app programming on freebsd amd64

[Nate Eldredge]

On Thu, 31 Jul 2008, Steve Kargl wrote:

> On Thu, Jul 31, 2008 at 06:58:56PM -0400, Chuck Robey wrote:
>> Peter Jeremy wrote:
>>>
>>> There are a couple of open PRs about this but fixing it is non-trivial.
>>>
>>> Your only current option is to install an i386 world (as well as your
>>> amd64 world) and chroot into it to build i386 apps.
>>
>> Oh, you're telling me that if I run one app as 32 bit (compiling it, the whole
>> enchilada, as 32 bit) would only work if I had the OS, kernel and all libs, as
>> 32 bits?  I couldn't just run the X11 as 32 bits?  I mean, not only run it as 32
>> bits, also compile it as 32 bits?  If I did that, it would use the OS and libs
>> as 64 bits, and be therefore incorrect?
>>
>> If that's so, it does throw a wrench into things, forcing another set of
>> decisions on me, so I need a confirmation, you'll understand.
>
> He's telling you that -m32 doesn't work because the necessary
> run time support is missing.

It's not really missing completely though.  Just that gcc isn't set up to 
look for it in the right place.

>
> troutmask:kargl[202] cat h.c
> #include <stdio.h>
> int main(void)
> {
>  printf("Hello world!\n");
>  return 0;
> }
> troutmask:kargl[203] cc -o z h.c
> troutmask:kargl[205] ldd z
> z:
>        libc.so.7 => /lib/libc.so.7 (0x20063c000)
> troutmask:kargl[206] file z
> z: ELF 64-bit LSB executable, x86-64, version 1 (FreeBSD), for FreeBSD 8.0 (800040), dynamically linked (uses shared libs), FreeBSD-style, not stripped
> troutmask:kargl[207] cc -o z -m32 h.c
> /usr/bin/ld: skipping incompatible /usr/lib/libgcc.a when searching for -lgcc
> /usr/bin/ld: skipping incompatible /usr/lib/libgcc.a when searching for -lgcc
> /usr/bin/ld: cannot find -lgcc

nate at vulcan:/tmp$ gcc -c -m32 h.c
nate at vulcan:/tmp$ gcc -v -o h -m32 h.o
Using built-in specs.
Target: amd64-undermydesk-freebsd
Configured with: FreeBSD/amd64 system compiler
Thread model: posix
gcc version 4.2.1 20070719  [FreeBSD]
  /usr/bin/ld --eh-frame-hdr -m elf_i386_fbsd -V -dynamic-linker 
/libexec/ld-elf.so.1 -o h /usr/lib/crt1.o /usr/lib/crti.o 
/usr/lib/crtbegin.o -L/usr/local/lib -L/usr/local/lib -L/usr/lib 
-L/usr/lib h.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc 
--as-needed -lgcc_s --no-as-needed /usr/lib/crtend.o /usr/lib/crtn.o
GNU ld version 2.15 [FreeBSD] 2004-05-23
   Supported emulations:
    elf_i386_fbsd
    elf_x86_64_fbsd
/usr/bin/ld: skipping incompatible /usr/lib/libgcc.a when searching for 
-lgcc
/usr/bin/ld: skipping incompatible /usr/lib/libgcc.a when searching for 
-lgcc
/usr/bin/ld: cannot find -lgcc

So it's still looking for things in /usr/lib when it should use 
/usr/lib32.  We can call ld directly and give it the right things:

nate at vulcan:/tmp$ /usr/bin/ld --eh-frame-hdr -m elf_i386_fbsd -V -dynamic-linker /libexec/ld-elf32.so.1 -o h /usr/lib32/crt1.o /usr/lib32/crti.o /usr/lib32/crtbegin.o -L/usr/lib32 h.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib32/crtend.o /usr/lib32/crtn.o
GNU ld version 2.15 [FreeBSD] 2004-05-23
   Supported emulations:
    elf_i386_fbsd
    elf_x86_64_fbsd
nate at vulcan:/tmp$ file ./h
./h: ELF 32-bit LSB executable, Intel 80386, version 1 (FreeBSD), for 
FreeBSD 7.0 (700055), dynamically linked (uses shared libs), 
FreeBSD-style, not stripped
nate at vulcan:/tmp$ ./h
Hello world!

It might be that there is some set of options to gcc itself that would 
make the right thing happen here without calling ld directly.  More likely 
someone would have to write a new specs file.  But that's a relatively 
minor issue; the guts are there.

Now it may be that the 32-bit runtime has bugs that would appear if we 
tried to do something more complicated.  But it isn't totally absent.

-- 
Nate Eldredge
nge at cs.hmc.edu