Messages in this thread Patch in this message | | | Date | Tue, 18 Apr 2017 16:44:29 -0500 | From | Josh Poimboeuf <> | Subject | [PATCH] x86/build: convert function graph '-Os' error to warning |
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On Tue, Apr 18, 2017 at 01:25:19PM -0700, Andi Kleen wrote: > On Tue, Apr 18, 2017 at 03:19:42PM -0500, Josh Poimboeuf wrote: > > On Tue, Apr 18, 2017 at 11:52:41AM -0700, Andi Kleen wrote: > > > Josh Poimboeuf <jpoimboe@redhat.com> writes: > > > > > > > > The error is working as designed. gcc < 4.6.0 doesn't have -mfentry, so > > > > it fails the above check on x86. Can you add a skip rule? It should > > > > skip building the following case: > > > > > > > > x86 && ((gcc < 4.6.0) || (CONFIG_X86_32 and !CONFIG_DYNAMIC_FTRACE)) > > > > && CONFIG_FUNCTION_GRAPH_TRACER && CONFIG_CC_OPTIMIZE_FOR_SIZE > > > > > > This will also break everyone's randconfig builds. The better way > > > would be to check this in the Makefile and disable one of the options > > > > I don't know how to disable a config option from the Makefile like that. > > You just don't do something in the Makefile, e.g. don't set the -Os > > For an example see the LTO Makefile here > > https://git.kernel.org/pub/scm/linux/kernel/git/ak/linux-misc.git/tree/scripts/Makefile.lto?h=lto-411-1
This seems to work:
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From: Josh Poimboeuf <jpoimboe@redhat.com> Subject: [PATCH] x86/build: convert function graph '-Os' error to warning
For pre-4.6.0 versions of GCC, which don't have '-mfentry', the '-maccumulate-outgoing-args' option is required for function graph tracing in order to avoid GCC bug 42109. However, GCC ignores '-maccumulate-outgoing-args' when '-Os' is also set.
Currently we force a build error to prevent that scenario, but that breaks randconfigs. So change the error to a warning which also disables CONFIG_CC_OPTIMIZE_FOR_SIZE.
Reported-by: Andi Kleen <andi@firstfloor.org> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> --- arch/x86/Makefile | 8 ++++++++ arch/x86/kernel/ftrace.c | 6 ------ 2 files changed, 8 insertions(+), 6 deletions(-)
diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 73604e1..4430dd4 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -154,6 +154,14 @@ ifdef CONFIG_FUNCTION_GRAPH_TRACER else ifeq ($(call cc-option-yn, -mfentry), n) ACCUMULATE_OUTGOING_ARGS := 1 + + # GCC ignores '-maccumulate-outgoing-args' when used with '-Os'. + # If '-Os' is enabled, disable it and print a warning. + ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE + undefine CONFIG_CC_OPTIMIZE_FOR_SIZE + $(warning Disabling CONFIG_CC_OPTIMIZE_FOR_SIZE. Your compiler does not have -mfentry so you cannot optimize for size with CONFIG_FUNCTION_GRAPH_TRACER.) + endif + endif endif endif diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c index 0e5ceac..5b71535 100644 --- a/arch/x86/kernel/ftrace.c +++ b/arch/x86/kernel/ftrace.c @@ -29,12 +29,6 @@ #include <asm/ftrace.h> #include <asm/nops.h> -#if defined(CONFIG_FUNCTION_GRAPH_TRACER) && \ - !defined(CC_USING_FENTRY) && \ - !defined(CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE) -# error The following combination is not supported: ((compiler missing -mfentry) || (CONFIG_X86_32 and !CONFIG_DYNAMIC_FTRACE)) && CONFIG_FUNCTION_GRAPH_TRACER && CONFIG_CC_OPTIMIZE_FOR_SIZE -#endif - #ifdef CONFIG_DYNAMIC_FTRACE int ftrace_arch_code_modify_prepare(void) -- 2.7.4
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