Date: Wed, 28 Nov 2007 08:56:02 GMT From: carl shapiro <carl.shapiro@gmail.com> To: freebsd-gnats-submit@FreeBSD.org Subject: misc/118304: freebsd 7 delivers unanticipated signal for page faults to freebsd <= 6 binaries Message-ID: <200711280856.lAS8u2hO048064@www.freebsd.org> Resent-Message-ID: <200711280900.lAS903q0070579@freefall.freebsd.org>
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>Number: 118304 >Category: misc >Synopsis: freebsd 7 delivers unanticipated signal for page faults to freebsd <= 6 binaries >Confidential: no >Severity: critical >Priority: high >Responsible: freebsd-bugs >State: open >Quarter: >Keywords: >Date-Required: >Class: sw-bug >Submitter-Id: current-users >Arrival-Date: Wed Nov 28 09:00:03 UTC 2007 >Closed-Date: >Last-Modified: >Originator: carl shapiro >Release: 7.0-BETA3 >Organization: self >Environment: FreeBSD freebsd7 7.0-BETA3 FreeBSD 7.0-BETA3 #0: Fri Nov 16 22:20:33 UTC 2007 root@logan.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC i386 >Description: Prior to FreeBSD 7 a SIGBUS is delivered if a page's protection is violated. FreeBSD 7 changed this to SIGSEGV. Older executables which expect SIGBUS when a page's protection is violated now unexpectedly receive a SIGSEGV. This breaks applications which attempt to handle page protection binaries. Garbage collectors that implement write barriers through page protection (boehm gc, cmucl, etc.) are one such application. >How-To-Repeat: Start on a FreeBSD 6 system. freebsd6 $ cc -o mmap6 mmap.c freebsd6 $ ./mmap6 __FreeBSD_version=601000 signum=10,info->si_code=12,context=0xbfbfe880 Transfer the mmap6 binary to a FreeBSD 7 system to resume the test case. freebsd7 $ ./mmap6 __FreeBSD_version=601000 signum=11,info->si_code=2,context=0xbfbfe9d0 freebsd7 $ cc -o mmap7 mmap.c freebsd7 $ ./mmap7 __FreeBSD_version=700055 signum=11,info->si_code=2,context=0xbfbfe9e0 Note the different signal and different subcode. Here is the test program. /* mmap.c */ #include <sys/mman.h> #include <signal.h> #include <stdio.h> #include <stdlib.h> #include <osreldate.h> void handler(int signum, siginfo_t *info, void *context) { fprintf(stderr, "__FreeBSD_version=%d\n", __FreeBSD_version); fprintf(stderr, "signum=%d,info->si_code=%d,context=%p\n", signum, info->si_code, context); exit(1); } int main(int argc, char *argv[]) { struct sigaction sa; size_t len = 0x1000; char *p = mmap(0, len, PROT_NONE, MAP_ANON, -1, 0); if (p == MAP_FAILED) { perror("mmap"); exit(1); } sa.sa_sigaction = handler; sa.sa_flags = SA_SIGINFO; sigaction(SIGBUS, &sa, NULL); sigaction(SIGSEGV, &sa, NULL); *p = 0xff; if (munmap(p, len) == -1) { perror("munmap"); exit(1); } return 0; } >Fix: >Release-Note: >Audit-Trail: >Unformatted:
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