RFC: Program Properties

[Suprateeka R Hegde]

On 13-Oct-2016 05:07 PM, Jose E. Marchesi wrote:
>
>     > 1. Minimum ISAs.  Executables and shared objects, which are optimized
>     > specifically to run on a particular processor, will not run on processors
>     > which don't support the same set of ISAs.  Since x86 only has EM_IAMCU,
>     > EM_386 and EM_X86_64 ELF machine codes, run-time loader needs additional
>     > information to tell if an executable or a shared object is compatible
>     > with available ISAs.
>
>     Why cant the following be defined as processor specific e_flags (like
>     other processors do) in elf.h itself?
>
> It is easy to exhaust the space of EF_* flags.  In sparc this happened
> many years ago, so we had to start using the tags Tag_GNU_SPARC_HWCAPS
> and Tag_GNU_SPARC_HWCAPS2 to denote hardware capabilities.

Hmm. Looks reasonable. But I still have some points to ponder:

e_flags is processor specific and I thought each processor has its own 
space. And e_flags is also 4 byte size (purpose is unsigned integer).

The proposed numbering scheme is already at 17 and 14 more left-shifts 
left. It would be same as e_flags capacity.

In addition, we can have arch-version mask just like Intel Itanium, 
MIPS, etc. Of course thats slightly expensive but gives more space. And 
if we can add asserts in compilers/binutils to check the range of 
e_flags to be within the mask, then we can make it efficient too.

Am I missing anything?/

--
Supra