Messages in this thread | | | From | Arnd Bergmann <> | Date | Fri, 3 Dec 2021 21:37:16 +0100 | Subject | Re: [PATCH v3 8/9] ARM: kprobes: Make a frame pointer on __kretprobe_trampoline |
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On Thu, Oct 21, 2021 at 2:55 AM Masami Hiramatsu <mhiramat@kernel.org> wrote: > > Currently kretprobe on ARM just fills r0-r11 of pt_regs, but > that is not enough for the stacktrace. Moreover, from the user > kretprobe handler, stacktrace needs a frame pointer on the > __kretprobe_trampoline. > > This adds a frame pointer on __kretprobe_trampoline for both gcc > and clang case. Those have different frame pointer so we need > different but similar stack on pt_regs. > > Gcc makes the frame pointer (fp) to point the 'pc' address of > the {fp, ip (=sp), lr, pc}, this means {r11, r13, r14, r15}. > Thus if we save the r11 (fp) on pt_regs->r12, we can make this > set on the end of pt_regs. > > On the other hand, Clang makes the frame pointer to point the > 'fp' address of {fp, lr} on stack. Since the next to the > pt_regs->lr is pt_regs->sp, I reused the pair of pt_regs->fp > and pt_regs->ip. > So this stores the 'lr' on pt_regs->ip and make the fp to point > pt_regs->fp. > > For both cases, saves __kretprobe_trampoline address to > pt_regs->lr, so that the stack tracer can identify this frame > pointer has been made by the __kretprobe_trampoline. > > Note that if the CONFIG_FRAME_POINTER is not set, this keeps > fp as is. > > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
This causes a regression that I see in randconfig builds with gcc-11:
/tmp/ccovvQNw.s: Assembler messages: /tmp/ccovvQNw.s:32: Error: invalid literal constant: pool needs to be closer make[5]: *** [/git/arm-soc/scripts/Makefile.build:288: arch/arm/probes/kprobes/core.o] Error 1
I have two randconfigs that reproduce it locally, here is a .config [1] and assembly output[2] for reference. I have not done any further analysis, but maybe you have an idea.
Arnd
[1] https://pastebin.com/y4rkH8qX [2] https://pastebin.com/9mEVU8Rd
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