[ELF] Simplify handling of exportDynamic and isPreemptible

In Writer::includeInDynSym(), exportDynamic is used by a Defined with
protected or default visibility, to record whether it is required to be
exported into .dynsym. It is set when any of the following conditions
hold:

1) There is an interposable symbol from a DSO (Undefined or SharedSymbol with default visibility)
2) If -shared or --export-dynamic is specified, any symbol in an object file/bitcode sets this property, unless suppressed by canBeOmittedFromSymbolTable().
3) --dynamic-list when producing an executable

4) protected symbol from a DSO preempted by copy relocation/canonical PLT when
  --ignore-{data,function}-address-equality is specified
5) ifunc is exported when -z ifunc-noplt is specified

Bullet points 4) and 5) are irrelevant in this patch.

Bullet 3) does not play well with 1) and 2). When -shared is specified,
exportDynamic of most symbols is true. This makes it incapable to record
--dynamic-list marked symbols. We thus have obscure:

    if (!config->shared)
      b->exportDynamic = true;
    else if (b->includeInDynsym())
      b->isPreemptible = true;

This patch adds another bit `Symbol::inDynamicList` to record
3). We can thus simplify handleDynamicList() by unifying the DSO and
  executable cases. It also allows us to simplify isPreemptible - now
the field is only used in finalizeSections() and later stages.

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D66091

llvm-svn: 368659

1 files changed, 3 insertions, 6 deletions

diff --git a/lld/ELF/SymbolTable.cpp b/lld/ELF/SymbolTable.cpp
index 143620e33c4..e978e0b8c41 100644
--- a/lld/ELF/SymbolTable.cpp
+++ b/lld/ELF/SymbolTable.cpp
@@ -77,6 +77,7 @@ Symbol *SymbolTable::insert(StringRef name) {
   sym->visibility = STV_DEFAULT;
   sym->isUsedInRegularObj = false;
   sym->exportDynamic = false;
+  sym->inDynamicList = false;
   sym->canInline = true;
   sym->scriptDefined = false;
   sym->partition = 1;
@@ -162,12 +163,8 @@ void SymbolTable::handleDynamicList() {
     else
       syms = findByVersion(ver);
 
-    for (Symbol *b : syms) {
-      if (!config->shared)
-        b->exportDynamic = true;
-      else if (b->includeInDynsym())
-        b->isPreemptible = true;
-    }
+    for (Symbol *sym : syms)
+      sym->inDynamicList = true;
   }
 }