Re: [coreboot] [PATCH] cld before call

[Carl-Daniel Hailfinger]

On 29.07.2009 00:36, Robert Millan wrote:
> The Multiboot spec is a bit too permissive about this, as it doesn't
> specify the state of direction flag when payload is called.  Some payloads
> (we found this in ReactOS FreeLDR) assume it is cleared, and fail otherwise.
>
> We adjusted GRUB to be sure it's always cleared.  I think coreboot should do
> the same.  Here's a patch for v3.

AFAIK this patch is unneeded. The GCC ABI on x86 and x86_64 states that
the direction flag must always be cleared before running any gcc
compiled code, so if you need to execute cld in the middle of C code, it
means that all C code before that cld had undefined behaviour.

The correct place for cld is early asm startup code before any C code
gets executed.

Regards,
Carl-Daniel