From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 14992 invoked by alias); 18 Jan 2013 15:12:24 -0000 Received: (qmail 14975 invoked by uid 22791); 18 Jan 2013 15:12:22 -0000 X-SWARE-Spam-Status: No, hits=-3.3 required=5.0 tests=BAYES_00,KHOP_THREADED,RP_MATCHES_RCVD,TW_EG X-Spam-Check-By: sourceware.org Received: from usmamail.tilera.com (HELO USMAMAIL.TILERA.COM) (12.216.194.151) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Fri, 18 Jan 2013 15:12:19 +0000 Received: from [192.168.0.103] (218.11.179.59) by USMAExch2.tad.internal.tilera.com (10.3.0.33) with Microsoft SMTP Server (TLS) id 14.0.694.0; Fri, 18 Jan 2013 10:12:17 -0500 Message-ID: <50F9664D.2090008@tilera.com> Date: Fri, 18 Jan 2013 15:12:00 -0000 From: Jiong Wang User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:17.0) Gecko/20130107 Thunderbird/17.0.2 MIME-Version: 1.0 To: Joel Brobecker CC: , Walter Lee Subject: Re: [RFC/TileGX 2/6] simplify the handling of skip prologue for plt stub References: <50F91516.6010204@tilera.com> <20130118131511.GF3564@adacore.com> In-Reply-To: <20130118131511.GF3564@adacore.com> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit 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: 2013-01/txt/msg00430.txt.bz2 >> for tilegx, when skip prologue, if the start_pc is a plt stub address, then >> stop to go further, just return the start_pc. >> >> gdb/ChangeLog: >> >> * tilegx-tdep.c (tilegx_skip_prologue): simplify the handling for >> plt stub. > Can you provide an example where this becomes necessary? I don't > see a problem with the patch per se, but I don't remember seeing > other ports doing this... > yes, there are some tricky thing. for the simple hello.c #include int main(int argc, char **argv) { printf("hello, %d\n", argc); return 0 } without this patch === -bash-4.1$ gcc -o hello.tile hello.c -bash-4.1$ ./gdb hello.tile (gdb) b printf Error accessing memory address 0x10a40: Success. after this patch === (gdb) b printf Breakpoint 1 at 0x10a40 this is because tilegx skip_prologue will invoke tilegx_analyze_prologue, which will prefetch 32*8 bytes. while for when the address is in plt stub, you can see it near the eh_frame_hdr section [14] .plt 0000000000010a00 000a00 0000a0 28 AX 0 0 64 ... [16] .eh_frame_hdr 0000000000010ac0 000ac0 000024 00 A 0 0 4 [17] .eh_frame 0000000000010ae8 000ae8 0000b4 00 A 0 0 8 the .eh_frame_hdr aligns to 4, there is a hole between .eh_frame_hdr and .eh_frame, and this will cause trouble for section_table_xfer_memory_partial. after fetch memory starting from 0x10ac0 to 0x10ae4, then the memaddr will be 0x10ae4 in section_table_xfer_memory_partial, while this function did not consider this hole situation, so goes to line 666, error occured. for other targets, like x86, I have done a brief exploration, seems they do not have large prefetch window