ELF: Handle R_ARM_V4BX correctly in PIC output files.

[pcc]

Summary

Previously we considered R_ARM_V4BX to be an absolute relocation,
which meant that we rejected it in read-only sections in PIC output
files. Instead, treat it as a hint relocation so that relocation
processing ignores it entirely.

Also fix a problem with the test case where it was never being run
because it has a .yaml extension and we don't run tests with that
extension.

[ruiu]

LGTM

lld/trunk/ELF/Arch/ARM.cpp

RelExpr ARM::getRelExpr(RelType Type, const Symbol &S,
   case R_ARM_REL32:
   case R_ARM_THM_MOVW_PREL_NC:
   case R_ARM_THM_MOVT_PREL:
     return R_PC;
   case R_ARM_NONE:
     return R_NONE;
   case R_ARM_TLS_LE32:
     return R_TLS;
+  case R_ARM_V4BX:
+    // V4BX is just a marker to indicate there's a "bx rN" instruction at the
+    // given address. It can be used to implement a special linker mode which
+    // rewrites ARMv4T inputs to ARMv4. Since we support only ARMv4 input and
+    // not ARMv4 output, we can just ignore it.
+    return R_HINT;
   default:
     return R_ABS;
   }
 }
 
 RelType ARM::getDynRel(RelType Type) const {
   if ((Type == R_ARM_ABS32) || (Type == R_ARM_TARGET1 && !Config->Target1Rel))
     return R_ARM_ABS32;
write16le(Loc,
               0xf240 |                     // opcode
                   ((Val >> 1) & 0x0400) |  // i
                   ((Val >> 12) & 0x000f)); // imm4
     write16le(Loc + 2,
               (read16le(Loc + 2) & 0x8f00) | // opcode
                   ((Val << 4) & 0x7000) |    // imm3
                   (Val & 0x00ff));           // imm8
     break;
-  case R_ARM_V4BX:
-    // V4BX is just a marker to indicate there's a "bx rN" instruction at the
-    // given address. It can be used to implement a special linker mode which
-    // rewrites ARMv4T inputs to ARMv4. Since we support only ARMv4 input and
-    // not ARMv4 output, we can just ignore it.
-    break;
   default:
     error(getErrorLocation(Loc) + "unrecognized reloc " + Twine(Type));
   }
 }
 
 int64_t ARM::getImplicitAddend(const uint8_t *Buf, RelType Type) const {
   switch (Type) {
   default:

lld/trunk/test/ELF/arm-v4bx.test

+# REQUIRES: arm
+# RUN: yaml2obj %s -o %t.o
+# RUN: ld.lld %t.o -o %t
+# RUN: llvm-readelf -sections %t | FileCheck %s
+# RUN: ld.lld -shared %t.o -o %t
+# RUN: llvm-readelf -sections %t | FileCheck %s
+
+# CHECK: .text
+
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS32
+  Data:            ELFDATA2LSB
+  Type:            ET_REL
+  Machine:         EM_ARM
+  Flags:           [ EF_ARM_EABI_VER5 ]
+Sections:
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    AddressAlign:    0x0000000000000004
+    Content:         1EFF2F01
+  - Name:            .rel.text
+    Type:            SHT_REL
+    Link:            .symtab
+    AddressAlign:    0x0000000000000004
+    Info:            .text
+    Relocations:
+      - Offset:          0x0000000000000000
+        Symbol:          ''
+        Type:            R_ARM_V4BX
+Symbols:
+  Global:
+    - Name:            _start
+      Section:         .text
+  Local:
+    - Name:            .text
+      Type:            STT_SECTION
+      Section:         .text
+DynamicSymbols:

lld/trunk/test/ELF/v4bx.yaml

-# REQUIRES: arm
-# RUN: yaml2obj %s -o %t.o
-# RUN: ld.lld %t.o -o %t
-# RUN: llvm-readelf -sections %t | FileCheck %s
-
-# CHECK: .text
-
---- !ELF
-FileHeader:
-  Class:           ELFCLASS32
-  Data:            ELFDATA2LSB
-  Type:            ET_REL
-  Machine:         EM_ARM
-  Flags:           [ EF_ARM_EABI_VER5 ]
-Sections:
-  - Name:            .text
-    Type:            SHT_PROGBITS
-    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
-    AddressAlign:    0x0000000000000004
-    Content:         1EFF2F01
-  - Name:            .rel.text
-    Type:            SHT_REL
-    Link:            .symtab
-    AddressAlign:    0x0000000000000004
-    Info:            .text
-    Relocations:
-      - Offset:          0x0000000000000000
-        Symbol:          ''
-        Type:            R_ARM_V4BX
-Symbols:
-  Global:
-    - Name:            _start
-      Section:         .text
-  Local:
-    - Name:            .text
-      Type:            STT_SECTION
-      Section:         .text
-DynamicSymbols: