Re: Building GCC 4.9 biarch (i686+x86_64) on Debian 6.0 i686

[Andrew Haley <aph at redhat dot com>]

On 03/18/2015 11:44 AM, Andrew Haley wrote:
> On 03/18/2015 11:11 AM, Alex Blekhman wrote:
>> Andrew Haley writes:
>>> On 18/03/15 06:37, Alex Blekhman wrote:
>>>> My goal is to be able to compile both i686 and x86_64 binaries on 
>> the 
>>>> same Debian 6.0 i686 machine. Default compilation target should be 
>> i686, 
>>>> and x86_64 should be available via switch -m64.
>>>
>>> That's the usual default.
>>
>> Thank you for answering. Are you saying that if I just compile GCC with 
>> all default settings, then it will be capable of 
>> building x86_64 binaries out of the box? I think I have to specify 
>> x86_64 as an additional target somewhere.
>>
>>> Do you really want i686-elf?
>>
>> I'm not sure which target name to use. I've never built GCC before, so 
>> I'm trying to make sense out of parameters. `uname' 
>> reports that the system is "i686 GNU/Linux", so I thought that "i686-
>> elf" would be the most generic target I can specify.
> 
> If you're not cross-compiling you should never set the target.  The
> same for sysroot.  GCC has sensible defaults for everything, and
> unless you know exactly what you're doing overriding them is only
> likely to break things.
> 
>> All I want to do is to have 32-bit compiler (and linker, of course), 
>> which is able to produce both 32- and 64-bit binaries.

I am very sorry.  I have told you an untruth.  I didn't read what you wrote.

Cross-compiling from 32- to 64-bit hosts is notoriously tricky.  People
almost always go in the opposite direction.  I don't even know if it
can be done.

Andrew.