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diff --git a/usr/klibc/README.klibc b/usr/klibc/README.klibc new file mode 100644 index 0000000..1a9e09f --- /dev/null +++ b/usr/klibc/README.klibc @@ -0,0 +1,147 @@ +Introduction +============ + +This is klibc, what is intended to be a minimalistic libc subset for +use with initramfs. It is deliberately written for small size, +minimal entanglement, and portability, not speed. It is definitely a +work in progress, and a lot of things are still missing. + +Building +======== + +The build procedure is not very polished yet, but for a native build +with the default configuration it should be simple: + +1. In a recent Linux kernel source directory, run: + make headers_install INSTALL_HDR_PATH=<klibc-source-dir>/linux +2. In the klibc source directory, run: + make + +Cross-compiling +--------------- + +If you're cross-compiling, you need to set KLIBCARCH to the +appropriate architecture, and set CROSS_COMPILE to your toolchain +prefix, on the "make" command line. You also need to set ARCH to the +appropriate kernel architecture name on the "make headers_install" +command line. + +IMPORTANT: if you're on a 64-bit machine with a 32-bit userland, and +you want to build the 32-bit version: you need to set KLIBCARCH to the +32-bit architecture. Building the 32-bit architecture usually (but +not always) produces smaller binaries. + +If you are on ARM, and want to build a thumb version of the library +(this is supported), change OPTFLAGS in arch/arm/MCONFIG to build +thumb code. + +Out-of-tree builds +------------------ + +It is possible to use a separate build directory so that build +products are not created in source directories. To do this, +create the build directory and in that directory run: + make -f <source-dir>/Makefile KBUILD_SRC=<source-dir> + +Build configuration +------------------- + +The build configuration is defined in a ".config" file in the +build directory. If this file does not already exist, it is +created as a copy of the "defconfig" source file. + +The configuration variables are: + +* CONFIG_KLIBC_ERRLIST (bool): Include standard error strings for + strerror(). If disabled, strerror() returns the error number as a + string. +* CONFIG_KLIBC_ZLIB (bool): Include zlib decompression functions. If + disabled, kinit can only load uncompressed ramdisk images. +* CONFIG_KLIBC_ZIP (bool): Include compression support in the gzip + command. +* CONFIG_DEBUG_INFO (bool): Install all executables and the shared + library with debug information and build IDs included. If + disabled, the executables and shared library are stripped when + installed. + +For arm only: + +* CONFIG_KLIBC_THUMB (bool): Compile all code to Thumb instructions, + which should reduce code size slightly. If disabled, regular ARM + instructions are used. +* CONFIG_AEABI (bool): Compile ARM code to use the ARM EABI and the + "new" system call ABI. + +If both CONFIG_KLIBC_THUMB and CONFIG_AEABI are disabled, the GNU APCS +and the old system call ABI are used. + +For i386 only: + +* CONFIG_REGPARM (bool): Optimise function calls by passing the first + 3 function parameters in registers. + +For mips64 only: + +* CONFIG_KLIBC_MIPS_USE_CB (bool): Use compact branch instructions. + This should be enabled when targetting MIPS R6 and must be disabled + for older MIPS ISAs. + +Building without kernel source +------------------------------ + +If you already have a copy of the current kernel UAPI headers, you +don't need the kernel source as well. You can either: + +1. Copy or link to the UAPI headers so that they appear under the + "linux/include" subdirectory. +2. Set the KLIBCKERNELSRC variable on the "make" command line to + point to the *parent* of the UAPI headers directory. + +Architecture support +==================== + +The following is the last known status of various architectures: + + alpha: Working + arm-thumb: Working + arm: Working + arm64: Working + h8300: Not yet ported + i386: Working + ia64: Working + m68k: Working + mips: Working + mips64: Working + parisc: Working + parisc64: Not yet ported + ppc: Working + ppc64: Working + riscv64: Working + s390: Working + s390x: Working + sh: Working + sparc: Working + sparc64: Working + x86-64: Working + xtensa: Not yet ported + +Shared library support requires recent binutils on many architectures. + +Note that even the "working" ones likely have bugs. Please report +them if you run into them. + +Testing +======= + +Try the test programs in the tests/ directory. They should run... + +Contact +======= + +Contact the klibc mailing list: + + https://www.zytor.com/mailman/listinfo/klibc + +... for more info. + + -hpa |