table of contents
- NAME
- SYNOPSIS
- DESCRIPTION
- RUN MODES
- OPTIONS
- EXTRA OPTIONS
- ENVIRONMENT VARIABLES
- CACHE SIZE MANAGEMENT
- CACHE COMPRESSION
- HOW CCACHE WORKS
- COMPILING IN DIFFERENT DIRECTORIES
- PRECOMPILED HEADERS
- SHARING A CACHE
- SHARING A CACHE ON NFS
- USING CCACHE WITH OTHER COMPILER WRAPPERS
- BUGS
- TROUBLESHOOTING
- MORE INFORMATION
- AUTHOR
CCACHE(1) | ccache Manual | CCACHE(1) |
NAME¶
ccache - a fast C/C++ compiler cacheSYNOPSIS¶
ccache [options] ccache compiler [compiler options] compiler [compiler options] (via symbolic link)
DESCRIPTION¶
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++. 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.Features¶
•Keeps statistics on hits/misses.
•Automatic cache size management.
•Can cache compilations that generate
warnings.
•Easy installation.
•Low overhead.
•Optionally uses hard links where possible to
avoid copies.
•Optionally compresses files in the cache to
reduce disk space.
Limitations¶
•Only knows how to cache the compilation of a
single C/C++/Objective-C/Objective-C++ file. Other types of compilations
(multi-file compilation, linking, etc) will silently fall back to running the
real compiler.
•Only works with GCC and compilers that behave
similar enough.
•Some compiler flags are not supported. If such a
flag is detected, ccache will silently fall back to running the real
compiler.
RUN MODES¶
There are two ways to use ccache. You can either prefix your compilation commands with ccache or you can let ccache masquerade as the compiler by creating a symbolic link (named as the compiler) to ccache. The first method is most convenient if you just want to try out ccache or wish to use it for some specific projects. The second method is most useful for when you wish to use ccache for all your compilations. To use the second method on a Debian system, it's easiest to just prepend /usr/lib/ccache to your PATH. /usr/lib/ccache contains symlinks for all compilers currently installed as Debian packages. Alternatively, you can create any symlinks you like yourself like this:ln -s /usr/bin/ccache /usr/local/bin/gcc ln -s /usr/bin/ccache /usr/local/bin/g++ ln -s /usr/bin/ccache /usr/local/bin/cc ln -s /usr/bin/ccache /usr/local/bin/c++
OPTIONS¶
These options only apply when you invoke ccache as “ccache”. When invoked as a compiler (via a symlink as described in the previous section), the normal compiler options apply and you should refer to the compiler’s documentation. -c, --cleanupClean up the cache by removing old cached files until the
specified file number and cache size limits are not exceeded. This also
recalculates the cache file count and size totals. Normally, it’s not
needed to initiate cleanup manually as ccache keeps the cache below the
specified limits at runtime and keeps statistics up to date on each
compilation. Forcing a cleanup is mostly useful if you manually modify the
cache contents or believe that the cache size statistics may be
inaccurate.
-C, --clear
Clear the entire cache, removing all cached files.
-F, --max-files=N
Set the maximum number of files allowed in the cache. The
value is stored inside the cache directory and applies to all future
compilations. Due to the way the value is stored the actual value used is
always rounded down to the nearest multiple of 16.
-h, --help
Print an options summary page.
-M, --max-size=SIZE
Set the maximum size of the files stored in the cache.
You can specify a value in gigabytes, megabytes or kilobytes by appending a G,
M or K to the value. The default is gigabytes. The actual value stored is
rounded down to the nearest multiple of 16 kilobytes.
-s, --show-stats
Print the current statistics summary for the cache.
-V, --version
Print version and copyright information.
-z, --zero-stats
Zero the cache statistics (but not the configured
limits).
