[Xen-changelog] Xen-friendly glibc selection: appropriate ld-linux can parse

[Xen patchbot -unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User kaf24@xxxxxxxxxxxxxxxxxxxx
# Node ID 32c3658d73916f127e19e8c77ca34ec49b9ab64c
# Parent  f1abe953e4019c023cccec46560052df7261828d
Xen-friendly glibc selection: appropriate ld-linux can parse
the vsyscall page ELF notes and use the "nosegneg" glibc variant
to ensure that things work fine.

Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Roland McGrath <roland@xxxxxxxxxx>

diff -r f1abe953e401 -r 32c3658d7391 
linux-2.6-xen-sparse/arch/xen/i386/kernel/Makefile
--- a/linux-2.6-xen-sparse/arch/xen/i386/kernel/Makefile        Fri Oct  7 
22:36:26 2005
+++ b/linux-2.6-xen-sparse/arch/xen/i386/kernel/Makefile        Sat Oct  8 
08:49:28 2005
@@ -86,7 +86,7 @@
        $(call if_changed,syscall)
 
 c-link :=
-s-link := vsyscall-int80.o vsyscall-sysenter.o vsyscall-sigreturn.o 
vsyscall.lds.o vsyscall-note.o
+s-link := vsyscall-int80.o vsyscall-sysenter.o vsyscall-sigreturn.o 
vsyscall.lds.o
 
 $(patsubst %.o,$(obj)/%.c,$(c-obj-y) $(c-obj-m) $(c-link)) $(patsubst 
%.o,$(obj)/%.S,$(s-obj-y) $(s-link)):
        @ln -fsn $(srctree)/arch/i386/kernel/$(notdir $@) $@
diff -r f1abe953e401 -r 32c3658d7391 
linux-2.6-xen-sparse/arch/xen/i386/kernel/vsyscall-note.S
--- /dev/null   Fri Oct  7 22:36:26 2005
+++ b/linux-2.6-xen-sparse/arch/xen/i386/kernel/vsyscall-note.S Sat Oct  8 
08:49:28 2005
@@ -0,0 +1,32 @@
+/*
+ * This supplies .note.* sections to go into the PT_NOTE inside the vDSO text.
+ * Here we can supply some information useful to userland.
+ * First we get the vanilla i386 note that supplies the kernel version info.
+ */
+
+#include "../../../i386/kernel/vsyscall-note.S"
+
+/*
+ * Now we add a special note telling glibc's dynamic linker a fake hardware
+ * flavor that it will use to choose the search path for libraries in the
+ * same way it uses real hardware capabilities like "mmx".
+ * We supply "nosegneg" as the fake capability, to indicate that we
+ * do not like negative offsets in instructions using segment overrides,
+ * since we implement those inefficiently.  This makes it possible to
+ * install libraries optimized to avoid those access patterns in someplace
+ * like /lib/i686/tls/nosegneg.  Note that an /etc/ld.so.conf.d/file
+ * corresponding to the bits here is needed to make ldconfig work right.
+ * It should contain:
+ *     hwcap 0 nosegneg
+ * to match the mapping of bit to name that we give here.
+ */
+#define NOTE_KERNELCAP_BEGIN(ncaps, mask) \
+       ASM_ELF_NOTE_BEGIN(".note.kernelcap", "a", "GNU", 2) \
+       .long ncaps, mask
+#define NOTE_KERNELCAP(bit, name) \
+       .byte bit; .asciz name
+#define NOTE_KERNELCAP_END ASM_ELF_NOTE_END
+
+NOTE_KERNELCAP_BEGIN(1, 1)
+NOTE_KERNELCAP(1, "nosegneg")  /* Change 1 back to 0 when glibc is fixed! */
+NOTE_KERNELCAP_END

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