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Re: RFC: Add SHT_GNU_PHDRS
- From: Carlos O'Donell <carlos at redhat dot com>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>, gnu-gabi at sourceware dot org, Binutils <binutils at sourceware dot org>
- Date: Wed, 26 Sep 2018 23:25:47 -0400
- Subject: Re: RFC: Add SHT_GNU_PHDRS
- References: <CAMe9rOoqcxZxPKgJn1JwG+ux4YRVbfWQBR=d9BOR3cfQgRn9QA@mail.gmail.com>
On 9/26/18 5:53 PM, H.J. Lu 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),
> 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,
This seems like a huge hack to me. Either ld ensures that the page-aligned
start of the PT_LOAD mapping includes the program headers, or we have to
define SHT_GNU_PHDRS as having exactly that semantic and we need to clearly
explain what a static linker needs to do to accomplish this task. What you
have here needs more documentation.
--
Cheers,
Carlos.