[clang] [libcxx] [libcxx]support freestanding libc++ (PR #208900)
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Sat Jul 11 03:06:43 PDT 2026
llvmorg-github-actions[bot] wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-libcxx
@llvm/pr-subscribers-backend-x86
Author: cqwrteur (trcrsired)
<details>
<summary>Changes</summary>
I am trying to add support fo freestanding C++. here is to check whether it passes CI.
---
Patch is 28.07 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/208900.diff
12 Files Affected:
- (added) clang/lib/Headers/errno.h (+164)
- (added) clang/lib/Headers/math.h (+29)
- (added) clang/lib/Headers/stdlib.h (+103)
- (added) clang/lib/Headers/string.h (+65)
- (added) clang/lib/Headers/wchar.h (+62)
- (modified) libcxx/CMakeLists.txt (+41-13)
- (modified) libcxx/include/__algorithm/sort.h (+4)
- (modified) libcxx/include/__config (+4)
- (modified) libcxx/include/__config_site.in (+3)
- (modified) libcxx/include/ctime (+10-5)
- (modified) libcxx/include/stdio.h (+5)
- (added) libcxx/test/libcxx/libcpp_freestanding.sh.cpp (+114)
``````````diff
diff --git a/clang/lib/Headers/errno.h b/clang/lib/Headers/errno.h
new file mode 100644
index 0000000000000..48fe84a9304ce
--- /dev/null
+++ b/clang/lib/Headers/errno.h
@@ -0,0 +1,164 @@
+/*===---- errno.h - Standard header for error numbers ---------------------===*\
+ *
+ * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+ * See https://llvm.org/LICENSE.txt for license information.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ *
+\*===----------------------------------------------------------------------===*/
+
+#ifndef __CLANG_ERRNO_H
+#define __CLANG_ERRNO_H
+
+/* If we're hosted, fall back to the system's errno.h, which might have
+ * additional definitions.
+ */
+#if __STDC_HOSTED__ && __has_include_next(<errno.h>)
+
+#include_next <errno.h>
+
+#else
+
+/* Adjusted to the linux asm/errno.h */
+#define EPERM 1 /* Operation not permitted */
+#define ENOENT 2 /* No such file or directory */
+#define ESRCH 3 /* No such process */
+#define EINTR 4 /* Interrupted system call */
+#define EIO 5 /* I/O error */
+#define ENXIO 6 /* No such device or address */
+#define E2BIG 7 /* Arg list too long */
+#define ENOEXEC 8 /* Exec format error */
+#define EBADF 9 /* Bad file number */
+#define ECHILD 10 /* No child processes */
+#define EAGAIN 11 /* Try again */
+#define ENOMEM 12 /* Out of memory */
+#define EACCES 13 /* Permission denied */
+#define EFAULT 14 /* Bad address */
+#define ENOTBLK 15 /* Block device required */
+#define EBUSY 16 /* Device or resource busy */
+#define EEXIST 17 /* File exists */
+#define EXDEV 18 /* Cross-device link */
+#define ENODEV 19 /* No such device */
+#define ENOTDIR 20 /* Not a directory */
+#define EISDIR 21 /* Is a directory */
+#define EINVAL 22 /* Invalid argument */
+#define ENFILE 23 /* File table overflow */
+#define EMFILE 24 /* Too many open files */
+#define ENOTTY 25 /* Not a typewriter */
+#define ETXTBSY 26 /* Text file busy */
+#define EFBIG 27 /* File too large */
+#define ENOSPC 28 /* No space left on device */
+#define ESPIPE 29 /* Illegal seek */
+#define EROFS 30 /* Read-only file system */
+#define EMLINK 31 /* Too many links */
+#define EPIPE 32 /* Broken pipe */
+#define EDOM 33 /* Math argument out of domain of func */
+#define ERANGE 34 /* Math result not representable */
+#define EDEADLK 35 /* Resource deadlock would occur */
+#define ENAMETOOLONG 36 /* File name too long */
