[PATCH] D95985: [ELF] Resolve defined symbols before undefined symbols

[Fangrui Song via Phabricator via llvm-commits]

MaskRay updated this revision to Diff 321280.
MaskRay edited the summary of this revision.
MaskRay added a comment.
Herald added a subscriber: wenlei.

Add test


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D95985/new/

https://reviews.llvm.org/D95985

Files:
  lld/ELF/InputFiles.cpp
  lld/test/ELF/interconnected-lazy.s


Index: lld/test/ELF/interconnected-lazy.s
===================================================================
--- /dev/null
+++ lld/test/ELF/interconnected-lazy.s
@@ -0,0 +1,42 @@
+# REQUIRES: x86
+
+# RUN: split-file %s %t
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/main.s -o %t/main.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/a.s -o %t/a.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/b.s -o %t/b.o
+
+## foo and __foo are interconnected and defined in two lazy object files.
+## Test we resolve both to the same file.
+# RUN: ld.lld -y a -y foo -y __foo %t/main.o --start-lib %t/a.o %t/b.o --end-lib -o /dev/null | FileCheck %s
+
+# CHECK:      a.o: lazy definition of __foo
+# CHECK-NEXT: a.o: lazy definition of a
+# CHECK-NEXT: a.o: lazy definition of foo
+# CHECK-NEXT: b.o: definition of __foo
+# CHECK-NEXT: b.o: definition of foo
+# CHECK-NEXT: b.o: reference to a
+# CHECK-NEXT: a.o: definition of a
+
+#--- main.s
+.globl _start
+_start:
+  call b
+
+#--- a.s
+.globl a
+.weak foo
+a:
+foo:
+
+.weak __foo
+__foo:
+
+#--- b.s
+.globl b
+.weak foo
+b:
+  call a
+foo:
+
+.weak __foo
+__foo:
Index: lld/ELF/InputFiles.cpp
===================================================================
--- lld/ELF/InputFiles.cpp
+++ lld/ELF/InputFiles.cpp
@@ -1134,6 +1134,7 @@
   }
 
   // Symbol resolution of non-local symbols.
+  SmallVector<size_t, 8> unds;
   for (size_t i = firstGlobal, end = eSyms.size(); i != end; ++i) {
     const Elf_Sym &eSym = eSyms[i];
     uint8_t binding = eSym.getBinding();
@@ -1150,8 +1151,7 @@
 
     // Handle global undefined symbols.
     if (eSym.st_shndx == SHN_UNDEF) {
-      this->symbols[i]->resolve(Undefined{this, name, binding, stOther, type});
-      this->symbols[i]->referenced = true;
+      unds.push_back(i);
       continue;
     }
 
@@ -1198,6 +1198,18 @@
 
     fatal(toString(this) + ": unexpected binding: " + Twine((int)binding));
   }
+
+  // Undefined symbols (not those defined relative to non-prevailing sections)
+  // can trigger recursive fetch. Process defined symbols first so that a set of
+  // interconnected symbols will all be resolved to same file, instead of being
+  // resolved to different files.
+  for (size_t i : unds) {
+    const Elf_Sym &eSym = eSyms[i];
+    StringRefZ name = this->stringTable.data() + eSym.st_name;
+    this->symbols[i]->resolve(Undefined{this, name, eSym.getBinding(),
+                                        eSym.st_other, eSym.getType()});
+    this->symbols[i]->referenced = true;
+  }
 }
 
 ArchiveFile::ArchiveFile(std::unique_ptr<Archive> &&file)


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