[lld] r368659 - [ELF] Simplify handling of exportDynamic and isPreemptible
Fangrui Song via llvm-commits
llvm-commits at lists.llvm.org
Tue Aug 13 02:12:52 PDT 2019
Author: maskray
Date: Tue Aug 13 02:12:52 2019
New Revision: 368659
URL: http://llvm.org/viewvc/llvm-project?rev=368659&view=rev
Log:
[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
Modified:
lld/trunk/ELF/SymbolTable.cpp
lld/trunk/ELF/Symbols.cpp
lld/trunk/ELF/Symbols.h
lld/trunk/ELF/Writer.cpp
Modified: lld/trunk/ELF/SymbolTable.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/SymbolTable.cpp?rev=368659&r1=368658&r2=368659&view=diff
==============================================================================
--- lld/trunk/ELF/SymbolTable.cpp (original)
+++ lld/trunk/ELF/SymbolTable.cpp Tue Aug 13 02:12:52 2019
@@ -77,6 +77,7 @@ Symbol *SymbolTable::insert(StringRef na
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;
}
}
Modified: lld/trunk/ELF/Symbols.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Symbols.cpp?rev=368659&r1=368658&r2=368659&view=diff
==============================================================================
--- lld/trunk/ELF/Symbols.cpp (original)
+++ lld/trunk/ELF/Symbols.cpp Tue Aug 13 02:12:52 2019
@@ -295,7 +295,7 @@ bool Symbol::includeInDynsym() const {
if (isUndefWeak() && config->pie && sharedFiles.empty())
return false;
- return isUndefined() || isShared() || exportDynamic;
+ return isUndefined() || isShared() || exportDynamic || inDynamicList;
}
// Print out a log message for --trace-symbol.
Modified: lld/trunk/ELF/Symbols.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Symbols.h?rev=368659&r1=368658&r2=368659&view=diff
==============================================================================
--- lld/trunk/ELF/Symbols.h (original)
+++ lld/trunk/ELF/Symbols.h Tue Aug 13 02:12:52 2019
@@ -116,12 +116,21 @@ public:
// are unreferenced except by other bitcode objects.
unsigned isUsedInRegularObj : 1;
- // If this flag is true and the symbol has protected or default visibility, it
- // will appear in .dynsym. This flag is set by interposable DSO symbols in
- // executables, by most symbols in DSOs and executables built with
- // --export-dynamic, and by dynamic lists.
+ // Used by a Defined symbol with protected or default visibility, to record
+ // whether it is required to be exported into .dynsym. This is set when any of
+ // the following conditions hold:
+ //
+ // - If there is an interposable symbol from a DSO.
+ // - If -shared or --export-dynamic is specified, any symbol in an object
+ // file/bitcode sets this property, unless suppressed by LTO
+ // canBeOmittedFromSymbolTable().
unsigned exportDynamic : 1;
+ // True if the symbol is in the --dynamic-list file. A Defined symbol with
+ // protected or default visibility with this property is required to be
+ // exported into .dynsym.
+ unsigned inDynamicList : 1;
+
// False if LTO shouldn't inline whatever this symbol points to. If a symbol
// is overwritten after LTO, LTO shouldn't inline the symbol because it
// doesn't know the final contents of the symbol.
@@ -233,10 +242,11 @@ protected:
: file(file), nameData(name.data), nameSize(name.size), binding(binding),
type(type), stOther(stOther), symbolKind(k), visibility(stOther & 3),
isUsedInRegularObj(!file || file->kind() == InputFile::ObjKind),
- exportDynamic(isExportDynamic(k, visibility)), canInline(false),
- referenced(false), traced(false), needsPltAddr(false), isInIplt(false),
- gotInIgot(false), isPreemptible(false), used(!config->gcSections),
- needsTocRestore(false), scriptDefined(false) {}
+ exportDynamic(isExportDynamic(k, visibility)), inDynamicList(false),
+ canInline(false), referenced(false), traced(false), needsPltAddr(false),
+ isInIplt(false), gotInIgot(false), isPreemptible(false),
+ used(!config->gcSections), needsTocRestore(false),
+ scriptDefined(false) {}
public:
// True the symbol should point to its PLT entry.
@@ -531,6 +541,7 @@ void Symbol::replace(const Symbol &newSy
visibility = old.visibility;
isUsedInRegularObj = old.isUsedInRegularObj;
exportDynamic = old.exportDynamic;
+ inDynamicList = old.inDynamicList;
canInline = old.canInline;
referenced = old.referenced;
traced = old.traced;
Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=368659&r1=368658&r2=368659&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Tue Aug 13 02:12:52 2019
@@ -1653,13 +1653,13 @@ static bool computeIsPreemptible(const S
if (!b.isDefined())
return true;
- // If we have a dynamic list it specifies which local symbols are preemptible.
- if (config->hasDynamicList)
- return false;
-
if (!config->shared)
return false;
+ // If the dynamic list is present, it specifies preemptable symbols in a DSO.
+ if (config->hasDynamicList)
+ return b.inDynamicList;
+
// -Bsymbolic means that definitions are not preempted.
if (config->bsymbolic || (config->bsymbolicFunctions && b.isFunc()))
return false;
@@ -1728,10 +1728,8 @@ template <class ELFT> void Writer<ELFT>:
for (Partition &part : partitions)
finalizeSynthetic(part.ehFrame);
- symtab->forEachSymbol([](Symbol *s) {
- if (!s->isPreemptible)
- s->isPreemptible = computeIsPreemptible(*s);
- });
+ symtab->forEachSymbol(
+ [](Symbol *s) { s->isPreemptible = computeIsPreemptible(*s); });
// Scan relocations. This must be done after every symbol is declared so that
// we can correctly decide if a dynamic relocation is needed.
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