On Tue, Jun 24, 2014 at 11:04:10AM -0700, Matthew Dempsky wrote: > SIGBUS/BUS_ADRERR: Accessing a mapped page that exceeds the end of > the underlying mapped file.
Generating SIGBUS for this case has proven controversial due to concern that this is Linux invented behavior and not compatible with Solaris, so I decided to collect some more background information on the subject. - SunOS 4.1.3's mmap() manual specifies: "Any reference to addresses beyond the end of the object, however, will result in the delivery of a SIGBUS signal." This wording was relaxed to "SIGBUS or SIGSEGV" in SunOS 5.6 and remains in current manuals. (I'm not sure, but I suspect this may be to simply reflect that memory protection violations take priority over bounds checking.) SunOS 4.1.3: http://www.freebsd.org/cgi/man.cgi?query=mmap&sektion=2&manpath=SunOS+4.1.3 SunOS 5.6: http://www.freebsd.org/cgi/man.cgi?query=mmap&sektion=2&manpath=SunOS+5.6 Solaris 11: http://docs.oracle.com/cd/E23824_01/html/821-1463/mmap-2.html - Many other SVR-derived OSes similarly document SIGBUS in their mmap() manuals too: AIX: http://www-01.ibm.com/support/knowledgecenter/ssw_aix_53/com.ibm.aix.basetechref/doc/basetrf1/mmap.htm?lang=en HPUX: http://h20566.www2.hp.com/portal/site/hpsc/template.BINARYPORTLET/public/kb/docDisplay/resource.process/?spf_p.tpst=kbDocDisplay_ws_BI&spf_p.rid_kbDocDisplay=docDisplayResURL&javax.portlet.begCacheTok=com.vignette.cachetoken&spf_p.rst_kbDocDisplay=wsrp-resourceState%3DdocId%253Demr_na-c02261243-2%257CdocLocale%253D&javax.portlet.endCacheTok=com.vignette.cachetoken UnixWare: http://uw714doc.sco.com/en/man/html.2/mmap.2.html - This behavior has been (awkwardly) specified for mmap() since SUSv2: "References within the address range starting at pa and continuing for len bytes to whole pages following the end of an object shall result in delivery of a SIGBUS signal." Later versions of POSIX have the same wording. SUSv2: http://pubs.opengroup.org/onlinepubs/007908799/xsh/mmap.html POSIX.2001: http://pubs.opengroup.org/onlinepubs/009695399/functions/mmap.html POSIX.2008: http://pubs.opengroup.org/onlinepubs/9699919799/functions/mmap.html - More generally, POSIX explains the SIGBUS/SIGSEGV distinction thusly: "When an object is mapped, various application accesses to the mapped region may result in signals. In this context, SIGBUS is used to indicate an error using the mapped object, and SIGSEGV is used to indicate a protection violation or misuse of an address." Specific examples are provided too: Memory Protection: http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_08_03_03