EXTRA OPTIONS¶
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 --ccache-skip. 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. Note: --ccache-skip currently only tells ccache not to interpret the next option as a special compiler option — the option will still be included in the direct mode hash. 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 --ccache-skip 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. Another case where --ccache-skip can be useful is if ccache interprets an option specially but shouldn’t, since the option has another meaning for your compiler than what ccache thinks.ENVIRONMENT VARIABLES¶
ccache uses a number of environment variables to control operation. In most cases you won’t need any of these as the defaults will be fine. CCACHE_BASEDIRIf you set the environment variable CCACHE_BASEDIR
to an absolute path to a directory, ccache rewrites absolute paths into
relative paths before computing the hash that identifies the compilation, but
only for paths under the specified directory. See the discussion under
COMPILING IN DIFFERENT DIRECTORIES.
CCACHE_CC
You can optionally set CCACHE_CC to force the name
of the compiler to use. If you don’t do this then ccache works it out
from the command line.
CCACHE_COMPILERCHECK
By default, ccache includes the modification time
(“mtime”) and size of the compiler in the hash to ensure that
results retrieved from the cache are accurate. The CCACHE_COMPILERCHECK
environment variable can be used to select another strategy. Possible values
are:
content
CCACHE_COMPRESS
Hash the content of the compiler binary. This makes
ccache very slightly slower compared to the mtime setting, but makes it
cope better with compiler upgrades during a build bootstrapping process.
mtime
Hash the compiler’s mtime and size, which is fast.
This is the default.
none
Don’t hash anything. This may be good for
situations where you can safely use the cached results even though the
compiler’s mtime or size has changed (e.g. if the compiler is built as
part of your build system and the compiler’s source has not changed, or
if the compiler only has changes that don’t affect code generation).
You should only use the none setting if you know what you are
doing.
a command string
Hash the standard output and standard error output of the
specified command. The string will be split on whitespace to find out the
command and arguments to run. No other interpretation of the command string
will be done, except that the special word “%compiler%” will be
replaced with the path to the compiler. Several commands can be specified with
semicolon as separator. Examples:
•%compiler% -v
•%compiler% -dumpmachine; %compiler%
-dumpversion
You should make sure that the specified command is as fast as possible since it
will be run once for each ccache invocation.
Identifying the compiler using a command is useful if you want to avoid cache
misses when the compiler has been rebuilt but not changed.
Another case is when the compiler (as seen by ccache) actually isn’t the
real compiler but another compiler wrapper — in that case, the default
mtime method will hash the mtime and size of the other compiler
wrapper, which means that ccache won’t be able to detect a compiler
upgrade. Using a suitable command to identify the compiler is thus safer, but
it’s also slower, so you should consider continue using the
mtime method in combination with CCACHE_PREFIX if possible. See
USING CCACHE WITH OTHER COMPILER WRAPPERS.If you set the environment variable
CCACHE_COMPRESS then ccache will compress object files and other
compiler output it puts in the cache. However, this setting has no effect on
how files are retrieved from the cache; compressed and uncompressed results
will still be usable regardless of this setting.
CCACHE_CPP2
If you set the environment variable CCACHE_CPP2
then 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
the intermediate filename extensions used in this optimisation, in which case
this option could allow ccache to be used anyway.
CCACHE_DETECT_SHEBANG
The CCACHE_DETECT_SHEBANG environment variable
only has meaning on Windows. It instructs ccache to open the executable file
to detect the #!/bin/sh string, in which case ccache will search for
sh.exe in PATH and use that to launch the executable.
CCACHE_DIR
The CCACHE_DIR environment variable specifies
where ccache will keep its cached compiler output. The default is
$HOME/.ccache.
CCACHE_DISABLE
If you set the environment variable CCACHE_DISABLE
then ccache will just call the real compiler, bypassing the cache
completely.
CCACHE_EXTENSION
ccache tries to automatically determine the extension to
use for intermediate preprocessor files based on the type of file being
compiled. Unfortunately this sometimes doesn’t work, for example when
using the “aCC” compiler on HP-UX. On systems like this you can
use the CCACHE_EXTENSION option to override the default. On HP-UX set
this environment variable to i if you use the “aCC”
compiler.
