Messages in this thread | | | Date | Thu, 06 Jan 2011 16:39:39 +0000 | From | "Jan Beulich" <> | Subject | Re: [RFC PATCH 1/2] x86: Fix rbp saving in pt_regs on irq entry |
| |
>>> On 06.01.11 at 17:22, Frederic Weisbecker <fweisbec@gmail.com> wrote: > On Thu, Jan 06, 2011 at 04:10:55PM +0000, Jan Beulich wrote: >> >>> On 06.01.11 at 16:45, Frederic Weisbecker <fweisbec@gmail.com> wrote: >> > Before we had: >> > >> > >> > leaveq >> > >> > CFI_RESTORE rbp >> > CFI_DEF_CFA_REGISTER rsp >> > CFI_ADJUST_CFA_OFFSET -8 >> > >> > So CFI_RESTORE means rbp has now the value of the base frame of >> > the calling frame (the base frame pointer of the interrupted proc) ? >> >> No - all it means is that %rbp now has its original (caller or >> interrupted procedure) value again (i.e. an unwinder should not >> try to read it from the stack [or other previously recorded >> location] anymore). >> >> > And what follows means that rsp-8 points to the return address? >> >> No - .cfi_def_cfa_register says which register serves as the frame >> pointer, and .cfi_adjust_cfa_offset says to adjust the offset from >> the frame pointer to the top [or bottom] of frame. At any time >> >> CFA = cfa_register + cfa_offset >> >> with CFA being what all locations on the stack are expressed >> relative to. > > Ok. > > So here rsp points to pt_regs::r11 > > I don't understand why locations relative to the stack must be > expressed here by taking rsp - 8 as a base.
Nothing says rsp-8. The annotations merely say to set the base register to rsp and to *adjust* the offset by -8 (after all, that's what the leaveq instruction does).
Jan
| |