'\" t
.\" Title: ccache
.\" Author: [see the "Author" section]
-.\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>
-.\" Date: 09/28/2016
+.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
+.\" Date: 02/11/2018
.\" Manual: ccache Manual
-.\" Source: ccache 3.2.9
+.\" Source: ccache 3.3.6+95_g181effa
.\" Language: English
.\"
-.TH "CCACHE" "1" "09/28/2016" "ccache 3\&.2\&.9" "ccache Manual"
+.TH "CCACHE" "1" "02/11/2018" "ccache 3\&.3\&.6+95_g181effa" "ccache Manual"
.\" -----------------------------------------------------------------
.\" * Define some portability stuff
.\" -----------------------------------------------------------------
.sp
ccache is a compiler cache\&. It speeds up recompilation by caching the result of previous compilations and detecting when the same compilation is being done again\&. Supported languages are C, C++, Objective\-C and Objective\-C++\&.
.sp
-ccache has been carefully written to always produce exactly the same compiler output that you would get without the cache\&. The only way you should be able to tell that you are using ccache is the speed\&. Currently known exceptions to this goal are listed under BUGS\&. If you ever discover an undocumented case where ccache changes the output of your compiler, please let us know\&.
+ccache has been carefully written to always produce exactly the same compiler output that you would get without the cache\&. The only way you should be able to tell that you are using ccache is the speed\&. Currently known exceptions to this goal are listed under CAVEATS\&. If you ever discover an undocumented case where ccache changes the output of your compiler, please let us know\&.
.SS "Features"
.sp
.RS 4
.sp -1
.IP \(bu 2.3
.\}
-Optionally uses hard links where possible to avoid copies\&.
-.RE
-.sp
-.RS 4
-.ie n \{\
-\h'-04'\(bu\h'+03'\c
-.\}
-.el \{\
-.sp -1
-.IP \(bu 2.3
-.\}
Optionally compresses files in the cache to reduce disk space\&.
.RE
.SS "Limitations"
.RE
.SH "EXTRA OPTIONS"
.sp
-When run as a compiler, ccache usually just takes the same command line options as the compiler you are using\&. The only exception to this is the option \fB\-\-ccache\-skip\fR\&. That option can be used to tell ccache to avoid interpreting the next option in any way and to pass it along to the compiler as\-is\&. \fBNote\fR: \fB\-\-ccache\-skip\fR currently only tells ccache not to interpret the next option as a special compiler option \(em the option will still be included in the direct mode hash\&.
+When run as a compiler, ccache usually just takes the same command line options as the compiler you are using\&. The only exception to this is the option \fB\-\-ccache\-skip\fR\&. That option can be used to tell ccache to avoid interpreting the next option in any way and to pass it along to the compiler as\-is\&.
+.if n \{\
+.sp
+.\}
+.RS 4
+.it 1 an-trap
+.nr an-no-space-flag 1
+.nr an-break-flag 1
+.br
+.ps +1
+\fBNote\fR
+.ps -1
+.br
+.sp
+\fB\-\-ccache\-skip\fR currently only tells ccache not to interpret the next option as a special compiler option \(em the option will still be included in the direct mode hash\&.
+.sp .5v
+.RE
.sp
The reason this can be important is that ccache does need to parse the command line and determine what is an input filename and what is a compiler option, as it needs the input filename to determine the name of the resulting object file (among other things)\&. The heuristic ccache uses when parsing the command line is that any argument that exists as a file is treated as an input file name\&. By using \fB\-\-ccache\-skip\fR you can force an option to not be treated as an input file name and instead be passed along to the compiler as a command line option\&.
.sp
.\}
.SS "Boolean values"
.sp
-Some settings are boolean values (i\&.e\&. truth values)\&. In a configuration file, such values must be set to the string \fBtrue\fR or \fBfalse\fR\&. For the corresponding environment variables, the semantics are a bit different: a set environment variable means \(lqtrue\(rq regardless of the value (even if set to the empty string), and an unset environment variable means \(lqfalse\(rq\&. Each boolean environment variable also has a negated form starting with \fBCCACHE_NO\fR\&. For example, \fBCCACHE_COMPRESS\fR can be set to force compression and \fBCCACHE_NOCOMPRESS\fR can be set to force no compression\&.
+Some settings are boolean values (i\&.e\&. truth values)\&. In a configuration file, such values must be set to the string \fBtrue\fR or \fBfalse\fR\&. For the corresponding environment variables, the semantics are a bit different: a set environment variable means \(lqtrue\(rq (even if set to the empty string), the following case\-insensitive negative values are considered an error (rather than surprising the user): \fB0\fR, \fBfalse\fR, \fBdisable\fR and \fBno\fR, and an unset environment variable means \(lqfalse\(rq\&. Each boolean environment variable also has a negated form starting with \fBCCACHE_NO\fR\&. For example, \fBCCACHE_COMPRESS\fR can be set to force compression and \fBCCACHE_NOCOMPRESS\fR can be set to force no compression\&.
