Messages in this thread Patch in this message | | | From | David Howells <> | Subject | Re: FRV/ARM unaligned access question | Date | Wed, 08 Oct 2008 12:16:06 +0100 |
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Harvey Harrison <harvey.harrison@gmail.com> wrote:
> If there isn't an issue I'm missing, could ARM/FRV move over to the > packed-struct version?
Using this source:
typedef unsigned char u8; typedef unsigned int u32;
struct __una_u32 { u32 x __attribute__((packed)); };
#if 0 // packed struct static inline u32 __get_unaligned_cpu32(const void *p) { const struct __una_u32 *ptr = (const struct __una_u32 *)p; return ptr->x; }
static inline u32 get_unaligned_be32(const void *p) { return __get_unaligned_cpu32((const u8 *)p); }
#else // manual byteshift static inline u32 __get_unaligned_be32(const u8 *p) { return p[0] << 24 | p[1] << 16 | p[2] << 8 | p[3]; }
static inline u32 get_unaligned_be32(const void *p) { return __get_unaligned_be32((const u8 *)p); } #endif
u32 jump(u32 *p) { return get_unaligned_be32(p); }
I see the packed struct version compile (with -O2) to:
jump: ldub @(gr8,gr0),gr6 ldubi @(gr8,1),gr4 ldubi @(gr8,2),gr5 ldubi @(gr8,3),gr8 slli gr6,#24,gr6 slli gr4,#16,gr4 or.p gr4, gr6, gr4 slli gr5,#8,gr5 or gr5, gr4, gr5 or.p gr8, gr5, gr8 ret
and the byteshift version compile to:
jump: ldubi.p @(gr8,1),gr7 mov gr8, gr5 ldubi @(gr5,2),gr6 ldub @(gr8,gr0),gr8 ldubi @(gr5,3),gr9 slli gr7,#16,gr7 slli gr6,#8,gr6 slli.p gr8,#24,gr8 or gr6, gr7, gr6 or gr8, gr9, gr8 or.p gr8, gr6, gr8 ret
so they're more or less equivalent, give or take the compiler using an extra instruction unnecessarily.
Switching to the packed struct algorithms also reduces the kernel size very slightly. Before:
warthog>size vmlinux text data bss dec hex filename 2207836 66588 150189 2424613 24ff25 vmlinux
After:
warthog>size vmlinux text data bss dec hex filename 2207804 66588 150189 2424581 24ff05 vmlinux
The attached patch boots okay over NFS.
David --- [PATCH] FRV: Use packed-struct unalignment rather than manual-shift
From: David Howells <dhowells@redhat.com>
Use the packed-struct unalignment algorithms rather than the manual-shift unalignment algorithms.
This makes the kernel very slightly smaller.
Signed-off-by: David Howells <dhowells@redhat.com> ---
include/asm-frv/unaligned.h | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/asm-frv/unaligned.h b/include/asm-frv/unaligned.h index 839a2fb..d06b9bc 100644 --- a/include/asm-frv/unaligned.h +++ b/include/asm-frv/unaligned.h @@ -12,8 +12,8 @@ #ifndef _ASM_UNALIGNED_H #define _ASM_UNALIGNED_H -#include <linux/unaligned/le_byteshift.h> -#include <linux/unaligned/be_byteshift.h> +#include <linux/unaligned/le_struct.h> +#include <linux/unaligned/be_struct.h> #include <linux/unaligned/generic.h> #define get_unaligned __get_unaligned_be
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