+#define ENOLCK 37 /* No record locks available */
+#define ENOSYS 38 /* Function not implemented */
+#define ENOTEMPTY 39 /* Directory not empty */
+#define ELOOP 40 /* Too many symbolic links encountered */
+#define EWOULDBLOCK EAGAIN /* Operation would block */
+#define ENOMSG 42 /* No message of desired type */
+#define EIDRM 43 /* Identifier removed */
+#define ECHRNG 44 /* Channel number out of range */
+#define EL2NSYNC 45 /* Level 2 not synchronized */
+#define EL3HLT 46 /* Level 3 halted */
+#define EL3RST 47 /* Level 3 reset */
+#define ELNRNG 48 /* Link number out of range */
+#define EUNATCH 49 /* Protocol driver not attached */
+#define ENOCSI 50 /* No CSI structure available */
+#define EL2HLT 51 /* Level 2 halted */
+#define EBADE 52 /* Invalid exchange */
+#define EBADR 53 /* Invalid request descriptor */
+#define EXFULL 54 /* Exchange full */
+#define ENOANO 55 /* No anode */
+#define EBADRQC 56 /* Invalid request code */
+#define EBADSLT 57 /* Invalid slot */
+#define EDEADLOCK EDEADLK
+#define EBFONT 59 /* Bad font file format */
+#define EFTYPE EBFONT /* Inappropriate file type or format */
+#define ENOSTR 60 /* Device not a stream */
+#define ENODATA 61 /* No data available */
+#define ETIME 62 /* Timer expired */
+#define ENOSR 63 /* Out of streams resources */
+#define ENONET 64 /* Machine is not on the network */
+#define ENOPKG 65 /* Package not installed */
+#define EREMOTE 66 /* Object is remote */
+#define ENOLINK 67 /* Link has been severed */
+#define EADV 68 /* Advertise error */
+#define ESRMNT 69 /* Srmount error */
+#define ECOMM 70 /* Communication error on send */
+#define EPROTO 71 /* Protocol error */
+#define EMULTIHOP 72 /* Multihop attempted */
+#define EDOTDOT 73 /* RFS specific error */
+#define EBADMSG 74 /* Not a data message */
+#define EOVERFLOW 75 /* Value too large for defined data type */
+#define ENOTUNIQ 76 /* Name not unique on network */
+#define EBADFD 77 /* File descriptor in bad state */
+#define EREMCHG 78 /* Remote address changed */
+#define ELIBACC 79 /* Can not access a needed shared library */
+#define ELIBBAD 80 /* Accessing a corrupted shared library */
+#define ELIBSCN 81 /* .lib section in a.out corrupted */
+#define ELIBMAX 82 /* Attempting to link in too many shared libraries */
+#define ELIBEXEC 83 /* Cannot exec a shared library directly */
+#define EILSEQ 84 /* Illegal byte sequence */
+#define ERESTART 85 /* Interrupted system call should be restarted */
+#define ESTRPIPE 86 /* Streams pipe error */
+#define EUSERS 87 /* Too many users */
+#define ENOTSOCK 88 /* Socket operation on non-socket */
+#define EDESTADDRREQ 89 /* Destination address required */
+#define EMSGSIZE 90 /* Message too long */
+#define EPROTOTYPE 91 /* Protocol wrong type for socket */
+#define ENOPROTOOPT 92 /* Protocol not available */
+#define EPROTONOSUPPORT 93 /* Protocol not supported */
+#define ESOCKTNOSUPPORT 94 /* Socket type not supported */
+#define EOPNOTSUPP 95 /* Operation not supported on transport endpoint */
+#define EPFNOSUPPORT 96 /* Protocol family not supported */
+#define EAFNOSUPPORT 97 /* Address family not supported by protocol */
+#define EADDRINUSE 98 /* Address already in use */
+#define EADDRNOTAVAIL 99 /* Cannot assign requested address */
+#define ENETDOWN 100 /* Network is down */
+#define ENETUNREACH 101 /* Network is unreachable */
+#define ENETRESET 102 /* Network dropped connection because of reset */
