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"Nano" C library

go/nanolibc

Description

This implements a small subset of a POSIX C library, mainly:

  • printf and sprintf function family
  • most common string.h functions: memcpy, memcmp, strcpy, strncpy, strcmp, etc.
  • strtol/strtoul/strtoll/strtoull and atol
  • ctype (no locale/encoding support)
  • a small subset of stdio.h: only stdout and stderr supported, fwrite/putc/etc. work on them
  • a tiny subset of C++ STL: vector<>, auto_ptr<>
  • a few functions are defined but their implementation is an empty shell (return error): signal, fopen/fclose/fread/fseek, getenv, localtime, isatty. See c/unsup.c

It should allow to compile C code that depends on a limited C POSIX subset without any modification.

This library takes the form of a generic archive, plus a per-target runtime adapter library. The interface of the per-target runtime library is defined as a structure of function pointers in c/libc.h. For now, EFI 64 target is the main target. We also provide a convenient tuntime library for testing, allowing to run nanolibc-based program on linux.

Source layout

Code lives in:

  • c/include/: declarations for the C library
  • c/noimpl/: empty header files for legacy code that includes them without using them
  • c/nostd/: google-specific header files, should work with any C library
  • c/*.c: implementation of the C library
  • cxx/include/: declarations for the C++ library
  • cxx/noimpl/: empty header files for legacy code that includes them without using them
  • cxx/nostd/: google-specific header files, should work with any C library
  • cxx/*.cc: implementation of the C++ library
  • efi/: code for EFI runtime adapter library, ie. implements interface c/libc.h for EFI
  • native/: for testing purposes only, runtime that allows to load and run a nanolibc-based program from linux, natively. Useful when debugging (eg. to use valgrind) or testing (eg. code coverage)

In tests/ directory, a few unit tests are implemented that provide good coverage of the core nanolibc functionality. The BUILD file in this directory builds 3 versions of the tests:

  • "native": tests don't actually include/link against nanolibc, run directly on the host OS. Convenient to make sure unit tests work as expected against usual (linux/eglibc) standards
  • "nanolib": tests are compiled and linked against the nanolibc objects and native/start_main.o, ie. they are piggybacked into a normal host linux libc executable. This means that the tests will be able to fully exercise nanolibc code (object files are actually the same used for EFI builds as well) from within a normal linux host. Allows to test nanolibc under valgrind (TODO: add support for blaze coverage info).
  • "efi": tests compiled and linked against nanolib with a small adapter for gnu-efi, take the form of EFI module ready to be executed in qemu or on real hardware.

In example/ directory: a simple "hello world" EFI & Linux program that is built with nanlolibc.

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decot@ 12/2016