building non-shared dynamic binaries on x86-64 linux-elf

building non-shared dynamic binaries on x86-64 linux-elf

[Mathieu Lacage]

hi,

The title pretty much says what I am trying to do: this works fine on
i386 but fails on x86-64. The compile-time error is:
"relocation R_X86_64_32 against `a local symbol' can not be used when
making a shared object; recompile with -fPIC".

What I am trying to do is generate a non-shared relocatable dynamic
binary which means that I really don't want to use -fPIC and I was
hoping that the dynamic linker would be able to finish relocating the
final binary. Is this impossible on linux-elf-x86-64 ?

Mathieu
-- 
Mathieu Lacage <mathieu.lacage@gmail.com>

Re: building non-shared dynamic binaries on x86-64 linux-elf

[Andrew Haley]

Mathieu Lacage wrote:

> What I am trying to do is generate a non-shared relocatable dynamic
> binary which means that I really don't want to use -fPIC and I was
> hoping that the dynamic linker would be able to finish relocating the
> final binary. Is this impossible on linux-elf-x86-64 ?

Yes, it is.  The fact that this works on 32-bit is something of an
historical accident.

Andrew.

Re: building non-shared dynamic binaries on x86-64 linux-elf

[Ian Lance Taylor]

Andrew Haley <aph@redhat.com> writes:

> Mathieu Lacage wrote:
>
>> What I am trying to do is generate a non-shared relocatable dynamic
>> binary which means that I really don't want to use -fPIC and I was
>> hoping that the dynamic linker would be able to finish relocating the
>> final binary. Is this impossible on linux-elf-x86-64 ?
>
> Yes, it is.  The fact that this works on 32-bit is something of an
> historical accident.

I would reverse the sense of this: non PIC shared libraries does work on
most processors (with some loss of efficiency), but not on x86_64
because it uses a small model by default.  It might work if you use
-mcmodel=large, but I haven't tried this.

Ian

Re: building non-shared dynamic binaries on x86-64 linux-elf

[Mathieu Lacage]

On Wed, Apr 22, 2009 at 3:32 PM, Ian Lance Taylor <iant@google.com> wrote:

> I would reverse the sense of this: non PIC shared libraries does work on
> most processors (with some loss of efficiency), but not on x86_64
> because it uses a small model by default.  It might work if you use
> -mcmodel=large, but I haven't tried this.

It does, indeed appear to work: it merely triggers an ICE for FC10's
(4.3.2) gcc with -O3 (-O0 works fine). gcc 4.4.0 works fine though.

Shall I report a bug for 4.3.2 ? (i.e., will there be further releases
of that compiler ?)

Mathieu
-- 
Mathieu Lacage <mathieu.lacage@gmail.com>

Re: building non-shared dynamic binaries on x86-64 linux-elf

[Ian Lance Taylor]

Mathieu Lacage <mathieu.lacage@gmail.com> writes:

> On Wed, Apr 22, 2009 at 3:32 PM, Ian Lance Taylor <iant@google.com> wrote:
>
>> I would reverse the sense of this: non PIC shared libraries does work on
>> most processors (with some loss of efficiency), but not on x86_64
>> because it uses a small model by default.  It might work if you use
>> -mcmodel=large, but I haven't tried this.
>
> It does, indeed appear to work: it merely triggers an ICE for FC10's
> (4.3.2) gcc with -O3 (-O0 works fine). gcc 4.4.0 works fine though.
>
> Shall I report a bug for 4.3.2 ? (i.e., will there be further releases
> of that compiler ?)

It is likely that there will be a 4.3.3 release.  However, even if you
file a bug report, I wouldn't count on anybody actually fixing it,
unless perhaps you also track down the change that fixed it in 4.4.0.  I
don't think that huge model support is high on anybody's priority list.

Ian

Re: building non-shared dynamic binaries on x86-64 linux-elf

[Andrew Haley]

Ian Lance Taylor wrote:
> Andrew Haley <aph@redhat.com> writes:
> 
>> Mathieu Lacage wrote:
>>
>>> What I am trying to do is generate a non-shared relocatable dynamic
>>> binary which means that I really don't want to use -fPIC and I was
>>> hoping that the dynamic linker would be able to finish relocating the
>>> final binary. Is this impossible on linux-elf-x86-64 ?
>> Yes, it is.  The fact that this works on 32-bit is something of an
>> historical accident.
> 
> I would reverse the sense of this: non PIC shared libraries does work on
> most processors (with some loss of efficiency), but not on x86_64
> because it uses a small model by default.  It might work if you use
> -mcmodel=large, but I haven't tried this.

It might well, but I would question the point.  Presumably the OP wants
non-PIC for performance's sake, but I wouldn't have thought he's going
to get it from the large model.  Benchmarks would be interesting.

Andrew.

Re: building non-shared dynamic binaries on x86-64 linux-elf

[Mathieu Lacage]

On Wed, Apr 22, 2009 at 4:53 PM, Andrew Haley <aph@redhat.com> wrote:

>> I would reverse the sense of this: non PIC shared libraries does work on
>> most processors (with some loss of efficiency), but not on x86_64
>> because it uses a small model by default.  It might work if you use
>> -mcmodel=large, but I haven't tried this.
>
> It might well, but I would question the point.  Presumably the OP wants
> non-PIC for performance's sake, but I wouldn't have thought he's going
> to get it from the large model.  Benchmarks would be interesting.

I did get some of the performance improvement I was after, at least on
my reference microbenchmark (which, I hope, is at least partly
representative of my target application):

-O3 -fpic:
a=1.70445e+06 packets/s
b=3.4965e+06 packets/s
c=2.20897e+06 packets/s
d=894214 packets/s

-O3 -mcmodel=large:
a=1.96967e+06 packets/s
b=3.77216e+06 packets/s
c=2.45881e+06 packets/s
d=1.07423e+06 packets/s

-O3 [static link in final executable]:
a=2.12857e+06 packets/s
b=4.26076e+06 packets/s
c=2.77546e+06 packets/s
d=1.27861e+06 packets/s

So, a full static link is best, but -mcmodel=large is still better
than -fpic. I wonder if I am not going to ditch -fpic builds
altogether.

Mathieu
-- 
Mathieu Lacage <mathieu.lacage@gmail.com>