On Mon, 23 Nov 2009, Szak�ts Viktor wrote:
Hi,
> I made a test on the Windows llvm-gcc build, and there apparently
> a similar problem exist where llvm-gcc.exe tries to execute
> as.exe (which is not supplied) instead of llvm-as.exe (which is).
> This means I have to add MinGW bin dir to PATH in order to make
> llvm-gcc.exe work. If I rename supplied llvm-as.exe to as.exe,
> it chokes on incompatible cmdline handling, telling:
> "as: Unknown command line argument '-ohbver.o'. Try: 'as --help'"
> The linking problem is apparently the same as on Linux.
> ld.exe will be called instead of llvm-gc.exe, with same error.
> It's a little strange such problems are still in this software,
> or could be that we (I) miss the concept.
It's not wrong that llvm-gcc calls native linker or assembler.
In some cases it's expect behavior. The problem is that it does
not check when it can use native tools and when it has to use
its own ones because files generated by LLVM tools are not compatible
with platform native tools, i.e.:
/*** tst.c ***/
#include <stdio.h>
int main( void )
{
printf( "Hello World !!!\n" );
return 0;
}
druzus:/tmp/3# llvm-gcc -O3 tst.c
works without any problems:
druzus:/tmp/3# file a.out
a.out: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically
linked (uses shared libs), for GNU/Linux 2.6.4, not stripped
but if you try to enable link time optimisations using -O4 then:
druzus:/tmp# llvm-gcc -O4 tst.c
/tmp/cc2wOHbI.o: file not recognized: File format not recognized
collect2: ld returned 1 exit status
so it generate .o file with meta code instead of machine code but it does
not switch to llvm-ld and internally still try to use native ld as linker
which of course cannot understand LLVM meta code. If you want to create final
application then you have to make it manually by:
druzus:/tmp/3# llvm-gcc -O4 tst.c -c
druzus:/tmp/3# llvm-ld tst.o -native
druzus:/tmp/3# file a.out
a.out: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically
linked (uses shared libs), for GNU/Linux 2.6.4, not stripped
Please note that llvm-ld is not real linker for native machine code but it
can generate ASM or C code from optimized meta code and then executes platform
native assembler or C compiler and linker. In current LLVM binaries the main
problem is caused by the fact that llvm-gcc does not automatically switch to
llvm-ld when it's necessary and seems that we do not have any llvm-gcc
switches to force using llvm-ld. In summary it seems to be minor problem
which should be easy to resolve by LLVM-GCC developers or even someone
else interested enough to look at LLVM-GCC code to fix it.
Anyhow I haven't looked at this code so all what I've wrote is only
result of short LLVM-GCC tests.
best regards,
Przemek
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