Messages in this thread | | | Subject | Re: [RFC PATCH -next v2 0/4] arm64/ftrace: support dynamic trampoline | From | "Wangshaobo (bobo)" <> | Date | Thu, 21 Apr 2022 09:13:01 +0800 |
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在 2022/4/21 2:11, Steven Rostedt 写道: > Is this going anywhere? > > -- Steve
Not yet, Steve, ftrace_location() looks has no help to find a right rec->ip in our case,
ftrace_location() can find a right rec->ip when input ip is in the range between
sym+0 and sym+$end, but our question is how to identify rec->ip from __mcount_loc,
this changed the patchable entry before bti to after in gcc:
[1] https://reviews.llvm.org/D73680
gcc tells the place of first nop of the 5 NOPs when using -fpatchable-function-entry=5,3,
but not tells the first nop after bti, so we don't know how to adjust our rec->ip for ftrace.
> > > On Wed, 16 Mar 2022 18:01:28 +0800 > Wang ShaoBo <bobo.shaobowang@huawei.com> wrote: > >> This implements dynamic trampoline in ARM64, as reference said, we >> complete whole design of supporting long jump in dynamic trampoline: >> >> .text section: >> funcA: | funcA(): funcB():| >> `-> +-----+ | | ... mov x9 | >> | ... | | | adrp <- bl <> | >> | nop | | | mov >> | nop | | | br x16 ---+ >> funcB | nop | | | ftrace_(regs_)caller_tramp: >> `-> +-----+ | `--> +---------------------+ >> | nop | | | ... | >> | nop | | ftrace callsite +---------------------+ >> | ... | | `-----> | PLT entry: | >> | nop | | | adrp | >> | nop | | | add | >> funcC: | nop | | ftrace graph callsite | br x16 | >> `-> +-----+ | `-----> +---------------------+ >> | nop | | | ... | >> | nop | | +---------------------+ >> >> But there is still a tricky problem that is how to adjust tracing ip, >> waiting to be solved: >> >> For ARM64, somecases there may be extra instructions inserted into the >> head of tracable functions(but not all) by compiler, for instance BTI[1]. >> >> This dump vmlinux with CONFIG_BTI=y: >> >> (1) function gic_handle_irq has bti in its head, so we adjust rec->ip+=5 to last nop >> ffffffc0080100e0: d53cd042 mrs x2, tpidr_el2 >> ... >> ffffffc0080100f0: d503201f nop //__mcount_loc tells the rec->ip >> ffffffc0080100f4: d503201f nop >> ffffffc0080100f8: d503201f nop >> >> ffffffc0080100fc <gic_handle_irq>: >> ffffffc0080100fc: d503245f bti c >> ffffffc008010100: d503201f nop >> ffffffc008010104: d503201f nop //we adjust origin rec->ip+5 to here >> ffffffc008010108: d503233f paciasp >> (2) name_to_dev_t.part.0 do not has bti in its head, so we should adjust rec->ip+=4 to last nop >> ffff8000080137d4: d503201f nop >> ffff8000080137d8: d503201f nop >> ffff8000080137dc: d503201f nop >> >> ffff8000080137e0 <name_to_dev_t.part.0>: >> ffff8000080137e0: d503201f nop >> ffff8000080137e4: d503201f nop >> ffff8000080137e8: d503233f paciasp >> >> So at this time we have no idea to identify rec->ip for each tracable function. >> >> we are looking forward to follow-up discussions. >> >> References: >> [1] https://developer.arm.com/documentation/100076/0100/a64-instruction-set-reference/a64-general-instructions/bti >> [2] https://lore.kernel.org/linux-arm-kernel/20200109142736.1122-1-cj.chengjian@huawei.com/ >> >> Cheng Jian (4): >> arm64: introduce aarch64_insn_gen_load_literal >> arm64/ftrace: introduce ftrace dynamic trampoline entrances >> arm64/ftrace: support dynamically allocated trampolines >> arm64/ftrace: implement long jump for dynamic trampolines >> >> arch/arm64/Makefile | 2 +- >> arch/arm64/include/asm/ftrace.h | 10 +- >> arch/arm64/include/asm/insn.h | 6 + >> arch/arm64/include/asm/module.h | 9 + >> arch/arm64/kernel/entry-ftrace.S | 88 ++++++-- >> arch/arm64/kernel/ftrace.c | 366 ++++++++++++++++++++++++++++--- >> arch/arm64/kernel/module-plts.c | 50 +++++ >> arch/arm64/lib/insn.c | 49 +++++ >> 8 files changed, 532 insertions(+), 48 deletions(-) >> > .
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