[llvm] r204555 - Propagate types from symbol to aliases.

Rafael Espindola rafael.espindola at gmail.com
Sat Mar 22 20:33:20 PDT 2014


Author: rafael
Date: Sat Mar 22 22:33:20 2014
New Revision: 204555

URL: http://llvm.org/viewvc/llvm-project?rev=204555&view=rev
Log:
Propagate types from symbol to aliases.

This is similar, but not identical to what gas does. The logic in MC is to just
compute the symbol table after parsing the entire file. GAS is mixed, given

.type b, @object
a = b
b:
.type b, @function

It will propagate the change and make 'a' a function. Given

.type b, @object
b:
a = b
.type b, @function

the type of 'a' is still object.

Since we do the computation in the end, we produce a function in both cases.

Added:
    llvm/trunk/test/MC/ELF/type-propagate.s
Modified:
    llvm/trunk/lib/MC/ELFObjectWriter.cpp

Modified: llvm/trunk/lib/MC/ELFObjectWriter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/ELFObjectWriter.cpp?rev=204555&r1=204554&r2=204555&view=diff
==============================================================================
--- llvm/trunk/lib/MC/ELFObjectWriter.cpp (original)
+++ llvm/trunk/lib/MC/ELFObjectWriter.cpp Sat Mar 22 22:33:20 2014
@@ -575,6 +575,22 @@ static uint8_t mergeTypeForSet(uint8_t o
   return Type;
 }
 
+static const MCSymbol *getBaseSymbol(const MCAsmLayout &Layout,
+                                     const MCSymbol &Symbol) {
+  if (!Symbol.isVariable())
+    return &Symbol;
+
+  const MCExpr *Expr = Symbol.getVariableValue();
+  MCValue Value;
+  if (!Expr->EvaluateAsRelocatable(Value, &Layout))
+    llvm_unreachable("Invalid Expression");
+  assert(!Value.getSymB());
+  const MCSymbolRefExpr *A = Value.getSymA();
+  if (!A)
+    return nullptr;
+  return getBaseSymbol(Layout, A->getSymbol());
+}
+
 void ELFObjectWriter::WriteSymbol(MCDataFragment *SymtabF,
                                   MCDataFragment *ShndxF,
                                   ELFSymbolData &MSD,
@@ -588,7 +604,12 @@ void ELFObjectWriter::WriteSymbol(MCData
 
   // Binding and Type share the same byte as upper and lower nibbles
   uint8_t Binding = MCELF::GetBinding(OrigData);
-  uint8_t Type = mergeTypeForSet(MCELF::GetType(OrigData), MCELF::GetType(Data));
+  uint8_t Type = MCELF::GetType(OrigData);
+  const MCSymbol *Base = getBaseSymbol(Layout, OrigData.getSymbol());
+  if (Base) {
+    MCSymbolData BaseSD = Layout.getAssembler().getSymbolData(*Base);
+    Type = mergeTypeForSet(Type, MCELF::GetType(BaseSD));
+  }
   if (OrigData.getFlags() & ELF_Other_ThumbFunc)
     Type = ELF::STT_FUNC;
   uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);

