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. All input arguments 17 * are castto a long stored in a register. These expressions always return 18 * the syscall's return value as a signed long value which is often either 19 * a pointer or the negated errno value. 20 * 21 * - The second level is mostly architecture-independent. It is made of 22 * static functions called sys_<name>() which rely on my_syscallN() 23 * depending on the syscall definition. These functions are responsible 24 * for exposing the appropriate types for the syscall arguments (int, 25 * pointers, etc) and for setting the appropriate return type (often int). 26 * A few of them are architecture-specific because the syscalls are not all 27 * mapped exactly the same among architectures. For example, some archs do 28 * not implement select() and need pselect6() instead, so the sys_select() 29 * function will have to abstract this. 30 * 31 * - The third level is the libc call definition. It exposes the lower raw 32 * sys_<name>() calls in a way that looks like what a libc usually does, 33 * takes care of specific input values, and of setting errno upon error. 34 * There can be minor variations compared to standard libc calls. 35 * 36 * The errno variable is declared static and unused. This way it can be 37 * optimized away if not used. However this means that a program made of 38 * multiple C files may observe different errno values (one per C file). For 39 * the type of programs this project targets it usually is not a problem. The 40 * resulting program may even be reduced by defining the NOLIBC_IGNORE_ERRNO 41 * macro, in which case the errno value will never be assigned. 42 * 43 * Some stdint-like integer types are defined. These are valid on all currently 44 * supported architectures, because signs are enforced, ints are assumed to be 45 * 32 bits, longs the size of a pointer and long long 64 bits. If more 46 * architectures have to be supported, this may need to be adapted. 47 * 48 * Some macro definitions like the O_* values passed to open(), and some 49 * structures like the sys_stat struct depend on the architecture. 50 * 51 * The definitions start with the architecture-specific parts, which are picked 52 * based on what the compiler knows about the target architecture, and are 53 * completed with the generic code. Since it is the compiler which sets the 54 * target architecture, cross-compiling normally works out of the box without 55 * having to specify anything. 56 * 57 * Finally some very common libc-level functions are provided. It is the case 58 * for a few functions usually found in string.h, ctype.h, or stdlib.h. 59 * 60 * The nolibc.h file is only a convenient entry point which includes all other 61 * files. It also defines the NOLIBC macro, so that it is possible for a 62 * program to check this macro to know if it is being built against and decide 63 * to disable some features or simply not to include some standard libc files. 64 * 65 * A simple static executable may be built this way : 66 * $ gcc -fno-asynchronous-unwind-tables -fno-ident -s -Os -nostdlib \ 67 * -static -include nolibc.h -o hello hello.c -lgcc 68 * 69 * Simple programs meant to be reasonably portable to various libc and using 70 * only a few common includes, may also be built by simply making the include 71 * path point to the nolibc directory: 72 * $ gcc -fno-asynchronous-unwind-tables -fno-ident -s -Os -nostdlib \ 73 * -I../nolibc -o hello hello.c -lgcc 74 * 75 * The available standard (but limited) include files are: 76 * ctype.h, errno.h, signal.h, stdarg.h, stdbool.h stdio.h, stdlib.h, 77 * string.h, time.h 78 * 79 * In addition, the following ones are expected to be provided by the compiler: 80 * float.h, stddef.h 81 * 82 * The following ones which are part to the C standard are not provided: 83 * assert.h, locale.h, math.h, setjmp.h, limits.h 84 * 85 * A very useful calling convention table may be found here : 86 * http://man7.org/linux/man-pages/man2/syscall.2.html 87 * 88 * This doc is quite convenient though not necessarily up to date : 89 * https://w3challs.com/syscalls/ 90 * 91 */ 92 #ifndef _NOLIBC_H 93 #define _NOLIBC_H 94 95 #include "std.h" 96 #include "arch.h" 97 #include "types.h" 98 #include "sys.h" 99 #include "sys/auxv.h" 100 #include "sys/ioctl.h" 101 #include "sys/mman.h" 102 #include "sys/mount.h" 103 #include "sys/prctl.h" 104 #include "sys/random.h" 105 #include "sys/reboot.h" 106 #include "sys/resource.h" 107 #include "sys/stat.h" 108 #include "sys/syscall.h" 109 #include "sys/sysmacros.h" 110 #include "sys/time.h" 111 #include "sys/timerfd.h" 112 #include "sys/utsname.h" 113 #include "sys/wait.h" 114 #include "ctype.h" 115 #include "elf.h" 116 #include "sched.h" 117 #include "signal.h" 118 #include "unistd.h" 119 #include "stdio.h" 120 #include "stdlib.h" 121 #include "string.h" 122 #include "time.h" 123 #include "stackprotector.h" 124 #include "dirent.h" 125 #include "fcntl.h" 126 #include "getopt.h" 127 #include "poll.h" 128 #include "math.h" 129 130 /* Used by programs to avoid std includes */ 131 #define NOLIBC 132 133 #endif /* _NOLIBC_H */ 134