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Diffstat (limited to 'Documentation/kbuild/makefiles.txt')
| -rw-r--r-- | Documentation/kbuild/makefiles.txt | 166 |
1 files changed, 97 insertions, 69 deletions
diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt index 443230b43e09..99d51a5bb0d9 100644 --- a/Documentation/kbuild/makefiles.txt +++ b/Documentation/kbuild/makefiles.txt @@ -17,6 +17,7 @@ This document describes the Linux kernel Makefiles. --- 3.8 Command line dependency --- 3.9 Dependency tracking --- 3.10 Special Rules + --- 3.11 $(CC) support functions === 4 Host Program support --- 4.1 Simple Host Program @@ -38,7 +39,6 @@ This document describes the Linux kernel Makefiles. --- 6.6 Commands useful for building a boot image --- 6.7 Custom kbuild commands --- 6.8 Preprocessing linker scripts - --- 6.9 $(CC) support functions === 7 Kbuild Variables === 8 Makefile language @@ -385,6 +385,102 @@ more details, with real examples. to prerequisites are referenced with $(src) (because they are not generated files). +--- 3.11 $(CC) support functions + + The kernel may be build with several different versions of + $(CC), each supporting a unique set of features and options. + kbuild provide basic support to check for valid options for $(CC). + $(CC) is useally the gcc compiler, but other alternatives are + available. + + as-option + as-option is used to check if $(CC) when used to compile + assembler (*.S) files supports the given option. An optional + second option may be specified if first option are not supported. + + Example: + #arch/sh/Makefile + cflags-y += $(call as-option,-Wa$(comma)-isa=$(isa-y),) + + In the above example cflags-y will be assinged the the option + -Wa$(comma)-isa=$(isa-y) if it is supported by $(CC). + The second argument is optional, and if supplied will be used + if first argument is not supported. + + cc-option + cc-option is used to check if $(CC) support a given option, and not + supported to use an optional second option. + + Example: + #arch/i386/Makefile + cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586) + + In the above example cflags-y will be assigned the option + -march=pentium-mmx if supported by $(CC), otherwise -march-i586. + The second argument to cc-option is optional, and if omitted + cflags-y will be assigned no value if first option is not supported. + + cc-option-yn + cc-option-yn is used to check if gcc supports a given option + and return 'y' if supported, otherwise 'n'. + + Example: + #arch/ppc/Makefile + biarch := $(call cc-option-yn, -m32) + aflags-$(biarch) += -a32 + cflags-$(biarch) += -m32 + + In the above example $(biarch) is set to y if $(CC) supports the -m32 + option. When $(biarch) equals to y the expanded variables $(aflags-y) + and $(cflags-y) will be assigned the values -a32 and -m32. + + cc-option-align + gcc version >= 3.0 shifted type of options used to speify + alignment of functions, loops etc. $(cc-option-align) whrn used + as prefix to the align options will select the right prefix: + gcc < 3.00 + cc-option-align = -malign + gcc >= 3.00 + cc-option-align = -falign + + Example: + CFLAGS += $(cc-option-align)-functions=4 + + In the above example the option -falign-functions=4 is used for + gcc >= 3.00. For gcc < 3.00 -malign-functions=4 is used. + + cc-version + cc-version return a numerical version of the $(CC) compiler version. + The format is <major><minor> where both are two digits. So for example + gcc 3.41 would return 0341. + cc-version is useful when a specific $(CC) version is faulty in one + area, for example the -mregparm=3 were broken in some gcc version + even though the option was accepted by gcc. + + Example: + #arch/i386/Makefile + cflags-y += $(shell \ + if [ $(call cc-version) -ge 0300 ] ; then \ + echo "-mregparm=3"; fi ;) + + In the above example -mregparm=3 is only used for gcc version greater + than or equal to gcc 3.0. + + cc-ifversion + cc-ifversion test the version of $(CC) and equals last argument if + version expression is true. + + Example: + #fs/reiserfs/Makefile + EXTRA_CFLAGS := $(call cc-ifversion, -lt, 0402, -O1) + + In this example EXTRA_CFLAGS will be assigned the value -O1 if the + $(CC) version is less than 4.2. + cc-ifversion takes all the shell operators: + -eq, -ne, -lt, -le, -gt, and -ge + The third parameter may be a text as in this example, but it may also + be an expanded variable or a macro. + === 4 Host Program support @@ -973,74 +1069,6 @@ When kbuild executes the following steps are followed (roughly): architecture specific files. ---- 6.9 $(CC) support functions - - The kernel may be build with several different versions of - $(CC), each supporting a unique set of features and options. - kbuild provide basic support to check for valid options for $(CC). - $(CC) is useally the gcc compiler, but other alternatives are - available. - - cc-option - cc-option is used to check if $(CC) support a given option, and not - supported to use an optional second option. - - Example: - #arch/i386/Makefile - cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586) - - In the above example cflags-y will be assigned the option - -march=pentium-mmx if supported by $(CC), otherwise -march-i586. - The second argument to cc-option is optional, and if omitted - cflags-y will be assigned no value if first option is not supported. - - cc-option-yn - cc-option-yn is used to check if gcc supports a given option - and return 'y' if supported, otherwise 'n'. - - Example: - #arch/ppc/Makefile - biarch := $(call cc-option-yn, -m32) - aflags-$(biarch) += -a32 - cflags-$(biarch) += -m32 - - In the above example $(biarch) is set to y if $(CC) supports the -m32 - option. When $(biarch) equals to y the expanded variables $(aflags-y) - and $(cflags-y) will be assigned the values -a32 and -m32. - - cc-option-align - gcc version >= 3.0 shifted type of options used to speify - alignment of functions, loops etc. $(cc-option-align) whrn used - as prefix to the align options will select the right prefix: - gcc < 3.00 - cc-option-align = -malign - gcc >= 3.00 - cc-option-align = -falign - - Example: - CFLAGS += $(cc-option-align)-functions=4 - - In the above example the option -falign-functions=4 is used for - gcc >= 3.00. For gcc < 3.00 -malign-functions=4 is used. - - cc-version - cc-version return a numerical version of the $(CC) compiler version. - The format is <major><minor> where both are two digits. So for example - gcc 3.41 would return 0341. - cc-version is useful when a specific $(CC) version is faulty in one - area, for example the -mregparm=3 were broken in some gcc version - even though the option was accepted by gcc. - - Example: - #arch/i386/Makefile - cflags-y += $(shell \ - if [ $(call cc-version) -ge 0300 ] ; then \ - echo "-mregparm=3"; fi ;) - - In the above example -mregparm=3 is only used for gcc version greater - than or equal to gcc 3.0. - - === 7 Kbuild Variables The top Makefile exports the following variables: |