Re: [Crash-utility] [PATCH] fix error crash: cannot resolve "schedulers"

----- Original Message ----- > Since Xen commit 666aca08175b ("sched: use the auto-generated list of > schedulers") crash cannot open Xen vmcores, because symbol 'schedulers' > does not exits. Xen 4.7 implemented schedulers as its own section. > > xen/arch/x86/xen.lds.S > __start_schedulers_array = .; > *(.data.schedulers) > __end_schedulers_array = .; > > Crash must not look up for "schedulers" symbol and fails, if symbol is > not found. It must check if __start_schedulers_array exits, and if it > does, use it and get size of the section. Otherwise, crash fallback to > looking up "schedulers" symbol. That way, crash can open vmcore before > and after Xen 4.7. > > Signed-off-by: Nikola Pajkovsky <npajkovsky(a)suse.cz&gt; Hi Nikola, I'm not at at familiar with this code, but xen_hyper_schedule_init() declares scheduler_buf[] with a fixed size of XEN_HYPER_SCHEDULERS_ARRAY_CNT (10): long schedulers_buf[XEN_HYPER_SCHEDULERS_ARRAY_CNT]; If the new __start_schedulers_array size (and therefore xen_hyper_nr_schedulers) could ever exceed 10, then there would be a buffer overflow when the buffer is filled. So probably it would be best to dynamically allocate the buffer with GETBUF/FREEBUF, or at least limit it to 10? Maybe 10 was picked as an absurdly large number that will never be reached?

> --- > xen_hyper.c | 40 +++++++++++++++++++++++++++++++++------- > 1 file changed, 33 insertions(+), 7 deletions(-) > > diff --git a/xen_hyper.c b/xen_hyper.c > index 27e44c6e733d..e8268cf40c78 100644 > --- a/xen_hyper.c > +++ b/xen_hyper.c > @@ -438,6 +438,19 @@ xen_hyper_misc_init(void) > #define XEN_HYPER_SCHEDULERS_ARRAY_CNT 10 > #define XEN_HYPER_SCHEDULER_NAME 1024 > > +/* > + * does similar function exits in crash?? > + */ > +static int section_size(char *start_section, char *end_section) > +{ > + ulong sp_start, sp_end; > + > + sp_start = symbol_value(start_section); > + sp_end = symbol_value(end_section); > + > + return (sp_end - sp_start) / sizeof(size_t); > +} > + > static void > xen_hyper_schedule_init(void) > { > @@ -448,6 +461,8 @@ xen_hyper_schedule_init(void) > char *buf; > char opt_name_buf[XEN_HYPER_OPT_SCHED_SIZE]; > int i, cpuid, flag; > + char *sp_name; > + int xen_hyper_nr_schedulers; > > /* get scheduler information */ > if((xhscht->scheduler_struct = > @@ -469,21 +484,32 @@ xen_hyper_schedule_init(void) > XEN_HYPER_OPT_SCHED_SIZE, "opt_sched,", RETURN_ON_ERROR)) { > error(FATAL, "cannot read opt_sched,.\n"); > } > - schedulers = symbol_value("schedulers"); > + > + if (symbol_exists("__start_schedulers_array")) { > + sp_name = "__start_schedulers_array"; > + xen_hyper_nr_schedulers = section_size("__start_schedulers_array", > + "__end_schedulers_array"); > + } else { > + sp_name = "schedulers"; > + xen_hyper_nr_schedulers = XEN_HYPER_SCHEDULERS_ARRAY_CNT; > + } > + > + schedulers = symbol_value(sp_name); > + > addr = schedulers; > while (xhscht->name == NULL) { > if (!readmem(addr, KVADDR, schedulers_buf, > - sizeof(long) * XEN_HYPER_SCHEDULERS_ARRAY_CNT, > - "schedulers", RETURN_ON_ERROR)) { > + sizeof(long) * xen_hyper_nr_schedulers, > + sp_name, RETURN_ON_ERROR)) { > error(FATAL, "cannot read schedulers.\n"); > } > - for (i = 0; i < XEN_HYPER_SCHEDULERS_ARRAY_CNT; i++) { > + for (i = 0; i < xen_hyper_nr_schedulers; i++) { > if (schedulers_buf[i] == 0) { > error(FATAL, "schedule data not found.\n"); > } > if (!readmem(schedulers_buf[i], KVADDR, > - xhscht->scheduler_struct, XEN_HYPER_SIZE(scheduler), > - "scheduler", RETURN_ON_ERROR)) { > + xhscht->scheduler_struct, XEN_HYPER_SIZE(scheduler), > + "scheduler", RETURN_ON_ERROR)) { > error(FATAL, "cannot read scheduler.\n"); > } > opt_name = ULONG(xhscht->scheduler_struct + > @@ -514,7 +540,7 @@ xen_hyper_schedule_init(void) > strncpy(xhscht->name, buf, strlen(buf)); > break; > } > - addr += sizeof(long) * XEN_HYPER_SCHEDULERS_ARRAY_CNT; > + addr += sizeof(long) * xen_hyper_nr_schedulers; > } > FREEBUF(buf); > > -- > 2.13.6 > > -- > Crash-utility mailing list > Crash-utility(a)redhat.com > https://www.redhat.com/mailman/listinfo/crash-utility >