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[MC] Fix compiler crash in AsmParser::Lex

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When an empty comment is present in an assembly file, the compiler will crash because it checks the first character for '\n' or '\r'.
The fix consists of also checking if the string is empty before accessing the *front* method of the StringRef.
A test is included for the x86 target, but this issue is reproducible with other targets as well.

Patch by Alexandru Guduleasa!

Reviewers: niravd, grosbach, llvm-commits

Reviewed By: niravd

Differential Revision: https://reviews.llvm.org/D33993

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@305077 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nirav Dave 2017-06-09 14:04:03 +00:00
parent b43da93f75
commit d73d6a2ee6
2 changed files with 6 additions and 2 deletions
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4
lib/MC/MCParser/AsmParser.cpp
View File

@ -703,7 +703,7 @@ const AsmToken &AsmParser::Lex() {
// if it's a end of statement with a comment in it
if (getTok().is(AsmToken::EndOfStatement)) {
// if this is a line comment output it.
if (getTok().getString().front() != '\n' &&
if (!getTok().getString().empty() && getTok().getString().front() != '\n' &&
getTok().getString().front() != '\r' && MAI.preserveAsmComments())
Out.addExplicitComment(Twine(getTok().getString()));
}
@ -1523,7 +1523,7 @@ bool AsmParser::parseStatement(ParseStatementInfo &Info,
Lex();
if (Lexer.is(AsmToken::EndOfStatement)) {
// if this is a line comment we can drop it safely
if (getTok().getString().front() == '\r' ||
if (getTok().getString().empty() || getTok().getString().front() == '\r' ||
getTok().getString().front() == '\n')
Out.AddBlankLine();
Lex();

4
test/MC/AsmParser/empty-comment.s Normal file
View File

@ -0,0 +1,4 @@
#RUN: llvm-mc -preserve-comments -n -triple i386-linux-gnu < %s > %t
.text
foo:
nop #