https://bugs.llvm.org/show_bug.cgi?id=43858
Bug ID: 43858
Summary: /GUARD:CF considers member function template
parameters to be address taken when they are not,
resulting in link errors
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Common Code Generator Code
Assignee: unassignedb...@nondot.org
Reporter: r...@google.com
CC: llvm-bugs@lists.llvm.org
I summarized this first here: https://crbug.com/1019970#c12
Related to issue 33143.
Consider this code:
$ cat t.cpp
struct Foo { void bar(); };
template <void (Foo::*FN)()> struct useNonTpParam {
static void donothing() {}
};
void addrTaken();
void (*gfp)();
int main() {
gfp = addrTaken;
useNonTpParam<&Foo::bar>::donothing();
}
$ clang -cc1 -triple i686-windows-msvc -fms-extensions t.cpp -gcodeview
-debug-info-kind=limited -S -o t.s -cfguard-no-checks && grep symidx t.s
.symidx "?addrTaken@@YAXXZ"
.symidx "?bar@Foo@@QAEXXZ"
Foo::bar is used as a non-type template parameter, but it is not actually
address taken. Debug info emission creates a constant bitcast of the function,
which remains around, causing Function::hasAddressTaken to return true for
Foo::bar later. This results in emitting .symidx for it.
Both linkers treat undefined symbols as strong references to Foo::bar, so this
can result in link errors. Even if the user "uses" Foo::bar, the behavior is
surprising, and the codegen depends on whether -g is enabled, which is bad.
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