Re: [PATCH -v5mkII 13/17] arm/ftrace: Use __patch_text()

Steven Rostedt
2020-01-08T14:16:33Z

On Wed, 8 Jan 2020 13:22:52 +0100
Arnd Bergmann <arnd@arndb.de> wrote:

> On Wed, Nov 13, 2019 at 10:29 AM Peter Zijlstra <peterz@infradead.org> wrote:
> > @@ -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
>
> This broke randconfig builds with big-endian ARMv5:
>
> ../arch/arm/kernel/patch.c: In function '__patch_text_real':
> ../arch/arm/kernel/patch.c:94:11: error: implicit declaration of
> function '__opcode_to_mem_thumb32'
> [-Werror=implicit-function-declaration]
> insn = __opcode_to_mem_thumb32(insn);
> ^~~~~~~~~~~~~~~~~~~~~~~
>
> The problem is that we don't have a BE32 definition of
> __opcode_to_mem_thumb32, mostly because no hardware
> supports that.
>
> One possible workaround is a big ugly:
>
> diff --git a/arch/arm/kernel/patch.c b/arch/arm/kernel/patch.c
> index d0a05a3bdb96..1067fd122897 100644
> --- a/arch/arm/kernel/patch.c
> +++ b/arch/arm/kernel/patch.c
> @@ -90,9 +90,11 @@ void __kprobes __patch_text_real(void *addr,
> unsigned int insn, bool remap)
>
> size = sizeof(u32);
> } else {
> +#ifdef CONFIG_THUMB2_KERNEL
> if (thumb2)

If we change the above to:

if (IS_ENABLED(CONFIG_THUMB2_KERNEL) && thumb2)

Would the compiler optmize out __opcode_to_mem_thumb32(). We would need
to add a declaration for it, but wont need to define it. At least we
wont have nasty #ifdef logic in the code.

-- Steve

> insn = __opcode_to_mem_thumb32(insn);
> else
> +#endif
> insn = __opcode_to_mem_arm(insn);
>
> *(u32 *)waddr = insn;
>
>
> Any other suggestions?
>
> Arnd