[lld] r330164 - Revert r329960 "Do not keep shared symbols created from garbage-collected eliminated DSOs."

[Reid Kleckner via llvm-commits]

Author: rnk
Date: Mon Apr 16 15:45:23 2018
New Revision: 330164

URL: http://llvm.org/viewvc/llvm-project?rev=330164&view=rev
Log:
Revert r329960 "Do not keep shared symbols created from garbage-collected eliminated DSOs."

This is causing large numbers of Chromium test executables to crash on
shutdown. The relevant symbol seems to be __cxa_finalize, which gets
removed from the dynamic symbol table for some of the support libraries.

Removed:
    lld/trunk/test/ELF/as-needed-weak.s
Modified:
    lld/trunk/ELF/Driver.cpp
    lld/trunk/test/ELF/gc-sections-shared.s

Modified: lld/trunk/ELF/Driver.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Driver.cpp?rev=330164&r1=330163&r2=330164&view=diff
==============================================================================
--- lld/trunk/ELF/Driver.cpp (original)
+++ lld/trunk/ELF/Driver.cpp Mon Apr 16 15:45:23 2018
@@ -1059,18 +1059,6 @@ template <class ELFT> static void handle
     Symtab->fetchLazy<ELFT>(Sym);
 }
 
-// If all references to a DSO happen to be weak, the DSO is not added
-// to DT_NEEDED. If that happens, we need to eliminate shared symbols
-// created from the DSO. Otherwise, they become dangling references
-// that point to a non-existent DSO.
-template <class ELFT> static void demoteSharedSymbols() {
-  for (Symbol *Sym : Symtab->getSymbols())
-    if (auto *S = dyn_cast<SharedSymbol>(Sym))
-      if (!S->getFile<ELFT>().IsNeeded)
-        replaceSymbol<Undefined>(S, nullptr, S->getName(), STB_WEAK, S->StOther,
-                                 S->Type);
-}
-
 // Do actual linking. Note that when this function is called,
 // all linker scripts have already been parsed.
 template <class ELFT> void LinkerDriver::link(opt::InputArgList &Args) {
@@ -1231,7 +1219,6 @@ template <class ELFT> void LinkerDriver:
   // Do size optimizations: garbage collection, merging of SHF_MERGE sections
   // and identical code folding.
   markLive<ELFT>();
-  demoteSharedSymbols<ELFT>();
   decompressSections();
   mergeSections();
   if (Config->ICF)

Removed: lld/trunk/test/ELF/as-needed-weak.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/as-needed-weak.s?rev=330163&view=auto
==============================================================================
--- lld/trunk/test/ELF/as-needed-weak.s (original)
+++ lld/trunk/test/ELF/as-needed-weak.s (removed)
@@ -1,22 +0,0 @@
-# REQUIRES: x86
-
-# RUN: echo '.globl foo; .type foo, @function; foo:' | \
-# RUN:   llvm-mc -filetype=obj -triple=x86_64-unknown-linux - -o %t1.o
-# RUN: ld.lld -shared -o %t1.so -soname libfoo %t1.o
-
-# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t2.o
-# RUN: ld.lld -o %t.exe %t2.o --as-needed %t1.so
-# RUN: llvm-readelf -dynamic-table -dyn-symbols %t.exe | FileCheck %s
-
-# CHECK-NOT: libfoo
-
-# CHECK:      Symbol table of .hash for image:
-# CHECK-NEXT: Num Buc:    Value          Size   Type   Bind Vis      Ndx Name
-# CHECK-NEXT:   1   1: 0000000000000000     0 FUNC    WEAK   DEFAULT UND foo@
-
-.globl _start
-.weak foo
-
-_start:
-  mov $foo, %eax
-  callq foo

Modified: lld/trunk/test/ELF/gc-sections-shared.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/gc-sections-shared.s?rev=330164&r1=330163&r2=330164&view=diff
==============================================================================
--- lld/trunk/test/ELF/gc-sections-shared.s (original)
+++ lld/trunk/test/ELF/gc-sections-shared.s Mon Apr 16 15:45:23 2018
@@ -9,6 +9,11 @@
 # RUN: ld.lld --gc-sections --export-dynamic-symbol foo -o %t %t.o --as-needed %t2.so %t3.so %t4.so
 # RUN: llvm-readobj --dynamic-table --dyn-symbols %t | FileCheck %s
 
+# This test the property that we have a needed line for every undefined.
+# It would also be OK to keep bar2 and the need for %t2.so
+# At the same time, weak symbols should not cause adding DT_NEEDED;
+# this case is checked with symbol qux and %t4.so.
+
 # CHECK:      DynamicSymbols [
 # CHECK-NEXT:   Symbol {
 # CHECK-NEXT:     Name:
@@ -46,6 +51,15 @@
 # CHECK-NEXT:     Other:
 # CHECK-NEXT:     Section: .text
 # CHECK-NEXT:   }
+# CHECK-NEXT:   Symbol {
+# CHECK-NEXT:     Name: qux
+# CHECK-NEXT:     Value:
+# CHECK-NEXT:     Size:
+# CHECK-NEXT:     Binding: Weak
+# CHECK-NEXT:     Type:
+# CHECK-NEXT:     Other:
+# CHECK-NEXT:     Section: Undefined
+# CHECK-NEXT:   }
 # CHECK-NEXT: ]
 
 # CHECK-NOT: NEEDED
@@ -83,6 +97,15 @@
 # CHECK2-NEXT:     Type:
 # CHECK2-NEXT:     Other:
 # CHECK2-NEXT:     Section: Undefined
+# CHECK2-NEXT:   }
+# CHECK2-NEXT:   Symbol {
+# CHECK2-NEXT:     Name: qux
+# CHECK2-NEXT:     Value:
+# CHECK2-NEXT:     Size:
+# CHECK2-NEXT:     Binding: Weak
+# CHECK2-NEXT:     Type:
+# CHECK2-NEXT:     Other:
+# CHECK2-NEXT:     Section: Undefined
 # CHECK2-NEXT:   }
 # CHECK2-NEXT:   Symbol {
 # CHECK2-NEXT:     Name: foo