Re: AARCH64 text start address: why so low?

[Andrew Pinski <pinskia at gmail dot com>]

On Mon, Jan 20, 2014 at 7:50 PM, Andrew Pinski <pinskia@gmail.com> wrote:
> On Mon, Jan 20, 2014 at 7:46 PM, Matt Thomas <matt@3am-software.com> wrote:
>>
>> As I was looking at the aarch64 text start address for Linux, I
>> wondered why it defaulted to 4MB (well within the first 4GB) instead
>> of (like alpha, mips64 elf, sparc64, hppa64, etc.) defaulting to a
>> starting address at or above 4GB.
>
> Because that is the default one for all elf files.   x86_64 is the
> same as aarch64 here.
>
>>
>> Given there is a minimum of 39 address bits (512GB) of address space,
>> skipping first 4 GB shouldn't be a problem.
>
> I think it matters due to how the different code models work.  The
> default code model is small which means fit in the lower 4 GB.  This
> is just like x86_64's code models.


And just like MIPS64 msym32 code model which we had this same
discussion as we are having now for changing MIPS64 default load
address too.

>
> Thanks,
> Andrew Pinski
>
>>
>> The reason for putting the text start above 4GB is to easily find
>> address truncation errors (loading a 32-bit pointer will quickly
>> cause a SEGV).