[IR/AsmWriter] Output escape sequences if the first character isdigit()

If the first character in a metadata attachment's name is a digit, it has
to be output using an escape sequence, otherwise it's not valid text IR.

Removed an over-zealous assert from LLVMContext which didn't allow this.
The rule should only apply to text IR. Actual names can have any sequence
of non-NUL bytes.

Also added some documentation on accepted names.

Bug found with AFL fuzz.

llvm-svn: 238867

2 files changed, 11 insertions, 9 deletions

diff --git a/llvm/lib/IR/AsmWriter.cpp b/llvm/lib/IR/AsmWriter.cpp
index 86bcd658185..715aad8b03a 100644
--- a/llvm/lib/IR/AsmWriter.cpp
+++ b/llvm/lib/IR/AsmWriter.cpp
@@ -2215,9 +2215,8 @@ void AssemblyWriter::printModule(const Module *M) {
   }
 }
 
-void AssemblyWriter::printNamedMDNode(const NamedMDNode *NMD) {
-  Out << '!';
-  StringRef Name = NMD->getName();
+static void printMetadataIdentifier(StringRef Name,
+                                    formatted_raw_ostream &Out) {
   if (Name.empty()) {
     Out << "<empty name> ";
   } else {
@@ -2235,6 +2234,11 @@ void AssemblyWriter::printNamedMDNode(const NamedMDNode *NMD) {
         Out << '\\' << hexdigit(C >> 4) << hexdigit(C & 0x0F);
     }
   }
+}
+
+void AssemblyWriter::printNamedMDNode(const NamedMDNode *NMD) {
+  Out << '!';
+  printMetadataIdentifier(NMD->getName(), Out);
   Out << " = !{";
   for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i) {
     if (i)
@@ -3006,9 +3010,10 @@ void AssemblyWriter::printMetadataAttachments(
   for (const auto &I : MDs) {
     unsigned Kind = I.first;
     Out << Separator;
-    if (Kind < MDNames.size())
-      Out << "!" << MDNames[Kind];
-    else
+    if (Kind < MDNames.size()) {
+      Out << "!";
+      printMetadataIdentifier(MDNames[Kind], Out);
+    } else
       Out << "!<unknown kind #" << Kind << ">";
     Out << ' ';
     WriteAsOperandInternal(Out, I.second, &TypePrinter, &Machine, TheModule);
diff --git a/llvm/lib/IR/LLVMContext.cpp b/llvm/lib/IR/LLVMContext.cpp
index e8bf442b3e1..7bcd829f9f5 100644
--- a/llvm/lib/IR/LLVMContext.cpp
+++ b/llvm/lib/IR/LLVMContext.cpp
@@ -242,9 +242,6 @@ void LLVMContext::emitError(unsigned LocCookie, const Twine &ErrorStr) {
 
 /// Return a unique non-zero ID for the specified metadata kind.
 unsigned LLVMContext::getMDKindID(StringRef Name) const {
-  assert(!std::isdigit(Name.front()) &&
-         "Named metadata may not start with a digit");
-
   // If this is new, assign it its ID.
   return pImpl->CustomMDKindNames.insert(
                                      std::make_pair(