.SS "Configuration settings"
.sp
Below is a list of available configuration settings\&. The corresponding environment variable name is indicated in parentheses after each configuration setting key\&.
.PP
\fBbase_dir\fR (\fBCCACHE_BASEDIR\fR)
.RS 4
-This setting should be an absolute path to a directory\&. ccache then rewrites absolute paths into relative paths before computing the hash that identifies the compilation, but only for paths under the specified directory\&. If set to the empty string (which is the default), no rewriting is done\&. See also the discussion under
+This setting should be an absolute path to a directory\&. ccache then rewrites absolute paths into relative paths before computing the hash that identifies the compilation, but only for paths under the specified directory\&. If set to the empty string (which is the default), no rewriting is done\&. A typical path to use as the base directory is your home directory or another directory that is a parent of your build directories\&. Don\(cqt use
+/
+as the base directory since that will make ccache also rewrite paths to system header files, which doesn\(cqt gain anything\&.
+.sp
+See also the discussion under
COMPILING IN DIFFERENT DIRECTORIES\&.
.RE
.PP
\fB%compiler%\fR
will be replaced with the path to the compiler\&. Several commands can be specified with semicolon as separator\&. Examples:
.sp
+.if n \{\
.RS 4
-.ie n \{\
-\h'-04'\(bu\h'+03'\c
-.\}
-.el \{\
-.sp -1
-.IP \(bu 2.3
.\}
+.nf
%compiler% \-v
+.fi
+.if n \{\
.RE
+.\}
.sp
+.if n \{\
.RS 4
-.ie n \{\
-\h'-04'\(bu\h'+03'\c
-.\}
-.el \{\
-.sp -1
-.IP \(bu 2.3
.\}
+.nf
%compiler% \-dumpmachine; %compiler% \-dumpversion
+.fi
+.if n \{\
.RE
+.\}
.sp
You should make sure that the specified command is as fast as possible since it will be run once for each ccache invocation\&.
.sp
.PP
\fBextra_files_to_hash\fR (\fBCCACHE_EXTRAFILES\fR)
.RS 4
-This setting is a list of paths to files that ccache will include in the the hash sum that idetifies the build\&. The list separator is semicolon on Windows systems and colon on other systems\&.
+This setting is a list of paths to files that ccache will include in the the hash sum that identifies the build\&. The list separator is semicolon on Windows systems and colon on other systems\&.
.RE
.PP
\fBhard_link\fR (\fBCCACHE_HARDLINK\fR or \fBCCACHE_NOHARDLINK\fR, see Boolean values above)
.RS 4
-If true, ccache will attempt to use hard links from the cache directory when creating the compiler output rather than using a file copy\&. Using hard links may be slightly faster in some situations, but can confuse programs like \(lqmake\(rq that rely on modification times\&. Another thing to keep in mind is that if the resulting object file is modified in any way, this corrupts the cached object file as well\&. Hard links are never made for compressed cache files\&. This means that you should not enable compression if you want to use hard links\&. The default is false\&.
+If true, ccache will attempt to use hard links from the cache directory when creating the compiler output rather than using a file copy\&. Hard links are never made for compressed cache files\&. This means that you should not enable compression if you want to use hard links\&. The default is false\&.
+.if n \{\
+.sp
+.\}
+.RS 4
+.it 1 an-trap
+.nr an-no-space-flag 1
+.nr an-break-flag 1
+.br
+.ps +1
+\fBWarning\fR
+.ps -1
+.br
+Do not enable this option unless you are aware of the consequences\&. Using hard links may be slightly faster in some situations, but there are several pitfalls since the resulting object file will share i\-node with the cached object file:
+.sp .5v
+.RE
+.sp
+.RS 4
+.ie n \{\
+\h'-04' 1.\h'+01'\c
+.\}
+.el \{\
+.sp -1
+.IP " 1." 4.2
+.\}
+If the resulting object file is modified in any way, the cached object file will be modified as well\&. For instance, if you run
+\fBstrip object\&.o\fR
+or
+\fBecho >object\&.o\fR, you will corrupt the cache\&.
+.RE
+.sp
+.RS 4
+.ie n \{\
+\h'-04' 2.\h'+01'\c
+.\}
+.el \{\
+.sp -1
+.IP " 2." 4.2
+.\}
+Programs that rely on modification times (like \(lqmake\(rq) can be confused since ccache updates the cached files\*(Aq modification times as part of the automatic cache size management\&. This will affect object files in the build tree as well, which can retrigger the linking step even though nothing really has changed\&.
