On Mon, Jun 27, 2016 at 05:17:17PM +0200, Torsten Duwe wrote: > Once gcc is enhanced to optionally generate NOPs at the beginning > of each function, like the concept proven in > https://gcc.gnu.org/ml/gcc-patches/2016-04/msg01671.html > (sans the "fprintf (... pad_size);", which spoils the data structure > for kernel use), the generated pads can nicely be used to reroute > function calls for tracing/profiling, or live patching. > > The pads look like > fffffc00081335f0 <hrtimer_init>: > fffffc00081335f0: d503201f nop > fffffc00081335f4: d503201f nop > fffffc00081335f8: a9bd7bfd stp x29, x30, [sp,#-48]! > fffffc00081335fc: 910003fd mov x29, sp > [...] > > This patch gets the pad locations from the compiler-generated > __prolog_pads_loc into the _mcount_loc array, and provides the > code patching functions to turn the pads at runtime into > > fffffc00081335f0 mov x9, x30 > fffffc00081335f4 bl 0xfffffc00080a08c0 <ftrace_caller> > fffffc00081335f8 stp x29, x30, [sp,#-48]! > fffffc00081335fc mov x29, sp > > as well as an ftrace_caller that can handle these call sites. > Now ARCH_SUPPORTS_FTRACE_OPS as a benefit, and the graph caller > still works, too. > > Signed-off-by: Li Bin <huawei.libin@xxxxxxxxxx> > Signed-off-by: Torsten Duwe <duwe@xxxxxxx> > --- > arch/arm64/Kconfig | 1 + > arch/arm64/Makefile | 4 ++ > arch/arm64/include/asm/ftrace.h | 8 ++++ > arch/arm64/kernel/Makefile | 6 +-- > arch/arm64/kernel/entry-ftrace.S | 89 +++++++++++++++++++++++++++++++++++++++ > arch/arm64/kernel/ftrace.c | 43 +++++++++++++++++-- > include/asm-generic/vmlinux.lds.h | 2 +- > include/linux/compiler.h | 4 ++ > 8 files changed, 150 insertions(+), 7 deletions(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 5a0a691..36a0e26 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -72,6 +72,7 @@ config ARM64 > select HAVE_DMA_API_DEBUG > select HAVE_DMA_CONTIGUOUS > select HAVE_DYNAMIC_FTRACE > + select HAVE_DYNAMIC_FTRACE_WITH_REGS > select HAVE_EFFICIENT_UNALIGNED_ACCESS > select HAVE_FTRACE_MCOUNT_RECORD > select HAVE_FUNCTION_TRACER > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile > index 648a32c..e5e335c 100644 > --- a/arch/arm64/Makefile > +++ b/arch/arm64/Makefile > @@ -35,6 +35,10 @@ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables > KBUILD_CFLAGS += $(call cc-option, -mpc-relative-literal-loads) > KBUILD_AFLAGS += $(lseinstr) > > +ifeq ($(CONFIG_DYNAMIC_FTRACE_WITH_REGS), y) > +CC_FLAGS_FTRACE := -fprolog-pad=2 -DCC_USING_PROLOG_PAD > +endif > + It would probably be good to print a warning for older gccs which don't support this option, so that when the build fails, there's at least a warning to indicate why. Something like: ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS CC_FLAGS_FTRACE := -fprolog-pad=2 -DCC_USING_PROLOG_PAD ifeq ($(call cc-option,-fprolog-pad=2),) $(warning Cannot use CONFIG_DYNAMIC_FTRACE_WITH_REGS: \ -fprolog-pad not supported by compiler) endif endif -- Josh -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
