ld assembles the x86-64 AT&T dialect emitted by the miniGCC C compiler into executable formats. It is self-contained: no external assembler or linker.

The test suite drives miniGCC and cvm2, so clone them as siblings of this repository (or point MINIGCC= and CVM2= at them):

git clone https://github.com/grisuno/miniGCC ../miniGCC
git clone https://github.com/grisuno/cvm     ../cvm

usage: ld [-f cvm|elf] [-o out] [-xstack N] input.s
  -f cvm     CVM v2 module (default)
  -f elf     static PIE Linux ELF executable
  -o out     output path (default: input.cvm / input.elf)
  -xstack N  x86 stack region size for the CVM backend (default 262144)

minigcc hello.c > hello.s
ld -f elf hello.s -o hello        # runs on Linux: ./hello
ld hello.s -o hello.cvm           # runs on cvm2 / inside MiniOS

ld also runs inside MiniOS, where it closes the toolchain loop without leaving the machine:

miniOS> edit p.c
miniOS> run minigcc.o p.c > p.s
miniOS> run ld.o -f elf -o p.elf p.s
miniOS> run p.elf

The ELF backend encodes x86-64 machine code directly. Output is a static, position-independent ET_DYN ELF64 with two PT_LOAD segments (RX text+rodata, RW data+bss), no runtime relocations. A built-in stub layer provides the mini libc used by miniGCC programs: write read exit exit_group open close lseek brk malloc free memcpy memset memmove memcmp strlen strcmp strncmp strcpy strncpy strchr plus stdio fopen fclose fread fwrite fseek ftell rewind fputc fputs fprintf printf sprintf puts putchar snprintf and the stdin stdout stderr stream slots. Any other undefined symbol is a hard error.

The built-in formatter understands %s %d %o %% with width, zero-fill and the l modifier. It truncates rather than reporting a would-be length, so the byte count handed to write can never exceed the format buffer. All four entry points share one core that reads arguments from an array; how many variadic arguments each accepts follows from the argument registers it has left over: printf 5, fprintf and sprintf 4, snprintf 3.

ld is the only assembler and linker miniGCC needs to bootstrap itself: miniGCC compiles its own source, ld links every generation, and the chain must reach the bootstrap fixed point. Two suites pin this milestone:

../miniGCC/test_ld_selfhost.sh   # GNU-free chain: fixed point + behaviour
RUN_SLOW=1 tests/run_tests.sh    # this repository's suite, self-host included

The same chain builds minigcc.elf for the MiniOS ramdisk (make selfhost in the miniOS repository): a compiler that is its own child, running inside the OS it was built with.

See CLAUDE.md for the full contract (SDD + TDD + BDD + mutation testing).

gcc -std=c99 -Wall -Wextra -Wpedantic -O2 -o ld ld.c
tests/run_tests.sh     # behavioral suite: cvm + elf + minigcc chain
tests/mutate.sh        # mutation testing (every mutant must be killed)

Fixtures are copied into a scratch directory and every tool runs against the copies: mutation testing deliberately builds broken binaries from this suite, and a mutant that mishandles an argument path must not be able to reach the pristine sources.

This project has been analyzed by ReadMenator, a zero-token polyglot static analysis tool. A comprehensive knowledge base is available:

• KNOWLEDGE_BASE.md -- Architecture reference with all classes, functions, imports, dependency graphs, UML class diagrams, security audit findings, community analysis, and more.

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