[PATCH v5 07/12] aarch64: enable BTI at runtime

[Szabolcs Nagy]

The 06/12/2020 08:18, H.J. Lu wrote:
> On Fri, Jun 12, 2020 at 8:08 AM Szabolcs Nagy <szabolcs.nagy@arm.com> wrote:
> > The 06/12/2020 06:43, H.J. Lu wrote:
> > > Can you make _dl_process_pt_gnu_property more generic so that it
> > > can be shared with x86?  If there is PT_GNU_PROPERTY, we don't
> > > need to check for multiple property notes.  Thanks.
> >
> > it can use a hook for NT_GNU_PROPERTY_TYPE_0 notes
> > that is called for each property, e.g.
> >
> > int
> > _dl_process_gnu_property_note0(uint32_t type, uint32_t datasz, const void *data);

i also had to pass the link_map.

> > however this only helps on x86 if PT_GNU_PROPERTY
> > processing is before PT_NOTE processing otherwise
> > you cannot skip handling the notes.
> 
> On x86-64, there are
> 
> Program Headers:
>   Type           Offset             VirtAddr           PhysAddr
>                  FileSiz            MemSiz              Flags  Align
...
>   NOTE           0x0000000000000338 0x0000000000000338 0x0000000000000338
>                  0x0000000000000020 0x0000000000000020  R      0x8
>   NOTE           0x0000000000000358 0x0000000000000358 0x0000000000000358
>                  0x0000000000000044 0x0000000000000044  R      0x4
>   GNU_PROPERTY   0x0000000000000338 0x0000000000000338 0x0000000000000338
>                  0x0000000000000020 0x0000000000000020  R      0x8
...
> Only the PT_NOTE segment with the correct alignment may contain property.
> In the first pass, we record such PT_NOTE segment, but don't process it.
> After all segments have been processed, we process the saved PT_NOTE segment
> if there is no GNU_PROPERTY segment.

i refactored the code but didn't change the x86 side.

note: in rtld there is only one pass (load segments
are already mapped) while dlopen does the property
handling in the second pass over program headers.

attaching v5 of the patch:

- moved _dl_process_pt_gnu_property to generic code
  (into dl-load.c), this assumes PT_GNU_PROPERTY
  is a gnu platform abi and the integer types used
  for accessing it work on all targets.

- made _dl_process_pt_gnu_property return type void
  and remove all failure handling (invalid notes
  are ignored).

- only handle one NT_GNU_PROPERTY_TYPE_0.

- added _dl_process_gnu_property target hook.

- removed reviewed-by because of significant changes.

tested on aarch64.

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