From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 31758 invoked by alias); 2 Dec 2013 21:17:34 -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 31732 invoked by uid 89); 2 Dec 2013 21:17:32 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=2.4 required=5.0 tests=AWL,BAYES_50,RDNS_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no version=3.3.2 X-HELO: mail-wi0-f178.google.com Received: from Unknown (HELO mail-wi0-f178.google.com) (209.85.212.178) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES128-SHA encrypted) ESMTPS; Mon, 02 Dec 2013 21:17:06 +0000 Received: by mail-wi0-f178.google.com with SMTP id ca18so5519455wib.17 for ; Mon, 02 Dec 2013 13:16:57 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:message-id:date:from:user-agent:mime-version:to :cc:subject:references:in-reply-to:content-type :content-transfer-encoding; bh=ov3lijfFGZ+7mbPAbrnxxCAcfDTmi9uPY65aqNoyYIA=; b=UzkM0SG05P7UR6VNjuibngTLVv+K31ApRoFDumtHRv+MTlDvXHvZwEfISkUx1v2JWP X/XLcK1eTbtiKl+zociXIFg3ctip/bWSzcX+LJT0moh8CapuGtOGzAGV7DQ+H8PoViL3 FKEad45wBgbpdMlX2h0TVvlqW76IowaH9RrGa6sXc7HvzOjtTyOXG4ZlxuM7OQJzGe9E NVsbr8tAdMdgbaxTQ4KatAu7+A8v2KR2KTWqs4dtKIzEwAAzV3dXDa4fTwci/qQFPgit 7aejrofpyzPWc2GRNGF+rbPiX9feThI/XKzz0GY+sTmIvO2OR7Ed2SA9D1tXywQ6QXsG rcfw== X-Gm-Message-State: ALoCoQkRBneoAsXDGqtA+rxGvwchft5U5yBYJs8KMH67IYLYVtTdj1VhCVaNvqoJsUY8jbH7YLCj X-Received: by 10.180.160.212 with SMTP id xm20mr19904626wib.33.1386019017081; Mon, 02 Dec 2013 13:16:57 -0800 (PST) Received: from [192.168.1.2] ([182.185.141.185]) by mx.google.com with ESMTPSA id nb16sm125926983wic.0.2013.12.02.13.16.40 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Mon, 02 Dec 2013 13:16:56 -0800 (PST) Message-ID: <529CF8B3.60906@linaro.org> Date: Mon, 02 Dec 2013 21:17:00 -0000 From: Omair Javaid User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.1 MIME-Version: 1.0 To: Pedro Alves CC: gdb-patches@sourceware.org, Patch Tracking Subject: Re: [PATCH] testsuite/gdb.dwarf2: Fix for dw2-dos-drive failure on ARM References: <51F7DDF0.8090605@redhat.com> <523B1DDE.2060002@redhat.com> <524AEB9A.8090303@redhat.com> In-Reply-To: <524AEB9A.8090303@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-IsSubscribed: yes X-SW-Source: 2013-12/txt/msg00049.txt.bz2 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 --