Re: [PATCH 1/3] module: deal with alignment issues in built-in module versions

[Linus Torvalds]

On Thu, Feb 17, 2011 at 9:31 AM, Dmitry Torokhov <dtor@xxxxxxxxxx> wrote:
>
> From what I understand __attribute__ ((aligned(x))) only guarantees
> minimum alignment, not exact (gapless) alignment. GCC seems to lay out
> pointers in the section without gaps on all arches that we have.

I still don't see the problem.

Have you actually _tried_ just adding the proper alignment to before
the __modver thing in include/asm-generic/vmlinux.lds.h ?

As far as I can tell, the bug is really simple:
 - the section is not aligned
 - but we told the compiler that that structure is aligned

End result: there is a gap between the section start and the first structure.

And the fix seems obvious: just make sure that the section is
sufficiently aligned.

IOW, why isn't the proper fix the obvious trivial one (attached)?

                                    Linus
 include/asm-generic/vmlinux.lds.h |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index fe77e33..31a4b1d 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -358,6 +358,7 @@
 	}								\
 									\
 	/* Built-in module parameters. */				\
+	STRUCT_ALIGN()							\
 	__param : AT(ADDR(__param) - LOAD_OFFSET) {			\
 		VMLINUX_SYMBOL(__start___param) = .;			\
 		*(__param)						\
@@ -365,6 +366,7 @@
 	}								\
 									\
 	/* Built-in module versions. */					\
+	STRUCT_ALIGN()							\
 	__modver : AT(ADDR(__modver) - LOAD_OFFSET) {			\
 		VMLINUX_SYMBOL(__start___modver) = .;			\
 		*(__modver)						\