linux/arch/um
Roland McGrath 0b0bf7a3cc [PATCH] vDSO hash-style fix
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: Roland 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: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-07-31 13:28:43 -07:00
..
drivers [PATCH] uml: make mconsole version requests happen in a process 2006-07-10 13:24:24 -07:00
include [PATCH] uml: header formatting cleanups 2006-07-14 21:53:52 -07:00
kernel [PATCH] vDSO hash-style fix 2006-07-31 13:28:43 -07:00
os-Linux [PATCH] uml: tidy longjmp macro 2006-07-14 21:53:52 -07:00
scripts kbuild: fix ia64 breakage after introducing make -rR 2006-07-01 09:58:02 +02:00
sys-i386 Merge git://git.kernel.org/pub/scm/linux/kernel/git/bunk/trivial 2006-06-30 15:39:30 -07:00
sys-ia64
sys-ppc Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
sys-x86_64 Merge git://git.kernel.org/pub/scm/linux/kernel/git/bunk/trivial 2006-06-30 15:39:30 -07:00
config.release
defconfig [PATCH] uml: remove syscall debugging 2006-07-10 13:24:24 -07:00
Kconfig [PATCH] uml: skas0 support for 2G/2G hosts 2006-05-01 18:17:43 -07:00
Kconfig.char
Kconfig.debug [PATCH] uml: remove syscall debugging 2006-07-10 13:24:24 -07:00
Kconfig.i386 [PATCH] uml: skas0 support for 2G/2G hosts 2006-05-01 18:17:43 -07:00
Kconfig.net
Kconfig.scsi
Kconfig.x86_64 [PATCH] um: fix undefined reference to hweight32 2006-03-26 08:57:09 -08:00
Makefile [PATCH] uml: uml-makefile-nicer uses SYMLINK incorrectly 2006-05-01 18:17:45 -07:00
Makefile-i386 [PATCH] uml: add -ffreestanding to CFLAGS 2006-06-05 12:29:17 -07:00
Makefile-ia64
Makefile-os-Linux
Makefile-ppc
Makefile-skas
Makefile-tt
Makefile-x86_64 [PATCH] uml: tidy biarch gcc support 2006-07-14 21:53:52 -07:00