[WebAssembly] Add -u/--undefined argument handling

Adds a new argument to wasm-lld, `--undefined`, with
similar semantics to the ELF linker. It pulls in symbols
from files contained within a `.a` archive, forcing them
to be included even if the translation unit would not
otherwise be pulled in.

Patch by Nicholas Wilson

Differential Revision: https://reviews.llvm.org/D40724

llvm-svn: 320004
This commit is contained in:
Sam Clegg 2017-12-07 03:19:53 +00:00
parent 8460b26403
commit 31de2f0ccf
5 changed files with 70 additions and 0 deletions

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@ -0,0 +1,38 @@
; Verify that the -u / --undefined option is able to pull in symbols from
; an archive, and doesn't error when uses to pull in a symbol already loaded.
;
; RUN: llc -filetype=obj -mtriple=wasm32-unknown-unknown-wasm %S/Inputs/ret64.ll -o %t.o
; RUN: llc -filetype=obj -mtriple=wasm32-unknown-unknown-wasm %S/Inputs/ret32.ll -o %t2.o
; RUN: llc -filetype=obj -mtriple=wasm32-unknown-unknown-wasm %s -o %t3.o
; RUN: llvm-ar rcs %t2.a %t2.o
; RUN: lld -flavor wasm %t3.o %t2.a %t.o -o %t.wasm -u ret32 --undefined ret64
; RUN: obj2yaml %t.wasm | FileCheck %s
define i32 @_start() local_unnamed_addr {
entry:
ret i32 1
}
; CHECK: - Type: EXPORT
; CHECK-NEXT: Exports:
; CHECK-NEXT: - Name: memory
; CHECK-NEXT: Kind: MEMORY
; CHECK-NEXT: Index: 0
; CHECK-NEXT: - Name: _start
; CHECK-NEXT: Kind: FUNCTION
; CHECK-NEXT: Index: 0
; CHECK-NEXT: - Name: ret32
; CHECK-NEXT: Kind: FUNCTION
; CHECK-NEXT: Index: 1
; CHECK-NEXT: - Name: ret64
; CHECK-NEXT: Kind: FUNCTION
; CHECK-NEXT: Index: 2
; CHECK-NEXT: - Type:
; Verify that referencing a symbol that doesn't exist won't work
; RUN: not lld -flavor wasm %t3.o -o %t.wasm -u symboldoesnotexist 2>&1 | FileCheck -check-prefix=CHECK-UNDEFINED1 %s
; CHECK-UNDEFINED1: error: undefined symbol: symboldoesnotexist
; RUN: not lld -flavor wasm %t3.o -o %t.wasm --undefined symboldoesnotexist --allow-undefined 2>&1 | FileCheck -check-prefix=CHECK-UNDEFINED2 %s
; CHECK-UNDEFINED2: function forced with --undefined not found: symboldoesnotexist

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@ -273,6 +273,8 @@ void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
if (Config->Relocatable && !Config->Entry.empty())
error("entry point specified for relocatable output file");
if (Config->Relocatable && Args.hasArg(OPT_undefined))
error("undefined symbols specified for relocatable output file");
if (!Config->Relocatable) {
if (Config->Entry.empty())
@ -280,6 +282,10 @@ void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
static WasmSignature Signature = {{}, WASM_TYPE_NORESULT};
addSyntheticUndefinedFunction(Config->Entry, &Signature);
// Handle the `--undefined <sym>` options.
for (StringRef S : args::getStrings(Args, OPT_undefined))
addSyntheticUndefinedFunction(S, nullptr);
Config->StackPointerSymbol = addSyntheticGlobal("__stack_pointer", 0);
}
@ -297,6 +303,18 @@ void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
Symtab->reportRemainingUndefines();
if (errorCount())
return;
} else {
// When we allow undefined symbols we cannot include those defined in
// -u/--undefined since these undefined symbols have only names and no
// function signature, which means they cannot be written to the final
// output.
for (StringRef S : args::getStrings(Args, OPT_undefined)) {
Symbol *Sym = Symtab->find(S);
if (!Sym->isDefined())
error("function forced with --undefined not found: " + Sym->getName());
}
if (errorCount())
return;
}
if (!Config->Entry.empty()) {

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@ -6,6 +6,11 @@ class F<string name>: Flag<["--", "-"], name>;
class J<string name>: Joined<["--", "-"], name>;
class S<string name>: Separate<["--", "-"], name>;
multiclass Eq<string name> {
def "": Separate<["--", "-"], name>;
def _eq: Joined<["--", "-"], name # "=">, Alias<!cast<Separate>(NAME)>;
}
def L: JoinedOrSeparate<["-"], "L">, MetaVarName<"<dir>">,
HelpText<"Add a directory to the library search path">;
@ -52,6 +57,9 @@ def strip_all: F<"strip-all">, HelpText<"Strip all symbols">;
def strip_debug: F<"strip-debug">, HelpText<"Strip debugging information">;
defm undefined: Eq<"undefined">,
HelpText<"Force undefined symbol during linking">;
def z: JoinedOrSeparate<["-"], "z">, MetaVarName<"<option>">,
HelpText<"Linker option extensions">;
@ -89,3 +97,4 @@ def alias_max_memory_m: Flag<["-"], "m">, Alias<max_memory>;
def alias_relocatable_r: Flag<["-"], "r">, Alias<relocatable>;
def alias_entry_e: JoinedOrSeparate<["-"], "e">, Alias<entry>;
def alias_entry_entry: J<"entry=">, Alias<entry>;
def alias_undefined_u: JoinedOrSeparate<["-"], "u">, Alias<undefined>;

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@ -118,6 +118,10 @@ static void checkSymbolTypes(const Symbol &Existing, const InputFile &F,
// For function symbols, optionally check the function signature matches too.
if (!NewIsFunction || !Config->CheckSignatures)
return;
// Skip the signature check if the existing function has no signature (e.g.
// if it is an undefined symbol generated by --undefined command line flag).
if (!Existing.hasFunctionType())
return;
DEBUG(dbgs() << "checkSymbolTypes: " << New.Name << "\n");
assert(NewSig);

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@ -69,6 +69,7 @@ public:
uint32_t getGlobalIndex() const;
uint32_t getFunctionIndex() const;
bool hasFunctionType() const { return FunctionType != nullptr; }
const WasmSignature &getFunctionType() const;
uint32_t getOutputIndex() const;