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authorAnton Blanchard <anton@samba.org>2012-11-26 18:39:03 +0100
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2013-01-10 07:00:25 +0100
commit5ac47f7a6efbd4fa9141c249e8af3f74e7944eb7 (patch)
tree33c65b022ecc9e3ca2c5d506bf7ceb4764f626d5 /arch/powerpc/kernel/vmlinux.lds.S
parentpowerpc/pasemi: Enable PRINTK_TIME in defconfig (diff)
downloadlinux-5ac47f7a6efbd4fa9141c249e8af3f74e7944eb7.tar.xz
linux-5ac47f7a6efbd4fa9141c249e8af3f74e7944eb7.zip
powerpc: Relocate prom_init.c on 64bit
The ppc64 kernel can get loaded at any address which means our very early init code in prom_init.c must be relocatable. We do this with a pretty nasty RELOC() macro that we wrap accesses of variables with. It is very fragile and sometimes we forget to add a RELOC() to an uncommon path or sometimes a compiler change breaks it. 32bit has a much more elegant solution where we build prom_init.c with -mrelocatable and then process the relocations manually. Unfortunately we can't do the equivalent on 64bit and we would have to build the entire kernel relocatable (-pie), resulting in a large increase in kernel footprint (megabytes of relocation data). The relocation data will be marked __initdata but it still creates more pressure on our already tight memory layout at boot. Alan Modra pointed out that the 64bit ABI is relocatable even if we don't build with -pie, we just need to relocate the TOC. This patch implements that idea and relocates the TOC entries of prom_init.c. An added bonus is there are very few relocations to process which helps keep boot times on simulators down. gcc does not put 64bit integer constants into the TOC but to be safe we may want a build time script which passes through the prom_init.c TOC entries to make sure everything looks reasonable. Signed-off-by: Anton Blanchard <anton@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Diffstat (limited to '')
-rw-r--r--arch/powerpc/kernel/vmlinux.lds.S5
1 files changed, 5 insertions, 0 deletions
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 65d1c08cf09e..654e479802f2 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -218,6 +218,11 @@ SECTIONS
.got : AT(ADDR(.got) - LOAD_OFFSET) {
__toc_start = .;
+#ifndef CONFIG_RELOCATABLE
+ __prom_init_toc_start = .;
+ arch/powerpc/kernel/prom_init.o*(.toc .got)
+ __prom_init_toc_end = .;
+#endif
*(.got)
*(.toc)
}