[U-Boot] [RFC] [PATCH V2] arm: arm926ejs: use ELF relocations

[Heiko Schocher]

Hello Albert,

Albert Aribaud wrote:
> HISTORY:
> 
> V1	Initial patch
> V2	Rebased on latest mainline master
> 
> This patch is *not* a submission for master!
> 
> It is a proof of concept of ELF relocations for ARM, hastily done
> in a day's work time for people on the list to try and to comment.
> All comments are welcome, as several suggestions have been made
> today on the list that I did not have time to incorporate, such as
> rewriting the elf table fixup code in C.
> 
> The basic idea of this patch is to replace the -fPIC compile-time
> option with the -pie link-time option. This removes the GOT but adds
> the .rel.dyn and .dynsym tables, which together allow fixing up code
> more completely than with -fPIC and the GOT; for instance, all pointers
> inside structures are fixed up with -pie, whereas they are not with GOT.
> 
> Note that references to linker-file-generated symbols were also made
> relative to _start rather than absolute. This is not needed as such,
> but it will be useful when optimizing the relocation tables. Actually
> I should have separated this from the ELF relocation support per se.
> 
> The edminiv2.h config file is there for reference only; this is the
> one I used for tests. Latest numbers are:
> 
> With GOT relocs:
> 
>    text	   data	    bss	    dec	    hex	filename	.bin size
>  141376	   4388	  16640	 162404	  27a64	./u-boot	145764
>  
> With ELF relocs:
> 
>    text	   data	    bss	    dec	    hex	filename	.bin size
>  149677	   3727	  16636	 170040	  29838	./u-boot	153408
> 
> The size difference is essentially due to .rel.dyn not being optimal.
> As discussed, an added build step should allow reducing it by half and
> making ELF sizes roughly similar to GOT ones.
> 
> Tests and comments not only welcome but also heartily called for.

Tested based on your patch on the magnesium board (ARM926ejs and
boots from NOR Flash). U-Boot works, with the following patch:

! I had to set TEXT_BASE to 0xc0000000 as u-boot starts from there,
a TEXT_BASE = 0 didn;t work for me!

diff --git a/board/logicpd/imx27lite/config.mk b/board/logicpd/imx27lite/config.mk
index 2f9c4e6..af1c82b 100644
--- a/board/logicpd/imx27lite/config.mk
+++ b/board/logicpd/imx27lite/config.mk
@@ -1 +1,4 @@
+# with relocation TEXT_BASE can be anything, and making it 0
+# makes relative and absolute relocation fixups interchangeable.
+#TEXT_BASE = 0
 TEXT_BASE = 0xc0000000
diff --git a/include/configs/imx27lite-common.h b/include/configs/imx27lite-common.h
index 812e5f2..58f3c49 100644
--- a/include/configs/imx27lite-common.h
+++ b/include/configs/imx27lite-common.h
@@ -236,7 +236,8 @@
 	"mtdparts=" MTDPARTS_DEFAULT "\0"				\

 /* additions for new relocation code, must added to all boards */
-#undef CONFIG_SYS_ARM_WITHOUT_RELOC /* This board is tested with relocation support */
+#define CONFIG_RELOC_FIXUP_WORKS
+#undef  CONFIG_SYS_ARM_WITHOUT_RELOC
 #define CONFIG_SYS_SDRAM_BASE		PHYS_SDRAM_1
 #define CONFIG_SYS_INIT_SP_ADDR		(CONFIG_SYS_SDRAM_BASE + 0x1000 - /* Fix this */ \
 					CONFIG_SYS_GBL_DATA_SIZE)

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