+#define ECONNABORTED 103 /* Software caused connection abort */
+#define ECONNRESET 104 /* Connection reset by peer */
+#define ENOBUFS 105 /* No buffer space available */
+#define EISCONN 106 /* Transport endpoint is already connected */
+#define ENOTCONN 107 /* Transport endpoint is not connected */
+#define ESHUTDOWN 108 /* Cannot send after transport endpoint shutdown */
+#define ETOOMANYREFS 109 /* Too many references: cannot splice */
+#define ETIMEDOUT 110 /* Connection timed out */
+#define ECONNREFUSED 111 /* Connection refused */
+#define EHOSTDOWN 112 /* Host is down */
+#define EHOSTUNREACH 113 /* No route to host */
+#define EALREADY 114 /* Operation already in progress */
+#define EINPROGRESS 115 /* Operation now in progress */
+#define ESTALE 116 /* Stale NFS file handle */
+#define EUCLEAN 117 /* Structure needs cleaning */
+#define ENOTNAM 118 /* Not a XENIX named type file */
+#define ENAVAIL 119 /* No XENIX semaphores available */
+#define EISNAM 120 /* Is a named type file */
+#define EREMOTEIO 121 /* Remote I/O error */
+#define EDQUOT 122 /* Quota exceeded */
+#define ENOMEDIUM 123 /* No medium found */
+#define EMEDIUMTYPE 124 /* Wrong medium type */
+#define ECANCELED 125 /* Operation Canceled */
+#define ENOKEY 126 /* Required key not available */
+#define EKEYEXPIRED 127 /* Key has expired */
+#define EKEYREVOKED 128 /* Key has been revoked */
+#define EKEYREJECTED 129 /* Key was rejected by service */
+#define EOWNERDEAD 130 /* Owner died */
+#define ENOTRECOVERABLE 131 /* State not recoverable */
+#define ERFKILL 132 /* Operation not possible due to RF-kill */
+#define EHWPOISON 133 /* Memory page has hardware error */
+
+/* Widely known to be a synonym in Linux. */
+#define ENOTSUP EOPNOTSUPP
+
+#define __ELASTERROR 2000 /* Users can add values starting here */
+
+#endif
+
+#endif
diff --git a/clang/lib/Headers/math.h b/clang/lib/Headers/math.h
new file mode 100644
index 0000000000000..3e316c891a1bc
--- /dev/null
+++ b/clang/lib/Headers/math.h
@@ -0,0 +1,29 @@
+/*===---- math.h - Standard header for C math ----------------------------===*\
+ *
+ * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+ * See https://llvm.org/LICENSE.txt for license information.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ *
+\*===----------------------------------------------------------------------===*/
+
+#ifndef __CLANG_MATH_H
+#define __CLANG_MATH_H
+
+/* If we're hosted, fall back to the system's math.h, which might have
+ * additional definitions.
+ */
+#if __STDC_HOSTED__ && __has_include_next(<math.h>)
+
+#include_next <math.h>
+
+#else
+
+#define NAN __builtin_nanf("")
+#define INFINITY __builtin_inff()
+#define FP_NAN 0
+#define FP_INFINITE 1
+#define FP_ZERO 2
+#define FP_SUBNORMAL 3
+#define FP_NORMAL 4
+
+#endif
diff --git a/clang/lib/Headers/stdlib.h b/clang/lib/Headers/stdlib.h
new file mode 100644
index 0000000000000..db5fa08385f58
--- /dev/null
+++ b/clang/lib/Headers/stdlib.h
@@ -0,0 +1,103 @@
+/*===---- stdlib.h - Standard header for general utilities ----------------===*\
+ *
+ * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+ * See https://llvm.org/LICENSE.txt for license information.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ *
+\*===----------------------------------------------------------------------===*/
+
+#ifndef __CLANG_STDLIB_H
+#define __CLANG_STDLIB_H
+
+/* If we're hosted, fall back to the system's math.h, which might have
+ * additional definitions.
