1.\"- 2.\" Copyright (c) 2024 M. Warner Losh <imp@FreeBSD.org> 3.\" 4.\" SPDX-License-Identifier: BSD-2-Clause 5.\" 6.Dd July 20, 2024 7.Dt CDEFS 9 8.Os 9.Sh NAME 10.Nm cdefs 11.Nd compiler portability macro definitions 12.Sh DESCRIPTION 13.In sys/cdefs.h 14defines macros for compiler, C language standard portability, POSIX standards 15compliance and symbol visibility. 16It defines programming interfaces for the system header files to adopt to the 17many environments 18.Fx 19supports compilation for. 20It defines convenience macros for the 21.Fx 22sources, tailored to the base 23system's needs. 24.Pp 25Most of these macros are for use inside the 26.Fx 27sources only. 28They are not intended as a general portability layer. 29.Sh Supported Compilers 30.Bl -tag -offset 2n -width 0 31.It Compilers supported for building programs on Fx : 32.Bl -column -offset 0n indent-two 33.It Sy Compiler Ta Sy Versions 34.It gcc Ta 9, 10, 11, 12, 13, 14 35.It clang Ta 10, 11, 12, 13, 14, 15, 16, 17, 18 36.It TinyC (tcc) Ta 0.9 37.It pcc Ta 1.1 38.El 39.Pp 40Due to testing constraints, tcc and pcc may not always work. 41.It Compilers supported for building Fx itself: 42.Bl -column -offset 0n indent-two 43.It Sy Compiler Ta Sy Major Versions Supported 44.It gcc Ta 12, 13, 14 45.It clang Ta 16, 17, 18 46.El 47.Pp 48Please note: Not every single minor versions of these compilers 49will work or are supported. 50.El 51.Sh Macros and Magic for Programming Environment 52.Nm 53defines (or refrains from defining) a number of macros to increase portability 54of compiled programs. 55These are to allow more advanced language features to appear in header files. 56The header files assume a compiler that accepts C prototype function 57declarations. 58They also assume that the compiler accepts ANSI C89 keywords for all language 59dialects. 60.Ss General Macros 61General macros that facilitate multiple language environments and language 62dialects. 63.Bl -column "---------------" 64.It Sy Macro Ta Sy Description 65.It Dv __volatile Ta expands to volatile in C++ and C89 and newer environments, 66__volatile in pre-ANSI environments that support this extension or nothing 67otherwise. 68.It Dv __inline Ta expands to inline in C++ and C89 and newer environments, 69__inline in pre-ANSI environments that support this extension or nothing 70otherwise. 71.It Dv __restrict Ta expands to restrict in C99 and newer environments, or 72__restrict otherwise. 73.It Dv __CONCAT Ta used to paste two pre-processor tokens. 74.It Dv __STRING Ta used to convert the argument to a string. 75.It Dv __BEGIN_DECLS Ta Start a group of functions. 76.It Dv __END_DECLS Ta End a group of functions. 77In a C environment, these are defined as nothing. 78In a C++ environment, these declare the functions to have 79.Dq C 80linkage. 81.El 82.Ss Function, Structure and Variable Modifiers 83.Bl -column "---------------" 84.It Sy Macro Ta Sy Description 85.It Sy __weak_symbol Ta Declare the symbol to be a weak symbol 86.It Sy __dead2 Ta Function will not return 87.It Sy __pure2 Ta Function has no side effects 88.It Sy __unused Ta To Variable may be unused (usually arguments), so do not warn about it 89.It Sy __used Ta Function really is used, so emit it even if it appears unused. 90.It Sy __packed Ta \&Do not have space between structure elements for natural alignment. 91Used when communicating with external protocols. 