[PATCH] ARM: Emit ".code 16" before global inline-asm instructions in thumb mode

[Saleem Abdulrasool]

On Thu, Jul 24, 2014 at 5:27 PM, Jim Grosbach <grosbach at apple.com> wrote:

> For the assembler, there’s no concept of that. It always starts in ARM
> mode. Even for the compiler, the defaulting to thumb mode for armv7 is a
> darwin only thing, I think. Used to be, anyway.
>

This is also the case for Windows on ARM.  WoA is a pure Thumb-2
environment (executing ARM code, while possible from a hardware
perspective, is not really allowed).


> From another point of view, it also keeps us more compatible with other
> tools like gas.
>
> -Jim
>
>
> > On Jul 24, 2014, at 5:24 PM, Eric Christopher <echristo at gmail.com>
> wrote:
> >
> > Why not just start the assembler in the right mode for the target
> > we're assembling?
> >
> > -eric
> >
> > On Thu, Jul 24, 2014 at 5:19 PM, Jim Grosbach <grosbach at apple.com>
> wrote:
> >> Hi Akira,
> >>
> >> Patch LGTM. The testcase should also run with ARM (a second RUN line w/
> a
> >> distinct check prefix) w/ check lines there to verify we don’t emit the
> >> “.code 16” then.
> >>
> >> -Jim
> >>
> >> On Jul 24, 2014, at 3:02 PM, Akira Hatanaka <ahatanak at gmail.com> wrote:
> >>
> >> ToT clang (correctly) errors-out when the target is armv7 (thumb2) and
> the
> >> program it's compiling has an ARM mode file-level inline assembly
> statement:
> >>
> >> $ cat test2.c
> >>
> >> __asm__ ("stmib sp, {r0-r14};");
> >>
> >> $ clang -arch armv7  -S -o - test2.c
> >> .section __TEXT,__text,regular,pure_instructions
> >> .ios_version_min 5, 0
> >> .section __TEXT,__textcoal_nt,coalesced,pure_instructions
> >> .section __TEXT,__const_coal,coalesced
> >> .section __TEXT,__picsymbolstub4,symbol_stubs,none,16
> >> .section __TEXT,__StaticInit,regular,pure_instructions
> >> .section __TEXT,__cstring,cstring_literals
> >> .syntax unified
> >>                                        @ Start of file scope inline
> >> assembly
> >> <inline asm>:1:1: error: instruction requires: arm-mode
> >> stmib sp, {r0-r14};
> >>
> >> However, when the .s file is generated with -no-integrated-as first, and
> >> then assembled later, clang completes assembling the .s file without any
> >> errors.
> >>
> >> $ clang -arch armv7  -S -o test2.s -no-integrated-as test2.c
> >> $ clang -arch armv7  test2.s -c
> >>
> >> The attached patch fixes this discrepancy in clang's behavior by
> emitting
> >> directive ".code 16" before global inline-asm instructions when the
> target
> >> is thumb. Without this directive, clang assembles the global inline-asm
> >> instruction in ARM mode, since the assembler always starts in ARM mode
> and
> >> stays in that mode until it sees directives that instruct it to switch
> to
> >> thumb.
> >>
> >> <rdar://problem/17757232>
> >>
> >> <code16.patch>_______________________________________________
> >> llvm-commits mailing list
> >> llvm-commits at cs.uiuc.edu
> >> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
> >>
> >>
> >>
> >> _______________________________________________
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> >> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
> >>
>
>
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-- 
Saleem Abdulrasool
compnerd (at) compnerd (dot) org
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