Nicely done, Petr -- I really appreciate this fix. Queued for crash-7.0.7: https://github.com/crash-utility/crash/commit/8e15958e1b7183bbfbdf004f0ad8f2b62f023f9f Thanks, Dave ----- Original Message ----- > Kernel commit 3f3c8b8c4b2a34776c3470142a7c8baafcda6eb0 changed the NMI stack > layout, adding 12 more values on the stack. The fix has two parts: > > 1. Determine if this kernel has the nested NMI layout and set a > machine-specific flag (NESTED_NMI) if it does. > > 2. When backtracing an NMI stack, use the saved values instead of those > found at the top of stack. > > Additionally, kernel commit 28696f434fef0efa97534b59986ad33b9c4df7f8 changed > the stack layout again, swapping the location of the "saved" and "copied" > registers. This can be detected automatically, because the "copied" registers > contain either a copy of the "saved" registers, or point to repeat_nmi. So, > if restart_nmi is found as the return address, assume that this is the old > layout and adjust the stack pointer again. > > Without the patch, wrong register values are shown in the NMI backtrace. > > Signed-off-by: Petr Tesarik <ptesarik@xxxxxxx> > --- > defs.h | 1 + > x86_64.c | 73 > +++++++++++++++++++++++++++++++++++++++++++++++++--------------- > 2 files changed, 57 insertions(+), 17 deletions(-) > > diff --git a/defs.h b/defs.h > index 711b154..4054de4 100644 > --- a/defs.h > +++ b/defs.h > @@ -5123,6 +5123,7 @@ struct machine_specific { > #define VM_XEN_RHEL4 (0x100) > #define FRAMEPOINTER (0x200) > #define GART_REGION (0x400) > +#define NESTED_NMI (0x800) > > #define VM_FLAGS (VM_ORIG|VM_2_6_11|VM_XEN|VM_XEN_RHEL4) > > diff --git a/x86_64.c b/x86_64.c > index 5364c30..fd384ac 100644 > --- a/x86_64.c > +++ b/x86_64.c > @@ -468,6 +468,8 @@ x86_64_init(int when) > else > x86_64_per_cpu_init(); > x86_64_ist_init(); > + if (symbol_exists("repeat_nmi")) > + machdep->flags |= NESTED_NMI; > machdep->in_alternate_stack = x86_64_in_alternate_stack; > if ((machdep->machspec->irqstack = (char *) > malloc(machdep->machspec->stkinfo.isize)) == NULL) > @@ -3009,6 +3011,8 @@ in_exception_stack: > } > > stacktop = bt->stacktop - SIZE(pt_regs); > + if ((machdep->flags & NESTED_NMI) && estack_index == NMI_STACK) > + stacktop -= 12*sizeof(ulong); > > bt->flags &= ~BT_FRAMESIZE_DISABLE; > > @@ -3046,21 +3050,37 @@ in_exception_stack: > } > > cs = x86_64_exception_frame(EFRAME_PRINT|EFRAME_CS, 0, > - bt->stackbuf + (bt->stacktop - bt->stackbase) - > - SIZE(pt_regs), bt, ofp); > + bt->stackbuf + (stacktop - bt->stackbase), > + bt, ofp); > > if (!BT_REFERENCE_CHECK(bt)) > fprintf(fp, "--- <%s exception stack> ---\n", > x86_64_exception_stacks[estack_index]); > > - /* > - * stack = (unsigned long *) estack_end[-2]; > + /* > + * Find the CPU-saved, or handler-saved registers > */ > up = (ulong *)(&bt->stackbuf[bt->stacktop - bt->stackbase]); > - up -= 2; > - rsp = bt->stkptr = *up; > - up -= 3; > - bt->instptr = *up; > + up -= 5; > + if ((machdep->flags & NESTED_NMI) && > + estack_index == NMI_STACK && > + bt->stkptr <= bt->stacktop - 17*sizeof(ulong)) { > + up -= 12; > + /* Copied and saved regs are swapped in pre-3.8 kernels */ > + if (*up == symbol_value("repeat_nmi")) > + up += 5; > + } > + > + /* Registers (as saved by CPU): > + * > + * up[4] SS > + * up[3] RSP > + * up[2] RFLAGS > + * up[1] CS > + * up[0] RIP > + */ > + rsp = bt->stkptr = up[3]; > + bt->instptr = up[0]; > if (cs & 3) > done = TRUE; /* user-mode exception */ > else > @@ -3513,27 +3533,46 @@ in_exception_stack: > } > > stacktop = bt->stacktop - SIZE(pt_regs); > - > + if ((machdep->flags & NESTED_NMI) && > + estack_index == NMI_STACK) > + stacktop -= 12*sizeof(ulong); > + > if (!done) { > level = dwarf_backtrace(bt, level, stacktop); > done = TRUE; > } > > cs = x86_64_exception_frame(EFRAME_PRINT|EFRAME_CS, 0, > - bt->stackbuf + (bt->stacktop - bt->stackbase) - > - SIZE(pt_regs), bt, ofp); > + bt->stackbuf + (stacktop - bt->stackbase), > + bt, ofp); > > if (!BT_REFERENCE_CHECK(bt)) > fprintf(fp, "--- <exception stack> ---\n"); > > - /* > - * stack = (unsigned long *) estack_end[-2]; > + /* > + * Find the CPU-saved, or handler-saved registers > */ > up = (ulong *)(&bt->stackbuf[bt->stacktop - bt->stackbase]); > - up -= 2; > - rsp = bt->stkptr = *up; > - up -= 3; > - bt->instptr = *up; > + up -= 5; > + if ((machdep->flags & NESTED_NMI) && > + estack_index == NMI_STACK && > + bt->stkptr <= bt->stacktop - 17*sizeof(ulong)) { > + up -= 12; > + /* Copied and saved regs are swapped in pre-3.8 kernels */ > + if (*up == symbol_value("repeat_nmi")) > + up += 5; > + } > + > + /* Registers (as saved by CPU): > + * > + * up[4] SS > + * up[3] RSP > + * up[2] RFLAGS > + * up[1] CS > + * up[0] RIP > + */ > + rsp = bt->stkptr = up[3]; > + bt->instptr = up[0]; > if (cs & 3) > done = TRUE; /* user-mode exception */ > else > -- > 1.8.4.5 > -- Crash-utility mailing list Crash-utility@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/crash-utility
