[Bug inline-asm/96081] New: changed placement of file scope asm() contents

[Bug inline-asm/96081] New: changed placement of file scope asm() contents

[jbeulich at suse dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96081

            Bug ID: 96081
           Summary: changed placement of file scope asm() contents
           Product: gcc
           Version: 9.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: inline-asm
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jbeulich at suse dot com
  Target Milestone: ---

>From 9.2 to 9.3 (and presumably then also to 10.1) a change in when, inside the
resulting assembly, file scope asm()-s get output has caused a breakage in one
of the Xen Project's auxiliary tools. What I can observe is that, with any kind
of optimization enabled, all asm()-s get processed first, whereas the data that
we want them to control gets output last.

I realize the output order is really unspecified, but I'd still like to
understand if there's at least a workaround here. What we want to achieve is
control over the ELF type of certain symbols, and this without triggering
modern gas'es "symbol '...' already has its type set" warnings (which the new
behavior not triggers, thus becoming aware of the change in the first place).
Up to gcc 9.2 we simply could put

        .type <symbol>, STT_NOTYPE;
        .type <symbol>, STT_FUNC;

after the data definition and get gcc's respective ".type <symbol>, @object"
overridden this way.

But of course in the more general case it may also be necessary / desirable to
have certain asm()-s take effect _after_ compiler output.

[Bug inline-asm/96081] changed placement of file scope asm() contents

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96081

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu.org
   Last reconfirmed|                            |2020-07-07
             Status|UNCONFIRMED                 |WAITING
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Can you provide a testcase?  Did you try -fno-toplevel-reorder?

[Bug inline-asm/96081] changed placement of file scope asm() contents

[jbeulich at suse dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96081

--- Comment #2 from jbeulich at suse dot com ---
I wasn't even aware of -fno-toplevel-reorder, this suffices as a workaround
here. Thanks.

If nevertheless you're still interested in a testcase, please let me know; for
the moment I'll assume this is intended behavior, even if such a change seems
somewhat odd to make between minor version releases.

[Bug inline-asm/96081] changed placement of file scope asm() contents

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96081

--- Comment #3 from rguenther at suse dot de <rguenther at suse dot de> ---
On Tue, 7 Jul 2020, jbeulich at suse dot com wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96081
> 
> --- Comment #2 from jbeulich at suse dot com ---
> I wasn't even aware of -fno-toplevel-reorder, this suffices as a workaround
> here. Thanks.
> 
> If nevertheless you're still interested in a testcase, please let me know; for
> the moment I'll assume this is intended behavior, even if such a change seems
> somewhat odd to make between minor version releases.

Yes, it's intended behavior and the order is not exactly random but it may
indeed appear so - there certainly wasn't an intention to change it.

You have to use -fno-toplevel-reorder if the order of asms, functions
and variables matter.

[Bug inline-asm/96081] changed placement of file scope asm() contents

[jbeulich at suse dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96081

--- Comment #4 from jbeulich at suse dot com ---
Turns out I was wrong here, and the re-ordering was done even by older than gcc
9. The move from 9.2 to 9.3 also included a move to a newer gas, which made the
issue noticable.

Feel free to close as invalid. I'm sorry for the noise.

[Bug inline-asm/96081] changed placement of file scope asm() contents

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96081

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |RESOLVED
         Resolution|---                         |INVALID

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
No problem.