Getting line number from pdb in release mode

Question

Is it possible for the debugger (or the CLR exception handler) to show the line where the exception happened in Release mode using the pdb?

The code, in release mode

Answer 1

[@Not Sure] has it almost right. The compiler makes a best effort at identifying an appropriate line number that closely matches the current machine code instruction.

The PDB and the debugger don't know anything about optimizations; the PDB file essentially maps address locations in the machine code to source code line numbers. In optimized code, it's not always possible to match exactly an assembly instruction to a specific line of source code, so the compiler will write to the PDB the closest thing it has at hand. This might be "the source code line before", or "the source code line of the enclosing context (loop, etc)" or something else.

Regardless, the debugger essentially finds the entry in the PDB map closest (as in "before or equal") to the current IP (Instruction Pointer) and highlights that line.

Sometimes the match is not very good, and that's when you see the highlighted area jumping all over the place.