Robert Watson schrieb am 2009-10-21: > On Wed, 21 Oct 2009, Alexander Best wrote:
> >this code serves only one purpose: to trigger a segfault. i don't > >use the code for any other purpose. i was under the impression that > >mmap() should either succeed or fail (tertium non datur). mmap's > >manual doesn't say anything about mmap() causing segfaults. > Have you tried ktracing the application? I think you'll find that > mmap(2) system call succeeded fine, and that the segfault comes from > attempting to execute the address in libc on return to userspace, as > a result of libc not being at that address anymore (since you > removed its mapping). You can use procstat -v to inspect address > space use by processes, but as a general rule you don't want to pass > anything other than an address of 0x0 to mmap(2) unless you're very > carefully managing the address space of the process. Many userspace > libraries are involved in using that address space, but especially > the runtime linker which begins execution in userspace when a binary > is started. > Robert N M Watson > Computer Laboratory > University of Cambridge you're right. this kdump shows that the segfault isn't being caused by the mmap() call: 88343 mmap_test CALL mmap(0x1000,0x80047000,PROT_NONE,MAP_FIXED|MAP_ANON,0xffffffff,0,0) 88343 mmap_test RET mmap 4096/0x1000 88343 mmap_test PSIG SIGSEGV SIG_DFL 88343 mmap_test NAMI "mmap_test.core" thanks for clearing things up. however i stil think mentioning this situation in the mmap(2) manual (maybe in section MAP_FIXED) would be a good idea. cheers. alex _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "freebsd-hackers-unsubscr...@freebsd.org"
