On 12/28/11 12:29, Lu, Hongjiu wrote:
From: "Lu, Hongjiu"<[email protected]>
Date: Wed, 28 Dec 2011 14:34:09 +0000
__AMD64__ is defined when 64bit x86 instruction set is used,
which is true for x32. The difference is x32 doesn't define
__LP64__.
Chapter 7, "Development Environment", of the AMD64 ABI (the non-x32
version) does not list __LP64__ as a predefined pre-processor symbol.
As far as I'm aware, it's just a GCC convention to define __LP64__ for
platforms that use the LP64 programming model, and even GCC didn't do
so very consistently in the past.
__LP64__ isn't the part of x86-64 psABI while GCC always define __LP64__
for 64bit long on x86. I can check if other compilers do the same.
In most cases, __amd64__ is checked for 64bit instructions and we have
ported those we have found so far to x32 so that we can use one __amd64__
block to support both x32 and x86-64.
C code checking __amd64__ mostly does so to find out the size of long &
pointers. Instructions are usually at the assembly level, not the C code level.
It would make far more sense for x32 to declare it's __i386__ with additional
instructions available (much like MMX, SSE, etc.) than to declare that it's
__amd64__ with incompatible types.
--
-Alan Coopersmith- [email protected]
Oracle Solaris Platform Engineering: X Window System
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