On 04/30/2010 07:29 PM, David W Noon wrote:
On Fri, 30 Apr 2010 15:20:02 +0200, Nikos Chantziaras wrote about
[gentoo-user] Re: Compiling 32 bit library on x86_64:
On 04/30/2010 03:09 PM, David W Noon wrote:
On Fri, 30 Apr 2010 12:10:02 +0200, Roger Mason wrote about
[gentoo-user] Compiling 32 bit library on x86_64:
Hello,
I need to compile a 32 bit version of libtermcap on an x86_64
(multilib) system. Can someone tell me how to set up CFLAGS? This
is what I have at the moment:
CFLAGS="-O2 -m32 -march=native -msse3 -pipe"
CXXFLAGS="-O2 -m32 -march=native -msse3 -pipe"
The -march=native will shoot you in the foot. Pick a 32-bit
architecture and use that instead; e.g. -march=i686
Then, -msse3 could also be problematic, unless the target is a very
late model Pentium 4. I would ditch that too.
None of those options are problematic. -march=native has nothing to
do with 32/64 bit. Every 64-bit CPU is 32-bit compatible and has zero
consequence.
I think you fell into the logical trap that 32-bit CPUs are not 64-bit
compatible but it's OK vice versa :) Meaning you can't use "-m64
-march=i686". But you *can* and *should* use "-m32 -march=core2".
No, I stand by what I wrote.
You are wrong.
The -march=native option tells the compiler to issue the CPUID
instruction to determine the architecture. This means that on an amd64
box it will return data for either an AMD K8 or an Intel Pentium D
architecture. This, in turn, allows the compiler to generate K8
instructions that are not valid on IA32 processors. It even allows
the compiler to use 64-bit registers, including the additional
registers that were not in an IA32 processor.
The OP was not interested whether the code runs on all IA32 processors.
Just on his. Yes, if you compile with "-m32 -march=native" the code
will not run everywhere else. But I fail to see what this has to do
with 32-bit vs 64-bit; it also happens if you omit "-m32".
The -m32 option instructs the compiler to generate code with 32-bit
pointers and relocation dictionary. It does not constrain the compiler
to generate code that will definitely run on an IA32 processor, but it
does ensure that the code can be linked with 32-bit libraries.
So, if one is compiling on, say, a Core2 Duo and one uses -march=native
and -m32, the compiler can use all kinds of instructions valid on the
Core2 Duo, but limits addressing to 32-bit.
Yes, which is what we want. Again, the OP was not interested whether
the code runs on other machines. If that was the case, he would not
have used -march=native in the first place.
And I have proof too. Compile whatever you want with -m32
-march=native. It will work just fine.
