path: root/scripts/Kbuild.include
diff options
authorRoland McGrath <roland@redhat.com>2006-07-30 03:04:06 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-07-31 13:28:43 -0700
commit0b0bf7a3ccb6f0b38ead71980e79f875046047b7 (patch)
tree1c7b0689d2f0f9839ff9a793ed3990d9c1591fc0 /scripts/Kbuild.include
parent072d3d1acb452f4abd8d3d20af661f2e28854b59 (diff)
[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>
Diffstat (limited to 'scripts/Kbuild.include')
1 files changed, 7 insertions, 0 deletions
diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 2180c88cfe89..f01132263535 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -85,6 +85,13 @@ cc-version = $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-version.sh \
cc-ifversion = $(shell if [ $(call cc-version, $(CC)) $(1) $(2) ]; then \
echo $(3); fi;)
+# ld-option
+# Usage: ldflags += $(call ld-option, -Wl$(comma)--hash-style=both)
+ld-option = $(shell if $(CC) $(1) \
+ -nostdlib -o ldtest$$$$.out -xc /dev/null \
+ > /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi; \
+ rm -f ldtest$$$$.out)
# Shorthand for $(Q)$(MAKE) -f scripts/Makefile.build obj=
# Usage:

Privacy Policy