Pass certain environment variables, meant to convey information about the toolchain to use, as make variables when creating a kernel config file. The kernel build system checks for toolchain capabilities when generating the merged config file and a valid toolchain is required to enable some options.
OpenEmbedded has attempted, for a couple years now, to specify the compiler by setting the CC environment variable: https://git.openembedded.org/openembedded-core/commit/?id=ff1bdd75d50f0ebac3d599e461685ace29559a82 This was unsuccessful due to the kernel's top-level Makefile explicitly assigning variables, such as CC, and ignoring what's present in the environment. It is possible to override this behavior by invoking make with the '-e' option but the make manual discourages this: Every environment variable that make sees when it starts up is transformed into a make variable with the same name and value. However, an explicit assignment in the makefile, or with a command argument, overrides the environment. (If the ‘-e’ flag is specified, then values from the environment override assignments in the makefile. See Summary of Options. But this is not recommended practice.) A simple test case is to create a defconfig while specifying clang as the compiler to use: $ make CC=clang-10 defconfig ... Create a config fragment that attempts to enable CONFIG_INIT_STACK_ALL_PATTERN which is currently only possible to enable when building with clang: $ echo "CONFIG_INIT_STACK_ALL_PATTERN=y" > init-stack-all.cfg Specify clang in the environment when running merge_config.sh and see that the option couldn't be enabled: $ CC=clang-10 merge_config.sh .config init-stack-all.cfg ... Value requested for CONFIG_INIT_STACK_ALL_PATTERN not in final .config Requested value: CONFIG_INIT_STACK_ALL_PATTERN=y Actual value: Note that the less secure CONFIG_INIT_STACK_NONE option is enabled, instead: $ grep CONFIG_INIT_STACK .config CONFIG_INIT_STACK_NONE=y Signed-off-by: Tyler Hicks <[email protected]> --- tools/merge_config.sh | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/tools/merge_config.sh b/tools/merge_config.sh index 14b4c1fbd04c..38eb85afc263 100755 --- a/tools/merge_config.sh +++ b/tools/merge_config.sh @@ -153,7 +153,8 @@ fi # Use the merged file as the starting point for: # alldefconfig: Fills in any missing symbols with Kconfig default # allnoconfig: Fills in any missing symbols with # CONFIG_* is not set -make LD="$LD" KCONFIG_ALLCONFIG=$TMP_FILE $OUTPUT_ARG $ALLTARGET +make HOSTCC="$HOSTCC" HOSTLD="$HOSTLD" CC="$CC" LD="$LD" \ + KCONFIG_ALLCONFIG=$TMP_FILE $OUTPUT_ARG $ALLTARGET # Check all specified config values took (might have missed-dependency issues) -- 2.17.1
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