+ */
+#if __STDC_HOSTED__ && __has_include_next(<stdlib.h>)
+
+#include_next <stdlib.h>
+
+#else
+
+#include <stddef.h>
+#include <stdint.h>
+
+#ifndef EXIT_FAILURE
+#define EXIT_FAILURE 1 /* freestanding */
+#endif
+#ifndef EXIT_SUCCESS
+#define EXIT_SUCCESS 0 /* freestanding */
+#endif
+
+#ifndef __cplusplus
+extern "C" {
+#endif
+
+typedef struct {
+ int quot;
+ int rem;
+} div_t; /* freestanding */
+typedef struct {
+ long quot;
+ long rem;
+} ldiv_t; /* freestanding */
+typedef struct {
+ long long quot;
+ long long rem;
+} lldiv_t; /* freestanding */
+typedef struct {
+ intmax_t quot;
+ intmax_t rem;
+} imaxdiv_t; /* freestanding */
+
+/*
+We offer declarations for these C functions,
+leaving the implementations to be handled by users.
+*/
+
+// start and termination
+
+#ifndef __CLANG_STDLIB_NOEXCEPT
+#ifdef __cplusplus
+#if __cplusplus >= 201103L
+#define __CLANG_STDLIB_NOEXCEPT noexcept
+#else
+#define __CLANG_STDLIB_NOEXCEPT throw()
+#endif
+#else
+#define __CLANG_STDLIB_NOEXCEPT
+#endif
+#endif
+
+[[noreturn]] void abort() __CLANG_STDLIB_NOEXCEPT; /* freestanding */
+int atexit(void (*)()) __CLANG_STDLIB_NOEXCEPT; /* freestanding */
+int at_quick_exit(void (*)()) __CLANG_STDLIB_NOEXCEPT; /* freestanding */
+[[noreturn]] void exit(int); /* freestanding */
+[[noreturn]] void _Exit(int) __CLANG_STDLIB_NOEXCEPT; /* freestanding */
+[[noreturn]] void quick_exit(int) __CLANG_STDLIB_NOEXCEPT; /* freestanding */
+
+#undef __CLANG_STDLIB_NOEXCEPT
+
+// C standard library algorithms
+void *bsearch(const void *, const void *, size_t, size_t,
+ int (*)(const void *, const void *)); /* freestanding */
+void qsort(void *, size_t, size_t,
+ int (*)(const void *, const void *)); /* freestanding */
+
+// absolute values
+int abs(int j); /* freestanding */
+long int abs(long int j); /* freestanding */
+long long int abs(long long int j); /* freestanding */
+long int labs(long int j); /* freestanding */
+long long int llabs(long long int j); /* freestanding */
+
+div_t div(int, int); /* freestanding */
+ldiv_t div(long int, long int); /* freestanding */
+lldiv_t div(long long int, long long int); /* freestanding */
+ldiv_t ldiv(long int, long int); /* freestanding */
+lldiv_t lldiv(long long int, long long int); /* freestanding */
+
+#ifndef __cplusplus
+}
+#endif
+
+#endif
diff --git a/clang/lib/Headers/string.h b/clang/lib/Headers/string.h
new file mode 100644
index 0000000000000..c256b3e35a95b
--- /dev/null
+++ b/clang/lib/Headers/string.h
@@ -0,0 +1,65 @@
+/*===---- string.h - Standard header for null-terminated string -----------===*\
+ *
+ * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+ * See https://llvm.org/LICENSE.txt for license information.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ *
+\*===----------------------------------------------------------------------===*/
+
+#ifndef __CLANG_STRING_H
+#define __CLANG_STRING_H
+
+/* If we're hosted, fall back to the system's string.h, which might have
+ * additional definitions.
