1 /* SPDX-License-Identifier: LGPL-2.1 OR MIT */ 2 /* nolibc.h 3 * Copyright (C) 2017-2018 Willy Tarreau <w@1wt.eu> 4 */ 5 6 /* 7 * This file is designed to be used as a libc alternative for minimal programs 8 * with very limited requirements. It consists of a small number of syscall and 9 * type definitions, and the minimal startup code needed to call main(). 10 * All syscalls are declared as static functions so that they can be optimized 11 * away by the compiler when not used. 12 * 13 * Syscalls are split into 3 levels: 14 * - The lower level is the arch-specific syscall() definition, consisting in 15 * assembly code in compound expressions. These are called my_syscall0() to 16 * my_syscall6() depending on the number of arguments. The MIPS 17 * implementation is limited to 5 arguments. All input arguments are cast 18 * to a long stored in a register. These expressions always return the 19 * syscall's return value as a signed long value which is often either a 20 * pointer or the negated errno value. 21 * 22 * - The second level is mostly architecture-independent. It is made of 23 * static functions called sys_<name>() which rely on my_syscallN() 24 * depending on the syscall definition. These functions are responsible 25 * for exposing the appropriate types for the syscall arguments (int, 26 * pointers, etc) and for setting the appropriate return type (often int). 27 * A few of them are architecture-specific because the syscalls are not all 28 * mapped exactly the same among architectures. For example, some archs do 29 * not implement select() and need pselect6() instead, so the sys_select() 30 * function will have to abstract this. 31 * 32 * - The third level is the libc call definition. It exposes the lower raw 33 * sys_<name>() calls in a way that looks like what a libc usually does, 34 * takes care of specific input values, and of setting errno upon error. 35 * There can be minor variations compared to standard libc calls. For 36 * example the open() call always takes 3 args here. 37 * 38 * The errno variable is declared static and unused. This way it can be 39 * optimized away if not used. However this means that a program made of 40 * multiple C files may observe different errno values (one per C file). For 41 * the type of programs this project targets it usually is not a problem. The 42 * resulting program may even be reduced by defining the NOLIBC_IGNORE_ERRNO 43 * macro, in which case the errno value will never be assigned. 44 * 45 * Some stdint-like integer types are defined. These are valid on all currently 46 * supported architectures, because signs are enforced, ints are assumed to be 47 * 32 bits, longs the size of a pointer and long long 64 bits. If more 48 * architectures have to be supported, this may need to be adapted. 49 * 50 * Some macro definitions like the O_* values passed to open(), and some 51 * structures like the sys_stat struct depend on the architecture. 52 * 53 * The definitions start with the architecture-specific parts, which are picked 54 * based on what the compiler knows about the target architecture, and are 55 * completed with the generic code. Since it is the compiler which sets the 56 * target architecture, cross-compiling normally works out of the box without 57 * having to specify anything. 58 * 59 * Finally some very common libc-level functions are provided. It is the case 60 * for a few functions usually found in string.h, ctype.h, or stdlib.h. 61 * 62 * The nolibc.h file is only a convenient entry point which includes all other 63 * files. It also defines the NOLIBC macro, so that it is possible for a 64 * program to check this macro to know if it is being built against and decide 65 * to disable some features or simply not to include some standard libc files. 66 * 67 * A simple static executable may be built this way : 68 * $ gcc -fno-asynchronous-unwind-tables -fno-ident -s -Os -nostdlib \ 69 * -static -include nolibc.h -o hello hello.c -lgcc 70 * 71 * Simple programs meant to be reasonably portable to various libc and using 72 * only a few common includes, may also be built by simply making the include 73 * path point to the nolibc directory: 74 * $ gcc -fno-asynchronous-unwind-tables -fno-ident -s -Os -nostdlib \ 75 * -I../nolibc -o hello hello.c -lgcc 76 * 77 * The available standard (but limited) include files are: 78 * ctype.h, errno.h, signal.h, stdio.h, stdlib.h, string.h, time.h 79 * 80 * In addition, the following ones are expected to be provided by the compiler: 81 * float.h, stdarg.h, stddef.h 82 * 83 * The following ones which are part to the C standard are not provided: 84 * assert.h, locale.h, math.h, setjmp.h, limits.h 85 * 86 * A very useful calling convention table may be found here : 87 * http://man7.org/linux/man-pages/man2/syscall.2.html 88 * 89 * This doc is quite convenient though not necessarily up to date : 90 * https://w3challs.com/syscalls/ 91 * 92 */ 93 #ifndef _NOLIBC_H 94 #define _NOLIBC_H 95 96 #include "std.h" 97 #include "arch.h" 98 #include "types.h" 99 #include "sys.h" 100 #include "ctype.h" 101 #include "signal.h" 102 #include "stdio.h" 103 #include "stdlib.h" 104 #include "string.h" 105 #include "time.h" 106 #include "unistd.h" 107 108 /* Used by programs to avoid std includes */ 109 #define NOLIBC 110 111 #endif /* _NOLIBC_H */ 112