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Subject[PATCH] x86: tell the world boot_params is 16-byte aligned
Date
It doesn't matter much, but this disassembly makes me cry a little bit:

ffffffff81f21223 <copy_bootdata>:
ffffffff81f21223: 55 push %rbp
ffffffff81f21224: 48 c7 c0 40 c2 02 82 mov $0xffffffff8202c240,%rax
ffffffff81f2122b: 48 89 fe mov %rdi,%rsi
ffffffff81f2122e: a8 01 test $0x1,%al

The reason is that boot_params is defined with
__attribute__((aligned(16))) in boot/main.c, but other translation
units only see the packed attribute on the definition of struct
boot_params, so assume the worst. Making the de facto alignment public
has this effect:

$ scripts/bloat-o-meter /tmp/vmlinux.{defconfig,align}
add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-230 (-230)
function old new delta
copy_bootdata 444 214 -230

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
arch/x86/include/asm/setup.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
index f69e06b283fb..dcd6d5fc2f12 100644
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -64,7 +64,7 @@ static inline void x86_ce4100_early_setup(void) { }
/*
* This is set up by the setup-routine at boot-time
*/
-extern struct boot_params boot_params;
+extern struct boot_params boot_params __attribute__((aligned(16)));

static inline bool kaslr_enabled(void)
{
--
2.1.3


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