From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 5824 invoked by alias); 20 Mar 2010 22:36:20 -0000 Received: (qmail 5801 invoked by uid 48); 20 Mar 2010 22:36:20 -0000 Date: Sat, 20 Mar 2010 22:36:00 -0000 Message-ID: <20100320223620.5800.qmail@sourceware.org> X-Bugzilla-Reason: CC References: Subject: [Bug libgcj/40860] [4.4/4.5 regression] regressions in libjava testsuite on arm-linux In-Reply-To: Reply-To: gcc-bugzilla@gcc.gnu.org To: java-prs@gcc.gnu.org From: "mikpe at it dot uu dot se" Mailing-List: contact java-prs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: java-prs-owner@gcc.gnu.org X-SW-Source: 2010-q1/txt/msg00171.txt.bz2 ------- Comment #26 from mikpe at it dot uu dot se 2010-03-20 22:36 ------- Created an attachment (id=20147) --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=20147&action=view) test program to take a stack trace using _Unwind_ API I'm attaching a test program which sets up a predictable call chain, and then uses _Unwind_Backtrace() and _Unwind_GetRegionStart() to get the entry points of the functions in the call chain into an array. It prints the corresponding function names and verifies that the function entry points are correct. With gcc-4.4.3 and binutils-2.19.1 on armv5tel-unknown-linux-gnueabi this works fine: > gcc -funwind-tables -fno-unit-at-a-time -O -o stacktrace-2.19.1 stacktrace.c > ./stacktrace-2.19.1 bar f2 main With the same gcc binary but binutils-20100316 the program fails: > PATH=/tmp/binutils-2.20.51-install/bin:$PATH gcc -funwind-tables -fno-unit-at-a-time -O stacktrace.c -o stacktrace-2.20.51 > ./stacktrace-2.20.51 bar f1 f1 Abort The reason for the failure is that ld merged the .ARM.exidx entries for f2 and main with the one for f1, which breaks _Unwind_GetRegionStart(). First we see that f1, f2, and main are adjacent in memory: > nm -v stacktrace-2.20.51 ... 00008588 T tracefn 000085bc T bar 0000865c T f1 0000866c T f2 0000867c T main 00008698 T __libc_csu_fini ... With binutils-2.19.1 they each get their own .ARM.exidx entry: > /tmp/binutils-2.20.51-install/bin/readelf --unwind stacktrace-2.19.1 Unwind table index '.ARM.exidx' at offset 0x778 contains 7 entries: 0x845c <_start>: 0x1 [cantunwind] 0x8508 : 0x80a8b0b0 Compact model 0 0xa8 pop {r4r14} 0xb0 finish 0xb0 finish 0x8588 : 0x80aab0b0 Compact model 0 0xaa pop {r4, r5, r6r14} 0xb0 finish 0xb0 finish 0x85bc : 0x8003a8b0 Compact model 0 0x03 vsp = vsp + 16 0xa8 pop {r4r14} 0xb0 finish 0x865c : 0x80a8b0b0 Compact model 0 0xa8 pop {r4r14} 0xb0 finish 0xb0 finish 0x866c : 0x80a8b0b0 Compact model 0 0xa8 pop {r4r14} 0xb0 finish 0xb0 finish 0x867c
: 0x80a8b0b0 Compact model 0 0xa8 pop {r4r14} 0xb0 finish 0xb0 finish But with binutils-20100316 f2 and main don't have their own entries, so PCs in them are reported as belonging to f1 instead: > /tmp/binutils-2.20.51-install/bin/readelf --unwind stacktrace-2.20.51 Unwind table index '.ARM.exidx' at offset 0x778 contains 6 entries: 0x845c <_start>: 0x1 [cantunwind] 0x8508 : 0x80a8b0b0 Compact model 0 0xa8 pop {r4r14} 0xb0 finish 0xb0 finish 0x8588 : 0x80aab0b0 Compact model 0 0xaa pop {r4, r5, r6r14} 0xb0 finish 0xb0 finish 0x85bc : 0x8003a8b0 Compact model 0 0x03 vsp = vsp + 16 0xa8 pop {r4r14} 0xb0 finish 0x865c : 0x80a8b0b0 Compact model 0 0xa8 pop {r4r14} 0xb0 finish 0xb0 finish 0x8698 <__libc_csu_fini>: 0x1 [cantunwind] This test program also works on i686-linux, sparc64-linux -m32/-m64, and powerpc64-linux -m32. I understand the benefits of shrinking .ARM.exidx tables, but it does break parts of gcc's implementation (and thus libjava), so should be opt-in via an explicit option and not done by default. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40860