Simplify PPC64::calcEFlags().

[ruiu]

Summary

In this file we only have to handle the v2 ABI, so what we need to do
is to just make sure that all object files have v2 or unspecified version
number.

[ruiu]

• simplify

[ruiu]

• simplify

[sfertile]

Other then the 1 comment this LGTM.

lld/ELF/Arch/PPC64.cpp

121 ↗

(On Diff #151085)

I think we should still emit 2 separate error messages:

1. if flags & 1 is set then emit an error message that reflects we don't support the V1 abi.
2. if any flags bits other then bits 1 or 2 are set then we emit a message for unrecognized e_flags.

[ruiu]

lld/ELF/Arch/PPC64.cpp

121 ↗

(On Diff #151085)

What do you suggest for the second message? I thought it would be something like "unsupported ABI version: 3" which is basically the same error message for v1.

[sfertile]

lld/ELF/Arch/PPC64.cpp

121 ↗

(On Diff #151085)

Maybe I am misunderstanding exactly what the eflags can be used for but I thought they can specify features/extensions as well as the abi versions. Right now only bits 0 and 1 are used to specify the abi, so if bit 1 is set we recognize that the user is giving us abi 1 input which isn't supported and let the user know exactly what the problem is.

If any bits above 1 are set we don't know if they are supposed to represent a new abi flag, a new feature flag or if the input is corrupted, and in that case a message like "Unrecognized feature flags: " + Twine (Flags & ~3) is likely to be more helpful.

[sfertile]

lld/ELF/Arch/PPC64.cpp

121 ↗

(On Diff #151085)

Sorry, I meant Unrecognized e_flags above

[ruiu]

• separated error message for v1 and unknown eflags
• added a test

[ruiu]

• clarified the error message

ELF/Arch/PPC64.cpp

PPC64::PPC64() {
   // use 0x10000000 as the starting address.
   DefaultImageBase = 0x10000000;
 
   TrapInstr =
       (Config->IsLE == sys::IsLittleEndianHost) ? 0x7fe00008 : 0x0800e07f;
 }
 
 static uint32_t getEFlags(InputFile *File) {
-  // Get the e_flag from the input file and issue an error if incompatible
-  // e_flag encountered.
-  uint32_t EFlags;
-  switch (Config->EKind) {
-  case ELF64BEKind:
-    EFlags = cast<ObjFile<ELF64BE>>(File)->getObj().getHeader()->e_flags;
-    break;
-  case ELF64LEKind:
-    EFlags = cast<ObjFile<ELF64LE>>(File)->getObj().getHeader()->e_flags;
-    break;
-  default:
-    llvm_unreachable("unknown Config->EKind");
-  }
-  if (EFlags > 2) {
-    error("incompatible e_flags: " +  toString(File));
-    return 0;
-  }
-  return EFlags;
+  if (Config->EKind == ELF64BEKind)
+    return cast<ObjFile<ELF64BE>>(File)->getObj().getHeader()->e_flags;
+  return cast<ObjFile<ELF64LE>>(File)->getObj().getHeader()->e_flags;
 }
 
+// This file implements v2 ABI. This function makes sure that all
+// object files have v2 or an unspecified version as an ABI version.
 uint32_t PPC64::calcEFlags() const {
-  assert(!ObjectFiles.empty());
-
-  uint32_t NonZeroFlag;
-  for (InputFile *F : makeArrayRef(ObjectFiles)) {
-    NonZeroFlag = getEFlags(F);
-    if (NonZeroFlag)
-      break;
-  }
-
-  // Verify that all input files have either the same e_flags, or zero.
   for (InputFile *F : makeArrayRef(ObjectFiles)) {
     uint32_t Flag = getEFlags(F);
-    if (Flag == 0 || Flag == NonZeroFlag)
-      continue;
-    error(toString(F) + ": ABI version " + Twine(Flag) +
-          " is not compatible with ABI version " + Twine(NonZeroFlag) +
-          " output");
-    return 0;
+    if (Flag == 1)
+      error(toString(F) + ": ABI version 1 is not supported");
+    else if (Flag > 2)
+      error(toString(F) + ": unrecognized e_flags: " + Twine(Flag));
   }
-
-  if (NonZeroFlag == 1) {
-    error("PPC64 V1 ABI not supported");
-    return 0;
-  }
-
   return 2;
 }
 
 void PPC64::relaxTlsGdToLe(uint8_t *Loc, RelType Type, uint64_t Val) const {
   // Reference: 3.7.4.2 of the 64-bit ELF V2 abi supplement.
   // The general dynamic code sequence for a global `x` will look like:
   // Instruction                    Relocation                Symbol
   // addis r3, r2, x@got@tlsgd@ha   R_PPC64_GOT_TLSGD16_HA      x

test/ELF/ppc64-abi-version.s

+# REQUIRES: ppc
+
+# RUN: echo '.abiversion 1' | llvm-mc -filetype=obj -triple=powerpc64le-unknown-linux - -o %t1.o
+# RUN: not ld.lld -o /dev/null %t1.o 2>&1 | FileCheck -check-prefix=ERR1 %s
+
+# ERR1: ABI version 1 is not supported
+
+# RUN: echo '.abiversion 3' | llvm-mc -filetype=obj -triple=powerpc64le-unknown-linux - -o %t1.o
+# RUN: not ld.lld -o /dev/null %t1.o 2>&1 | FileCheck -check-prefix=ERR2 %s
+
+# ERR2: unrecognized e_flags: 3