On Mon, Jan 13, 2014 at 10:07:50AM +0100, Albert ARIBAUD wrote:
Hi Wolfgang,
On Fri, 29 Nov 2013 07:14:13 +0100, Wolfgang Denk wd@denx.de wrote:
Dear Tom Rini,
In message 1385580930-9830-1-git-send-email-trini@ti.com you wrote:
The code in arch/arm/lib/board.c::board_init_f that sets gd->start_addr_sp has already make sure we're 8-byte aligned, so we don't need to do that again.
Cc: Albert ARIBAUD albert.u.boot@aribaud.net Signed-off-by: Tom Rini trini@ti.com
arch/arm/lib/crt0.S | 1 - 1 file changed, 1 deletion(-)
diff --git a/arch/arm/lib/crt0.S b/arch/arm/lib/crt0.S index ac54b93..6b5ec01 100644 --- a/arch/arm/lib/crt0.S +++ b/arch/arm/lib/crt0.S @@ -82,7 +82,6 @@ ENTRY(_main) */
ldr sp, [r9, #GD_START_ADDR_SP] /* sp = gd->start_addr_sp */
- bic sp, sp, #7 /* 8-byte alignment for ABI compliance */ ldr r9, [r9, #GD_BD] /* r9 = gd->bd */ sub r9, r9, #GD_SIZE /* new GD is below bd */
I recommend to keep this instruction. It's just a bit of defensive programming, and removing it does not save any measurable amount of memory footprint nor execution time.
I would even go further: it is the setting of SP in C code which should not be kept. I doubt the C specification mentions what should / might happen when changing the stack pointer on the fly in code which might need the stack at any point.
I'm fine with dropping this patch (I noticed as I was tracing something else). But please note that in C we're just setting gd->start_addr_sp and aligning it there, we don't modify sp at all until the snippet of asm above.