[Bug target/64224] New: [ARM] -mapcs -marm uses deprecated forms (as of ARMv7-A) of LDM in epilogues

[Bug target/64224] New: [ARM] -mapcs -marm uses deprecated forms (as of ARMv7-A) of LDM in epilogues

[ktkachov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64224

            Bug ID: 64224
           Summary: [ARM] -mapcs -marm uses deprecated forms (as of
                    ARMv7-A) of LDM in epilogues
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: ktkachov at gcc dot gnu.org
          Reporter: ktkachov at gcc dot gnu.org
            Target: arm*

The ARMv7-A specification says on the load-multiple (LDM) instruction:
"The SP can be in the list. However, ARM deprecates using these instructions
with SP in the list."

and

"ARM deprecates using these instructions with both the LR and the PC in the
list."

However GCC generates both forms in function epilogues when compiling with
-mapcs. gas doesn't have a warning for these (I'm working on a patch to add
those to gas) which is probably why this hasn't been noticed yet.

We should fix GCC so that it doesn't generate deprecated sequences for ARMv7-A
and later.

[Bug target/64224] [ARM] -mapcs -marm uses deprecated forms (as of ARMv7-A) of LDM in epilogues

[ktkachov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64224

ktkachov at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2014-12-08
     Ever confirmed|0                           |1

--- Comment #1 from ktkachov at gcc dot gnu.org ---
I'm working on it.

[Bug target/64224] [ARM] -mapcs -marm uses deprecated forms (as of ARMv7-A) of LDM in epilogues

[rearnsha at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64224

--- Comment #2 from Richard Earnshaw <rearnsha at gcc dot gnu.org> ---
Might be better to just deprecate -mapcs; it's a feature of the old ABI anyway,
so there's not much point in trying to make it fully conform to the latest
specs.

[Bug target/64224] [ARM] -mapcs -marm uses deprecated forms (as of ARMv7-A) of LDM in epilogues

[ktkachov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64224

--- Comment #3 from ktkachov at gcc dot gnu.org ---
(In reply to Richard Earnshaw from comment #2)
> Might be better to just deprecate -mapcs; it's a feature of the old ABI
> anyway, so there's not much point in trying to make it fully conform to the
> latest specs.

-mapcs is used in the Linux kernel though.

[Bug target/64224] [ARM] -mapcs -marm uses deprecated forms (as of ARMv7-A) of LDM in epilogues

[mshawcroft at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64224

mshawcroft at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
                 CC|                            |mshawcroft at gcc dot gnu.org
         Resolution|---                         |WONTFIX

--- Comment #4 from mshawcroft at gcc dot gnu.org ---
-mapcs is now deprecated in gcc5