DHowett-MSFT added inline comments.
================
Comment at: clang/lib/CodeGen/CGObjCGNU.cpp:188
+ Twine ManglePublicSymbol(StringRef Name) {
+ return StringRef(CGM.getTriple().isOSBinFormatCOFF() ? "$_" : "._") + Name;
----------------
DHowett-MSFT wrote:
> As of the latest revision, this now fails at runtime:
>
> ```
> 0x01342976 (0x03D8D530 0x03D8DCA0 0x04045A08 0x04045A08),
> llvm::Twine::str() + 0x166 bytes(s), e:\src\llvm\lib\suppor
> t\twine.cpp, line 29 + 0x5F byte(s)
> 0x01664F99 (0x03D8D5C4 0x0000000A 0x00000000 0x03D8DCA0), `anonymous
> namespace'::CGObjCGNUstep2::GetClassVar() + 0xB9
> bytes(s), e:\src\llvm\tools\clang\lib\codegen\cgobjcgnu.cpp, line 1207 +
> 0x10 byte(s)
> ```
>
> I believe we're running afoul of StringRef's lifetime here. I haven't had a
> chance to dig in.
Alright, I don't completely understand why Twine is the way that it is, but
here:
```
Twine ManglePublicSymbol(StringRef Name)
```
When we construct `Twine(const char*, StringRef)`, the newly-minted Twine
contains a _pointer to_ the passed-in StringRef. It's invalid immediately after
`ManglePublicSymbol` returns. After a few layers of stack pop off, we end up
with random garbage and undefined behavior.
A quick and effective fix is to switch `Name` to be of type `const Twine&`.
```
Twine ManglePublicSymbol(const Twine& Name)
```
Name ends up being a twine rvalue with a LHSType of cString, and all is right
in the world.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D58724/new/
https://reviews.llvm.org/D58724
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