Date: Thu, 14 Aug 2008 18:40:17 -0700 (PDT) From: Douglas William Thrift <douglas@douglasthrift.net> To: FreeBSD-gnats-submit@FreeBSD.org Subject: amd64/126543: [amd64] __builtin_frame_address does not return 0 when reaching the top of the stack Message-ID: <200808150140.m7F1eH8p008466@slowhand.douglasthrift.net> Resent-Message-ID: <200808150150.m7F1o3O2049465@freefall.freebsd.org>
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>Number: 126543 >Category: amd64 >Synopsis: [amd64] __builtin_frame_address does not return 0 when reaching the top of the stack >Confidential: no >Severity: non-critical >Priority: medium >Responsible: freebsd-amd64 >State: open >Quarter: >Keywords: >Date-Required: >Class: sw-bug >Submitter-Id: current-users >Arrival-Date: Fri Aug 15 01:50:03 UTC 2008 >Closed-Date: >Last-Modified: >Originator: Douglas William Thrift >Release: FreeBSD 7.0-STABLE-jc2 amd64 >Organization: >Environment: System: FreeBSD slowhand.douglasthrift.net 7.0-STABLE-jc2 FreeBSD 7.0-STABLE-jc2 #0: Thu Jun 26 21:33:03 PDT 2008 user@jail8.johncompanies.com:/usr/obj/usr/src/sys/jail8 amd64 >Description: On the amd64 architecture the gcc builtin function __builtin_frame_address does not return 0 when it is called for the level that should be the top of the stack. Instead it seems to continue returning addresses and then causes a bus error. GCC documentation: http://gcc.gnu.org/onlinedocs/gcc-4.2.4/gcc/Return-Address.html I've seen this occur on this system and also on two systems running FreeBSD 7.0-RELEASE-p3. This causes devel/libexecinfo to be completely useless and crashy. >How-To-Repeat: Compile the following C program: #include <stdio.h> int main(int argc, char *argv[]) { void *address; int index; for (index = 0; address != NULL && index != 5; ++index) { switch (index) { case 0: address = __builtin_frame_address(0); break; case 1: address = __builtin_frame_address(1); break; case 2: address = __builtin_frame_address(2); break; case 3: address = __builtin_frame_address(3); break; case 4: address = __builtin_frame_address(4); break; } printf("0x%x\n", address); } return 0; } Run on an i386 machine its output is fine: [douglas@backhome:~]$ ./test 0xbfbfec68 0xbfbfec9c 0x0 Run on an amd64 machine is not so fine: [douglas@justonenight:~]$ ./test 0xffffeaf0 0xffffeb40 0xffffecef 0x4c454853 Bus error: 10 (core dumped) The last hex value printed seems to consistently be a string from the environment variables. Judging by the two stack frame addresses printed on i386, perhaps the third address printed on amd64 is the one that should be a zero. >Fix: >Release-Note: >Audit-Trail: >Unformatted:
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