92.It Sy __aligned(x) Ta Specify in bytes the minimum alignment for the specified field, structure or variable 93.It Sy __section(x) Ta Place function or variable in section Fa x 94.It Sy __writeonly Ta Hint that the variable is only assigned to, but do not warn about it. 95Useful for macros and other places the eventual use of the result is unknown. 96.It Sy __alloc_size(x) Ta The function always returns at least the number of 97bytes determined by argument number Fa x 98.It Sy __alloc_size2(x,n) Ta The function always returns an array, whose size 99is at least the number of bytes determined by argument number Fa x times the 100number of elements specified by argument number Fa n 101.It Sy __alloc_align(x) Ta Function either returns a pointer aligned to Fa x bytes 102or Dv NULL. 103.It Sy __min_size Ta Declare the array to have a certain, minimum size 104.It Sy __malloc_like Ta Function behaves like the 105.Dq malloc 106family of functions. 107.It Sy __pure Ta Function has no side effects 108.It Sy __always_inline Ta Always inline this function when called 109.It Sy __fastcall Ta Use the 110.Dq fastcall 111ABI to call and name mangle this function. 112.It Sy __result_use_check Ta Warn if function caller does not use it's return value 113.It Sy __result_use_or_ignore_check Ta Warn if function caller does not use it's return value. 114Allows the value to be explicitly ignored with a (void) cast. 115.It Sy __returns_twice Ta Returns multiple times, like 116.Xr fork 2 117.It Sy __unreachable Ta This code is not reachable at runtime 118.It Sy __predict_true(x) Ta Hint to the compiler that 119.Fa x 120is true most of the time. 121Should only be used when performance is improved for a frequently called bit of code. 122.It Sy __predict_false(x) Ta Hint to the compiler that 123.Fa x 124is false most of the time. 125Should only be used when performance is improved for a frequently called bit of code. 126.It Sy __null_sentinel Ta The varadic function contains a parameter that is 127a NULL sentinel to mark the end of its arguments. 128.It Sy __exported Ta 129.It Sy __hidden Ta 130.It Sy __printflike(fmtarg,firstvararg) Ta Function is similar to 131.Fn printf 132which specifies the format argument with 133.Fa fmtarg 134and where the arguments formatted by that format start with the 135.Fa firstvararg , 136with 0 meaning that 137.Dv va_arg 138is used and cannot be checked. 139.It Sy __scanflike(fmtarg,firstvararg) Ta Function is similar to 140.Fn scanf 141which specifies the format argument with 142.Fa fmtarg 143and where the arguments formatted by that format start with the 144.Fa firstvararg , 145with 0 meaning that 146.Dv va_arg 147is used and cannot be checked. 148.It Sy __format_arg(f) Ta Specifies that arg 149.Fa f 150contains a string that will be passed to a function like 151.Fn printf 152or 153.Fa scanf 154after being translated in some way. 155.It Sy __strfmonlike(fmtarg,firstvararg) Ta Function is similar to 156.Fn scanf 157which specifies the format argument with 158.Fa fmtarg 159and where the arguments formatted by that format start with the 160.Fa firstvararg , 161with 0 meaning that 162.Dv va_arg 163is used and cannot be checked. 164.It Sy __strtimelike(fmtarg,firstvararg) Ta Function is similar to 165.Fn scanf 166which specifies the format argument with 167.Fa fmtarg 168and where the arguments formatted by that format start with the 169.Fa firstvararg , 170with 0 meaning that 171.Dv va_arg 172is used and cannot be checked. 