Fix for pr24346: arm asm label calculation error in sub

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

Patch by Ting-Yuan Huang!

llvm-svn: 265122

3 files changed, 36 insertions, 0 deletions

diff --git a/llvm/test/MC/ARM/arm_fixups.s b/llvm/test/MC/ARM/arm_fixups.s
index 1f56e128524..a7655092a7a 100644
--- a/llvm/test/MC/ARM/arm_fixups.s
+++ b/llvm/test/MC/ARM/arm_fixups.s
@@ -32,3 +32,10 @@
 @ CHECK: @   fixup A - offset: 0, value: fred, kind: fixup_arm_movw_lo16
 @ CHECK-BE: movw  r2, :lower16:fred                 @ encoding: [0xe3,0b0000AAAA,0x20'A',A]
 @ CHECK-BE: @   fixup A - offset: 0, value: fred, kind: fixup_arm_movw_lo16
+
+    add r0, r0, #(L1 - L2)
+
+@ CHECK: add     r0, r0, #L1-L2          @ encoding: [A,0b0000AAAA,0x80,0xe2]
+@ CHECK: @   fixup A - offset: 0, value: L1-L2, kind: fixup_arm_mod_imm
+@ CHECK-BE: add     r0, r0, #L1-L2          @ encoding: [0xe2,0x80,0b0000AAAA,A]
+@ CHECK-BE: @   fixup A - offset: 0, value: L1-L2, kind: fixup_arm_mod_imm
diff --git a/llvm/test/MC/ARM/modified-immediate-fixup-error.s b/llvm/test/MC/ARM/modified-immediate-fixup-error.s
new file mode 100644
index 00000000000..2d111751cc1
--- /dev/null
+++ b/llvm/test/MC/ARM/modified-immediate-fixup-error.s
@@ -0,0 +1,14 @@
+@ PR24346
+@ RUN: not llvm-mc -triple=arm-linux-gnueabi -filetype=obj < %s 2>&1 | FileCheck %s
+
+    .data
+    .align 8
+L2:
+    .word 0
+    .align 8
+    .byte 0
+L1:
+
+    .text
+@ CHECK: error: out of range immediate fixup value
+    add r0, r0, #(L1 - L2)
diff --git a/llvm/test/MC/ARM/modified-immediate-fixup.s b/llvm/test/MC/ARM/modified-immediate-fixup.s
new file mode 100644
index 00000000000..288814b4009
--- /dev/null
+++ b/llvm/test/MC/ARM/modified-immediate-fixup.s
@@ -0,0 +1,15 @@
+@ PR24346
+@ RUN: llvm-mc < %s -triple=arm-linux-gnueabi -filetype=obj -o - \
+@ RUN: | llvm-objdump --disassemble -arch=arm - | FileCheck %s
+
+    .data
+    .align 8
+L2:
+    .word 0
+    .align 8
+    .word 0
+L1:
+
+    .text
+@ CHECK: add r0, r0, #260
+    add r0, r0, #(L1 - L2)