[COFF][ARM] Apply an existing offset in MOV32T relocations

[mstorsjo]

Summary

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.)

[compnerd]

Hmm, does the input actually contain a relocation with an addend? I see that you updated the test but not the input?

[mstorsjo]

In D23057#506457, @compnerd wrote:

Hmm, does the input actually contain a relocation with an addend? I see that you updated the test but not the input?

I updated the input SectionData of the test as well, to contain a movw/movt pair with a nonzero addend.

[mstorsjo]

This one should apply cleanly on top of the latest SVN trunk now that D23053 is applied in r277836 (they both touched the same SectionData line in the test).

[compnerd]

SVN r277846

COFF/Chunks.cpp

void SectionChunk::applyRelX86(uint8_t *Off, uint16_t Type, Defined *Sym,
   case IMAGE_REL_I386_SECTION:  add16(Off, Sym->getSectionIndex()); break;
   case IMAGE_REL_I386_SECREL:   add32(Off, Sym->getSecrel()); break;
   default:
     fatal("unsupported relocation type");
   }
 }
 
 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
 }
 
 static void applyBranch20T(uint8_t *Off, int32_t V) {
   uint32_t S = V < 0 ? 1 : 0;
   uint32_t J1 = (V >> 19) & 1;
   uint32_t J2 = (V >> 18) & 1;

test/COFF/reloc-arm.test

 # RUN: yaml2obj < %s > %t.obj
 # RUN: lld-link /out:%t.exe /entry:main %t.obj
 # RUN: llvm-objdump -s %t.exe | FileCheck %s
 
 # 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
 # CHECK: 402060 fef0cef7 00000000 00000000 00000000
 
 --- !COFF
 header:
   Machine:         IMAGE_FILE_MACHINE_ARMNT
   Characteristics: []
 sections:
   - Name:            .aaa
     Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_PURGEABLE, IMAGE_SCN_MEM_16BIT, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
     Alignment:       4096
     SectionData:     0000000000000000
   - 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
         Type:            1  # IMAGE_REL_ARM_ADDR32
       - VirtualAddress:  16
         SymbolName:      foo
         Type:            2  # IMAGE_REL_ARM_ADDR32NB
       - VirtualAddress:  32