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Re: AARCH64 text start address: why so low?
- From: Andrew Pinski <pinskia at gmail dot com>
- To: Matt Thomas <matt at 3am-software dot com>
- Cc: binutils <binutils at sourceware dot org>
- Date: Mon, 20 Jan 2014 19:51:28 -0800
- Subject: Re: AARCH64 text start address: why so low?
- Authentication-results: sourceware.org; auth=none
- References: <209F1186-6425-4EB3-9DDE-7B7DCEAA8CE4 at 3am-software dot com> <CA+=Sn1kZ+qefjbUFWbMQBjzXG4=+rMeugawxpmtTrTkz9pUucA at mail dot gmail dot com>
On Mon, Jan 20, 2014 at 7:50 PM, Andrew Pinski <email@example.com> wrote:
> On Mon, Jan 20, 2014 at 7:46 PM, Matt Thomas <firstname.lastname@example.org> 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
> 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).