Re: 3.1-rc6 boot problem reason searching

[Linus Torvalds]

On Thu, Sep 15, 2011 at 11:15 AM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> It *used* to have an alignment of 8 back before your patch to make the
> pointers be relative due to the 64-bit pointers. But now all fields
> are 32-bit, and it could easily have a size of just 12 bytes, getting
> rid of the 'pad2' field, and getting rid of the '.balign 8's.

IOW, maybe the correct patch is just the attached one.

Werner, does this fix the boot for you? It gets rid of all the bogus
alignment stuff, it's all wrong anyway, the altinstructions section
entries are all 12 bytes long so it starts out sufficiently aligned,
and it *stays* aligned because if anybody ever adds a non-12-byte
entry that would be a huge bug regardless. So any extra alignment is
just likely to be buggy and hide much bigger issues.

This is COMPLETELY UNTESTED, just looking at the source.

                     Linus
 arch/x86/include/asm/alternative-asm.h |    1 -
 arch/x86/include/asm/alternative.h     |    4 ----
 arch/x86/include/asm/cpufeature.h      |    2 --
 3 files changed, 0 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/alternative-asm.h b/arch/x86/include/asm/alternative-asm.h
index 4554cc6fb96a..091508b533b4 100644
--- a/arch/x86/include/asm/alternative-asm.h
+++ b/arch/x86/include/asm/alternative-asm.h
@@ -16,7 +16,6 @@
 #endif
 
 .macro altinstruction_entry orig alt feature orig_len alt_len
-	.align 8
 	.long \orig - .
 	.long \alt - .
 	.word \feature
diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index 23fb6d79f209..37ad100a2210 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -48,9 +48,6 @@ struct alt_instr {
 	u16 cpuid;		/* cpuid bit set for replacement */
 	u8  instrlen;		/* length of original instruction */
 	u8  replacementlen;	/* length of new instruction, <= instrlen */
-#ifdef CONFIG_X86_64
-	u32 pad2;
-#endif
 };
 
 extern void alternative_instructions(void);
@@ -83,7 +80,6 @@ static inline int alternatives_text_reserved(void *start, void *end)
 									\
       "661:\n\t" oldinstr "\n662:\n"					\
       ".section .altinstructions,\"a\"\n"				\
-      _ASM_ALIGN "\n"							\
       "	 .long 661b - .\n"			/* label           */	\
       "	 .long 663f - .\n"			/* new instruction */	\
       "	 .word " __stringify(feature) "\n"	/* feature bit     */	\
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index 4258aac99a6e..88b23a43f340 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -332,7 +332,6 @@ static __always_inline __pure bool __static_cpu_has(u16 bit)
 		asm goto("1: jmp %l[t_no]\n"
 			 "2:\n"
 			 ".section .altinstructions,\"a\"\n"
-			 _ASM_ALIGN "\n"
 			 " .long 1b - .\n"
 			 " .long 0\n"		/* no replacement */
 			 " .word %P0\n"		/* feature bit */
@@ -350,7 +349,6 @@ static __always_inline __pure bool __static_cpu_has(u16 bit)
 		asm volatile("1: movb $0,%0\n"
 			     "2:\n"
 			     ".section .altinstructions,\"a\"\n"
-			     _ASM_ALIGN "\n"
 			     " .long 1b - .\n"
 			     " .long 3f - .\n"
 			     " .word %P1\n"		/* feature bit */