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Updated: Wednesday, July 27, 2022

clang (1)


clang - C compiler


clang [options] filename ...


CLANG(1)                             Clang                            CLANG(1)

       clang - the Clang C, C++, and Objective-C compiler

       clang [options] filename ...

       clang  is  a C, C++, and Objective-C compiler which encompasses prepro-
       cessing, 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

              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),  ".ii"  (for  C++), ".mi" (for Objective-C), or ".mii"
              (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 parse 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-specific  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 tar-
              get 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.

       Clang Static Analyzer

       The  Clang  Static  Analyzer is a tool that scans source code to try to
       find bugs through code analysis.  This tool uses many  parts  of  Clang
       and    is    built    into    the   same   driver.    Please   see   <-
       https://clang-analyzer.llvm.org> for more details on  how  to  use  the
       static analyzer.

   Stage Selection Options
       -E     Run the preprocessor stage.

              Run the preprocessor, parser and type checking stages.

       -S     Run the previous stages as well as LLVM generation and optimiza-
              tion 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 exe-
              cutable or shared library.

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

              Specify the language standard to compile for.

              Supported values for the C language are:

                     ISO C 1990

                     ISO C 1990 with amendment 1

                     ISO C 1990 with GNU extensions

                     ISO C 1999

                     ISO C 1999 with GNU extensions

                     ISO C 2011

                     ISO C 2011 with GNU extensions

                     ISO C 2017

                     ISO C 2017 with GNU extensions

              The default C language standard is gnu17, except on  PS4,  where
              it is gnu99.

              Supported values for the C++ language are:

                     ISO C++ 1998 with amendments

                     ISO C++ 1998 with amendments and GNU extensions

                     ISO C++ 2011 with amendments

                     ISO C++ 2011 with amendments and GNU extensions

                     ISO C++ 2014 with amendments

                     ISO C++ 2014 with amendments and GNU extensions

                     ISO C++ 2017 with amendments

                     ISO C++ 2017 with amendments and GNU extensions

                     Working draft for ISO C++ 2020

                     Working draft for ISO C++ 2020 with GNU extensions

              The default C++ language standard is gnu++14.

              Supported values for the OpenCL language are:

                     OpenCL 1.0

                     OpenCL 1.1

                     OpenCL 1.2

                     OpenCL 2.0

              The default OpenCL language standard is cl1.0.

              Supported values for the CUDA language are:

                     NVIDIA CUDA(tm)

              Specify  the  C++ standard library to use; supported options are
              libstdc++ and libc++. If not specified, platform default will be

              Specify  the  compiler runtime library to use; supported options
              are libgcc and compiler-rt. If not specified,  platform  default
              will be used.

       -ansi  Same as -std=c89.

       -ObjC, -ObjC++
              Treat  source  input  files as Objective-C and Object-C++ inputs

              Enable trigraphs.

              Indicate that the file should be compiled  for  a  freestanding,
              not  a hosted, environment. Note that it is assumed that a free-
              standing environment will additionally provide memcpy,  memmove,
              memset and memcmp implementations, as these are needed for effi-
              cient codegen for many programs.

              Disable special handling and optimizations of builtin  functions
              like strlen() and malloc().

              Indicate  that  math  functions  should  be  treated as updating

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

              Enable support for Microsoft extensions.

              Set _MSC_VER. Defaults to 1300 on Windows. Not set otherwise.

              Enable support for Borland extensions.

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

       -flax-vector-conversions,              -flax-vector-conversions=<kind>,
              Allow loose type checking rules for implicit vector conversions.
              Possible values of <kind>:

              o none: allow no implicit conversions between vectors

              o integer:  allow  implicit  bitcasts between integer vectors of
                the same overall bit-width

              o all: allow implicit bitcasts between any vectors of  the  same
                overall bit-width

              <kind> defaults to integer if unspecified.

              Enable the "Blocks" language feature.

              Select  the  Objective-C  ABI version to use. Available versions
              are 1 (legacy "fragile" ABI),  2  (non-fragile  ABI  1),  and  3
              (non-fragile ABI 2).

              Select  the  Objective-C  non-fragile  ABI  version  to  use  by
              default. This will only be used as the Objective-C ABI when  the
              non-fragile ABI is enabled (either via -fobjc-nonfragile-abi, or
              because it is the platform default).

       -fobjc-nonfragile-abi, -fno-objc-nonfragile-abi
              Enable use of the Objective-C non-fragile ABI. On platforms  for
              which  this  is  the  default  ABI,  it  can  be  disabled  with

   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.

              When  building  for macOS, specify the minimum version supported
              by your application.

              When building for iPhone OS, specify the  minimum  version  sup-
              ported by your application.

              Print  out  a  list of supported processors for the given target
              (specified through --target=<architecture> or  -arch  <architec-
              ture>).  If  no  target  is specified, the system default target
              will be used.

       -mcpu=?, -mtune=?
              Aliases of --print-supported-cpus

              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, -O3, -Ofast, -Os, -Oz, -Og, -O, -O4
              Specify which optimization level to use:
                 -O0 Means "no optimization": this level compiles the  fastest
                 and generates the most debuggable code.

                 -O1 Somewhere between -O0 and -O2.

                 -O2  Moderate  level of optimization which enables most opti-

                 -O3 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).

                 -Ofast Enables all the  optimizations  from  -O3  along  with
                 other  aggressive  optimizations that may violate strict com-
                 pliance with language standards.

                 -Os Like -O2 with extra optimizations to reduce code size.

                 -Oz Like -Os (and thus -O2), but reduces code size further.

                 -Og Like -O1. In future versions, this option  might  disable
                 different optimizations in order to improve debuggability.

                 -O Equivalent to -O1.

