El Tue, Mar 20, 2018 at 11:18:33PM +0000 Russell King - ARM Linux ha dit: > On Wed, Mar 21, 2018 at 12:02:06AM +0100, Stefan Agner wrote: > > Use cc-options call for compiler options which are not available > > in clang. With this patch an ARMv7 multi platform kernel can be > > successfully build using clang (tested with version 5.0.1). > > > > Based-on-patches-by: Behan Webster <beh...@converseincode.com> > > Signed-off-by: Stefan Agner <ste...@agner.ch>
Great to see your work on bringing clang support for 32-bit ARM upstream! > > --- > > arch/arm/Makefile | 2 +- > > arch/arm/boot/compressed/Makefile | 2 +- > > 2 files changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/arch/arm/Makefile b/arch/arm/Makefile > > index e9e3fde3c657..20e9fee1ccc5 100644 > > --- a/arch/arm/Makefile > > +++ b/arch/arm/Makefile > > @@ -39,7 +39,7 @@ KBUILD_CFLAGS += $(call > > cc-option,-mno-unaligned-access) > > endif > > > > ifeq ($(CONFIG_FRAME_POINTER),y) > > -KBUILD_CFLAGS +=-fno-omit-frame-pointer -mapcs -mno-sched-prolog > > +KBUILD_CFLAGS +=-fno-omit-frame-pointer $(call cc-option,-mapcs,) > > $(call cc-option,-mno-sched-prolog,) > > Some of these options here are to ensure that we generate the following > code, so we can backtrace: > > mov ip, sp > stmfd sp!, {fp, ip, lr, pc} > sub fp, ip, #4 > > If clang isn't producing that code at the start of functions with > CONFIG_FRAME_POINTER=y, then backtracing will not work, and arguably > CONFIG_FRAME_POINTER=y is useless there. In that circumstance, it's > probably better to fail so the user can configure something more > debuggable, rather than having the kernel potentially producing > undebuggable oopses. Which option in particular is important to generate the above code for backstracing? According to the gcc doc -mapcs(-frame) is deprecated. For -mno-sched-prolog the doc says: "Prevent the reordering of instructions in the function prologue, or the merging of those instruction with the instructions in the function’s body. This means that all functions start with a recognizable set of instructions (or in fact one of a choice from a small set of different function prologues), and this information can be used to locate the start of functions inside an executable piece of code. The default is -msched-prolog." Thanks Matthias