• Daisuke HATAYAMA's avatar
    coredump: unify dump_seek() implementations for each binfmt_*.c · 05f47fda
    Daisuke HATAYAMA authored
    The current ELF dumper can produce broken corefiles if program headers
    exceed 65535.  In particular, the program in 64-bit environment often
    demands more than 65535 mmaps.  If you google max_map_count, then you can
    find many users facing this problem.
    Solaris has already dealt with this issue, and other OSes have also
    adopted the same method as in Solaris.  Currently, Sun's document and AMD
    64 ABI include the description for the extension, where they call the
    extension Extended Numbering.  See Reference for further information.
    I believe that linux kernel should adopt the same way as they did, so I've
    written this patch.
    I am also preparing for patches of GDB and binutils.
    How to fix
    In new dumping process, there are two cases according to weather or
    not the number of program headers is equal to or more than 65535.
     - if less than 65535, the produced corefile format is exactly the same
       as the ordinary one.
     - if equal to or more than 65535, then e_phnum field is set to newly
       introduced constant PN_XNUM(0xffff) and the actual number of program
       headers is set to sh_info field of the section header at index 0.
    Compatibility Concern
     * As already mentioned in Summary, Sun and AMD64 has already adopted
       this.  See Reference.
     * There are four combinations according to whether kernel and userland
       tools are respectively modified or not.  The next table summarizes
       shortly for each combination.
                         Original Kernel    |   Modified Kernel
        	            < 65535  | >= 65535 | < 65535  | >= 65535
       Original Tools |    OK    |  broken  |   OK     | broken (#)
       Modified Tools |    OK    |  broken  |   OK     |    OK
      Note that there is no case that `OK' changes to `broken'.
      (#) Although this case remains broken, O-M behaves better than
      O-O. That is, while in O-O case e_phnum field would be extremely
      small due to integer overflow, in O-M case it is guaranteed to be at
      least 65535 by being set to PN_XNUM(0xFFFF), much closer to the
      actual correct value than the O-O case.
    Test Program
    Here is a test program mkmmaps.c that is useful to produce the
    corefile with many mmaps. To use this, please take the following
    $ ulimit -c unlimited
    $ sysctl vm.max_map_count=70000 # default 65530 is too small
    $ sysctl fs.file-max=70000
    $ mkmmaps 65535
    Then, the program will abort and a corefile will be generated.
    If failed, there are two cases according to the error message
     * ``out of memory'' means vm.max_map_count is still smaller
     * ``too many open files'' means fs.file-max is still smaller
    So, please change it to a larger value, and then retry it.
    #include <stdio.h>
    #include <stdlib.h>
    #include <sys/mman.h>
    #include <fcntl.h>
    #include <unistd.h>
    int main(int argc, char **argv)
    	int maps_num;
    	if (argc < 2) {
    		fprintf(stderr, "mkmmaps [number of maps to be created]\n");
    	if (sscanf(argv[1], "%d", &maps_num) == EOF) {
    	if (maps_num < 0) {
    		fprintf(stderr, "%d is invalid\n", maps_num);
    	for (; maps_num > 0; --maps_num) {
    		if (MAP_FAILED == mmap((void *)NULL, (size_t) 1, PROT_READ,
    					MAP_SHARED | MAP_ANONYMOUS, (int) -1,
    					(off_t) NULL)) {
    		char buffer[128];
    		sprintf(buffer, "wc -l /proc/%u/maps", getpid());
    	return 0;
    Tested on i386, ia64 and um/sys-i386.
    Built on sh4 (which covers fs/binfmt_elf_fdpic.c)
     - Sun microsystems: Linker and Libraries.
       Part No: 817-1984-17, September 2008.
       URL: http://docs.sun.com/app/docs/doc/817-1984
     - System V ABI AMD64 Architecture Processor Supplement
       Draft Version 0.99., May 11, 2009.
       URL: http://www.x86-64.org/
    This patch:
    There are three different definitions for dump_seek() functions in
    binfmt_aout.c, binfmt_elf.c and binfmt_elf_fdpic.c, respectively.  The
    only for binfmt_elf.c.
    My next patch will move dump_seek() into a header file in order to share
    the same implementations for dump_write() and dump_seek().  As the first
    step, this patch unify these three definitions for dump_seek() by applying
    the past commits that have been applied only for binfmt_elf.c.
    Specifically, the modification made here is part of the following commits:
      * d025c9db
      * 7f14daa1
    This patch does not change a shape of corefiles.
    Signed-off-by: default avatarDaisuke HATAYAMA <d.hatayama@jp.fujitsu.com>
    Cc: "Luck, Tony" <tony.luck@intel.com>
    Cc: Jeff Dike <jdike@addtoit.com>
    Cc: David Howells <dhowells@redhat.com>
    Cc: Greg Ungerer <gerg@snapgear.com>
    Cc: Roland McGrath <roland@redhat.com>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Alexander Viro <viro@zeniv.linux.org.uk>
    Cc: Andi Kleen <andi@firstfloor.org>
    Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
    Cc: <linux-arch@vger.kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
binfmt_aout.c 13.2 KB