+.RE
.RE
.PP
\fBhash_dir\fR (\fBCCACHE_HASHDIR\fR or \fBCCACHE_NOHASHDIR\fR, see Boolean values above)
.RS 4
-If true, ccache will include the current working directory in the hash that is used to distinguish two compilations\&. This prevents a problem with the storage of the current working directory in the debug info of an object file, which can lead ccache to give a cached object file that has the working directory in the debug info set incorrectly\&. This option is off by default as the incorrect setting of this debug info rarely causes problems\&. If you strike problems with GDB not using the correct directory then enable this option\&.
+If true (which is the default), ccache will include the current working directory (CWD) in the hash that is used to distinguish two compilations when generating debug info (compiler option
+\fB\-g\fR
+with variations)\&. Exception: The CWD will not be included in the hash if
+\fBbase_dir\fR
+is set (and matches the CWD) and the compiler option
+\fB\-fdebug\-prefix\-map\fR
+is used\&. See also the discussion under
+COMPILING IN DIFFERENT DIRECTORIES\&.
+.sp
+The reason for including the CWD in the hash by default is to prevent a problem with the storage of the current working directory in the debug info of an object file, which can lead ccache to return a cached object file that has the working directory in the debug info set incorrectly\&.
+.sp
+You can disable this setting to get cache hits when compiling the same source code in different directories if you don\(cqt mind that CWD in the debug info might be incorrect\&.
+.RE
+.PP
+\fBignore_headers_in_manifest\fR (\fBCCACHE_IGNOREHEADERS\fR)
+.RS 4
+This setting is a list of paths to files (or directories with headers) that ccache will
+\fBnot\fR
+include in the manifest list that makes up the direct mode\&. Note that this can cause stale cache hits if those headers do indeed change\&. The list separator is semicolon on Windows systems and colon on other systems\&.
+.RE
+.PP
+\fBkeep_comments_cpp\fR (\fBCCACHE_COMMENTS\fR or \fBCCACHE_NOCOMMENTS\fR, see Boolean values above)
+.RS 4
+If true, ccache will not discard the comments before hashing preprocessor output\&. This can be used to check documentation with
+\fB\-Wdocumentation\fR\&.
+.RE
+.PP
+\fBlimit_multiple\fR (\fBCCACHE_LIMIT_MULTIPLE\fR)
+.RS 4
+Sets the limit when cleaning up\&. Files are deleted (in LRU order) until the levels are below the limit\&. The default is 0\&.8 (= 80%)\&. See
+AUTOMATIC CLEANUP
+for more information\&.
.RE
.PP
\fBlog_file\fR (\fBCCACHE_LOGFILE\fR)
.PP
\fBmax_files\fR (\fBCCACHE_MAXFILES\fR)
.RS 4
-This option specifies the maximum number of files to keep in the cache\&. Use 0 for no limit (which is the default)\&.
+This option specifies the maximum number of files to keep in the cache\&. Use 0 for no limit (which is the default)\&. See also
+CACHE SIZE MANAGEMENT\&.
.RE
.PP
\fBmax_size\fR (\fBCCACHE_MAXSIZE\fR)
.RS 4
-This option specifies the maximum size of the cache\&. Use 0 for no limit\&. The default value is 5G\&. Available suffixes: k, M, G, T (decimal) and Ki, Mi, Gi, Ti (binary)\&. The default suffix is "G"\&.
+This option specifies the maximum size of the cache\&. Use 0 for no limit\&. The default value is 5G\&. Available suffixes: k, M, G, T (decimal) and Ki, Mi, Gi, Ti (binary)\&. The default suffix is "G"\&. See also
+CACHE SIZE MANAGEMENT\&.
.RE
.PP
\fBpath\fR (\fBCCACHE_PATH\fR)
USING CCACHE WITH OTHER COMPILER WRAPPERS\&.
.RE
.PP
+\fBprefix_command_cpp\fR (\fBCCACHE_PREFIX_CPP\fR)
+.RS 4
+This option adds a list of prefixes (separated by space) to the command line that ccache uses when invoking the preprocessor\&.
+.RE
+.PP
\fBread_only\fR (\fBCCACHE_READONLY\fR or \fBCCACHE_NOREADONLY\fR, see Boolean values above)
.RS 4
If true, ccache will attempt to use existing cached object files, but it will not to try to add anything new to the cache\&. If you are using this because your ccache directory is read\-only, then you need to set
.PP
\fBrun_second_cpp\fR (\fBCCACHE_CPP2\fR or \fBCCACHE_NOCPP2\fR, see Boolean values above)
.RS 4
-If true, ccache will not use the optimisation of avoiding the second call to the preprocessor by compiling the preprocessed output that was used for finding the hash in the case of a cache miss\&. This is primarily a debugging option, although it is possible that some unusual compilers will have problems with compiling the preprocessed output, in which case this option could allow ccache to be used anyway\&.
