Messages in this thread Patch in this message | | | From | Ard Biesheuvel <> | Date | Sat, 4 Dec 2021 09:45:11 +0100 | Subject | Re: [PATCH v3 8/9] ARM: kprobes: Make a frame pointer on __kretprobe_trampoline |
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On Fri, 3 Dec 2021 at 21:38, Arnd Bergmann <arnd@arndb.de> wrote: > > 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.
Does this help?
diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c index 9090c3a74dcc..88999ed2cfc4 100644 --- a/arch/arm/probes/kprobes/core.c +++ b/arch/arm/probes/kprobes/core.c @@ -408,6 +408,7 @@ void __naked __kprobes __kretprobe_trampoline(void) #else "mov pc, lr \n\t" #endif + ".ltorg \n\t" : : : "memory"); }
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