https://bugs.llvm.org/show_bug.cgi?id=39517
Bug ID: 39517
Summary: Control Flow Guard on a simple program causes a crash
Product: lld
Version: unspecified
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: All Bugs
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
When compiling the following program
#include <iostream>
#include <sstream>
int main()
{
std::wostringstream str;
str << L"Lorem ipsum dolor sit amet";
std::wcout << str.str();
}
using the following commands
clang-cl /c control-bug.cpp -m32 /guard:cf /MDd
--- OR ---
clang-cl /c control-bug.cpp -m32 /guard:cf /MD
lld-link /guard:cf control-bug.obj
will cause a binary that crashes before printing Lorem Ipsum to the command
prompt.
Using the static (/MT and /MTd) over the DLL (/MD and /MDd) Microsoft Runtime
Library will make a correctly working executable, as well as replacing lld-link
by link and/or clang-cl by cl.
After further debugging by setting a breakpoint on the failing
_guard_check_icall_fptr call in x32dbg, it seems that
std::basic_streambuf<unsigned short, std::char_traits<unsigned short>>::sputn
(which is a function embedded in the MS Runtime library) is calling
std::basic_streambuf<unsigned short, std::char_traits<unsigned short>>::xsputn
(which is a function embedded in the main executable file) by function pointer
but it is not registered as a valid call target to Control Flow Guard.
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