convert it to an integer. */ >> if (target_read_memory (pc, buf, 4)) >> break; >> op = extract_unsigned_integer (buf, 4, byte_order); >> >> But not all do that. SPARC also doesn't throw. But others do throw >> an error like ARM. I tried SH and that throws error like ARM; MIPS >> and xtensa, from inspection, look like they'll throw but I haven't >> tried it. AAarch64 throws like ARM, but that's not surprising. >> Anyway, there's no standard. >> >>> 33 gdbarch_skip_prologue() gdbarch.c:2603 0x00176e5c >>> 32 skip_prologue_sal() symtab.c:2869 0x0013dad2 >>> 31 find_function_start_sal() symtab.c:2782 0x0013d9aa >>> 30 symbol_to_sal() linespec.c:3622 0x0014f722 >>> 29 convert_linespec_to_sals() linespec.c:2028 0x0014d6fa >>> 28 parse_linespec() linespec.c:2319 0x0014dc04 >>> 27 decode_line_full() linespec.c:2430 0x0014df44 >>> 26 parse_breakpoint_sals() breakpoint.c:9323 0x00108560 >> ... >> >>> I guess only way to address it is to either use the patch I have >>> posted or may be disable the test for arm? Any suggestions? >> >> Another other way to handle this would be to make the prologue >> scanner cope with this, and not error out, like some ports do. But >> it's not clear at all to me that's a useful behavior. Even if we >> pretended we found the end of the prologue in this case, the address >> we would find in this particular case would never be a valid address >> to put a breakpoint at (the function's first address). If we tried >> setting a breakpoint there, who knows what is it would be overwritten >> by the bytes that fall off the section (we can be 99.99% sure >> the next section would be aligned, and the gap wouldn't be used >> for anything, but still... So, I think it might be better to leave >> the scanner as is, throwing the error while it has context about >> it, and let the user (or higher-level code) decide what to do. >> >> Another way to tackle this could be to actually disable prologue >> skipping, by setting the breakpoint at exactly the func's first >> instruction, with the '*'/address operator: >> >> -gdb_test "break 'z:file.c':func" {Breakpoint [0-9]+ at .*} >> +gdb_test "break *'z:file.c'::func" {Breakpoint [0-9]+ at .*} >> >> This doesn't actually work, though I think that's a bug. I'll >> file a PR. >> >> But, even if it did, that converts a linespec to an expression, >> which may not be a universal solution, as tests with this issue >> might need to use a "real" linespec... >> >> So, in the end, it'd be fine with me to just go in the >> direction of your original patch then. But I think it deserves >> a comment: >> >> pc_start: >> /* Enough space to fit one instruction. */ >> - .byte 0 >> + .4byte 0 >> pc_end: >> >> Could you resend your patch, with that change, a fixed commit >> log description and fixed ChangeLog? >> >> Thanks, >> > > Sorry about responding late to this. I have attached the patch along with commit message and a ChangeLog. > > Commit Log Message: > > Avoid test failure due to error thrown from skip prologue code by > an illegal memory access in case of single byte text section > > gdb/testsuite/ChangeLog: > > 2013-12-02 Omair Javaid > > * gdb.dwarf2/dw2-dos-drive.S: Changed text section size to 4 bytes > > --- > gdb/testsuite/gdb.dwarf2/dw2-dos-drive.S | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/gdb/testsuite/gdb.dwarf2/dw2-dos-drive.S b/gdb/testsuite/gdb.dwarf2/dw2-dos-drive.S > index 682ba4e..f226912 100644 > --- a/gdb/testsuite/gdb.dwarf2/dw2-dos-drive.S > +++ b/gdb/testsuite/gdb.dwarf2/dw2-dos-drive.S > @@ -15,7 +15,7 @@ > > .text > pc_start: > - .byte 0 > + .4byte 0 > pc_end: > > .section .debug_info > -- Ping! OK to commit?