Messages in this thread | | | From | Wang ShaoBo <> | Subject | [RFC PATCH -next v2 0/4] arm64/ftrace: support dynamic trampoline | Date | Wed, 16 Mar 2022 18:01:28 +0800 |
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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(-)
-- 2.25.1
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