


CLANG(1)            Clang Tools Documentation            CLANG(1)


NAME
       clang - the Clang C and Objective-C compiler

SYNOPSIS
       clang [-c|-S|-E] -std=standard -g
         [-O0|-O1|-O2|-Os|-O3|-O4]
         -Wwarnings... -pedantic
         -Idir... -Ldir...
         -Dmacro[=defn]
         -ffeature-option...
         -mmachine-option...
         -o output-file
         input-filenames

DESCRIPTION
       clang is a C and Objective-C compiler which encompasses preprocessing,
       parsing, optimization, code generation, assembly, and linking.
       Depending on which high-level mode setting is passed, Clang will stop
       before doing a full link.  While Clang is highly integrated, it is
       important to understand the stages of compilation, to understand how to
       invoke it.  These stages are:

       Driver
           The clang executable is actually a small driver which controls the
           overall execution of other tools such as the compiler, assembler
           and linker.  Typically you do not need to interact with the driver,
           but you transparently use it to run the other tools.

       Preprocessing
           This stage handles tokenization of the input source file, macro
           expansion, #include expansion and handling of other preprocessor
           directives.  The output of this stage is typically called a ".i"
           (for C) or ".mi" (for Objective-C) file.

       Parsing and Semantic Analysis
           This stage parses the input file, translating preprocessor tokens
           into a parse tree.  Once in the form of a parser tree, it applies
           semantic analysis to compute types for expressions as well and
           determine whether the code is well formed. This stage is
           responsible for generating most of the compiler warnings as well as
           parse errors.  The output of this stage is an "Abstract Syntax
           Tree" (AST).

       Code Generation and Optimization
           This stage translates an AST into low-level intermediate code
           (known as "LLVM IR") and ultimately to machine code.  This phase is
           responsible for optimizing the generated code and handling target-
           specfic code generation.  The output of this stage is typically
           called a ".s" file or "assembly" file.

           Clang also supports the use of an integrated assembler, in which
           the code generator produces object files directly. This avoids the
           overhead of generating the ".s" file and of calling the target
           assembler.



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       Assembler
           This stage runs the target assembler to translate the output of the
           compiler into a target object file.  The output of this stage is
           typically called a ".o" file or "object" file.

       Linker
           This stage runs the target linker to merge multiple object files
           into an executable or dynamic library.  The output of this stage is
           typically called an "a.out", ".dylib" or ".so" file.

       The Clang compiler supports a large number of options to control each
       of these stages.  In addition to compilation of code, Clang also
       supports other tools:

       Clang Static Analyzer

       The Clang Static Analyzer is a tool that scans source code to try to
       find bugs though code analysis.  This tool uses many parts of Clang and
       is built into the same driver.

OPTIONS
   Stage Selection Options
       -E  Run the preprocessor stage.

       -fsyntax-only
           Run the preprocessor, parser and type checking stages.

       -S  Run the previous stages as well as LLVM generation and optimization
           stages and target-specific code generation, producing an assembly
           file.

       -c  Run all of the above, plus the assembler, generating a target ".o"
           object file.

       no stage selection option
           If no stage selection option is specified, all stages above are
           run, and the linker is run to combine the results into an
           executable or shared library.

       --analyze
           Run the Clang Static Analyzer.

   Language Selection and Mode Options
       -x language
           Treat subsequent input files as having type language.

       -std=language
           Specify the language standard to compile for.

       -ansi
           Same as -std=c89.

       -ObjC++
           Treat source input files as Objective-C++ inputs.



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       -ObjC
           Treat source input files as Objective-C inputs.

       -trigraphs
           Enable trigraphs.

       -ffreestanding
           Indicate that the file should be compiled for a freestanding, not a
           hosted, environment.

       -fno-builtin
           Disable special handling and optimizations of builtin functions
           like strlen and malloc.

       -fmath-errno
           Indicate that math functions should be treated as updating errno.

       -fpascal-strings
           Enable support for Pascal-style strings with "\pfoo".

       -fms-extensions
           Enable support for Microsoft extensions.

       -fborland-extensions
           Enable support for Borland extensions.

       -fwritable-strings
           Make all string literals default to writable.  This disables
           uniquing of strings and other optimizations.

       -flax-vector-conversions
           Allow loose type checking rules for implicit vector conversions.

       -fblocks
           Enable the "Blocks" language feature.

       -fobjc-gc-only
           Indicate that Objective-C code should be compiled in GC-only mode,
           which only works when Objective-C Garbage Collection is enabled.

       -fobjc-gc
           Indicate that Objective-C code should be compiled in hybrid-GC
           mode, which works with both GC and non-GC mode.

   Target Selection Options
       Clang fully supports cross compilation as an inherent part of its
       design.  Depending on how your version of Clang is configured, it may
       have support for a number of cross compilers, or may only support a
       native target.

       -arch architecture
           Specify the architecture to build for.





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       -mmacosx-version-min=version
           When building for Mac OS/X, specify the minimum version supported
           by your application.

       -miphoneos-version-min
           When building for iPhone OS, specify the minimum version supported
           by your application.

       -march=cpu
           Specify that Clang should generate code for a specific processor
           family member and later.  For example, if you specify -march=i486,
           the compiler is allowed to generate instructions that are valid on
           i486 and later processors, but which may not exist on earlier ones.

