linux-kernel - [PATCH 2/4] powerpc: enable text relative kallsyms for ppc64

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Message-Id: <1453280738-18721-3-git-send-email-ard.biesheuvel@linaro.org>
Date:	Wed, 20 Jan 2016 10:05:36 +0100
From:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
	keescook@...omium.org, akpm@...ux-foundation.org, mingo@...nel.org,
	hpa@...or.com, heiko.carstens@...ibm.com, benh@...nel.crashing.org,
	mpe@...erman.id.au, mmarek@...e.cz, rusty@...tcorp.com.au
Cc:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: [PATCH 2/4] powerpc: enable text relative kallsyms for ppc64

This enables the newly introduced text-relative kallsyms support when
building 64-bit targets. This cuts the size of the kallsyms address
table in half, and drastically reduces the size of the PIE dynamic
relocation section when building with CONFIG_RELOCATABLE=y (by about
3 MB for ppc64_defconfig)

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
---

Results for ppc64_defconfig:

BEFORE:
=======
$ size vmlinux
   text	   data	    bss	    dec	    hex	filename
19827996	2008456	 849612	22686064	15a2970	vmlinux

$ readelf -S .tmp_kallsyms2.o
There are 9 section headers, starting at offset 0x4513f8:

Section Headers:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  ...
  [ 4] .rodata           PROGBITS         0000000000000000  00000100
       00000000001fcf00  0000000000000000   A       0     0     256
  [ 5] .rela.rodata      RELA             0000000000000000  001fd1d8
       0000000000254220  0000000000000018   I       7     4     8
  [ 6] .shstrtab         STRTAB           0000000000000000  001fd000
       0000000000000039  0000000000000000           0     0     1
  ...

$ ls -l arch/powerpc/boot/zImage
-rwxrwxr-x 2 ard ard 7533160 Jan 20 08:43 arch/powerpc/boot/zImage

AFTER:
======
$ size vmlinux
   text	   data	    bss	    dec	    hex	filename
16979516	2009992	 849612	19839120	12eb890	vmlinux

$ readelf -S .tmp_kallsyms2.o
There are 8 section headers, starting at offset 0x199bb0:

Section Headers:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  ...
  [ 4] .rodata           PROGBITS         0000000000000000  00000100
       0000000000199900  0000000000000000   A       0     0     256
  [ 5] .shstrtab         STRTAB           0000000000000000  00199a00
       0000000000000034  0000000000000000           0     0     1
  ...

$ ls -l arch/powerpc/boot/zImage
-rwxrwxr-x 2 ard ard 6985672 Jan 20 08:45 arch/powerpc/boot/zImage
---
 arch/powerpc/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 94f6c5089e0c..d1c26749632b 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -158,6 +158,7 @@ config PPC
 	select ARCH_HAS_DMA_SET_COHERENT_MASK
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select HAVE_ARCH_SECCOMP_FILTER
+	select KALLSYMS_TEXT_RELATIVE if PPC64
 
 config GENERIC_CSUM
 	def_bool CPU_LITTLE_ENDIAN
-- 
2.5.0