173.It Sy __printf0like(fmtarg,firstvararg) Ta Exactly the same 174as 175.Sy __printflike 176except 177.Fa fmtarg 178may be 179.Dv NULL. 180.It Sy __strong_reference(sym,aliassym) Ta 181.It Sy __weak_reference(sym,alias) Ta 182.It Sy __warn_references(sym,msg) Ta 183.It Sy __sym_compat(sym,impl,verid) Ta 184.It Sy __sym_default(sym,impl,verid) Ta 185.It Sy __GLOBAL(sym) Ta 186.It Sy __WEAK(sym) Ta 187.It Sy __DECONST(type,var) Ta 188.It Sy __DEVOLATILE(type,var) Ta 189.It Sy __DEQUALIFY(type,var) Ta 190.It Sy __RENAME(x) Ta 191.It Sy __arg_type_tag Ta 192.It Sy __datatype_type_tag Ta 193.It Sy __align_up(x,y) Ta 194.It Sy __align_down(x,y) Ta 195.It Sy __is_aligned(x,y) Ta 196.El 197.Ss Locking and Debugging Macros 198Macros for lock annotation and debugging, as well as some general debugging 199macros for address sanitizers. 200.Bl -column "---------------" 201.It Sy __lock_annotate(x) Ta 202.It Sy __lockable Ta 203.It Sy __locks_exclusive Ta 204.It Sy __locks_shared Ta 205.It Sy __trylocks_exclusive Ta 206.It Sy __trylocks_shared Ta 207.It Sy __unlocks Ta 208.It Sy __asserts_exclusive Ta 209.It Sy __asserts_shared Ta 210.It Sy __requires_exclusive Ta 211.It Sy __requires_shared Ta 212.It Sy __requires_unlocked Ta 213.It Sy __no_lock_analysis Ta 214.It Sy __nosanitizeaddress Ta 215.It Sy __nosanitizememory Ta 216.It Sy __nosanitizethread Ta 217.It Sy __nostackprotector Ta 218.It Sy __guarded_by(x) Ta 219.It Sy __pt_guarded_by(x) Ta 220.El 221.Ss Emulated Keywords 222As C evolves, many of the old macros we once used have been incorporated into 223the standard language. 224As this happens, we add support for these keywords as macros for older 225compilation environments. 226Sometimes this results in a nop in the older environment. 227.Bl -column "---------------" 228.It Sy Keyword Ta Sy Description 229.It Sy _Alignas(x) Ta 230.It Sy _Alignof(x) Ta 231.It Sy _Noreturn Ta Expands to 232.Dq [[noreturn]] 233in C++-11 and newer compilation environments, otherwise 234.Dq __dead2 235.It Sy _Static_assert(x, y) Ta Compile time assertion that 236.Fa x 237is true, otherwise emit 238.Fa y 239as the error message. 240.It Sy _Thread_local Ta Designate variable as thread local storage 241.It Sy __generic Ta implement _Generic-like features which aren't entirely possible to emulate the _Generic keyword 242.It Sy __noexcept Ta to emulate the C++11 argument-less noexcept form 243.It Sy __noexcept_if Ta to emulate the C++11 conditional noexcept form 244.It Sy _Nonnull Ta 245.It Sy _Nullable Ta 246.It Sy _Null_unspecified Ta 247.El 248.Ss Support Macros 249The following macros are defined, or have specific values, to denote certain 250things about the build environment. 251.Bl -column "---------------" 252.It Sy Macro Ta Sy Description 253.It Sy __LONG_LONG_SUPPORTED Ta Variables may be declared 254.Dq long long . 255This is defined for C99 or newer and C++ environments. 256.It Sy __STDC_LIMIT_MACROS Ta 257.It Sy __STDC_CONSTANT_MACROS Ta 258.El 259.Ss Convenience Macros 260These macros make it easier to do a number of things, even though strictly 261speaking the standard places their normal form in another header. 262.Bl -column "---------------" 263.It Sy Macro Ta Sy Description 264.It Sy __offsetof(type,field) Ta 265.It Sy __rangeof(type,start,end) Ta 266.It Sy __containerof(x,s,m) Ta 267.El 268.Ss ID Strings 269This section is deprecated, but is kept around because too much contrib software 270still uses these. 