Messages in this thread | | | Subject | Re: [RFC PATCH] arm64/ftrace: support dynamically allocated trampolines | From | "chengjian (D)" <> | Date | Mon, 13 Jan 2020 14:18:14 +0800 |
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On 2020/1/10 20:12, Mark Rutland wrote: > On Fri, Jan 10, 2020 at 07:28:17PM +0800, chengjian (D) wrote: >> On 2020/1/10 0:48, Mark Rutland wrote: >>> On Thu, Jan 09, 2020 at 02:27:36PM +0000, Cheng Jian wrote: >>>> + /* >>>> + * Update the trampoline ops REF >>>> + * >>>> + * OLD INSNS : ldr_l x2, function_trace_op >>>> + * adrp x2, sym >>>> + * ldr x2, [x2, :lo12:\sym] >>>> + * >>>> + * NEW INSNS: >>>> + * nop >>>> + * ldr x2, <ftrace_ops> >>>> + */ >>>> + op_offset -= start_offset_common; >>>> + ip = (unsigned long)trampoline + caller_size + op_offset; >>>> + nop = aarch64_insn_gen_nop(); >>>> + memcpy((void *)ip, &nop, AARCH64_INSN_SIZE); >>>> + >>>> + op_offset += AARCH64_INSN_SIZE; >>>> + ip = (unsigned long)trampoline + caller_size + op_offset; >>>> + offset = (unsigned long)ptr - ip; >>>> + if (WARN_ON(offset % AARCH64_INSN_SIZE != 0)) >>>> + goto free; >>>> + offset = offset / AARCH64_INSN_SIZE; >>>> + pc_ldr |= (offset & mask) << shift; >>>> + memcpy((void *)ip, &pc_ldr, AARCH64_INSN_SIZE); >>> I think it would be much better to have a separate template for the >>> trampoline which we don't have to patch in this way. It can even be >>> placed into a non-executable RO section, since the template shouldn't be >>> executed directly. >> A separate template ! >> >> This may be a good way, and I think the patching here is very HACK too(Not >> very friendly). >> >> I had thought of other ways before, similar to the method on X86_64, >> remove the ftrace_common(), directly modifying >> ftrace_caller/ftrace_reg_caller, We will only need to copy the code >> once in this way, and these is no need to modify call ftrace_common to >> NOP. >> >> Using a trampoline template sounds great. but this also means that we >> need to aintain a template(or maybe two templates: one for caller, >> another for regs_caller). >> >> Hi, Mark, what do you think about it ? > I think that having two templates is fine. We can factor > ftrace_common_return into a macro mirroring ftrace_regs_entry, and I > suspect we can probably figure out some way to factor the common > portion. > > Thanks, > Mark. > > .
OK, I will do it.
Thank you, Mark.
--Cheng Jian
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