[PATCH] D28950: [LLD][ELF] Correct sh_info for static symbol table

[Peter Smith via Phabricator via llvm-commits]

peter.smith created this revision.
Herald added a subscriber: nemanjai.

The sh_info field of the SHT_SYMTAB section holds the index for the first non-local symbol. When there are global symbols that are output with STB_LOCAL binding due to having hidden visibility or matching the local version from a version script, the calculated value of NumLocals + 1 does not account for them. This change adds in the number of local symbols that aren't covered by NumLocals.

I think that this property is of marginal use in an Executable/Shared object but there could be an ELF processing tool that could get confused if it skips all the local symbols in the file using the sh_info field.

The test updates are where we have a global symbol output with local binding and a check of a sh_info field.

I noticed this while working on support for synthetic local symbols. It feels like a bit of a hack, but if NumLocals is interpreted as number of locals stored outside of the SymbolTableSection::Symbols in Files it makes a bit more sense.


https://reviews.llvm.org/D28950

Files:
  ELF/SyntheticSections.cpp
  test/ELF/basic-mips.s
  test/ELF/basic-ppc.s


Index: test/ELF/basic-ppc.s
===================================================================
--- test/ELF/basic-ppc.s
+++ test/ELF/basic-ppc.s
@@ -178,7 +178,7 @@
 // CHECK-NEXT:     Offset: 0x2038
 // CHECK-NEXT:     Size: 32
 // CHECK-NEXT:     Link: 9
-// CHECK-NEXT:     Info: 1
+// CHECK-NEXT:     Info: 2
 // CHECK-NEXT:     AddressAlignment: 4
 // CHECK-NEXT:     EntrySize: 16
 // CHECK-NEXT:     SectionData (
Index: test/ELF/basic-mips.s
===================================================================
--- test/ELF/basic-mips.s
+++ test/ELF/basic-mips.s
@@ -176,7 +176,7 @@
 # CHECK-NEXT:     Offset: 0x20010
 # CHECK-NEXT:     Size: 48
 # CHECK-NEXT:     Link: 10
-# CHECK-NEXT:     Info: 1
+# CHECK-NEXT:     Info: 2
 # CHECK-NEXT:     AddressAlignment: 4
 # CHECK-NEXT:     EntrySize: 16
 # CHECK-NEXT:   }
Index: ELF/SyntheticSections.cpp
===================================================================
--- ELF/SyntheticSections.cpp
+++ ELF/SyntheticSections.cpp
@@ -1079,6 +1079,14 @@
           return L.Symbol->symbol()->computeBinding() == STB_LOCAL &&
                  R.Symbol->symbol()->computeBinding() != STB_LOCAL;
         });
+    // Last local symbol should account for Symbols with a computed Binding
+    // of STB_LOCAL as these will not be represented by NumLocals.
+    for(const SymbolTableEntry &S : Symbols) {
+      if (S.Symbol->symbol()->computeBinding() != STB_LOCAL)
+        return;
+      this->Info++;
+      this->OutSec->Info++;
+    }
     return;
   }
   if (In<ELFT>::GnuHashTab)


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