+If true, ccache will first run the preprocessor to preprocess the source code (see
+THE PREPROCESSOR MODE) and then on a cache miss run the compiler on the source code to get hold of the object file\&. This is the default\&.
+.sp
+If false, ccache will first run preprocessor to preprocess the source code and then on a cache miss run the compiler on the
+\fIpreprocessed source code\fR
+instead of the original source code\&. This makes cache misses slightly faster since the source code only has to be preprocessed once\&. The downside is that some compilers won\(cqt produce the same result (for instance diagnostics warnings) when compiling preprocessed source code\&.
+.sp
+A solution to the above mentioned downside is to set
+\fBrun_second_cpp\fR
+to false and pass
+\fB\-fdirectives\-only\fR
+(for GCC) or
+\fB\-frewrite\-includes\fR
+(for Clang) to the compiler\&. This will cause the compiler to leave the macros and other preprocessor information, and only process the
+\fB#include\fR
+directives\&. When run in this way, the preprocessor arguments will be passed to the compiler since it still has to do
+\fIsome\fR
+preprocessing (like macros)\&.
.RE
.PP
\fBsloppiness\fR (\fBCCACHE_SLOPPINESS\fR)
.PP
\fBfile_stat_matches\fR
.RS 4
-ccache normally examines a file\(cqs contents to determine whether it matches the cached version\&. With this option set, ccache will consider a file as matching its cached version if the sizes, mtimes and ctimes match\&.
+ccache normally examines a file\(cqs contents to determine whether it matches the cached version\&. With this option set, ccache will consider a file as matching its cached version if the mtimes and ctimes match\&.
.RE
.PP
\fBinclude_file_ctime\fR
By default, ccache will not cache a file if it includes a header whose mtime is too new\&. This option disables that check\&.
.RE
.PP
+\fBno_system_headers\fR
+.RS 4
+By default, ccache will also include all system headers in the manifest\&. With this option set, ccache will only include system headers in the hash but not add the system header files to the list of include files\&.
+.RE
+.PP
\fBpch_defines\fR
.RS 4
-Be sloppy about #defines when precompiling a header file\&. See
+Be sloppy about
+\fB#define\fRs when precompiling a header file\&. See
PRECOMPILED HEADERS
for more information\&.
.RE
\fB\-g\fR
option is not used\&. The unifier is slower than a normal hash, so setting this environment variable loses a little bit of speed, but it means that ccache can take advantage of not recompiling when the changes to the source code consist of reformatting only\&. Note that enabling the unifier changes the hash, so cached compilations produced when the unifier is enabled cannot be reused when the unifier is disabled, and vice versa\&. Enabling the unifier may result in incorrect line number information in compiler warning messages and expansions of the
\fB__LINE__\fR
-macro\&. Also note that enabling the unifier implies turning off the direct mode\&.
+macro\&.
.RE
.SH "CACHE SIZE MANAGEMENT"
.sp
-By default, ccache has a five gigabyte limit on the total size of files in the cache and no maximum number of files\&. You can set different limits using the \fB\-M\fR/\fB\-\-max\-size\fR and \fB\-F\fR/\fB\-\-max\-files\fR options\&. Use \fBccache \-s/\-\-show\-stats\fR to see the cache size and the currently configured limits (in addition to other various statistics)\&.
+By default, ccache has a 5 GB limit on the total size of files in the cache and no limit on the number of files\&. You can set different limits using the \fB\-M\fR/\fB\-\-max\-size\fR and \fB\-F\fR/\fB\-\-max\-files\fR options\&. Use \fBccache \-s/\-\-show\-stats\fR to see the cache size and the currently configured limits (in addition to other various statistics)\&.
+.sp
+Cleanup can be triggered in two different ways: automatic and manual\&.
+.SS "Automatic cleanup"
+.sp
+ccache maintains counters for various statistics about the cache, including the size and number of all cached files\&. In order to improve performance and reduce issues with concurrent ccache invocations, there is one statistics file for each of the sixteen subdirectories in the cache\&.
+.sp
+After a new compilation result has been written to the cache, ccache will update the size and file number statistics for the subdirectory (one of sixteen) to which the result was written\&. Then, if the size counter for said subdirectory is greater than \fBmax_size / 16\fR or the file number counter is greater than \fBmax_files / 16\fR, automatic cleanup is triggered\&.
+.sp
+When automatic cleanup is triggered for a subdirectory in the cache, ccache will:
+.sp
+.RS 4
+.ie n \{\
+\h'-04' 1.\h'+01'\c
+.\}
+.el \{\
+.sp -1
+.IP " 1." 4.2
+.\}
+Count all files in the subdirectory and compute their aggregated size\&.
