how to know host endianness in binutils

how to know host endianness in binutils

[Jan Beulich]

Hello,

looking around, I can't seem to be able to find any standardized way of
knowing host endianness in binutils (in gas/ in particular). As was
pointed out to me, the new cpu_flags_from_attr() in config/tc-i386.c
won't work as is on big-endian hosts, yet I would really, really like
to avoid needing to enumerate all of the dozens of bitfields in that
function (converting one kind of bitfield to another). That's not the
least because this set constantly grows.

I can see config/tc-bpf.c checking WORDS_BIGENDIAN, but I couldn't
convince myself (from looking at the generated config.h) that one can
really rely on that.

Jan

Re: how to know host endianness in binutils

[H.J. Lu]

On Thu, Dec 21, 2023 at 6:31 AM Jan Beulich <jbeulich@suse.com> wrote:
>
> Hello,
>
> looking around, I can't seem to be able to find any standardized way of
> knowing host endianness in binutils (in gas/ in particular). As was
> pointed out to me, the new cpu_flags_from_attr() in config/tc-i386.c
> won't work as is on big-endian hosts, yet I would really, really like
> to avoid needing to enumerate all of the dozens of bitfields in that
> function (converting one kind of bitfield to another). That's not the
> least because this set constantly grows.
>
> I can see config/tc-bpf.c checking WORDS_BIGENDIAN, but I couldn't
> convince myself (from looking at the generated config.h) that one can
> really rely on that.
>
> Jan

WORDS_BIGENDIAN is generated by AC_C_BIGENDIAN.  It
should be correct.

-- 
H.J.

Re: how to know host endianness in binutils

[Nick Clifton]

Hi Jan,

> looking around, I can't seem to be able to find any standardized way of
> knowing host endianness in binutils (in gas/ in particular).

There is a CYG_AC_C_ENDIAN function in config/acinclude.m4 that defines
LITTLE_ENDIAN_HOST for little endian hosts, but as far as I can tell this
function is never invoked.

> I can see config/tc-bpf.c checking WORDS_BIGENDIAN, but I couldn't
> convince myself (from looking at the generated config.h) that one can
> really rely on that.

Other code seems to rely upon this define too.  For example gdb/tracectf.c.

Also as H.J. mentioned it does appear that the code in the script configure
does do the right thing.  I would suggest that you can safely use it.

Cheers
   Nick

Re: how to know host endianness in binutils

[Michael Matz]

Hey,

On Thu, 21 Dec 2023, Jan Beulich wrote:

> looking around, I can't seem to be able to find any standardized way of
> knowing host endianness in binutils (in gas/ in particular).

I've added a use of AC_C_BIGENDIAN into bfd/ last year (defining 
WORDS_BIGENDIAN).  Seems to have worked fine so far.


Ciao,
Michael.