CCACHE_EXTRAFILES
If you set the environment variable
CCACHE_EXTRAFILES to a list of paths then ccache will include the
contents of those files when calculating the hash sum. The list separator is
semicolon in Windows systems and colon on other systems.
CCACHE_HARDLINK
If you set the environment variable
CCACHE_HARDLINK then 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 “make” 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 set the
CCACHE_COMPRESS variable if you want to use hard links.
CCACHE_HASHDIR
This tells ccache to hash the current working directory
when calculating 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 a 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.
CCACHE_LOGFILE
If you set the CCACHE_LOGFILE environment variable
then ccache will write information on what it is doing to the specified file.
This is useful for tracking down problems.
CCACHE_NLEVELS
The environment variable CCACHE_NLEVELS allows you
to choose the number of levels of hash in the cache directory. The default is
2. The minimum is 1 and the maximum is 8.
CCACHE_NODIRECT
If you set the environment variable
CCACHE_NODIRECT then ccache will not use the direct mode.
CCACHE_NOSTATS
If you set the environment variable CCACHE_NOSTATS
then ccache will not update the statistics files on each compilation.
CCACHE_PATH
You can optionally set CCACHE_PATH to a
colon-separated path where ccache will look for the real compilers. If you
don’t do this then ccache will look for the first executable matching
the compiler name in the normal PATH that isn’t a symbolic link
to ccache itself.
CCACHE_PREFIX
This option adds a prefix to the command line that ccache
runs when invoking the compiler. Also see the section below on using ccache
with “distcc”.
CCACHE_READONLY
The CCACHE_READONLY environment variable tells
ccache to attempt to use existing cached object files, but not to try to add
anything new to the cache. If you are using this because your
CCACHE_DIR is read-only, then you may find that you also need to set
CCACHE_TEMPDIR as otherwise ccache will fail to create temporary
files.
CCACHE_RECACHE
This forces ccache to not use any cached results, even if
it finds them. New results are still cached, but existing cache entries are
ignored.
CCACHE_SLOPPINESS
By default, ccache tries to give as few false cache hits
as possible. However, in certain situations it’s possible that you know
things that ccache can’t take for granted. The CCACHE_SLOPPINESS
environment variable makes it possible to tell ccache to relax some checks in
order to increase the hit rate. The value should be a comma-separated string
with options. Available options are:
file_macro
CCACHE_TEMPDIR
Ignore __FILE__ being present in the source.
include_file_mtime
Don’t check the modification time of include files
in the direct mode.
pch_defines
Be sloppy about #defines when precompiling a header file.
See PRECOMPILED HEADERS for more information.
time_macros
Ignore __DATE__ and __TIME__ being present
in the source code.
See the discussion under TROUBLESHOOTING for more information.The CCACHE_TEMPDIR environment variable specifies
where ccache will put temporary files. The default is $CCACHE_DIR/tmp.
Note
In previous versions of ccache, CCACHE_TEMPDIR had to be on the same
filesystem as the CCACHE_DIR path, but this requirement has been
relaxed.)
CCACHE_UMASK
This sets the umask for ccache and all child processes
(such as the compiler). This is mostly useful when you wish to share your
cache with other users. Note that this also affects the file permissions set
on the object files created from your compilations.
CCACHE_UNIFY
If you set the environment variable CCACHE_UNIFY
then ccache will use a C/C++ unifier when hashing the preprocessor output if
the -g 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 using CCACHE_UNIFY
changes the hash, so cached compilations with CCACHE_UNIFY set cannot
be used when CCACHE_UNIFY is not set and vice versa. The reason the
unifier is off by default is that it can give incorrect line number
information in compiler warning messages. Also note that enabling the unifier
implies turning off the direct mode.
