https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114643
Bug ID: 114643
Summary: Call to a template function emitted but without the
code for the template function itself
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: abbeyj+gcc at gmail dot com
Target Milestone: ---
When building the following example, a linker error is produced.
```
void foo();
template <class> class DynArray {
public:
virtual void SetAlloc(unsigned);
int *m_pElems;
unsigned m_nNumElems;
unsigned m_nNumAlloc;
long m_nChunkSize;
};
void *DoRealloc(void *, long);
template <class T> void DynArray<T>::SetAlloc(unsigned new_size) {
if (m_nChunkSize)
new_size = m_nChunkSize * m_nChunkSize - 1 / m_nChunkSize;
else if (m_nNumAlloc)
if (new_size > m_nNumAlloc / 2)
new_size = new_size > m_nNumAlloc + 1 ? new_size : m_nNumAlloc * 1.5 + 1;
if (m_nNumElems && m_nNumAlloc && (new_size || m_pElems))
m_pElems = (T *)DoRealloc(m_pElems, 0);
}
struct object {
DynArray<int> d;
void f(int size);
};
template <typename T> void deser(int size, T &x) {
x.SetAlloc(0);
if (size) {
x.SetAlloc(size);
foo();
}
}
void object::f(int size) {
deser(size, d);
}
```
Build with:
$ g++ -fPIC -O3 -Wall -Werror -fvisibility=hidden reloc.cxx -shared
Output:
> /usr/bin/ld: /tmp/ccLaKma6.o: relocation R_X86_64_PC32 against undefined
> symbol `_ZN8DynArrayIiE8SetAllocEj' can not be used when making a shared
> object; recompile with -fPIC
> /usr/bin/ld: final link failed: Bad value
> collect2: error: ld returned 1 exit status
The symbol in the above error message demangles to
`DynArray<int>::SetAlloc(unsigned int)`.
The error message suggests to compile with `-fPIC` but this is already being
compiled with `-fPIC`. The issue seems to be that GCC emits a call to
`DynArray<int>::SetAlloc` but doesn't emit code for `DynArray<int>::SetAlloc`
itself.
The reproducer was minimized with the help of C-Reduce. Very minor changes to
the code result in the problem not reproducing anymore. This is the smallest
that I could manage to get it.
Godbolt link: https://godbolt.org/z/1Ynz1Khac
This appears to have started sometime around GCC 8.1 and still happens on the
trunk version that's currently available on Godbolt.
