Nov 27, 2016 Alternatively, you could use the explicity linking options to link the static library (-L switch specifies the static library path and -l followed by the name of the static library): 1 gcc -o test.out test.c -L. Oct 17, 2016 ssion While understanding why syscall.Read is 2x slower on darwin/amd64, I found out that, contrary to popular belief, the slowdown is not due to the migration to use libSystem.dylib instead of direct SYSCALLs, i.e., CL 141639 (and #17490), but due to a subtle change introduced in CL 141639. Previously, syscall.Read used syscall.Syscall(SYS.
Name
libc - overview of standard C libraries on Linux
Description
The term 'libc' is commonly used as a shorthand for the 'standard C library', a library of standard functions that can be used by all C programs (andsometimes by programs in other languages). Because of some history (see below), use of the term 'libc' to refer to the standard C library is somewhat ambiguouson Linux.
glibc
By far the most widely used C library on Linux is the GNU C Library often referred to as glibcMacos Cl Link For Libc 1
. This is the C library that is nowadays used in allmajor Linux distributions. It is also the C library whose details are documented in the relevant pages of the man-pages project (primarily in Section 3of the manual). Documentation of glibc is also available in the glibc manual, available via the command info libc. Release 1.0 of glibc was made inSeptember 1992. (There were earlier 0.x releases.) The next major release of glibc was 2.0, at the beginning of 1997.The pathname /lib/libc.so.6 (or something similar) is normally a symbolic link that points to the location of the glibc library, and executing thispathname will cause glibc to display various information about the version installed on your system.
Linux libc
- man-pages no longer takescare to document Linux libc details. Nevertheless, the history is visible in vestiges of information about Linux libc that remain in some manual pages, inparticular, references to libc4 and libc5.)
Other C libraries
Default: ON
Toggle the installation of the libc++ headers.
LIBCXX_ENABLE_ASSERTIONS:BOOL¶Default: OFF
Build libc++ with assertions enabled.
LIBCXX_BUILD_32_BITS:BOOL¶Default: OFF
Build libc++ as a 32 bit library. Also see LLVM_BUILD_32_BITS.
LIBCXX_ENABLE_SHARED:BOOL¶Default: ON
Build libc++ as a shared library. Either LIBCXX_ENABLE_SHARED orLIBCXX_ENABLE_STATIC has to be enabled.
LIBCXX_ENABLE_STATIC:BOOL¶Default: ON
Macos Cl Link For Libc 7
Build libc++ as a static library. Either LIBCXX_ENABLE_SHARED orLIBCXX_ENABLE_STATIC has to be enabled.
LIBCXX_LIBDIR_SUFFIX:STRING¶Extra suffix to append to the directory where libraries are to be installed.This option overrides LLVM_LIBDIR_SUFFIX.
LIBCXX_INSTALL_PREFIX:STRING¶Default: '
Define libc++ destination prefix.
LIBCXX_HERMETIC_STATIC_LIBRARY:BOOL¶Default: OFF
Do not export any symbols from the static libc++ library.This is useful when the static libc++ library is being linked into sharedlibraries that may be used in with other shared libraries that use differentC++ library. We want to avoid exporting any libc++ symbols in that case.
LIBCXX_ENABLE_FILESYSTEM:BOOL¶Default: ON except on Windows.
This option can be used to enable or disable the filesystem components onplatforms that may not support them. For example on Windows.
LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY:BOOL¶Default: ON
Build and test libc++experimental.a.
LIBCXX_INSTALL_EXPERIMENTAL_LIBRARY:BOOL¶Default: LIBCXX_ENABLE_EXPERIMENTAL_LIBRARYANDLIBCXX_INSTALL_LIBRARY
Install libc++experimental.a alongside libc++.
LIBCXX_CXX_ABI:STRING¶Macos Cl Link For Libc 5
Values: none, libcxxabi, libcxxrt, libstdc++, libsupc++.
Select the ABI library to build libc++ against.
LIBCXX_CXX_ABI_INCLUDE_PATHS:PATHS¶Provide additional search paths for the ABI library headers.
LIBCXX_CXX_ABI_LIBRARY_PATH:PATH¶Provide the path to the ABI library that libc++ should link against.
LIBCXX_ENABLE_STATIC_ABI_LIBRARY:BOOL¶Default: OFF
If this option is enabled, libc++ will try and link the selected ABI librarystatically.
LIBCXX_ENABLE_ABI_LINKER_SCRIPT:BOOL¶Default: ON by default on UNIX platforms other than Apple unless‘LIBCXX_ENABLE_STATIC_ABI_LIBRARY’ is ON. Otherwise the default value is OFF.
This option generate and installs a linker script as libc++.so whichlinks the correct ABI library.
LIBCXXABI_USE_LLVM_UNWINDER:BOOL¶Default: OFF
Build and use the LLVM unwinder. Note: This option can only be used whenlibc++abi is the C++ ABI library used.
LIBCXX_ENABLE_EXCEPTIONS:BOOL¶Default: ON
Build libc++ with exception support.
LIBCXX_ENABLE_RTTI:BOOL¶Default: ON
Build libc++ with run time type information.
LIBCXX_INCLUDE_TESTS:BOOL¶Default: ON (or value of LLVM_INCLUDE_DIR)
Build the libc++ tests.
LIBCXX_INCLUDE_BENCHMARKS:BOOL¶Default: ON
Build the libc++ benchmark tests and the Google Benchmark library neededto support them.
