[PATCH] ppc64: add PT_NOTE section to vDSO

This patch from Roland adds a PT_NOTE section to both 32 and 64 bits vDSOs
to expose the kernel version to glibc, thus avoiding a uname syscall on
every launch.  This is equivalent to the patches Roland posted already for
x86 and x86-64.

Note: the 64 bits .note is actually using the 32 bits format.  This is
normal.  The ELF spec specifies a different format for 64 bits .note, but
for some reason, this was never properly implemented, the core dumps for
example are all using 32 bits format .note, and binutils cannot even read a
64 bits format .note.  Talking to our toolchain folks, they think we'd
rather stick to 32 bits format .note everywhere and get the spec fixed some
day ...

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 25 insertions, 0 deletions

diff --git a/arch/ppc64/kernel/vdso32/note.S b/arch/ppc64/kernel/vdso32/note.S
new file mode 100644
index 000000000000..d4b5be4f3d5f
--- /dev/null
+++ b/arch/ppc64/kernel/vdso32/note.S
@@ -0,0 +1,25 @@
+/*
+ * This supplies .note.* sections to go into the PT_NOTE inside the vDSO text.
+ * Here we can supply some information useful to userland.
+ */
+
+#include <linux/uts.h>
+#include <linux/version.h>
+
+#define ASM_ELF_NOTE_BEGIN(name, flags, vendor, type)                         \
+        .section name, flags;                                                 \
+        .balign 4;                                                            \
+        .long 1f - 0f;          /* name length */                             \
+        .long 3f - 2f;          /* data length */                             \
+        .long type;             /* note type */                               \
+0:      .asciz vendor;          /* vendor name */                             \
+1:      .balign 4;                                                            \
+2:
+
+#define ASM_ELF_NOTE_END                                                      \
+3:      .balign 4;              /* pad out section */                         \
+        .previous
+
+        ASM_ELF_NOTE_BEGIN(".note.kernel-version", "a", UTS_SYSNAME, 0)
+        .long LINUX_VERSION_CODE
+        ASM_ELF_NOTE_END