+ */
+
+#if __STDC_HOSTED__ && __has_include_next(<string.h>)
+
+#include_next <string.h>
+
+#else
+
+#include <stddef.h>
+
+#ifndef __cplusplus
+extern "C" {
+#endif
+
+/*
+We offer declarations for these C functions,
+leaving the implementations to be handled by users.
+*/
+
+void *memcpy(void *, const void *, size_t); /* freestanding */
+void *memmove(void *, const void *, size_t); /* freestanding */
+char *strcpy(char *, const char *); /* freestanding */
+char *strncpy(char *, const char *, size_t); /* freestanding */
+char *strcat(char *, const char *); /* freestanding */
+char *strncat(char *, const char *, size_t); /* freestanding */
+int memcmp(const void *, const void *, size_t); /* freestanding */
+int strcmp(const char *, const char *); /* freestanding */
+int strncmp(const char *, const char *, size_t); /* freestanding */
+const void *memchr(const void *, int, size_t); /* freestanding */
+void *memchr(void *, int, size_t); /* freestanding */
+const char *strchr(const char *, int); /* freestanding */
+char *strchr(char *, int); /* freestanding */
+size_t strcspn(const char *, const char *); /* freestanding */
+const char *strpbrk(const char *, const char *); /* freestanding */
+char *strpbrk(char *, const char *); /* freestanding */
+const char *strrchr(const char *, int); /* freestanding */
+char *strrchr(char *, int); /* freestanding */
+size_t strspn(const char *, const char *); /* freestanding */
+const char *strstr(const char *, const char *); /* freestanding */
+char *strstr(char *, const char *); /* freestanding */
+char *strtok(char *, const char *); /* freestanding */
+void *memset(void *, int, size_t); /* freestanding */
+size_t strlen(const char *); /* freestanding */
+void *memset_explicit(void *, int, size_t); /* freestanding */
+
+#ifndef __cplusplus
+}
+#endif
+
+#endif
+
+#endif
diff --git a/clang/lib/Headers/wchar.h b/clang/lib/Headers/wchar.h
new file mode 100644
index 0000000000000..ca232c0cd6356
--- /dev/null
+++ b/clang/lib/Headers/wchar.h
@@ -0,0 +1,62 @@
+/*===---- wchar.h - Standard header for wide character types --------------===*\
+ *
+ * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+ * See https://llvm.org/LICENSE.txt for license information.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ *
+\*===----------------------------------------------------------------------===*/
+
+#ifndef __CLANG_WCHAR_H
+#define __CLANG_WCHAR_H
+
+/* If we're hosted, fall back to the system's wchar.h, which might have
+ * additional definitions.
+ */
+
+#if __STDC_HOSTED__ && __has_include_next(<wchar.h>)
+
+#include_next <wchar.h>
+
+#else
+
+#ifndef __cplusplus
+extern "C" {
+#endif
+
+/*
+We offer declarations for these C functions,
+leaving the implementations to be handled by users.
