[llvm-bugs] [Bug 38559] New: Driver does not honour "-mthumb" for pre-processed assembler and assembler jobs.

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=38559

            Bug ID: 38559
           Summary: Driver does not honour "-mthumb" for pre-processed
                    assembler and assembler jobs.
           Product: new-bugs
           Version: trunk
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: iains-llvm at btconnect.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 20710
  --> https://bugs.llvm.org/attachment.cgi?id=20710&action=edit
Recognise -mthumb for assembler tasks.

Ran into this trying to build newlib.

case 1;

we invoke with
 ./bin/clang -target arm-none-linux-gnu -mcpu=cortex-a7 -mfpu=neon-vfpv4
-mfloat-abi=hard -mthumb /src/test-arm/thumb-mode.S -c

The driver constructs two jobs (1) to pre-process the ".S" file and (2) to
assemble the resulting ".s" file.

the ivocation for the first job is correct ; the "triple" is updated to
"thumbv7".
./bin/clang -cc1 -triple thumbv7-none-linux-gnu -E -save-temps=cwd 

the invocation for the second is not : the triple is not updated :

./bin/clang -cc1as -triple armv7-none-linux-gnu

case 2:

./bin/clang -target arm-none-linux-gnu -mcpu=cortex-a7 -mfpu=neon-vfpv4
-mfloat-abi=hard -mthumb thumb-mode.s -c -save-temps

the 'triple' is again not updated to include the thumb component - the cc1as
mode does not recognise -mthumb (but only -Wa/Xassembler -mthumb).

output in both cases:
/src/test-arm/thumb-mode.S:16:2: error: instruction requires: thumb
 cbnz r0, .Ltail


===

proposed fix (attached) - recognise the -mthumb flag for assembler tasks this
is consistent with other tools.


alternate fix ; the driver could intercept the thumb flag and push back the
Xassembler -mthumb option.  This seems more complex.

===

However, since the current behaviour seems deliberate (there is a driver test
case matching it) - so it's not clear what the intent should be (e.g. does we
expect the user to enter "-mthumb -Wa,-mthumb" ?)

===

test-case

$ more /src/test-arm/thumb-mode.S
#define synd            r0

        .syntax unified
        .arch   armv7-a
        .fpu    neon

        .text
        .thumb_func

        .global foo
        .type foo,%function
        .cfi_startproc

foo:

        cbnz synd, .Ltail
        nop
        nop
        nop
.Ltail:
        nop

        bx      lr

        .cfi_endproc
        .size   foo, . - foo

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