Infcall of a template function in a C++ program

Aktemur, Tankut Baris tankut.baris.aktemur@intel.com
Fri Jun 7 14:45:00 GMT 2019


Dear All,

Suppose we have the following small C++ program:

~~~
#include <iostream>

template <typename T>
T foo (T t)
{
  return t;
}

int main (void)
{
  std::cout << foo (5) << std::endl;
  std::cout << foo ('a') << std::endl;

  return 0;
}
~~~

The compiler is able to do the type inference, template function
instantiation, and function invocation based on the expressions `foo (5)`
and `foo ('a')`.  When we start GDB and attempt to evaluate these
expressions, the corresponding functions are not resolved, though.
Here is a sample session:

~~~
(gdb) start
...
(gdb) print foo(5)
No symbol "foo" in current context.
(gdb) print foo<int>(5)
$1 = 5
(gdb) print foo<char>('a')
$2 = 97 'a'
~~~

The DWARF info contains DIE's for the subprograms named "foo<int>" and
"foo<char>":

0x00002849:   DW_TAG_subprogram
                DW_AT_name      ("foo<char>")
...
0x00002882:   DW_TAG_subprogram
                DW_AT_name      ("foo<int>")
...

Is there any on-going or planned work to add type inference/resolution
capability to GDB so that an expression such as `foo (5)` would be evaluated
correctly? This might not be possible in general, but does GDB try any heuristics
to find the right template instance?

Regards,
-Tankut Baris Aktemur

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