Re: [PATCH] x86: Add a GNU_PROPERTY_X86_ISA_1_USED note if needed

[Szabolcs Nagy <szabolcs dot nagy at arm dot com>]

On 19/07/18 22:33, H.J. Lu wrote:
> Here is the updated patch.  Any comments?
>
>
> H.J.
> --
> When -z separate-code, which is enabled by default for Linux/x86, 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.  This patch inserts a GNU_PROPERTY_X86_ISA_1_USED note if
> there may be no data sections before the text section so that the
> first PT_LOAD segment won't be code-only and will contain the program
> header.

i agree with Rich's comment on the bugzilla ticket:
simply always adding a .phdrs section that covers
the program headers would ensure that this kind of
bug is not introduced on other targets and seems
less hackish than adding a note.

i don't know why there is no such section already,
or if there is any drawback adding such a section,
is the requirement to access program headers in a
static linked executable a linux only thing?

> Testcases are adjusted to either pass "-z noseparate-code" to ld or
> discard the .note.gnu.property section.  A Linux/x86 run-time test is
> added.
>
> bfd/
>
> 	PR ld/23428
> 	* elfxx-x86.c (_bfd_x86_elf_link_setup_gnu_properties): If the
> 	separate code program header is needed, make sure that the first
> 	read-only PT_LOAD segment has no code by adding a
> 	GNU_PROPERTY_X86_ISA_1_USED note.