[syslinux] [PATCH 0/2] Do not use the "red zone" on EFI

[Ady]

> From: Sylvain Gault <sylvain.gault at gmail.com>
> 
> The System V ABI for x86-64 specify that a "red zone" is an area of 128 bytes
> above the current stack frame. This area can be used by a called function in
> order to avoid the overhead of modifying the stack pointer. The direct effect
> is that interrupt/event/signal handlers must not write to this area. In the
> UEFI calling convention, there is no such thing and the event handlers do write
> their data just above the current stack frame.
> 
> However, gcc generate by default code that uses the red zone. This has to be
> disabled explicitely with the option -mno-red-zone. Not doing so lead to some
> functions behaving randomly once in a while.
> 
> Fixing this revealed that some Makefiles out of the efi/ directory have some
> specific options when building for BIOS or for EFI. These Makefiles do this by
> testing the EFI_BUILD variable. However, this variable wasn't passed down the
> Makefiles making these specific options never used.
> 
 
The addition of the EFI_BUILD variable inside Makefiles could potentially 
affect scripts such as package builders, perhaps even the way the 
official (pre)release archives are built(?).

For further details and explanation, see the commit "The make files have 
undergone changes to support both i386 and x86_64 platforms" (2012Jun):
 repo.or.cz/syslinux.git/commit/38e58635d3868c23537fc5dce87b152a52df34ad 

Perhaps we should consider how to improve the Makefiles without 
potentially breaking backwards compatibility?

Regards,
Ady.

PS: Shouldn't this type of things (as described in the aforementioned 
commit from 2012Jun) be included in "./doc/building.txt" and in the 
corresponding wiki page?