Cross-Compilation Checklist for Custom MIPS VMs

Cross-Compilation Checklist for Custom MIPS VMs

Use this checklist to ensure all critical steps are completed when cross-compiling for a custom MIPS VM.

Pre-Compilation Analysis

• Read and analyze VM source code thoroughly
• Document syscall numbers and their mappings
• Identify syscall calling convention (register usage)
• Determine endianness (little-endian vs big-endian)
• Identify floating-point support (hard vs soft)
• Document memory layout (entry point, stack, heap)
• List any instruction limitations or unimplemented opcodes
• Identify ELF format expectations (sections, entry symbol)

Header Preparation

• Scan all source files for #include statements
• Create complete list of required system headers
• Create stub headers for ALL required headers before first compile
• Verify stdarg.h handling for variadic functions
• Include proper type definitions (size_t, ssize_t, etc.)

Standard Library Implementation

Critical Functions (Must Be Complete)

• printf - with format specifier support (%d, %s, %x, %c, %p minimum)
• sprintf / snprintf - same format support
• fprintf - with file descriptor support
• sscanf - for configuration parsing
• malloc / free / realloc - proper heap management
• memcpy / memset / memmove - memory operations
• strlen / strcmp / strcpy / strncpy - string operations
• atoi / atol / strtol - number parsing
• fopen / fread / fwrite / fclose - file operations
• fseek / ftell - file positioning
• open / read / write / close - low-level I/O

Verification Checklist

• No functions return 0 unconditionally
• No empty function bodies
• No TODO/stub comments in critical functions
• Format specifiers properly parsed and handled
• Error conditions properly reported

Linker Configuration

• Entry point symbol matches VM expectations
• Text section address is correct
• Data section address is correct
• BSS section properly placed and zeroed
• Stack pointer initialized in startup code
• Map file generation enabled (-Wl,-Map=output.map)

Compilation Verification

• No implicit function declaration warnings
• No ABI mismatch warnings (or properly addressed)
• ELF entry point verified with readelf
• Symbol table checked with nm
• Section layout verified with objdump

Testing Progression

1. Minimal test program (print "Hello")
2. Syscall test program (test each syscall)
3. Memory allocation test
4. File I/O test
5. Complex string operations test
6. Full application

Debugging When Things Go Wrong

Program Terminates Early

• Get termination PC address from VM
• Look up address in map file
• Identify failing function
• Check for unimplemented instructions
• Verify syscall parameters are valid
• Check for stack overflow
• Verify memory addresses are in valid range

No Output Produced

• Verify write syscall implementation
• Check stdout file descriptor (usually 1)
• Trace from printf to write syscall
• Check buffer flushing

Unexpected Behavior

• Add diagnostic output at checkpoints
• Log all syscall invocations
• Verify data file paths
• Check endianness of data files