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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 19:50:21 -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>
On Mon, Jan 20, 2014 at 7:46 PM, Matt Thomas <email@example.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.
> 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).