Phipps, Alan via llvm-dev
2020-Nov-04 19:57 UTC
[llvm-dev] llvm-objdump -d unable to disassemble some Arm instructions
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
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