+.RE
+.sp
+.RS 4
+.ie n \{\
+\h'-04' 2.\h'+01'\c
+.\}
+.el \{\
+.sp -1
+.IP " 2." 4.2
+.\}
+Remove files in LRU (least recently used) order until the size is at most
+\fBlimit_multiple * max_size / 16\fR
+and the number of files is at most
+\fBlimit_multiple * max_files / 16\fR, where
+\fBlimit_multiple\fR,
+\fBmax_size\fR
+and
+\fBmax_files\fR
+are configuration settings\&.
+.RE
+.sp
+.RS 4
+.ie n \{\
+\h'-04' 3.\h'+01'\c
+.\}
+.el \{\
+.sp -1
+.IP " 3." 4.2
+.\}
+Set the size and file number counters to match the files that were kept\&.
+.RE
+.sp
+The reason for removing more files than just those needed to not exceed the max limits is that a cleanup is a fairly slow operation, so it would not be a good idea to trigger it often, like after each cache miss\&.
+.SS "Manual cleanup"
+.sp
+You can run \fBccache \-c/\-\-cleanup\fR to force cleanup of the whole cache, i\&.e\&. all of the sixteen subdirectories\&. This will recalculate the statistics counters and make sure that the \fBmax_size\fR and \fBmax_files\fR settings are not exceeded\&. Note that \fBlimit_multiple\fR is not taken into account for manual cleanup\&.
.SH "CACHE COMPRESSION"
.sp
ccache can optionally compress all files it puts into the cache using the compression library zlib\&. While this may involve a tiny performance slowdown, it increases the number of files that fit in the cache\&. You can turn on compression with the \fBcompression\fR configuration setting and you can also tweak the compression level with \fBcompression_level\fR\&.
+.SH "CACHE STATISTICS"
+.sp
+\fBccache \-s/\-\-show\-stats\fR can show the following statistics:
+.TS
+allbox tab(:);
+ltB ltB.
+T{
+Name
+T}:T{
+Description
+T}
+.T&
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt
+lt lt.
+T{
+.sp
+autoconf compile/link
+T}:T{
+.sp
+Uncachable compilation or linking by an autoconf test\&.
+T}
+T{
+.sp
+bad compiler arguments
+T}:T{
+.sp
+Malformed compiler argument, e\&.g\&. missing a value for an option that requires an argument or failure to read a file specified by an option argument\&.
+T}
+T{
+.sp
+cache file missing
+T}:T{
+.sp
+A file was unexpectedly missing from the cache\&. This only happens in rare situations, e\&.g\&. if one ccache instance is about to get a file from the cache while another instance removed the file as part of cache cleanup\&.
+T}
+T{
+.sp
+cache hit (direct)
+T}:T{
+.sp
+A result was successfully found using the direct mode\&.
+T}
+T{
+.sp
+cache hit (preprocessed)
+T}:T{
+.sp
+A result was successfully found using the preprocessor mode\&.
+T}
+T{
+.sp
+cache miss
+T}:T{
+.sp
+No result was found\&.
+T}
+T{
+.sp
+cache size
+T}:T{
+.sp
+Current size of the cache\&.
+T}
+T{
+.sp
+called for link
+T}:T{
+.sp
+The compiler was called for linking, not compiling\&.
+T}
+T{
+.sp
+called for preprocessing
+T}:T{
+.sp
+The compiler was called for preprocessing, not compiling\&.
+T}
+T{
+.sp
+can\(cqt use precompiled header
+T}:T{
+.sp
+Preconditions for using precompiled headers were not fulfilled\&.
+T}
+T{
+.sp
+ccache internal error
+T}:T{
+.sp
+Unexpected failure, e\&.g\&. due to problems reading/writing the cache\&.
+T}
+T{
+.sp
+cleanups performed
+T}:T{
+.sp
+Number of cleanups performed, either implicitly due to the cache size limit being reached or due to explicit \fBccache \-c/\-\-cleanup\fR calls\&.
+T}
+T{
+.sp
+compile failed
+T}:T{
+.sp
+The compilation failed\&. No result stored in the cache\&.
+T}
+T{
+.sp
+compiler check failed
+T}:T{
+.sp
+A compiler check program specified by \fBcompiler_check\fR (\fBCCACHE_COMPILERCHECK\fR) failed\&.
+T}
+T{
+.sp
+compiler produced empty output
+T}:T{
+.sp
+The compiler\(cqs output file (typically an object file) was empty after compilation\&.
+T}
+T{
+.sp
+compiler produced no output
+T}:T{
+.sp
+The compiler\(cqs output file (typically an object file) was missing after compilation\&.