   Code Generation Options
       -O0 -O1 -O2 -Os -O3 -O4
           Specify which optimization level to use.  -O0 means "no
           optimization": this level compiles the fastest and generates the
           most debuggable code.  -O2 is a moderate level of optimization
           which enables most optimizations.  -Os is like -O2 with extra
           optimizations to reduce code size.  -O3 is like -O2, except that it
           enables optimizations that take longer to perform or that may
           generate larger code (in an attempt to make the program run
           faster).  On supported platforms, -O4 enables link-time
           optimization; object files are stored in the LLVM bitcode file
           format and whole program optimization is done at link time. -O1 is
           somewhere between -O0 and -O2.

       -g  Generate debug information.  Note that Clang debug information
           works best at -O0.  At higher optimization levels, only line number
           information is currently available.

       -fexceptions
           Enable generation of unwind information, this allows exceptions to
           be thrown through Clang compiled stack frames.  This is on by
           default in x86-64.

       -ftrapv
           Generate code to catch integer overflow errors.  Signed integer
           overflow is undefined in C, with this flag, extra code is generated
           to detect this and abort when it happens.

       -fvisibility
           This flag sets the default visibility level.

       -fcommon
           This flag specifies that variables without initializers get common
           linkage.  It can be disabled with -fno-common.

       -flto -emit-llvm
           Generate output files in LLVM formats, suitable for link time
           optimization. When used with -S this generates LLVM intermediate
           language assembly files, otherwise this generates LLVM bitcode
           format object files (which may be passed to the linker depending on



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           the stage selection options).

   Driver Options
       -###
           Print the commands to run for this compilation.

       --help
           Display available options.

       -Qunused-arguments
           Don't emit warning for unused driver arguments.

       -Wa,args
           Pass the comma separated arguments in args to the assembler.

       -Wl,args
           Pass the comma separated arguments in args to the linker.

       -Wp,args
           Pass the comma separated arguments in args to the preprocessor.

       -Xanalyzer arg
           Pass arg to the static analyzer.

       -Xassembler arg
           Pass arg to the assembler.

       -Xclang arg
           Pass arg to the clang compiler frontend.

       -Xlinker arg
           Pass arg to the linker.

       -mllvm arg
           Pass arg to the LLVM backend.

       -Xpreprocessor arg
           Pass arg to the preprocessor.

       -o file
           Write output to file.

       -print-file-name=file
           Print the full library path of file.

       -print-libgcc-file-name
           Print the library path for "libgcc.a".

       -print-prog-name=name
           Print the full program path of name.

       -print-search-dirs
           Print the paths used for finding libraries and programs.




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       -save-temps
           Save intermediate compilation results.

       -integrated-as -no-integrated-as
           Used to enable and disable, respectively, the use of the integrated
           assembler. Whether the integrated assembler is on by default is
           target dependent.

       -time
           Time individual commands.

       -ftime-report
           Print timing summary of each stage of compilation.

       -v  Show commands to run and use verbose output.

   Diagnostics Options
       -fshow-column -fshow-source-location -fcaret-diagnostics
       -fdiagnostics-fixit-info -fdiagnostics-parseable-fixits
       -fdiagnostics-print-source-range-info -fprint-source-range-info
       -fdiagnostics-show-option -fmessage-length
           These options control how Clang prints out information about
           diagnostics (errors and warnings).  Please see the Clang User's
           Manual for more information.

   Preprocessor Options
       -Dmacroname=value
           Adds an implicit #define into the predefines buffer which is read
           before the source file is preprocessed.

       -Umacroname
           Adds an implicit #undef into the predefines buffer which is read
           before the source file is preprocessed.

       -include filename
           Adds an implicit #include into the predefines buffer which is read
           before the source file is preprocessed.

       -Idirectory
           Add the specified directory to the search path for include files.

       -Fdirectory
           Add the specified directory to the search path for framework
           include files.

       -nostdinc
           Do not search the standard system directories for include files.

       -nobuiltininc
           Do not search clang's builtin directory for include files.

ENVIRONMENT
       TMPDIR, TEMP, TMP
           These environment variables are checked, in order, for the location



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           to write temporary files used during the compilation process.

       CPATH
           If this environment variable is present, it is treated as a
           delimited list of paths to be added to the default system include
           path list. The delimiter is the platform dependent delimitor, as
           used in the PATH environment variable.

           Empty components in the environment variable are ignored.

       C_INCLUDE_PATH, OBJC_INCLUDE_PATH, CPLUS_INCLUDE_PATH,
       OBJCPLUS_INCLUDE_PATH
           These environment variables specify additional paths, as for CPATH,
           which are only used when processing the appropriate language.

       MACOSX_DEPLOYMENT_TARGET
           If -mmacosx-version-min is unspecified, the default deployment
           target is read from this environment variable.  This option only
           affects darwin targets.

BUGS
       To report bugs, please visit <http://llvm.org/bugs/>.  Most bug reports
       should include preprocessed source files (use the -E option) and the
       full output of the compiler, along with information to reproduce.

SEE ALSO
        as(1), ld(1)

AUTHOR
       Maintained by the Clang / LLVM Team (<http://clang.llvm.org>).



























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