CACHE SIZE MANAGEMENT¶
By default ccache has a one gigabyte limit on the total size of files in the cache and no maximum number of files. You can set different limits using the -M/--max-size and -F/--max-files options. Use ccache -s/--show-stats to see the cache size and the currently configured limits (in addition to other various statistics).CACHE COMPRESSION¶
ccache can optionally compress all files it puts into the cache using the compression library zlib. While this involves a negligible performance slowdown, it significantly increases the number of files that fit in the cache. You can turn on compression by setting the CCACHE_COMPRESS environment variable.HOW CCACHE WORKS¶
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. ccache has two ways of doing the detection:•the direct mode, where ccache hashes the
source code and include files directly
•the preprocessor mode, where ccache runs
the preprocessor on the source code and hashes the result
The direct mode is generally faster since running the preprocessor has some
overhead.
Common hashed information¶
For both modes, the following information is included in the hash:•the extension used by the compiler for a file
with preprocessor output (normally .i for C code and .ii for C++
code)
•the compiler’s size and modification time
(or other compiler-specific information specified by
CCACHE_COMPILERCHECK)
•the name of the compiler
•the current directory (if CCACHE_HASHDIR
is set)
•contents of files specified by
CCACHE_EXTRAFILES (if any)
The direct mode¶
In the direct mode, the hash is formed of the common information and:•the input source file
•the command line options
Based on the hash, a data structure called “manifest” is looked up
in the cache. The manifest contains:
•references to cached compilation results (object
file, dependency file, etc) that were produced by previous compilations that
matched the hash
•paths to the include files that were read at the
time the compilation results were stored in the cache
•hash sums of the include files at the time the
compilation results were stored in the cache
The current contents of the include files are then hashed and compared to the
information in the manifest. If there is a match, ccache knows the result of
the compilation. If there is no match, ccache falls back to running the
preprocessor. The output from the preprocessor is parsed to find the include
files that were read. The paths and hash sums of those include files are then
stored in the manifest along with information about the produced compilation
result.
The direct mode will be disabled if any of the following holds:
•the environment variable CCACHE_NODIRECT
is set
•a modification time of one of the include files
is too new (needed to avoid a race condition)
•the unifier is enabled (the environment variable
CCACHE_UNIFY is set)
•a compiler option not supported by the direct
mode is used:
•a -Wp,X compiler option
other than -Wp,-MD,path and
-Wp,-MMD,path
•-Xpreprocessor
•the string “__TIME__” is present
outside comments and string literals in the source code
The preprocessor mode¶
In the preprocessor mode, the hash is formed of the common information and:•the preprocessor output from running the compiler
with -E
•the command line options except options that
affect include files ( -I, -include, -D, etc; the theory
is that these options will change the preprocessor output if they have any
effect at all)
•any standard error output generated by the
preprocessor
Based on the hash, the cached compilation result can be looked up directly in
the cache.
COMPILING IN DIFFERENT DIRECTORIES¶
Some information included in the hash that identifies a unique compilation may contain absolute paths:•The preprocessed source code may contain absolute
paths to include files if the compiler option -g is used or if absolute
paths are given to -I and similar compiler options.
•Paths specified by compiler options (such as
-I, -MF, etc) may be absolute.
•The source code file path may be absolute, and
that path may substituted for __FILE__ macros in the source code or
included in warnings emitted to standard error by the preprocessor.
This means that if you compile the same code in different locations, you
can’t 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 “base
directory” by setting the CCACHE_BASEDIR variable 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’t use / as the base directory since that will
make ccache also rewrite paths to system header files, which doesn’t
gain anything.)
The drawbacks of using CCACHE_BASEDIR are:
•If you specify an absolute path to the source
code file, __FILE__ macros will be expanded to a relative path
instead.
•If you specify an absolute path to the source
code file and compile with -g, 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 “cd” command in GDB.
