[PATCH] D64238: [WebAssembly] Add static_assert(sizeof(SymbolUnion) <= 96)
Fangrui Song via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Fri Jul 5 02:52:39 PDT 2019
MaskRay created this revision.
MaskRay added reviewers: ruiu, sbc100.
Herald added subscribers: llvm-commits, sunfish, aheejin, jgravelle-google, dschuff.
Herald added a project: LLVM.
On Windows, the bitfield layout rule places `ussigned Referenced : 1` at
byte offset 40, instead of byte offset 37 on *NIX. The consequence is that
sizeof(SymbolUnion) == 104 on Windows while 96 on *NIX.
To eliminate this difference, change these unsigned bitfields to bool.
Repository:
rLLD LLVM Linker
https://reviews.llvm.org/D64238
Files:
wasm/Symbols.h
Index: wasm/Symbols.h
===================================================================
--- wasm/Symbols.h
+++ wasm/Symbols.h
@@ -131,26 +131,26 @@
uint32_t OutputSymbolIndex = INVALID_INDEX;
uint32_t GOTIndex = INVALID_INDEX;
Kind SymbolKind;
- unsigned Referenced : 1;
+ bool Referenced : 1;
public:
// True if the symbol was used for linking and thus need to be added to the
// output file's symbol table. This is true for all symbols except for
// unreferenced DSO symbols, lazy (archive) symbols, and bitcode symbols that
// are unreferenced except by other bitcode objects.
- unsigned IsUsedInRegularObj : 1;
+ bool IsUsedInRegularObj : 1;
// True if ths symbol is explicity marked for export (i.e. via the -e/--export
// command line flag)
- unsigned ForceExport : 1;
+ bool ForceExport : 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.
- unsigned CanInline : 1;
+ bool CanInline : 1;
// True if this symbol is specified by --trace-symbol option.
- unsigned Traced : 1;
+ bool Traced : 1;
};
class FunctionSymbol : public Symbol {
@@ -475,6 +475,11 @@
alignas(SectionSymbol) char I[sizeof(SectionSymbol)];
};
+// It is important to keep the size of SymbolUnion small for performance and
+// memory usage reasons. 96 bytes is a soft limit based on the size of
+// UndefinedFunction on a 64-bit system.
+static_assert(sizeof(SymbolUnion) <= 96, "SymbolUnion too large");
+
void printTraceSymbol(Symbol *Sym);
void printTraceSymbolUndefined(StringRef Name, const InputFile* File);
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