RFC: Add SHT_GNU_PHDRS

[Roland McGrath]

Just put the rodata segment first.  That's what lld does and it works
great.  There is also the nacl layout that specifically addresses exactly
this issue for a platform that requires the code segment to have the lowest
address, but I don't think any other modern platform actually had such a
requirement.

On Wed, Sep 26, 2018, 14:54 H.J. Lu <hjl.tools@gmail.com> wrote:

> When -z separate-code is used to create executable, ld won't place any
> data in the code-only PT_LOAD segment.  If there are no data sections
> placed before the code-only PT_LOAD segment, the program headers
> won't be mapped into any PT_LOAD segment.  When the executable tries
> to access it (based on the program header address passed in AT_PHDR),ri
> it will lead to segfault.
>
> I am proposing
>
> #define SHT_GNU_PHDRS  0x6ffffff4  /* Dummy section for program header */
>
> This is a special read-only SHF_ALLOC zero-size data section.  It is the
> first output section, which will force a data PT_LOAD segment with program
> header before the code-only PT_LOAD segment,
>
> --
> H.J.
>
> --


Thanks,
Roland