On Sat, Jan 10, 2015 at 2:00 PM, Borislav Petkov <[email protected]> wrote: > On Sat, Jan 10, 2015 at 09:14:03PM +0100, Denys Vlasenko wrote: >> From 2f636e0a92db898f2bdb592027aa302fcb32a326 Mon Sep 17 00:00:00 2001 >> From: Denys Vlasenko <[email protected]> >> To: [email protected] >> Subject: [PATCH 3/4] x86: open-code register save/restore in trace_hardirqs >> thunks >> >> This is a preparatory patch for change in "struct pt_regs" >> handling in entry_64.S. >> >> trace_hardirqs thunks were (ab)using a part of pt_regs >> handling code, namely SAVE_ARGS/RESTORE_ARGS macros, >> to save/restore registers across C function calls. >> >> Since SAVE_ARGS is going to be changed, open-code >> register saving/restoring here. Take a page from thunk_32.S >> and use push/pop insns instead of movq, they are far shorter: >> 1 or 2 bytes versus 5, and no need for insns to adjust %rsp: >> >> text data bss dec hex filename >> 333 40 0 373 175 thunk_64_movq.o >> 104 40 0 144 90 thunk_64_push_pop.o >> >> Incidentally, this removes a bit of dead code: >> one SAVE_ARGS was used just to emit a CFI annotation, >> but it also generated unreachable assembly insns. >> >> Signed-off-by: Denys Vlasenko <[email protected]> >> CC: Linus Torvalds <[email protected]> >> CC: Oleg Nesterov <[email protected]> >> CC: "H. Peter Anvin" <[email protected]> >> CC: Borislav Petkov <[email protected]> >> CC: Andy Lutomirski <[email protected]> >> CC: Frederic Weisbecker <[email protected]> >> CC: X86 ML <[email protected]> >> CC: Alexei Starovoitov <[email protected]> >> CC: Will Drewry <[email protected]> >> CC: Kees Cook <[email protected]> >> CC: [email protected] >> --- >> arch/x86/lib/thunk_64.S | 46 ++++++++++++++++++++++++++++++++++++++++++---- >> 1 file changed, 42 insertions(+), 4 deletions(-) >> >> diff --git a/arch/x86/lib/thunk_64.S b/arch/x86/lib/thunk_64.S >> index b30b5eb..8ec443a 100644 >> --- a/arch/x86/lib/thunk_64.S >> +++ b/arch/x86/lib/thunk_64.S >> @@ -17,9 +17,27 @@ >> CFI_STARTPROC >> >> /* this one pushes 9 elems, the next one would be %rIP */ >> - SAVE_ARGS >> + pushq_cfi %rdi >> + CFI_REL_OFFSET rdi, 0 > > Btw, why the second CFI annotation? > > pushq_cfi does already CFI_ADJUST_CFA_OFFSET 8. Can't we use one and > hide it in the macro?
By my imperfect understanding of CFI: CFI_ADJUST_CFA_OFFSET means that the offset between rsp and the "canonical frame address" is increased by 8 (because we just subtracted 8 from rsp) and CFI_REL_OFFSET reg, 0 means that the unwinder can find reg at offset 0 + (cfa offset here) from the CFA. IOW, one is to keep the stack frame tracking consistent and the other is to tell the unwinder about the register we just saved. --Andy > > Btw, patch boots fine in the guest. > > -- > Regards/Gruss, > Boris. > > Sent from a fat crate under my desk. Formatting is fine. > -- -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
