[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>

arch/ppc64/kernel/vdso32/Makefile

 
 # List of files in the vdso, has to be asm only for now
 
-obj-vdso32 = sigtramp.o gettimeofday.o datapage.o cacheflush.o
+obj-vdso32 = sigtramp.o gettimeofday.o datapage.o cacheflush.o note.o
 
 # Build rules
 

arch/ppc64/kernel/vdso32/note.S

+/*
+ * 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

arch/ppc64/kernel/vdso32/vdso32.lds.S

@@ -20,6 +20,8 @@ SECTIONS
   .gnu.version_d  : { *(.gnu.version_d) }
   .gnu.version_r  : { *(.gnu.version_r) }
 
+  .note		  : { *(.note.*) } 			:text	:note
+
   . = ALIGN (16);
   .text :
   {
@@ -87,6 +89,7 @@ SECTIONS
 PHDRS
 {
   text PT_LOAD FILEHDR PHDRS FLAGS(5); /* PF_R|PF_X */
+  note PT_NOTE FLAGS(4); /* PF_R */
   dynamic PT_DYNAMIC FLAGS(4); /* PF_R */
   eh_frame_hdr 0x6474e550; /* PT_GNU_EH_FRAME, but ld doesn't match the name */
 }

arch/ppc64/kernel/vdso64/Makefile

 # List of files in the vdso, has to be asm only for now
 
-obj-vdso64 = sigtramp.o gettimeofday.o datapage.o cacheflush.o
+obj-vdso64 = sigtramp.o gettimeofday.o datapage.o cacheflush.o note.o
 
 # Build rules
 

arch/ppc64/kernel/vdso64/note.S

+#include "../vdso32/note.S"

arch/ppc64/kernel/vdso64/vdso64.lds.S

@@ -18,12 +18,14 @@ SECTIONS
   .gnu.version_d  : { *(.gnu.version_d) }
   .gnu.version_r  : { *(.gnu.version_r) }
 
+  .note		  : { *(.note.*) }		:text	:note
+
   . = ALIGN (16);
   .text           :
   {
     *(.text .stub .text.* .gnu.linkonce.t.*)
     *(.sfpr .glink)
-  }
+  }						:text
   PROVIDE (__etext = .);
   PROVIDE (_etext = .);
   PROVIDE (etext = .);
@@ -88,6 +90,7 @@ SECTIONS
 PHDRS
 {
   text PT_LOAD FILEHDR PHDRS FLAGS(5); /* PF_R|PF_X */
+  note PT_NOTE FLAGS(4); /* PF_R */
   dynamic PT_DYNAMIC FLAGS(4); /* PF_R */
   eh_frame_hdr 0x6474e550; /* PT_GNU_EH_FRAME, but ld doesn't match the name */
 }