llvm dev - Nov 2006 - [LLVMdev] Byte code portability (was Re: libstdc++ as bytecode, and compiling C++ to C)

On Tue, 21 Nov 2006, Emil Mikulic wrote:
> LLVMers, given the same endianness and pointersize, can one mix and
> match LLVM bytecode files produced on different platforms?
No, not in general.  For example, on the mac, printf it often #defined to 
printf$ldbl, which doesn't exist on linux.  System headers generally foil 
the ability to move stuff around like that.

-Chris

-- 
http://nondot.org/sabre/
http://llvm.org/

Chris Lattner wrote:
> On Tue, 21 Nov 2006, Emil Mikulic wrote:
>> LLVMers, given the same endianness and pointersize, can one mix and
>> match LLVM bytecode files produced on different platforms?
> 
> No, not in general.  For example, on the mac, printf it often #defined to 
> printf$ldbl, which doesn't exist on linux.  System headers generally
foil
> the ability to move stuff around like that.
Aside from stuff that depends on system headers, are there any other
dependencies on the host system? In other words, will llvm-gcc produce
exactly the same byte code for a given set of source files regardless of
where compilation takes place? This has obvious implications on
using LLVM as a cross compiler and on how libraries can be distributed.
-- 
Pertti

On Wed, 22 Nov 2006, [ISO-8859-1] Pertti Kellom�ki
wrote:
> Aside from stuff that depends on system headers, are there any other
> dependencies on the host system? In other words, will llvm-gcc produce
> exactly the same byte code for a given set of source files regardless of
> where compilation takes place? This has obvious implications on
Yes.  Many aspects of the target compiler can leak through.  One trivial 
example is:

int X = sizeof(long);

gcc evaluates 'sizeof' before LLVM gets control, therefore the var will 
get initialized with 8 or 4 depending on the target.

Another example is code like:

#ifdef __POWERPC__
int X = 1;
#else
int X = 0;
#endif

There are many other examples.

-Chris

-- 
http://nondot.org/sabre/
http://llvm.org/