+*/
+
+wchar_t *wcscpy(wchar_t *, const wchar_t *); /* freestanding */
+wchar_t *wcsncpy(wchar_t *, const wchar_t *, size_t); /* freestanding */
+wchar_t *wmemcpy(wchar_t *, const wchar_t *, size_t); /* freestanding */
+wchar_t *wmemmove(wchar_t *, const wchar_t *, size_t); /* freestanding */
+wchar_t *wcscat(wchar_t *, const wchar_t *); /* freestanding */
+wchar_t *wcsncat(wchar_t *, const wchar_t *, size_t); /* freestanding */
+int wcscmp(const wchar_t *, const wchar_t *); /* freestanding */
+int wcsncmp(const wchar_t *, const wchar_t *, size_t); /* freestanding */
+int wmemcmp(const wchar_t *, const wchar_t *, size_t); /* freestanding */
+const wchar_t *wcschr(const wchar_t *, wchar_t); /* freestanding */
+wchar_t *wcschr(wchar_t *, wchar_t); /* freestanding */
+size_t wcscspn(const wchar_t *, const wchar_t *); /* freestanding */
+const wchar_t *wcspbrk(const wchar_t *, const wchar_t *); /* freestanding */
+wchar_t *wcspbrk(wchar_t *, const wchar_t *); /* freestanding */
+const wchar_t *wcsrchr(const wchar_t *, wchar_t); /* freestanding */
+wchar_t *wcsrchr(wchar_t *, wchar_t); /* freestanding */
+size_t wcsspn(const wchar_t *, const wchar_t *); /* freestanding */
+const wchar_t *wcsstr(const wchar_t *, const wchar_t *); /* freestanding */
+wchar_t *wcsstr(wchar_t *, const wchar_t *); /* freestanding */
+wchar_t *wcstok(wchar_t *, const wchar_t *, wchar_t **); /* freestanding */
+const wchar_t *wmemchr(const wchar_t *, wchar_t, size_t); /* freestanding */
+wchar_t *wmemchr(wchar_t *, wchar_t, size_t); /* freestanding */
+size_t wcslen(const wchar_t *); /* freestanding */
+wchar_t *wmemset(wchar_t *, wchar_t, size_t); /* freestanding */
+
+#ifndef __cplusplus
+}
+#endif
+
+#endif
+
+#endif
diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
index 31aaf2977a9af..b92ff4b07777a 100644
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -156,21 +156,43 @@ option(LIBCXX_ENABLE_VENDOR_AVAILABILITY_ANNOTATIONS
the shared library they shipped should turn this on and see `include/__configuration/availability.h`
for more details." OFF)
-if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
- set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-shared-gcc.cfg.in")
-elseif(MINGW)
- set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-mingw.cfg.in")
-elseif(WIN32) # clang-cl
- if (LIBCXX_ENABLE_SHARED)
- set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-shared-clangcl.cfg.in")
- else()
- set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-static-clangcl.cfg.in")
- endif()
+option(LIBCXX_FREESTANDING
+ "Build libc++ in freestanding mode. This toggle allows the libc++ to work without libc
+ for environments like operating systems kernels or embedded systems." OFF)
+
+if (LIBCXX_FREESTANDING)
+ set(LIBCXX_ENABLE_FILESYSTEM OFF)
+ set(LIBCXX_ENABLE_RANDOM_DEVICE OFF)
+ set(LIBCXX_ENABLE_PARALLEL_ALGORITHMS OFF)
+ set(LIBCXX_ENABLE_SHARED OFF)
+ set(LIBCXX_ENABLE_STATIC OFF)
+ set(CMAKE_ASM_COMPILER_WORKS ON)
+ set(CMAKE_C_COMPILER_WORKS ON)
+ set(CMAKE_CXX_COMPILER_WORKS ON)
+ set(LIBCXX_ENABLE_LOCALIZATION OFF)
+ set(LIBCXX_ENABLE_FSTREAM OFF)
+ set(LIBCXX_ENABLE_STD_MODULES OFF)
+ set(LIBCXX_INCLUDE_BENCHMARKS OFF)
+ set(LIBCXX_ENABLE_WIDE_CHARACTERS OFF)
+ set(LIBCXX_ENABLE_TIME_ZONE_DATABASE OFF)
+ set(LIBCXX_INCLUDE_TESTS Off)
else()
- if (LIBCXX_ENABLE_SHARED)
- set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-shared.cfg.in")
+ if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
+ set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-shared-gcc.cfg.in")
+ elseif(MINGW)
+ set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-mingw.cfg.in")
+ elseif(WIN32) # clang-cl
+ if (LIBCXX_ENABLE_SHARED)
...
[truncated]
``````````
</details>
https://github.com/llvm/llvm-project/pull/208900
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