[llvm-dev] llvm-objdump -d unable to disassemble some Arm instructions

[Phipps, Alan via llvm-dev]

Using llvm-objdump -d to disassemble some Arm object files does not always provide a full disassembly of some instructions.  For example, movw/movt instructions end up being disassembled as “<unknown>” when objdump -d is run without any other options:

 

cat test.s:

   movw    r0, #0

   movw    r3, #0

   movt    r3, #0

   movt    r0, #0

 

clang -mcpu=cortex-r5 -mthumb test.s -c

 

llvm-objdump -d test.o:

       0:       00 00 00 e3  <unknown>

       4:       00 30 00 e3  <unknown>

       8:       00 30 40 e3  <unknown>

       c:       00 00 40 e3  <unknown>

 

On cursory examination, it appears that llvm-objdump does not extract all of the information from the obj file required to correctly decode the bits, including endianness.  GNU’s objdump tool does not appear to have this problem:

 

arm-none-eabi-objdump -d test.o

         0:   e3000000        movw    r0, #0

   4:   e3003000        movw    r3, #0

   8:   e3403000        movt    r3, #0

   c:   e3400000        movt    r0, #0

 

I’m curious if anyone has looked into this and would be willing to upstream a fix?

 

On a related note, there are some outstanding LLVM defects filed that seem to pertain to this but for different cases:

 

https://bugs.llvm.org/show_bug.cgi?id=46701

https://bugs.llvm.org/show_bug.cgi?id=46088

https://bugs.llvm.org/show_bug.cgi?id=44626

https://bugs.llvm.org/show_bug.cgi?id=38721

 

Thank you!

 

Alan Phipps

Texas Instruments