[LLVM][MIPS] Fix createStubFunction to emit JR encoding based on Arch.

[nitesh.jain]

Summary

The RuntimeDyldImpl::createStubFunction() contains hard coded JR encoding. The encoding given in this function is incorrect in case of R6 so it results in illegal instruction at runtime while evaluating expression in LLDB for MIPS32r6. This patch emit JR encoding based on Arch.

[dsanders]

This change looks correct but it ought to have a testcase.

@lhames: Is there a good way to test that the stub function was created correctly?

[nitesh.jain]

Hi Daniel,

Please could you find some time to review this ?

Thanks

[dsanders]

LGTM on the basis that the code looks right and we don't know of any means to add a test case.

llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp

if (Arch == Triple::aarch64 || Arch == Triple::aarch64_be) {
     writeBytesUnaligned(0xe51ff004, Addr, 4); // ldr pc,<label>
     return Addr + 4;
   } else if (IsMipsO32ABI) {
     // 0:   3c190000        lui     t9,%hi(addr).
     // 4:   27390000        addiu   t9,t9,%lo(addr).
     // 8:   03200008        jr      t9.
     // c:   00000000        nop.
     const unsigned LuiT9Instr = 0x3c190000, AdduiT9Instr = 0x27390000;
-    const unsigned JrT9Instr = 0x03200008, NopInstr = 0x0;
+    const unsigned NopInstr = 0x0;
+    unsigned JrT9Instr = 0x03200008;
+    if ((AbiVariant & ELF::EF_MIPS_ARCH) == ELF::EF_MIPS_ARCH_32R6)
+        JrT9Instr = 0x03200009;
 
     writeBytesUnaligned(LuiT9Instr, Addr, 4);
     writeBytesUnaligned(AdduiT9Instr, Addr+4, 4);
     writeBytesUnaligned(JrT9Instr, Addr+8, 4);
     writeBytesUnaligned(NopInstr, Addr+12, 4);
     return Addr;
   } else if (Arch == Triple::ppc64 || Arch == Triple::ppc64le) {
     // Depending on which version of the ELF ABI is in use, we need to

llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp

if (RelType == ELF::R_MIPS_26) {
       if (i != Stubs.end()) {
         RelocationEntry RE(SectionID, Offset, RelType, i->second);
         addRelocationForSection(RE, SectionID);
         DEBUG(dbgs() << " Stub function found\n");
       } else {
         // Create a new stub function.
         DEBUG(dbgs() << " Create a new stub function\n");
         Stubs[Value] = Section.getStubOffset();
+
+        unsigned AbiVariant;
+        O.getPlatformFlags(AbiVariant);
+
         uint8_t *StubTargetAddr = createStubFunction(
-            Section.getAddressWithOffset(Section.getStubOffset()));
+            Section.getAddressWithOffset(Section.getStubOffset()), AbiVariant);
 
         // Creating Hi and Lo relocations for the filled stub instructions.
         RelocationEntry REHi(SectionID, StubTargetAddr - Section.getAddress(),
                              ELF::R_MIPS_HI16, Value.Addend);
         RelocationEntry RELo(SectionID,
                              StubTargetAddr - Section.getAddress() + 4,
                              ELF::R_MIPS_LO16, Value.Addend);