[ELF] - Ignore R_386_NONE.

[grimar]

Summary

R_X86_64_NONE is ignored starting from r288485,
I guess we want to do the same for R_386_NONE ?
Currently we error out this relocation as not supported and
ignoring seems to be correct behavior.

[ruiu]

I guess that all psABIs define R_*_NONE relocations. If that's the case, you want to add R_*_NONE relocations for all archs.

[davide]

In D28552#643017, @ruiu wrote:

I guess that all psABIs define R_*_NONE relocations. If that's the case, you want to add R_*_NONE relocations for all archs.

I wasn't able to find the semantic of R_X86_64_NONE in (https://software.intel.com/sites/default/files/article/402129/mpx-linux64-abi.pdf), I'm pretty sure dtrace (ab)uses of it but that's kind of a special case (not sure if gas can ever emit that). I think it should be clarified (maybe starting a discussion on the psABI mailing list).

[ruiu]

How does dtrace use that? I was thinking that the semantics of the relocation is pretty clear -- that is a relocation which doesn't change the target values.

[davide]

In D28552#643063, @ruiu wrote:

How does dtrace use that? I was thinking that the semantics of the relocation is pretty clear -- that is a relocation which doesn't change the target values.

Then why you need to emit a reloc in the first place (if that reloc is de facto a nop)?

See http://llvm.org/viewvc/llvm-project?rev=288485&view=rev for the dtrace use.

ELF/Target.cpp

RelExpr X86TargetInfo::getRelExpr(uint32_t Type, const SymbolBody &S) const {
   case R_386_TLS_GOTIE:
     return R_GOT_FROM_END;
   case R_386_GOTOFF:
     return R_GOTREL_FROM_END;
   case R_386_TLS_LE:
     return R_TLS;
   case R_386_TLS_LE_32:
     return R_NEG_TLS;
+  case R_386_NONE:
+    return R_HINT;
   default:
     error("do not know how to handle relocation " + toString(Type) + " (" +
           Twine(Type) + ")");
     return R_HINT;
   }
 }
 
 RelExpr X86TargetInfo::adjustRelaxExpr(uint32_t Type, const uint8_t *Data,

test/ELF/relocation-none-i686.test

+# RUN: yaml2obj %s -o %t.o
+# RUN: ld.lld %t.o -o %t.out
+
+# Test that we can handle R_386_NONE.
+
+!ELF
+FileHeader:
+  Class:           ELFCLASS32
+  Data:            ELFDATA2LSB
+  Type:            ET_REL
+  Machine:         EM_386
+Sections:
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC ]
+  - Name:            .rel.text
+    Type:            SHT_RELA
+    Link:            .symtab
+    Info:            .text
+    Relocations:
+      - Offset:          0x0000000000000000
+        Symbol:          ''
+        Type:            R_386_NONE