Re: [PATCH v5 02/10] x86: Compile-time asm code validation

Andy Lutomirski
2015-06-10T17:22:03Z

On Jun 10, 2015 5:07 AM, "Josh Poimboeuf" <jpoimboe@redhat.com> wrote:
>
> Add a new CONFIG_ASM_VALIDATION option which adds an asmvalidate host
> tool which runs on every compiled .S file. Its goal is to enforce sane
> rules on all asm code, so that stack debug metadata (frame/back chain
> pointers and/or DWARF CFI metadata) can be made reliable.
>
> It enforces the following rules:
>
> 1. Each callable function must be annotated with the ELF STT_FUNC type.
> This is typically done using the ENTRY/ENDPROC macros. If
> asmvalidate finds a return instruction outside of a function, it
> flags an error, since that usually indicates callable code which
> should be annotated accordingly.
>
> 2. Each callable function must never leave its own bounds (i.e. with a
> jump to outside the function) except when returning.

Won't that break with sibling/tail calls? GCC can generate those, and
the ia32_ptregs_common label is an example of such a thing.

I'd rather have the script understand tail calls and possibly require
that ia32_ptregs_common have a dummy frame pointer save in front
before the label if needed.

--Andy