271.Bl -column "---------------" 272.It Sy Macro Ta Sy Description 273.It Sy __IDSTRING(name,string) Ta 274.It Sy __FBSDID(s) Ta 275.It Sy __RCSID(s) Ta 276.It Sy __RCSID_SOURCE(s) Ta 277.It Sy __SCCSID(s) Ta 278.It Sy __COPYRIGHT(s) Ta 279.El 280.Sh Supported C Environments 281.Fx 282supports a number C standard environments. 283Selection of the language dialect is a compiler-dependent command line option, 284though it is usually 285.Fl std=XX 286where XX is the standard to set for compiling, such as c89 or c23. 287.Fx 288provides a number of selection macros to control visibility of symbols. 289Please see the section on Selection Macros for the specifics. 290.Pp 291.Bl -tag 292.It K \*(Am R 293Pre-ANSI Kernighan and Ritchie C. 294Sometimes called 295.Dq knr 296or 297.Dq C78 298to distinguish it from newer standards. 299Support for this compilation environment is dependent on compilers supporting 300this configuration. 301Most of the old forms of C have been deprecated or removed in 302ISO/IEC 9899:2024 (“ISO C23”). 303Compilers make compiling in this mode increasingly difficult and support for it 304may ultimately be removed from the tree. 305.It St -ansiC 306.Dv __STDC__ 307is defined, however 308.Dv __STDC_VERSION__ 309is not. 310.Pp 311Strict environment selected with 312.Dv _ANSI_SOURCE . 313.It St -isoC-99 314.Dv __STDC_VERSION__ = 199901L 315.Pp 316Strict environment selected with 317.Dv _C99_SOURCE . 318.It St -isoC-2011 319.Dv __STDC_VERSION__ = 201112L 320.Pp 321Strict environment selected with 322.Dv _C11_SOURCE . 323.It ISO/IEC 9899:2018 (“ISO C17”) 324.Dv __STDC_VERSION__ = 201710L 325.Pp 326Strict environment selected with 327.Dv _C11_SOURCE 328since there are no new C17 only symbols or macros. 329.Pp 330This version of the standard did not introduce any new features, only made 331minor, technical corrections. 332.It ISO/IEC 9899:2024 (“ISO C23”) 333.Dv __STDC_VERSION__ = 202311L 334Strict environment selected with 335.Dv _C23_SOURCE 336though this is not yet implemented. 337.El 338.Pp 339For more information on C standards, see 340.Xr c 7 . 341.Ss Programming Environment Selection Macros 342Defining the macros outlined below requests that the system header files provide 343only the functions, structures and macros (symbols) defined by the appropriate 344standard, while suppressing all extensions. 345However, system headers not defined by that standard may define extensions. 346.Bl -column "---------------" 347.It Sy Macro Ta Sy Environment 348.It Dv _POSIX_SOURCE Ta St -p1003.1-88 including St -ansiC 349.It Dv _POSIX_C_SOURCE = 1 Ta St -p1003.1-88 including St -ansiC 350.It Dv _POSIX_C_SOURCE = 2 Ta St -p1003.1-90 including St -ansiC 351.It Dv _POSIX_C_SOURCE = 199309 Ta St -p1003.1b-93 including St -ansiC 352.It Dv _POSIX_C_SOURCE = 199506 Ta St -p1003.1c-95 including St -ansiC 353.It Dv _POSIX_C_SOURCE = 200112 Ta St -p1003.1-2001 including St -isoC-99 354.It Dv _POSIX_C_SOURCE = 200809 Ta St -p1003.1-2008 including St -isoC-99 355.It Dv _POSIX_C_SOURCE = 202405 Ta in the future IEEE Std 1003.1-2024 (“POSIX.1”) including ISO/IEC 9899:2024 (“ISO C23”) 356.It Dv _XOPEN_SOURCE = 500 Ta St -p1003.1c-95 and XPG extensions to St -susv2 including St -ansiC 357.It Dv _XOPEN_SOURCE = 600 Ta St -p1003.1-2001 and XPG