Re: [PATCH -v5 13/17] arm/ftrace: Use __patch_text_real()

Will Deacon
2019-11-12T11:30:00Z

On Mon, Nov 11, 2019 at 06:25:41PM +0100, Peter Zijlstra wrote:
> On Mon, Nov 11, 2019 at 06:19:55PM +0100, Peter Zijlstra wrote:
>
> > If you can give me a Tested-by, I'll replace it with the below... :-)
> >
> > --- a/arch/arm/kernel/ftrace.c
> > +++ b/arch/arm/kernel/ftrace.c
> > @@ -22,6 +22,7 @@
> > #include <asm/ftrace.h>
> > #include <asm/insn.h>
> > #include <asm/set_memory.h>
> > +#include <asm/patch.h>
> >
> > #ifdef CONFIG_THUMB2_KERNEL
> > #define NOP 0xf85deb04 /* pop.w {lr} */
> > @@ -35,9 +36,7 @@ static int __ftrace_modify_code(void *da
> > {
> > int *command = data;
> >
> > - set_kernel_text_rw();
> > ftrace_modify_all_code(*command);
> > - set_kernel_text_ro();
> >
> > return 0;
> > }
> > @@ -59,13 +58,11 @@ static unsigned long adjust_address(stru
> >
> > int ftrace_arch_code_modify_prepare(void)
> > {
> > - set_all_modules_text_rw();
> > return 0;
> > }
> >
> > int ftrace_arch_code_modify_post_process(void)
> > {
> > - set_all_modules_text_ro();
> > /* Make sure any TLB misses during machine stop are cleared. */
> > flush_tlb_all();
> > return 0;
> > @@ -97,10 +94,7 @@ static int ftrace_modify_code(unsigned l
> > return -EINVAL;
> > }
> >
> > - if (probe_kernel_write((void *)pc, &new, MCOUNT_INSN_SIZE))
> > - return -EPERM;
> > -
> > - flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);
> > + __patch_text_real((void *)pc, new, true);
>
> I'll even make that: __patch_text((void *)pc, new);

This fails to compile. I bodged it as below, but maybe this stuff should
actually live in insn.c. Not fussed either way. I ran the ftrace tests,
loaded a module and toggled ftrace on/off with this applied and it looks
like it works to me:

Tested-by: Will Deacon <will@kernel.org>

Will

--->8

diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 8cad59465af3..a885172e504c 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -49,8 +49,8 @@ obj-$(CONFIG_HAVE_ARM_SCU) += smp_scu.o
obj-$(CONFIG_HAVE_ARM_TWD) += smp_twd.o
obj-$(CONFIG_ARM_ARCH_TIMER) += arch_timer.o
obj-$(CONFIG_FUNCTION_TRACER) += entry-ftrace.o
-obj-$(CONFIG_DYNAMIC_FTRACE) += ftrace.o insn.o
-obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o insn.o
+obj-$(CONFIG_DYNAMIC_FTRACE) += ftrace.o insn.o patch.o
+obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o insn.o patch.o
obj-$(CONFIG_JUMP_LABEL) += jump_label.o insn.o patch.o
obj-$(CONFIG_KEXEC) += machine_kexec.o relocate_kernel.o
# Main staffs in KPROBES are in arch/arm/probes/ .