PRECOMPILED HEADERS¶
ccache has support for GCC’s precompiled headers. However, you have to do some things to make it work properly:•You must set CCACHE_SLOPPINESS to
pch_defines,time_macros. The reason is that ccache can’t tell
whether __TIME__ or __DATE__ is used when using a precompiled
header. Further, it can’t detect changes in #defines in the source code
because of how preprocessing works in combination with precompiled
headers.
•You must either:
•use the -include compiler option to
include the precompiled header (i.e., don’t use #include in the
source code to include the header); or
•add the -fpch-preprocess compiler option
when compiling.
If you don’t do this, either the non-precompiled version of the header
file will be used (if available) or ccache will fall back to running the real
compiler and increase the statistics counter “preprocessor
error” (if the non-precompiled header file is not available).SHARING A CACHE¶
A group of developers can increase the cache hit rate by sharing a cache directory. To share a cache without unpleasant side effects, the following conditions should to be met:•Use the same CCACHE_DIR environment
variable setting.
•Unset the CCACHE_HARDLINK environment
variable.
•Make sure everyone sets the CCACHE_UMASK
environment variable to 002. This ensures that cached files are accessible to
everyone in the group.
•Make sure that all users have write permission in
the entire cache directory (and that you trust all users of the shared
cache).
•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 “find $CCACHE_DIR -type d | xargs
chmod g+s” might be useful for this.
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’s
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.
You may also want to make sure that the developers have CCACHE_BASEDIR
set appropriately, as discussed in the previous section.
SHARING A CACHE ON NFS¶
It is possible to put the cache directory on an NFS filesystem (or similar filesystems), but keep in mind that:•Having the cache on NFS may slow down
compilation. Make sure to do some benchmarking to see if it’s worth
it.
•ccache hasn’t been tested very thoroughly
on NFS.
A tip is to set CCACHE_TEMPDIR to a directory on the local host to avoid
NFS traffic for temporary files.
USING CCACHE WITH OTHER COMPILER WRAPPERS¶
The recommended way of combining ccache with another compiler wrapper (such as “distcc”) is by using the CCACHE_PREFIX option. You just need to set the environment variable CCACHE_PREFIX to the name of the wrapper (e.g. distcc) and ccache will prefix the command line with the specified command when running the compiler. Unless you set CCACHE_COMPILERCHECK to a suitable command (see the description of that configuration option), it is not recommended to use the form ccache anotherwrapper compiler args as the compilation command. It’s also not recommended to use the masquerading technique for the other compiler wrapper. The reason is that by default, ccache will in both cases hash the mtime and size of the other wrapper instead of the real compiler, which means that:•Compiler upgrades will not be detected
properly.
•The cached results will not be shared between
compilations with and without the other wrapper.
Another minor thing is that if CCACHE_PREFIX is not used, ccache will
needlessly invoke the other wrapper when running the preprocessor.
BUGS¶
•ccache doesn’t handle the GNU
Assembler’s .incbin directive correctly. This directive can be
embedded in the source code inside an asm statement in order to
include a file verbatim in the object file. If the included file is modified,
ccache doesn’t pick up the change since the inclusion isn’t done
by the preprocessor. A workaround of this problem is to set
CCACHE_EXTRAFILES to the path of the included file.
TROUBLESHOOTING¶
General¶
A general tip for getting information about what ccache is doing is to enable debug logging by setting CCACHE_LOGFILE. The log contains executed commands, important decisions that ccache makes, read and written files, etc. Another way of keeping track of what is happening is to check the output of ccache -s.Performance¶
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. 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. A good way of monitoring how well ccache works is to run ccache -s 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:•If “cache hit (preprocessed)” has
been incremented instead of “cache hit (direct)”, ccache has
fallen back to preprocessor mode, which is generally slower. Some possible
reasons are:
•The source code has been modified in such a way
that the preprocessor output is not affected.
•Compiler arguments that are hashed in the direct
mode but not in the preprocessor mode have changed ( -I,
-include, -D, etc) and they didn’t affect the
preprocessor output.
•The compiler option -Xpreprocessor or
-Wp, X (except -Wp,-MD,path and
Wp,-MMD, path) is used.