extensions to St -susv3 including St -isoC-99 358.It Dv _XOPEN_SOURCE = 700 Ta St -p1003.1-2008 and XPG extensions to St -susv4 including St -isoC-99 359.It Dv _XOPEN_SOURCE = 800 Ta in the future IEEE Std 1003.1-2024 (“POSIX.1”) and XPG extensions to Version 5 of the Single UNIX Specification (“SUSv5”) including ISO/IEC 9899:2024 (“ISO C23”) 360.It Dv _ANSI_SOURCE Ta St -ansiC 361.It Dv _C99_SOURCE Ta St -isoC-99 362.It Dv _C11_SOURCE Ta St -isoC-2011 363.It Dv _C23_SOURCE Ta in the future ISO/IEC 9899:2024 (“ISO C23”) 364.It Dv _BSD_SOURCE Ta Everything, including Fx extensions 365.El 366.Pp 367When both POSIX and C environments are selected, the POSIX environment selects 368which C environment is used. 369However, when C11 dialect is selected with 370.St -p1003.1-2008 , 371definitions for 372.St -isoC-2011 373are included. 374.Ss Header Visibility Macros 375These macros are set by 376.Nm 377to control the visibility of different standards. 378Users should not use these, but they are documented here for developers. 379.Bl -column "---------------" 380.It Dv __XSI_VISIBLE Ta Restricts the visibility of XOPEN Single Unix Standard version. 381Possible values are 500, 600, 700 or 800, corresponding to Issue 5, 6, 7, or 8 382of the Single Unix Standard. 383These are extra functions in addition to the normal POSIX ones. 384.It Dv __POSIX_VISIBLE Ta Make symbols associated with certain standards versions visible. 385Set to the value assigned to 386.Dv _POSIX_C_SOURCE 387by convention with 199009 for 388.St -p1003.1-88 389and 199209 390.St -p1003.1-90 . 391.It Dv __ISO_C_VISIBLE Ta The C level that's visible. 392Possible values include 1990, 1999, and 2011 for 393.St -isoC-90 , 394.St -isoC-99 395and 396.St -isoC-2011 397respectively. 398In the future, 2023 will be used for ISO C2023. 399.It Dv __BSD_VISIBLE Ta 1 if the 400.Fx 401extensions are visible, 0 otherwise. 402.It Dv __EXT1_VISIBLE Ta 1 if the 403.St -isoC-2011 404Appendix K 3.7.4.1 405extensions are visible, 0 otherwise. 406.El 407.Sh Supported C++ Environments 408.Fx 409supports C++11 and newer standards fully. 410.Bl -tag 411.It ISO/IEC 14882:1998 ("C++98") 412.Dv __cplusplus = 199711 413.Pp 414The first standardized version of C++. 415Unlike K \*(Am R support in C, compilers dropped support for versions of 416the language prior to C++98. 417.It ISO/IEC 14882:2003 ("C++03") 418.Dv __cplusplus = 199711 419.Pp 420Note, this is the same value as C++98. 421C++03 did not define a new value for 422.Dv __cplusplus . 423There is no way, at compile time, to detect the difference. 424The standard resolved a number of defect reports and slightly 425expanded value initialization. 426Most compilers support it the same as C++98. 427.It ISO/IEC 14882:2011 ("C++11") 428.Dv __cplusplus = 201103 429.It ISO/IEC 14882:2014 ("C++14") 430.Dv __cplusplus = 201402 431.It ISO/IEC 14882:2017 ("C++17") 432.Dv __cplusplus = 201703 433.It ISO/IEC 14882:2020 ("C++20") 434.Dv __cplusplus = 202002 435.It ISO/IEC 14882:2023 ("C++23") 436.Dv __cplusplus = 202302 437.El 438.Pp 439.Fx 440uses llvm project's libc++. 441However, they are removing support for C++ prior to C++11. 442While programs can still build with earlier environments for now, these changes 443mean that 444.Fl pedantic-errors 445cannot be reliably enabled for standards older than C++11. 446.Sh HISTORY 447.In sys/cdefs.h 448first appeared in 449.Bx 4.3 NET/2 . 450