[LTO] Prevent dead stripping and internalization of symbols with sections

Summary:
ELF linkers generate __start_<secname> and __stop_<secname> symbols
when there is a value in a section <secname> where the name is a valid
C identifier.  If dead stripping determines that the values declared
in section <secname> are dead, and we then internalize (and delete)
such a symbol, programs that reference the corresponding start and end
section symbols will get undefined reference linking errors.

To fix this, add the section name to the IRSymtab entry when a symbol is
defined in a specific section. Then use this in the gold-plugin to mark
the symbol as external and visible from outside the summary when the
section name is a valid C identifier.

Reviewers: pcc

Subscribers: mehdi_amini, inglorion, eraman, llvm-commits

Differential Revision: https://reviews.llvm.org/D35639

llvm-svn: 309009

1 files changed, 4 insertions, 0 deletions

diff --git a/llvm/lib/Object/IRSymtab.cpp b/llvm/lib/Object/IRSymtab.cpp
index 7a6424a76a9..668cf62d1e8 100644
--- a/llvm/lib/Object/IRSymtab.cpp
+++ b/llvm/lib/Object/IRSymtab.cpp
@@ -156,6 +156,7 @@ Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
     Unc = &Uncommons.back();
     *Unc = {};
     setStr(Unc->COFFWeakExternFallbackName, "");
+    setStr(Unc->SectionName, "");
     return *Unc;
   };
 
@@ -240,6 +241,9 @@ Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
     }
   }
 
+  if (!Base->getSection().empty())
+    setStr(Uncommon().SectionName, Saver.save(Base->getSection()));
+
   return Error::success();
 }