LIBCXX_BENCHMARK_TEST_ARGS:STRING¶Default: --benchmark_min_time=0.01
A semicolon list of arguments to pass when running the libc++ benchmarks using thecheck-cxx-benchmarks rule. By default we run the benchmarks for a very short amount of time,since the primary use of check-cxx-benchmarks is to get test and sanitizer coverage, not toget accurate measurements.
LIBCXX_BENCHMARK_NATIVE_STDLIB:STRING¶Default:: '
Values:: libc++, libstdc++
Build the libc++ benchmark tests and Google Benchmark library against thespecified standard library on the platform. On Linux this can be used tocompare libc++ to libstdc++ by building the benchmark tests against bothstandard libraries.
LIBCXX_BENCHMARK_NATIVE_GCC_TOOLCHAIN:STRING¶Use the specified GCC toolchain and standard library when building the nativestdlib benchmark tests.
LIBCXX_HIDE_FROM_ABI_PER_TU_BY_DEFAULT:BOOL¶Default: OFF
Pick the default for whether to constrain ABI-unstable symbols toeach individual translation unit. This setting controls whether_LIBCPP_HIDE_FROM_ABI_PER_TU_BY_DEFAULT is defined by default –see the documentation of that macro for details.
The following options allow building libc++ for a different ABI version.
LIBCXX_ABI_VERSION:STRING¶Default: 1
Defines the target ABI version of libc++.
LIBCXX_ABI_UNSTABLE:BOOL¶Default: OFF
Build the “unstable” ABI version of libc++. Includes all ABI changing featureson top of the current stable version.
LIBCXX_ABI_NAMESPACE:STRING¶Default: __n where n is the current ABI version.
This option defines the name of the inline ABI versioning namespace. It can be used for buildingcustom versions of libc++ with unique symbol names in order to prevent conflicts or ODR issueswith other libc++ versions.
Warning
When providing a custom namespace, it’s the users responsibility to ensure the name won’t causeconflicts with other names defined by libc++, both now and in the future. In particular, inlinenamespaces of the form __[0-9]+ are strictly reserved by libc++ and may not be used by users.Doing otherwise could cause conflicts and hinder libc++ ABI evolution.
LIBCXX_ABI_DEFINES:STRING¶Default: '
A semicolon-separated list of ABI macros to persist in the site config header.See include/__config for the list of ABI macros.
LIBCXX_TYPEINFO_COMPARISON_IMPLEMENTATION¶Default: None, which lets the library figure out which implementationto use based on the object format.
This setting defines what implementation to use for comparing typeinfo objects.There are two main implementations, which differ on whether we make the assumptionthat type info names for a type have been fully merged are unique across the entireprogram. This may not be the case for libraries built with -Bsymbolic or due tocompiler or linker bugs (Ex. llvm.org/PR37398).
When the value is set to 1, we assume that typeinfos are unique across thewhole program, and typeinfo comparisons compare only the pointer value.
When the value is set to 2, we do not assume that typeinfos are unique acrossthe whole program. We first compare the pointers, and then use strcmp on thetypeinfo names as a fallback.
LLVM_LIBDIR_SUFFIX:STRING¶Extra suffix to append to the directory where libraries are to beinstalled. On a 64-bit architecture, one could use -DLLVM_LIBDIR_SUFFIX=64to install libraries to /usr/lib64.
LLVM_BUILD_32_BITS:BOOL¶Build 32-bits executables and libraries on 64-bits systems. This option isavailable only on some 64-bits Unix systems. Defaults to OFF.
LLVM_LIT_ARGS:STRING¶Arguments given to lit. makecheck and makeclang-test are affected.By default, '-sv--no-progress-bar' on Visual C++ and Xcode, '-sv' onothers.
You will need libstdc++ in order to provide libsupc++.
Figure out where the libsupc++ headers are on your system. On Ubuntu thisis /usr/include/c++/<version> and /usr/include/c++/<version>/<target-triple>
You can also figure this out by running
Note that the first two entries happen to be what we are looking for. Thismay not be correct on other platforms.
We can now run CMake:
You can also substitute -DLIBCXX_CXX_ABI=libsupc++above, which will cause the library to be linked to libsupc++ insteadof libstdc++, but this is only recommended if you know that you willnever need to link against libstdc++ in the same executable as libc++.GCC ships libsupc++ separately but only as a static library. If aprogram also needs to link against libstdc++, it will provide itsown copy of libsupc++ and this can lead to subtle problems.
You can now run clang with -stdlib=libc++.
You will need to keep the source tree of libcxxrt availableon your build machine and your copy of the libcxxrt shared library mustbe placed where your linker will find it.
We can now run CMake like:
Unfortunately you can’t simply run clang with “-stdlib=libc++” at this point, asclang is set up to link for libc++ linked to libsupc++. To get around thisyou’ll have to set up your linker yourself (or patch clang). For example,
Alternately, you could just add libcxxrt to your libraries list, which in mostsituations will give the same result:
Warning
This is not recommended in almost all cases.
These instructions should only be used when you can’t install your ABI library.
Normally you must link libc++ against a ABI shared library that thelinker can find. If you want to build and test libc++ against an ABIlibrary not in the linker’s path you need to set-DLIBCXX_CXX_ABI_LIBRARY_PATH=/path/to/abi/lib when configuring CMake.
An example build using libc++abi would look like:
When testing libc++ LIT will automatically link against the proper ABIlibrary.