dwarf-torture

Test suite for DWARF debug information on the MOS 6502 architecture. These tests validate that source-level debugging works correctly with LLVM-MOS and LLDB.

Overview

The MOS 6502 has a unique dual-stack architecture:

• Hardware stack (S register, 0x0100-0x01FF): return addresses and callee-saved registers
• Soft stack (RS0 pointer): local variables and spilled values

This creates challenges for DWARF CFI (Call Frame Information) that these tests are designed to stress.

Prerequisites

• LLVM-MOS built and installed at ~/git/llvm-mos/build/install
• picolibc for MOS at ~/git/picolibc/build-mos/install
• MAME with the zbcm6502 machine (for running tests)

Building

mkdir -p build && cd build
cmake ..
make

Or use the integrated build script in llvm-mos:

~/git/llvm-mos/.vscode/build-all.sh

This builds llvm-mos, picolibc, and dwarf-torture together.

Test Programs

hello_world.c

Simple sanity check. Verifies the build system works.

float_qsort.c

Quicksort implementation with floating-point values. Tests:

• Function calls and recursion
• Local variable inspection across optimization levels
• Built at -O0, -O1, and -O2

many_locals.c

Function with 20+ local variables of various types (int8_t, int16_t, uint8_t, uint16_t, int). Tests:

• Soft stack frame with many variables
• Variable inspection at nested call depths
• Type correctness for different integer sizes

nested_structs.c

Complex type hierarchies including:

• Nested structs (Point inside Rectangle)
• Unions with multiple interpretations
• Pointers to structs
• Both global and local struct instances

deep_recursion.c

Recursive functions reaching 15+ stack frames. Tests:

• Stack unwinding through many frames
• Distinct local variables at each recursion level
• Mixed recursion patterns (alternating functions)

Output Binaries

Test binaries are ELF files in build/bin/, suitable for:

• mame zbcm6502 -elfload <binary> (direct execution)
• mame zbcm6502 -debugger gdbstub -debug -elfload <binary> (debugging)