                 -O4 and higher
                     Currently equivalent to -O3

       -g, -gline-tables-only, -gmodules
              Control  debug information output.  Note that Clang debug infor-
              mation works best at -O0.  When more than  one  option  starting
              with -g is specified, the last one wins:
                 -g Generate debug information.

                 -gline-tables-only  Generate  only  line table debug informa-
                 tion. This allows for symbolicated backtraces  with  inlining
                 information, but does not include any information about vari-
                 ables, their locations or types.

                 -gmodules Generate debug information that  contains  external
                 references  to  types defined in Clang modules or precompiled
                 headers instead of emitting redundant debug type  information
                 into  every  object file.  This option transparently switches
                 the Clang module format to object file containers  that  hold
                 the  Clang  module together with the debug information.  When
                 compiling a program that uses Clang  modules  or  precompiled
                 headers, this option produces complete debug information with
                 faster compile times and much smaller object files.

                 This option should not be used when building static libraries
                 for  distribution  to  other  machines because the debug info
                 will contain references to the module cache  on  the  machine
                 the object files in the library were built on.

       -fstandalone-debug -fno-standalone-debug
              Clang  supports  a number of optimizations to reduce the size of
              debug information in the binary. They work based on the  assump-
              tion that the debug type information can be spread out over mul-
              tiple compilation units.  For instance, Clang will not emit type
              definitions  for types that are not needed by a module and could
              be replaced with a forward  declaration.   Further,  Clang  will
              only  emit  type info for a dynamic C++ class in the module that
              contains the vtable for the class.

              The -fstandalone-debug option  turns  off  these  optimizations.
              This  is useful when working with 3rd-party libraries that don't
              come with debug information.  This is  the  default  on  Darwin.
              Note  that Clang will never emit type information for types that
              are not referenced at all by the program.

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

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

              This flag sets the default visibility level.

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

              Set  the  default  thread-local  storage  (TLS) model to use for
              thread-local  variables.  Valid  values  are:  "global-dynamic",
              "local-dynamic", "initial-exec" and "local-exec". The default is
              "global-dynamic". The default model can be overridden  with  the
              tls_model  attribute.  The  compiler  will  try to choose a more
              efficient model if possible.

       -flto, -flto=full, -flto=thin, -emit-llvm
              Generate output files in LLVM formats, suitable  for  link  time
              optimization.   When used with -S this generates LLVM intermedi-
              ate language assembly files, otherwise this generates LLVM  bit-
              code  format  object  files  (which  may be passed to the linker
              depending on the stage selection options).

              The default for -flto is "full", in which the  LLVM  bitcode  is
              suitable  for monolithic Link Time Optimization (LTO), where the
              linker merges all such modules into a single combined module for
              optimization.   With  "thin",  ThinLTO  compilation  is  invoked

                 On Darwin, when using -flto along with -g and  compiling  and
                 linking   in   separate   steps,   you   also  need  to  pass
                 -Wl,-object_path_lto,<lto-filename>.o at the linking step  to
                 instruct  the  ld64 linker not to delete the temporary object
                 file generated during Link Time Optimization  (this  flag  is
                 automatically  passed  to  the linker by Clang if compilation
                 and linking are done in a single step). This allows debugging
                 the  executable  as well as generating the .dSYM bundle using

   Driver Options
       -###   Print (but do not run) the commands to run for this compilation.

       --help Display available options.

              Do not emit any warnings for unused driver arguments.

              Pass the comma separated arguments in args to the assembler.

              Pass the comma separated arguments in args to the linker.

              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.

       -Xlinker <arg>
              Pass arg to the linker.

       -Xpreprocessor <arg>
              Pass arg to the preprocessor.

       -o <file>
              Write output to file.

              Print the full library path of file.

              Print the library path for the currently used  compiler  runtime
              library ("libgcc.a" or "libclang_rt.builtins.*.a").

              Print the full program path of name.

              Print the paths used for finding libraries and programs.

              Save intermediate compilation results.

       -save-stats, -save-stats=cwd, -save-stats=obj
              Save internal code generation (LLVM) statistics to a file in the
              current directory (-save-stats/"-save-stats=cwd") or the  direc-
              tory of the output file ("-save-state=obj").

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

       -time  Time individual commands.

              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, -fdiagnos-
       tics-fixit-info,       -fdiagnostics-parseable-fixits,       -fdiagnos-
       tics-print-source-range-info,   -fprint-source-range-info,   -fdiagnos-
       tics-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
              Adds an implicit #define into the  predefines  buffer  which  is
              read before the source file is preprocessed.

              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.

              Add  the  specified  directory  to  the  search path for include

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

              Do  not  search  the  standard  system  directories  or compiler
              builtin directories for include files.

              Do not search the standard system directories for include files,
              but do search compiler builtin include directories.

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

              These environment variables are checked, in order, for the loca-
              tion to  write  temporary  files  used  during  the  compilation

       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
              delimiter, as used in the PATH environment variable.

              Empty components in the environment variable are ignored.

              These  environment  variables  specify  additional paths, as for
              CPATH, which are only used when processing the appropriate  lan-

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

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

       See attributes(7) for descriptions of the following attributes:

       |Availability   | developer/llvm/clang |
       |Stability      | Uncommitted          |

       as(1), ld(1)

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

       2007-2022, The Clang Team

       Source code for open source software components in Oracle  Solaris  can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-

       This    software    was    built    from    source     available     at
       https://github.com/oracle/solaris-userland.    The  original  community
       source    was    downloaded     from      https://github.com/llvm/llvm-

       Further information about this software can be found on the open source
       community website at https://llvm.org/.

11                               Jun 28, 2022                         CLANG(1)