[PATCH] D15442: Fix for pr24346: arm asm label calculation error in sub

[Ting-Yuan Huang via llvm-commits]

laszio created this revision.
laszio added a reviewer: llvm-commits.
laszio added a subscriber: llvm-commits.
Herald added subscribers: rengolin, aemerson.

Some ARM instructions encode 32-bit immediates as a 8-bit integer (0-255)
and a 4-bit rotation (0-30, even) in its least significant 12 bits. The
original fixup, FK_Data_4, patches the instruction by the value bit-to-bit,
regardless of the encoding. For example, assuming the label L1 and L2 are
0x0 and 0x104 respectively, the following instruction:

add r0, r0, #(L2 - L1) ; expects 0x104, i.e., 260

would be assembled to the following, which adds 1 to r0, instead of 260:

e2800104  add r0, r0, #4, 2 ; equivalently 1

The new fixup kind fixup_arm_mod_imm takes care of the encoding:

e2800f41  add r0, r0, #260


http://reviews.llvm.org/D15442

Files:
  lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
  lib/Target/ARM/MCTargetDesc/ARMFixupKinds.h
  lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp
  test/MC/ARM/arm_fixups.s
  test/MC/ARM/modified-immediate-fixup-error.s
  test/MC/ARM/modified-immediate-fixup.s

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