• Roland McGrath's avatar
    [PATCH] vDSO hash-style fix · 0b0bf7a3
    Roland McGrath authored
    The latest toolchains can produce a new ELF section in DSOs and
    dynamically-linked executables.  The new section ".gnu.hash" replaces
    ".hash", and allows for more efficient runtime symbol lookups by the
    dynamic linker.  The new ld option --hash-style={sysv|gnu|both} controls
    whether to produce the old ".hash", the new ".gnu.hash", or both.  In some
    new systems such as Fedora Core 6, gcc by default passes --hash-style=gnu
    to the linker, so that a standard invocation of "gcc -shared" results in
    producing a DSO with only ".gnu.hash".  The new ".gnu.hash" sections need
    to be dealt with the same way as ".hash" sections in all respects; only the
    dynamic linker cares about their contents.  To work with older dynamic
    linkers (i.e.  preexisting releases of glibc), a binary must have the old
    ".hash" section.  The --hash-style=both option produces binaries that a new
    dynamic linker can use more efficiently, but an old dynamic linker can
    still handle.
    The new section runs afoul of the custom linker scripts used to build vDSO
    images for the kernel.  On ia64, the failure mode for this is a boot-time
    panic because the vDSO's PT_IA_64_UNWIND segment winds up ill-formed.
    This patch addresses the problem in two ways.
    First, it mentions ".gnu.hash" in all the linker scripts alongside ".hash".
     This produces correct vDSO images with --hash-style=sysv (or old tools),
    with --hash-style=gnu, or with --hash-style=both.
    Second, it passes the --hash-style=sysv option when building the vDSO
    images, so that ".gnu.hash" is not actually produced.  This is the most
    conservative choice for compatibility with any old userland.  There is some
    concern that some ancient glibc builds (though not any known old production
    system) might choke on --hash-style=both binaries.  The optimizations
    provided by the new style of hash section do not really matter for a DSO
    with a tiny number of symbols, as the vDSO has.  If someone wants to use
    =gnu or =both for their vDSO builds and worry less about that
    compatibility, just change the option and the linker script changes will
    make any choice work fine.
    Signed-off-by: default avatarRoland McGrath <roland@redhat.com>
    Cc: "Luck, Tony" <tony.luck@intel.com>
    Cc: Kyle McMartin <kyle@mcmartin.ca>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    Cc: Jeff Dike <jdike@addtoit.com>
    Cc: Andi Kleen <ak@muc.de>
    Cc: Sam Ravnborg <sam@ravnborg.org>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
Kbuild.include 5.42 KB