[PATCH] D80791: [AArch64] Generate .note.gnu.property based on module flags.

Tue Aug 11 08:08:56 PDT 2020

chill added a comment.

In D80791#2210124 <https://reviews.llvm.org/D80791#2210124>, @danielkiss wrote:

>>> it is not useful to have a bti annotated function unless everything else is bti compatible too: it is all or nothing per elf module.
>>
>> This is false. Some functions in an elf module could be in a guarded region, some in a non-guarded region. Some function may always
>> be called in a "BTI-safe" way, which may be unknown to the compiler.
>
> Right now the elf and all of the `text` sections considered BTI enabled or not. The dynamic linkers/loaders can't support this
> use case without additional information to be encoded somewhere (and specified). To support such we need to consider grouping/align to page
> boundaries these functions in the linker because BTI could be controlled by flags in PTE.
> With the current spec this usecase is not supported in this way. The user have to link the BTI protected code into another elf.
> Side note: The `force-bti` linker option can't work with half BTI enabled objects.

I suppose this is valid for typical Linux-based systems today.

Is it valid in general, across the whole spectre of operating systems or for bare-metal targets?

Guess not.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D80791/new/

https://reviews.llvm.org/D80791