Commit 1e97b278 authored by Arnout Vandecappelle's avatar Arnout Vandecappelle Committed by Peter Korsgaard
Browse files

ccache: support changing the output directory 



When building in a different output directory than the original build,
there will currently be a lot of ccache misses because in many cases
there is some -I/... absolute path in the compilation. Ccache has an
option CCACHE_BASEDIR to substitute absolute paths with relative paths,
so they wil be the same in the hash (and in the output).

Since there are some disadvantages to this path rewriting, it is made
optional as BR2_CCACHE_USE_BASEDIR. It defaults to y because the
usefulness of ccache is severely reduced without this option.

In addition to CCACHE_BASEDIR, we also substitute away the occurences
of $(HOST_DIR) in the calculation of the compiler hash. This is done
regardless of the setting of BR2_CCACHE_USE_BASEDIR because it's
quite harmless.

Signed-off-by: default avatarArnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: default avatarPeter Korsgaard <peter@korsgaard.com>
parent f4682cf9

Config.in

+27 −0
Original line number Diff line number Diff line
@@ -286,6 +286,33 @@ config BR2_CCACHE_INITIAL_SETUP 


	  These initial settings are applied after ccache has been compiled.



config BR2_CCACHE_USE_BASEDIR

	bool "Use relative paths"

	default y

	help

	  Allow ccache to convert absolute paths within the output

	  directory into relative paths.



	  During the build, many -I include directives are given with

	  an absolute path. These absolute paths end up in the hashes

	  that are computed by ccache. Therefore, when you build from a

	  different directory, the hash will be different and the

	  cached object will not be used.



	  To improve cache performance, set this option to y. This

	  allows ccache to rewrite absolute paths within the output

	  directory into relative paths. Note that only paths within

	  the output directory will be rewritten; therefore, if you

	  change BR2_HOST_DIR to point outside the output directory and

	  subsequently move it to a different location, this will lead

	  to cache misses.



	  This option has as a result that the debug information in the

	  object files also has only relative paths. Therefore, make

	  sure you cd to the build directory before starting gdb. See

	  the section "COMPILING IN DIFFERENT DIRECTORIES" in the

	  ccache manual for more information.



endif



config BR2_DEPRECATED

docs/manual/ccache-support.txt

+20 −0
Original line number Diff line number Diff line
@@ -33,3 +33,23 @@ make CCACHE_OPTIONS="--max-size=5G" ccache-options 
# zero statistics counters

make CCACHE_OPTIONS="--zero-stats" ccache-options

-----------------



+ccache+ makes a hash of the source files and of the compiler options.

If a compiler option is different, the cached object file will not be

used. Many compiler options, however, contain an absolute path to the

staging directory. Because of this, building in a different output

directory would lead to many cache misses.



To avoid this issue, buildroot has the +Use relative paths+ option

(+BR2_CCACHE_USE_BASEDIR+). This will rewrite all absolute paths that

point inside the output directory into relative paths. Thus, changing

the output directory no longer leads to cache misses.



A disadvantage of the relative paths is that they also end up to be

relative paths in the object file. Therefore, for example, the debugger

will no longer find the file, unless you cd to the output directory

first.



See https://ccache.samba.org/manual.html#_compiling_in_different_directories[the

ccache manual's section on "Compiling in different directories"] for

more details about this rewriting of absolute paths.

package/gcc/gcc.mk

+3 −1
Original line number Diff line number Diff line
@@ -256,8 +256,10 @@ HOST_GCC_COMMON_CCACHE_HASH_FILES += package/gcc/$(GCC_VERSION)/1000-powerpc-lin 
endif

endif



# _CONF_OPTS contains some references to the absolute path of $(HOST_DIR),

# so substitute those away.

HOST_GCC_COMMON_TOOLCHAIN_WRAPPER_ARGS += -DBR_CCACHE_HASH=\"`\

	printf '%s' $($(PKG)_CONF_OPTS) $(GCC_VERSION) \

	printf '%s' $(subst $(HOST_DIR),@HOST_DIR@,$($(PKG)_CONF_OPTS)) \

		| sha256sum - $(HOST_GCC_COMMON_CCACHE_HASH_FILES) \

		| cut -c -64 | tr -d '\n'`\"

endif # BR2_CCACHE

toolchain/toolchain-wrapper.c

+11 −0
Original line number Diff line number Diff line
@@ -267,6 +267,10 @@ int main(int argc, char **argv) 
#ifdef BR_CCACHE_HASH

			fprintf(stderr, "%sCCACHE_COMPILERCHECK='string:" BR_CCACHE_HASH "'",

				(debug == 2) ? "\n    " : " ");

#endif

#ifdef BR_CCACHE_BASEDIR

			fprintf(stderr, "%sCCACHE_BASEDIR='" BR_CCACHE_BASEDIR "'",

				(debug == 2) ? "\n    " : " ");

#endif

			for (i = 0; exec_args[i]; i++)

				fprintf(stderr, "%s'%s'",
@@ -282,6 +286,13 @@ int main(int argc, char **argv) 
		return 3;

	}

#endif

#ifdef BR_CCACHE_BASEDIR

	/* Allow compilercheck to be overridden through the environment */

	if (setenv("CCACHE_BASEDIR", BR_CCACHE_BASEDIR, 0)) {

		perror(__FILE__ ": Failed to set CCACHE_BASEDIR");

		return 3;

	}

#endif



	if (execv(exec_args[0], exec_args))

		perror(path);

toolchain/toolchain-wrapper.mk

+4 −0
Original line number Diff line number Diff line
@@ -20,6 +20,10 @@ ifeq ($(BR2_CCACHE),y) 
TOOLCHAIN_WRAPPER_ARGS += -DBR_CCACHE

endif



ifeq ($(BR2_CCACHE_USE_BASEDIR),y)

TOOLCHAIN_WRAPPER_ARGS += -DBR_CCACHE_BASEDIR='"$(BASE_DIR)"'

endif



# For simplicity, build directly into the install location

define TOOLCHAIN_BUILD_WRAPPER

	$(Q)mkdir -p $(HOST_DIR)/usr/bin