libsdcc-z80

introduction

libsdcc-z80 is a bare-metal runtime library for the SDCC C compiler targeting the Z80 processor. It is intended for builds where the standard SDCC runtime is disabled using --nostdlib, --nostdinc, and --no-std-crt0.

In this mode, SDCC does not provide startup code or runtime support. This is commonly used when targeting custom or unsupported Z80 systems, or when writing firmware or operating systems with full control over memory layout and startup.

The Z80 processor lacks native support for many C language operations, such as integer and floating-point arithmetic and certain type conversions. SDCC replaces these operations with calls to helper functions, which are normally supplied by the standard runtime.

libsdcc-z80 provides these missing helper routines as optimized Z80 assembly. The C source code remains unchanged, helper calls are generated automatically by the compiler, and all symbols are resolved by the linker.

features

• 100% Z80 assembly (zero C in the runtime)
• Optimized for speed
• Supports int, long, long long, float
• Full coverage of arithmetic, comparisons, shifts, and type conversions
• Docker-based build (no local toolchain required)
• Comprehensive ZX Spectrum automated tests

building

using makefile

The project is built using make and runs entirely inside Docker. No local SDCC installation is required.

make          # build library and tests
make lib      # build library only
make clean

The library is placed in the bin/ directory.

To integrate the build into another project, override the output directories using relative paths:

make BUILD_DIR=obj BIN_DIR=output

Note
When custom output directories are used, the same variables must also be provided when cleaning:

make BUILD_DIR=obj BIN_DIR=output clean

directory structure

The project is split into a small runtime library and a ZX Spectrum–based test suite.
All builds run inside Docker.

.
├── Makefile
├── src/
│   ├── int/
│   └── float/
└── test/
    ├── lib/
    ├── include/
    └── src/
        ├── compile/
        └── execute/

path	description
Makefile	Top-level build entry point. Pulls the Docker image and delegates builds to subdirectories.
src/	libsdcc-z80 runtime library (Z80 assembly only).
src/int/	Integer arithmetic and helper routines.
src/float/	Floating-point arithmetic and helper routines.
test/	ZX Spectrum test suite and bare-metal SDCC examples.
test/lib/	ZX Spectrum–specific support code and crt0.
test/include/	Header files used by tests.
test/src/	Test sources.
test/src/compile/	Compile-only tests (symbol resolution, no binaries produced).
test/src/execute/	Runtime ZX Spectrum tests for integer and floating-point operations.

Note
All builds use the Docker image
wischner/sdcc-z80-zx-spectrum:latest

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