From c3fa3c7975a537df2e668ea59f074ce5be95b4f5 Mon Sep 17 00:00:00 2001
From: Saleem Abdulrasool <compnerd@compnerd.org>
Date: Fri, 5 Aug 2016 18:20:31 +0000
Subject: [PATCH 5/5] COFF ARM: Apply an existing offset in MOV32T relocations
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Don't blindly OR in the new value, but clear the existing one, since it can be
nonzero. Read out the existing value before, and add into the desired offset.
(The add is done outside of the applyMOV, to handle potential overflow between
the two.)

Patch by Martin Storsjö!

Cherry-picked from SVN trunk commit 277846, git mirror commit
3d39965b0cdd0.
---
 COFF/Chunks.cpp          | 16 ++++++++++++++--
 test/COFF/reloc-arm.test |  4 ++--
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/COFF/Chunks.cpp b/COFF/Chunks.cpp
index fb60a8b..b8d706e 100644
--- a/COFF/Chunks.cpp
+++ b/COFF/Chunks.cpp
@@ -81,11 +81,23 @@ void SectionChunk::applyRelX86(uint8_t *Off, uint16_t Type, Defined *Sym,
 }
 
 static void applyMOV(uint8_t *Off, uint16_t V) {
-  or16(Off, ((V & 0x800) >> 1) | ((V >> 12) & 0xf));
-  or16(Off + 2, ((V & 0x700) << 4) | (V & 0xff));
+  write16le(Off, (read16le(Off) & 0xfbf0) | ((V & 0x800) >> 1) | ((V >> 12) & 0xf));
+  write16le(Off + 2, (read16le(Off + 2) & 0x8f00) | ((V & 0x700) << 4) | (V & 0xff));
+}
+
+static uint16_t readMOV(uint8_t *Off) {
+  uint16_t Opcode1 = read16le(Off);
+  uint16_t Opcode2 = read16le(Off + 2);
+  uint16_t Imm = (Opcode2 & 0x00ff) | ((Opcode2 >> 4) & 0x0700);
+  Imm |= ((Opcode1 << 1) & 0x0800) | ((Opcode1 & 0x000f) << 12);
+  return Imm;
 }
 
 static void applyMOV32T(uint8_t *Off, uint32_t V) {
+  uint16_t ImmW = readMOV(Off);     // read MOVW operand
+  uint16_t ImmT = readMOV(Off + 4); // read MOVT operand
+  uint32_t Imm = ImmW | (ImmT << 16);
+  V += Imm;                         // add the immediate offset
   applyMOV(Off, V);           // set MOVW operand
   applyMOV(Off + 4, V >> 16); // set MOVT operand
 }
diff --git a/test/COFF/reloc-arm.test b/test/COFF/reloc-arm.test
index f7656e7..b9699e8 100644
--- a/test/COFF/reloc-arm.test
+++ b/test/COFF/reloc-arm.test
@@ -5,7 +5,7 @@
 # CHECK: .text:
 # CHECK: 402000 01104000 00000000 00000000 00000000
 # CHECK: 402010 01100000 00000000 00000000 00000000
-# CHECK: 402020 01000100 00004000 00000000 00000000
+# CHECK: 402020 41f20009 c0f24009 00000000 00000000
 # CHECK: 402030 fe07e62f 00000000 00000000 00000000
 # CHECK: 402040 3e04de2f 00000000 00000000 00000000
 # CHECK: 402050 fe07d62f 00000000 00000000 00000000
@@ -23,7 +23,7 @@ sections:
   - Name:            .text
     Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_PURGEABLE, IMAGE_SCN_MEM_16BIT, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
     Alignment:       4096
-    SectionData:     00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000f000f8000000000000000000000000
+    SectionData:     00000000000000000000000000000000000000000000000000000000000000004ff6ff79cff6ff79000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000f000f8000000000000000000000000
     Relocations:
       - VirtualAddress:  0
         SymbolName:      foo
-- 
2.7.4