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

[Jim Grosbach]

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.

>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>
>> 
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