+T}
+T{
+.sp
+compiler produced stdout
+T}:T{
+.sp
+The compiler wrote data to standard output\&. This is something that compilers normally never do, so ccache is not designed to store such output in the cache\&.
+T}
+T{
+.sp
+couldn\(cqt find the compiler
+T}:T{
+.sp
+The compiler to execute could not be found\&.
+T}
+T{
+.sp
+error hashing extra file
+T}:T{
+.sp
+Failure reading a file specified by \fBextra_files_to_hash\fR (\fBCCACHE_EXTRAFILES\fR)\&.
+T}
+T{
+.sp
+files in cache
+T}:T{
+.sp
+Current number of files in the cache\&.
+T}
+T{
+.sp
+multiple source files
+T}:T{
+.sp
+The compiler was called to compile multiple source files in one go\&. This is not supported by ccache\&.
+T}
+T{
+.sp
+no input file
+T}:T{
+.sp
+No input file was specified to the compiler\&.
+T}
+T{
+.sp
+output to a non\-regular file
+T}:T{
+.sp
+The output path specified with \fB\-o\fR is not a file (e\&.g\&. a directory or a device node)\&.
+T}
+T{
+.sp
+output to stdout
+T}:T{
+.sp
+The compiler was instructed to write its output to standard output using \fB\-o \-\fR\&. This is not supported by ccache\&.
+T}
+T{
+.sp
+preprocessor error
+T}:T{
+.sp
+Preprocessing the source code using the compiler\(cqs \fB\-E\fR option failed\&.
+T}
+T{
+.sp
+unsupported code directive
+T}:T{
+.sp
+Code like the assembler \(lq\&.incbin\(rq directive was found\&. This is not supported by ccache\&.
+T}
+T{
+.sp
+unsupported compiler option
+T}:T{
+.sp
+A compiler option not supported by ccache was found\&.
+T}
+T{
+.sp
+unsupported source language
+T}:T{
+.sp
+A source language e\&.g\&. specified with \fB\-x\fR was unsupported by ccache\&.
+T}
+.TE
+.sp 1
.SH "HOW CCACHE WORKS"
.sp
The basic idea is to detect when you are compiling exactly the same code a second time and reuse the previously produced output\&. The detection is done by hashing different kinds of information that should be unique for the compilation and then using the hash sum to identify the cached output\&. ccache uses MD4, a very fast cryptographic hash algorithm, for the hashing\&. (MD4 is nowadays too weak to be useful in cryptographic contexts, but it should be safe enough to be used to identify recompilations\&.) On a cache hit, ccache is able to supply all of the correct compiler outputs (including all warnings, dependency file, etc) from the cache\&.
.sp -1
.IP \(bu 2.3
.\}
-the unifier is enabled (the configuration setting
-\fBunify\fR
-is true)
-.RE
-.sp
-.RS 4
-.ie n \{\
-\h'-04'\(bu\h'+03'\c
-.\}
-.el \{\
-.sp -1
-.IP \(bu 2.3
-.\}
a compiler option not supported by the direct mode is used:
.sp
.RS 4
a
\fB\-Wp,\fR\fB\fIX\fR\fR
compiler option other than
-\fB\-Wp,\-MD,\fR\fB\fIpath\fR\fR
-and
+\fB\-Wp,\-MD,\fR\fB\fIpath\fR\fR,
\fB\-Wp,\-MMD,\fR\fB\fIpath\fR\fR
+and
+\fB\-Wp,\-D_define_\fR
.RE
.sp
.RS 4
Based on the hash, the cached compilation result can be looked up directly in the cache\&.
.SH "COMPILING IN DIFFERENT DIRECTORIES"
.sp
-Some information included in the hash that identifies a unique compilation may contain absolute paths:
+Some information included in the hash that identifies a unique compilation can contain absolute paths:
.sp
.RS 4
.ie n \{\
.\}
Paths specified by compiler options (such as
\fB\-I\fR,
-\fB\-MF\fR, etc) may be absolute\&.
+\fB\-MF\fR, etc) on the command line may be absolute\&.
.RE
.sp
.RS 4
macros in the source code or included in warnings emitted to standard error by the preprocessor\&.
.RE
.sp
-This means that if you compile the same code in different locations, you can\(cqt share compilation results between the different build directories since you get cache misses because of the absolute build directory paths that are part of the hash\&. To mitigate this problem, you can specify a \(lqbase directory\(rq in the configuration setting \fBbase_dir\fR to an absolute path to the directory\&. ccache will then rewrite absolute paths that are under the base directory (i\&.e\&., paths that have the base directory as a prefix) to relative paths when constructing the hash\&. A typical path to use as the base directory is your home directory or another directory that is a parent of your build directories\&. (Don\(cqt use / as the base directory since that will make ccache also rewrite paths to system header files, which doesn\(cqt gain anything\&.)