Added: llvm/trunk/test/MC/ELF/type-propagate.s
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/ELF/type-propagate.s?rev=204555&view=auto
==============================================================================
--- llvm/trunk/test/MC/ELF/type-propagate.s (added)
+++ llvm/trunk/test/MC/ELF/type-propagate.s Sat Mar 22 22:33:20 2014
@@ -0,0 +1,157 @@
+// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | llvm-readobj -t - | FileCheck %s
+
+// This tests that types are propagated from symbols to their aliases. Our
+// behavior is a bit different than gas. If the type of a symbol changes,
+// gas will update the type of the aliases only if those aliases were declare
+// at a point in the file where the aliased symbol was already define.
+
+// The lines marked with GAS illustrate this difference.
+
+
+	.type sym01, @object
+sym01:
+	.type sym02, @function
+sym02:
+
+	sym03 = sym01
+	sym04 = sym03
+.type sym03, @function
+	sym05 = sym03
+	sym06 = sym01 - sym02
+	sym07 = sym02 - sym01
+
+	sym08 = sym10
+	sym09 = sym10 + 1
+	.type sym10, @object
+sym10:
+
+	sym11 = sym10
+	sym12 = sym10 + 1
+	.type sym10, @function
+
+// CHECK:       Symbol {
+// CHECK:         Name: sym01
+// CHECK-NEXT:    Value: 0x0
+// CHECK-NEXT:    Size: 0
+// CHECK-NEXT:    Binding: Local (0x0)
+// CHECK-NEXT:    Type: Object (0x1)
+// CHECK-NEXT:    Other: 0
+// CHECK-NEXT:    Section: .text (0x1)
+// CHECK-NEXT:  }
+// CHECK-NEXT:  Symbol {
+// CHECK-NEXT:    Name: sym02
+// CHECK-NEXT:    Value: 0x0
+// CHECK-NEXT:    Size: 0
+// CHECK-NEXT:    Binding: Local (0x0)
+// CHECK-NEXT:    Type: Function (0x2)
+// CHECK-NEXT:    Other: 0
+// CHECK-NEXT:    Section: .text (0x1)
+// CHECK-NEXT:  }
+// CHECK-NEXT:  Symbol {
+// CHECK-NEXT:    Name: sym03
+// CHECK-NEXT:    Value: 0x0
+// CHECK-NEXT:    Size: 0
+// CHECK-NEXT:    Binding: Local (0x0)
+// CHECK-NEXT:    Type: Function (0x2)
+// CHECK-NEXT:    Other: 0
+// CHECK-NEXT:    Section: .text (0x1)
+// CHECK-NEXT:  }
+// CHECK-NEXT:  Symbol {
+// CHECK-NEXT:    Name: sym04
+// CHECK-NEXT:    Value: 0x0
+// CHECK-NEXT:    Size: 0
+// CHECK-NEXT:    Binding: Local (0x0)
+// CHECK-NEXT:    Type: Object (0x1)
+// CHECK-NEXT:    Other: 0
+// CHECK-NEXT:    Section: .text (0x1)
+// CHECK-NEXT:  }
+// CHECK-NEXT:  Symbol {
+// CHECK-NEXT:    Name: sym05
+// CHECK-NEXT:    Value: 0x0
+// CHECK-NEXT:    Size: 0
+// CHECK-NEXT:    Binding: Local (0x0)
+
+// GAS:           Type: Function (0x2)
+// CHECK-NEXT:    Type: Object (0x1)
+
+// CHECK-NEXT:    Other: 0
+// CHECK-NEXT:    Section: .text (0x1)
+// CHECK-NEXT:  }
+// CHECK-NEXT:  Symbol {
+// CHECK-NEXT:    Name: sym06
+// CHECK-NEXT:    Value: 0x0
+// CHECK-NEXT:    Size: 0
+// CHECK-NEXT:    Binding: Local (0x0)
+// CHECK-NEXT:    Type: None (0x0)
+// CHECK-NEXT:    Other: 0
+// CHECK-NEXT:    Section:  (0xFFF1)
+// CHECK-NEXT:  }
+// CHECK-NEXT:  Symbol {
+// CHECK-NEXT:    Name: sym07
+// CHECK-NEXT:    Value: 0x0
+// CHECK-NEXT:    Size: 0
+// CHECK-NEXT:    Binding: Local (0x0)
+// CHECK-NEXT:    Type: None (0x0)
+// CHECK-NEXT:    Other: 0
+// CHECK-NEXT:    Section:  (0xFFF1)
+// CHECK-NEXT:  }
+// CHECK-NEXT:  Symbol {
+// CHECK-NEXT:    Name: sym08
+// CHECK-NEXT:    Value: 0x0
+// CHECK-NEXT:    Size: 0
+// CHECK-NEXT:    Binding: Local (0x0)
+// CHECK-NEXT:    Type: Function (0x2)
+// CHECK-NEXT:    Other: 0
+// CHECK-NEXT:    Section: .text (0x1)
+// CHECK-NEXT:  }
+// CHECK-NEXT:  Symbol {
+// CHECK-NEXT:    Name: sym09
+// CHECK-NEXT:    Value: 0x1
+// CHECK-NEXT:    Size: 0
+// CHECK-NEXT:    Binding: Local (0x0)
+
+// GAS:           Type: None (0x0)
+// CHECK-NEXT:    Type: Function (0x2)
+
+// CHECK-NEXT:    Other: 0
+
+// GAS:           Section: .text (0x1)
+// CHECK-NEXT:    Section: (0xFFF1)
+
+// CHECK-NEXT:  }
+// CHECK-NEXT:  Symbol {
+// CHECK-NEXT:    Name: sym10
+// CHECK-NEXT:    Value: 0x0
+// CHECK-NEXT:    Size: 0
+// CHECK-NEXT:    Binding: Local (0x0)
+// CHECK-NEXT:    Type: Function (0x2)
+// CHECK-NEXT:    Other: 0
+// CHECK-NEXT:    Section: .text (0x1)
+// CHECK-NEXT:  }
+// CHECK-NEXT:  Symbol {
+// CHECK-NEXT:    Name: sym11
+// CHECK-NEXT:    Value: 0x0
+// CHECK-NEXT:    Size: 0
+// CHECK-NEXT:    Binding: Local (0x0)
+
+// GAS:           Type: Object (0x1)
+// CHECK-NEXT:    Type: Function (0x2)
+
+// CHECK-NEXT:    Other: 0
+// CHECK-NEXT:    Section: .text (0x1)
+// CHECK-NEXT:  }
+// CHECK-NEXT:  Symbol {
+// CHECK-NEXT:    Name: sym12
+// CHECK-NEXT:    Value: 0x1
+// CHECK-NEXT:    Size: 0
+// CHECK-NEXT:    Binding: Local (0x0)
+
+// GAS:           Type: Object (0x1)
+// CHECK-NEXT:    Type: Function (0x2)
+
+// CHECK-NEXT:    Other: 0
+
+// GAS:           Section: .text (0x1)
+// CHECK-NEXT:    Section: (0xFFF1)
+
+// CHECK-NEXT:  }





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