On Fri, May 10, 2019 at 12:21:03PM +0900, Masami Hiramatsu wrote: > On Thu, 9 May 2019 13:43:16 -0400 > Steven Rostedt <rost...@goodmis.org> wrote: > > > On Thu, May 09, 2019 at 09:20:06AM -0700, Andy Lutomirski wrote: > > > > +END(call_to_exception_trampoline) > > > > --- a/arch/x86/kernel/kprobes/core.c > > > > +++ b/arch/x86/kernel/kprobes/core.c > > > > @@ -731,29 +731,8 @@ asm( > > > > ".global kretprobe_trampoline\n" > > > > ".type kretprobe_trampoline, @function\n" > > > > "kretprobe_trampoline:\n" > > > > - /* We don't bother saving the ss register */ > > > > -#ifdef CONFIG_X86_64 > > > > - " pushq %rsp\n" > > > > - " pushfq\n" > > > > - SAVE_REGS_STRING > > > > - " movq %rsp, %rdi\n" > > > > - " call trampoline_handler\n" > > > > - /* Replace saved sp with true return address. */ > > > > - " movq %rax, 19*8(%rsp)\n" > > > > - RESTORE_REGS_STRING > > > > - " popfq\n" > > > > -#else > > > > - " pushl %esp\n" > > > > - " pushfl\n" > > > > - SAVE_REGS_STRING > > > > - " movl %esp, %eax\n" > > > > - " call trampoline_handler\n" > > > > - /* Replace saved sp with true return address. */ > > > > - " movl %eax, 15*4(%esp)\n" > > > > - RESTORE_REGS_STRING > > > > - " popfl\n" > > > > -#endif > > > > - " ret\n" > > > > + "push trampoline_handler\n" > > > > + "jmp call_to_exception_trampoline\n" > > > > ".size kretprobe_trampoline, .-kretprobe_trampoline\n" > > > > ); > > > > > > > > > Potentially minor nit: you’re doing popfl, but you’re not doing > > > TRACE_IRQ_whatever. This makes me think that you should either add the > > > tracing (ugh!) or you should maybe just skip the popfl. > > > > > > Note, kprobes (and ftrace for that matter) are not saving flags for > > interrupts, but because it must not modify the sign, zero and carry flags.
Uh, C ABI considers those clobbered over function calls, surely. Relying on those flags over a CALL would be _insane_.