+This means that if you compile the same code in different locations, you can\(cqt share compilation results between the different build directories since you get cache misses because of the absolute build directory paths that are part of the hash\&.
.sp
-The drawbacks of using a base directory are:
+Here\(cqs what can be done to enable cache hits between different build directories:
.sp
.RS 4
.ie n \{\
.sp -1
.IP \(bu 2.3
.\}
-If you specify an absolute path to the source code file,
-\fB__FILE__\fR
-macros will be expanded to a relative path instead\&.
+If you build with
+\fB\-g\fR
+(or similar) to add debug information to the object file, you must either:
+.sp
+.RS 4
+.ie n \{\
+\h'-04'\(bu\h'+03'\c
+.\}
+.el \{\
+.sp -1
+.IP \(bu 2.3
+.\}
+use the
+\fB\-fdebug\-prefix\-map=\fR\fB\fIold\fR\fR\fB=\fR\fB\fInew\fR\fR
+option for relocating debug info to a common prefix (e\&.g\&.
+\fB\-fdebug\-prefix\-map=$PWD=\&.\fR); or
+.RE
+.sp
+.RS 4
+.ie n \{\
+\h'-04'\(bu\h'+03'\c
+.\}
+.el \{\
+.sp -1
+.IP \(bu 2.3
+.\}
+set
+\fBhash_dir = false\fR\&.
+.RE
.RE
.sp
.RS 4
.sp -1
.IP \(bu 2.3
.\}
-If you specify an absolute path to the source code file and compile with
-\fB\-g\fR, the source code path stored in the object file may point to the wrong directory, which may prevent debuggers like GDB from finding the source code\&. Sometimes, a work\-around is to change the directory explicitly with the \(lqcd\(rq command in GDB\&.
+If you use absolute paths anywhere on the command line (e\&.g\&. the source code file path or an argument to compiler options like
+\fB\-I\fR
+and
+\fB\-MF\fR), you must to set
+\fBbase_dir\fR
+to an absolute path to a \(lqbase directory\(rq\&. ccache will then rewrite absolute paths under that directory to relative before computing the hash\&.
.RE
.SH "PRECOMPILED HEADERS"
.sp
\fB__TIME__\fR
or
\fB__DATE__\fR
-is used when using a precompiled header\&. Further, it can\(cqt detect changes in #defines in the source code because of how preprocessing works in combination with precompiled headers\&.
+is used when using a precompiled header\&. Further, it can\(cqt detect changes in
+\fB#define\fRs in the source code because of how preprocessing works in combination with precompiled headers\&.
.RE
.sp
.RS 4
.sp -1
.IP \(bu 2.3
.\}
-Make sure that the setgid bit is set on all directories in the cache\&. This tells the filesystem to inherit group ownership for new directories\&. The command \(lqfind $CCACHE_DIR \-type d | xargs chmod g+s\(rq might be useful for this\&.
+Make sure that the setgid bit is set on all directories in the cache\&. This tells the filesystem to inherit group ownership for new directories\&. The following command might be useful for this:
+.sp
+.if n \{\
+.RS 4
+.\}
+.nf
+find $CCACHE_DIR \-type d | xargs chmod g+s
+.fi
+.if n \{\
+.RE
+.\}
.RE
.sp
The reason to avoid the hard link mode is that the hard links cause unwanted side effects, as all links to a cached file share the file\(cqs modification timestamp\&. This results in false dependencies to be triggered by timestamp\-based build systems whenever another user links to an existing file\&. Typically, users will see that their libraries and binaries are relinked without reason\&.
The cached results will not be shared between compilations with and without the other wrapper\&.
.RE
.sp
-Another minor thing is that if \fBprefix_command\fR is used, ccache will not invoke the other wrapper when running the preprocessor, which increase performance\&.
-.SH "BUGS"
+Another minor thing is that if \fBprefix_command\fR is used, ccache will not invoke the other wrapper when running the preprocessor, which increases performance\&. You can use the \fBprefix_command_cpp\fR configuration setting if you also want to invoke the other wrapper when doing preprocessing (normally by adding \fB\-E\fR)\&.
+.SH "CAVEATS"
.sp
.RS 4
.ie n \{\
.sp -1
.IP \(bu 2.3
.\}
-ccache doesn\(cqt handle the GNU Assembler\(cqs
-\fB\&.incbin\fR
-directive correctly\&. This directive can be embedded in the source code inside an
-\fB\fIasm\fR\fR
-statement in order to include a file verbatim in the object file\&. If the included file is modified, ccache doesn\(cqt pick up the change since the inclusion isn\(cqt done by the preprocessor\&. A workaround of this problem is to set
-\fBextra_files_to_hash\fR
-to the path of the included file\&.
