/* $OpenBSD: namespace.h,v 1.7 2015/09/11 09:18:27 guenther Exp $ */ #ifndef _LIBC_NAMESPACE_H_ #define _LIBC_NAMESPACE_H_ /* * Copyright (c) 2015 Philip Guenther * * Permission to use, copy, modify, and distribute this software for any * purpose with or without fee is hereby granted, provided that the above * copyright notice and this permission notice appear in all copies. * * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */ /* * The goal: calls from inside libc to other libc functions should be via * identifiers that are of hidden visibility and--to avoid confusion--are * in the reserved namespace. By doing this these calls are protected * from overriding by applications and on many platforms can avoid creation * or use of GOT or PLT entries. I've chosen a prefix of underbar-C-underbar * ("_libc_") for this. These will not be declared directly; instead, the * gcc "asm labels" extension will be used rename the function. * * For syscalls which are cancellation points, such as wait4(), there * are identifiers that do not provide cancellation: * _libc_wait4 hidden alias, for use internal to libc only * _thread_sys_wait4 global name, for use outside libc only * ...and identifiers that do provide cancellation: * wait4 weak alias, for general use * _libc_wait4_cancel hidden alias, for use internal to libc only * Inside libc, the bare name ("wait4") binds to the version *without* * cancellation; the few times where cancellation is desired it can be * obtained by calling CANCEL(x) instead of just x. * * Some other calls need to be wrapped for reasons other than cancellation, * such as to provide functionality beyond the underlying syscall (e.g., * setlogin). For these, there are identifiers for the raw call, without * the wrapping: * _libc_setlogin hidden alias, for use internal to libc only * _thread_sys_setlogin global name, for use outside libc only * ...and identifiers that do provide the libc wrapping: * setlogin weak alias, for general use * _libc_setlogin_wrap hidden alias, for use internal to libc only * Inside libc, the bare name ("setlogin") binds to the wrapper; when the * raw version is necessary it can be obtained by calling HIDDEN(x) instead of * just x. * * For syscalls which are not cancellation points, such as getpid(), * the identifiers are just: * _libc_getpid hidden alias, for use internal to libc only * _thread_sys_getpid global name, for use outside libc only * getpid weak alias, for use outside libc only * * By using gcc's "asm label" extension, we can usually avoid having * to type those prefixes in the .h and .c files. However, for those * cases where a non-default binding is necessary we can use these macros * to get the desired identifier: * * CANCEL(x) * This expands to the internal, hidden name of a cancellation * wrapper: _libc_x_cancel. ex: CANCEL(fsync)(fd) * * WRAP(x) * This expands to the internal, hidden name of a non-cancellation * wrapper: _libc_x_wrap. ex: WRAP(sigpending)(set) * * * In order to actually set up the desired asm labels, we use these in * the internal .h files: * PROTO_NORMAL(x) Symbols used both internally and externally * This makes gcc convert use of x to use _libc_x instead * ex: PROTO_NORMAL(getpid) * * PROTO_STD_DEPRECATED(x) Standard C symbols that we don't want to use * This just marks the symbol as deprecated, with no renaming. * ex: PROTO_STD_DEPRECATED(strcpy) * * PROTO_DEPRECATED(x) Symbols not in ISO C that we don't want to use * This marks the symbol as both weak and deprecated, with no renaming * ex: PROTO_DEPRECATED(creat) * * PROTO_CANCEL(x) Functions that have cancellation wrappers * Like PROTO_NORMAL(x), but also declares _libc_x_cancel * ex: PROTO_CANCEL(wait4) * * PROTO_WRAP(x) Functions that have wrappers for other reasons * This makes gcc convert use of x to use _libc_x_wrap instead. * ex: PROTO_WRAP(setlogin) * * * Finally, to create the expected aliases, we use these in the .c files * where the definitions are: * DEF_STRONG(x) Symbols reserved to or specified by ISO C * This defines x as a strong alias for _libc_x; this must only * be used for symbols that are reserved by the C standard * (or reserved in the external identifier namespace). * Matches with PROTO_NORMAL() * ex: DEF_STRONG(fopen) * * DEF_WEAK(x) Symbols used internally and not in ISO C * This defines x as a weak alias for _libc_x * Matches with PROTO_NORMAL() * ex: DEF_WEAK(lseek) * * DEF_CANCEL(x) Symbols that have a cancellation wrapper * This defines x as a weak alias for _libc_x_cancel. * Matches with PROTO_CANCEL() * ex: DEF_CANCEL(read) * * DEF_WRAP(x) * This defines x as a weak alias for _libc_x_wrap. * Matches with PROTO_WRAP() * ex: DEF_WRAP(setlogin) * * DEF_SYS(x) * This defines _thread_sys_x as a strong alias for _libc_x. This should * only be needed for syscalls that have C instead of asm stubs. * Matches with PROTO_NORMAL(), PROTO_CANCEL(), or PROTO_WRAP() * ex: DEF_SYS(pread) * * MAKE_CLONE(dst, src) Symbols that are exact clones of other symbols * This declares _libc_dst as being the same type as dst, and makes * _libc_dst a strong, hidden alias for _libc_src. You still need to * DEF_STRONG(dst) or DEF_WEAK(dst) to alias dst itself * ex: MAKE_CLONE(SHA224Pad, SHA256Pad) */ #include /* for __dso_hidden and __{weak,strong}_alias */ #define HIDDEN(x) _libc_##x #define CANCEL(x) _libc_##x##_cancel #define WRAP(x) _libc_##x##_wrap #define HIDDEN_STRING(x) "_libc_" __STRING(x) #define WRAP_STRING(x) "_libc_" __STRING(x) "_wrap" #define PROTO_NORMAL(x) __dso_hidden typeof(x) x asm(HIDDEN_STRING(x)) #define PROTO_STD_DEPRECATED(x) typeof(x) x __attribute__((deprecated)) #define PROTO_DEPRECATED(x) typeof(x) x __attribute__((deprecated, weak)) #define PROTO_CANCEL(x) PROTO_NORMAL(x), CANCEL(x) #define PROTO_WRAP(x) __dso_hidden typeof(x) x asm(WRAP_STRING(x)) #define DEF_STRONG(x) __strong_alias(x, HIDDEN(x)) #define DEF_WEAK(x) __weak_alias(x, HIDDEN(x)) #define DEF_CANCEL(x) __weak_alias(x, CANCEL(x)) #define DEF_WRAP(x) __weak_alias(x, WRAP(x)) #define DEF_SYS(x) __strong_alias(_thread_sys_##x, HIDDEN(x)) #define MAKE_CLONE(dst, src) __dso_hidden typeof(dst) HIDDEN(dst) \ __attribute__((alias (HIDDEN_STRING(src)))) /* * gcc will generate calls to the functions below. * Declare and redirect them here so we always go * directly to our hidden aliases. */ #include void *memcpy(void *__restrict, const void *__restrict, __size_t); void *memset(void *, int, __size_t); void __stack_smash_handler(const char [], int __attribute__((__unused__))); PROTO_NORMAL(memcpy); PROTO_NORMAL(memset); PROTO_NORMAL(__stack_smash_handler); #endif /* _LIBC_NAMESPACE_H_ */