•This was the first compilation with a new value
of CCACHE_BASEDIR.
•A modification time of one of the include files
is too new (created the same second as the compilation is being done). This
check is made to avoid a race condition. To fix this, create the include file
earlier in the build process, if possible, or set CCACHE_SLOPPINESS to
include_file_mtime if you are willing to take the risk. (The race
condition consists of these events: the preprocessor is run; an include file
is modified by someone; the new include file is hashed by ccache; the real
compiler is run on the preprocessor’s output, which contains data from
the old header file; the wrong object file is stored in the cache.)
•The __TIME__ preprocessor macro is
(potentially) being used. ccache turns off direct mode if
“__TIME__” is present in the source code outside comments and
string literals. This is done as a safety measure since the string indicates
that a __TIME__ macro may affect the output. (To be sure, ccache
would have to run the preprocessor, but the sole point of the direct mode is
to avoid that.) If you know that __TIME__ isn’t used in
practise, or don’t care if ccache produces objects where
__TIME__ is expanded to something in the past, you can set
CCACHE_SLOPPINESS to time_macros.
•The __DATE__ preprocessor macro is
(potentially) being used and the date has changed. This is similar to how
__TIME__ is handled. If “__DATE__” is present in the
source code outside comments and string literals, ccache hashes the current
date in order to be able to produce the correct object file if the
__DATE__ macro affects the output. If you know that __DATE__
isn’t used in practise, or don’t care if ccache produces objects
where __DATE__ is expanded to something in the past, you can set
CCACHE_SLOPPINESS to time_macros.
•The __FILE__ preprocessor macro is
(potentially) being used and the file path has changed. If
“__FILE__” is present in the source code outside comments and
string literals, ccache hashes the current input file path in order to be able
to produce the correct object file if the __FILE__ macro affects the
output. If you know that __FILE__ isn’t used in practise, or
don’t care if ccache produces objects where __FILE__ is expanded
to the wrong path, you can set CCACHE_SLOPPINESS to
file_macro.
•If “cache miss” has been
incremented even though the same code has been compiled and cached before,
ccache has either detected that something has changed anyway or a cleanup has
been performed (either explicitly or implicitly when a cache limit has been
reached). Some perhaps unobvious things that may result in a cache miss are
usage of __TIME__ or __DATE__ macros, or use of automatically
generated code that contains a timestamp, build counter or other volatile
information.
•If “multiple source files” has been
incremented, it’s an indication that the compiler has been invoked on
several source code files at once. ccache doesn’t support that. Compile
the source code files separately if possible.
•If “unsupported compiler option”
has been incremented, enable debug logging and check which option was
rejected.
•If “preprocessor error” has been
incremented, one possible reason is that precompiled headers are being used.
See PRECOMPILED HEADERS for how to remedy this.
•If “can’t use precompiled
header” has been incremented, see PRECOMPILED HEADERS.
Errors when compiling with ccache¶
If compilation doesn’t work with ccache, but it works without it, one possible reason is that the compiler can’t compile preprocessed output correctly. A workaround that may work is to set CCACHE_CPP2. This will make cache misses slower, though, so it is better to find and fix the root cause.Corrupt object files¶
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 CCACHE_PREFIX command or compiler wrapper. If this happens, the easiest way of fixing it is this: 1.Build so that the bad object file ends up in the build
tree.
2.Remove the bad object file from the build tree.
3.Rebuild with CCACHE_RECACHE set.
An alternative is to clear the whole cache with ccache -C if you
don’t mind losing other cached results.
There are no reported issues about ccache producing broken object files
reproducibly. That doesn’t mean it can’t happen, so if you find
a repeatable case, please report it.
MORE INFORMATION¶
Credits, mailing list information, bug reporting instructions, source code, etc, can be found on ccache’s web site: http://ccache.samba.org.AUTHOR¶
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.07/12/2016 | ccache 3.1.12 |