+The direct mode fails to pick up new header files in some rare scenarios\&. See
+THE DIRECT MODE
+above\&.
.RE
.sp
.RS 4
.sp -1
.IP \(bu 2.3
.\}
-The direct mode fails to pick up new header files in some rare scenarios\&. See
-THE DIRECT MODE
-above\&.
+When run via ccache, warning messages produced by GCC 4\&.9 and newer will only be colored when the environment variable
+\fBGCC_COLORS\fR
+is set\&. An alternative to setting
+\fBGCC_COLORS\fR
+is to pass
+\-fdiagnostics\-color
+explicitly when compiling (but then color codes will also be present when redirecting stderr to a file)\&.
+.RE
+.sp
+.RS 4
+.ie n \{\
+\h'-04'\(bu\h'+03'\c
+.\}
+.el \{\
+.sp -1
+.IP \(bu 2.3
+.\}
+If ccache guesses that the compiler may emit colored warnings, then a compilation with stderr referring to a TTY will be considered different from a compilation with a redirected stderr, thus not sharing cache entries\&. This happens for clang by default and for GCC when
+\fBGCC_COLORS\fR
+is set as mentioned above\&. If you want to share cache hits, you can pass
+\-f[no\-]diagnostics\-color
+(GCC) or
+\-f[no\-]color\-diagnostics
+(clang) explicitly when compiling (but then color codes will be either on or off for both the TTY and the redirected case)\&.
.RE
.SH "TROUBLESHOOTING"
.SS "General"
.sp
ccache has been written to perform well out of the box, but sometimes you may have to do some adjustments of how you use the compiler and ccache in order to improve performance\&.
.sp
-Since ccache works best when I/O is fast, put the cache directory on a fast storage device if possible\&. Having lots of free memory so that files in the cache directory stay in the disk cache is also preferrable\&.
+Since ccache works best when I/O is fast, put the cache directory on a fast storage device if possible\&. Having lots of free memory so that files in the cache directory stay in the disk cache is also preferable\&.
.sp
A good way of monitoring how well ccache works is to run \fBccache \-s\fR before and after your build and then compare the statistics counters\&. Here are some common problems and what may be done to increase the hit rate:
.sp
or
\fB\-Wp,\fR\fB\fIX\fR\fR
(except
-\fB\-Wp,\-MD,\fR\fB\fIpath\fR\fR
-and
-\fBWp,\-MMD,\fR\fB\fIpath\fR\fR) is used\&.
+\fB\-Wp,\-MD,\fR\fB\fIpath\fR\fR,
+\fB\-Wp,\-MMD,\fR\fB\fIpath\fR\fR, and
+\fB\-Wp,\-D_define_\fR) is used\&.
.RE
.sp
.RS 4
If \(lqcan\(cqt use precompiled header\(rq has been incremented, see
PRECOMPILED HEADERS\&.
.RE
-.SS "Errors when compiling with ccache"
-.sp
-If compilation doesn\(cqt work with ccache, but it works without it, one possible reason is that the compiler can\(cqt compile preprocessed output correctly\&. A workaround that may work is to enable \fBrun_second_cpp\fR*\&. This will make cache misses slower, though, so it is better to find and fix the root cause\&.
.SS "Corrupt object files"
.sp
It should be noted that ccache is susceptible to general storage problems\&. If a bad object file sneaks into the cache for some reason, it will of course stay bad\&. Some possible reasons for erroneous object files are bad hardware (disk drive, disk controller, memory, etc), buggy drivers or file systems, a bad \fBprefix_command\fR or compiler wrapper\&. If this happens, the easiest way of fixing it is this:
There are no reported issues about ccache producing broken object files reproducibly\&. That doesn\(cqt mean it can\(cqt happen, so if you find a repeatable case, please report it\&.
.SH "MORE INFORMATION"
.sp
-Credits, mailing list information, bug reporting instructions, source code, etc, can be found on ccache\(cqs web site: http://ccache\&.samba\&.org\&.
+Credits, mailing list information, bug reporting instructions, source code, etc, can be found on ccache\(cqs web site: https://ccache\&.samba\&.org\&.
.SH "AUTHOR"
.sp
-ccache was originally written by Andrew Tridgell and is currently developed and maintained by Joel Rosdahl\&. See AUTHORS\&.txt or AUTHORS\&.html and http://ccache\&.samba\&.org/credits\&.html for a list of contributors\&.
+ccache was originally written by Andrew Tridgell and is currently developed and maintained by Joel Rosdahl\&. See AUTHORS\&.txt or AUTHORS\&.html and https://ccache\&.samba\&.org/credits\&.html for a list of contributors\&.
projects / platform / upstream / ccache.git / blobdiff