Re: [Crash-utility] [PATCH] defs.h: fix breakage of compatibility of struct machdep_table for extension modules

On Fri, Dec 10, 2021 at 12:44 PM HAGIO KAZUHITO(萩尾　一仁) <k-hagio-ab(a)nec.com&gt; wrote: > > (sorry, I mistook the email to reply.. this is the correct one.) > > -----Original Message----- > > Commit 2f967fb5ebd737ce5eadba462df35935122e8865 (crash_taget: > > fetch_registers support) added new member get_cpu_reg in the middle of > > struct machdep_table as: > > > > @@ -1013,6 +1013,7 @@ struct machdep_table { > > ulong (*processor_speed)(void); > > int (*uvtop)(struct task_context *, ulong, physaddr_t *, int); > > int (*kvtop)(struct task_context *, ulong, physaddr_t *, int); > > + int (*get_cpu_reg)(int, int, const char *, int, void *); > > ulong (*get_task_pgd)(ulong); > > void (*dump_irq)(int); > > void (*get_stack_frame)(struct bt_info *, ulong *, ulong *); > > > > which breaks compatibility of struct machdep_table for extension > > modules. In general, new member variables must be added at the end of > > structures to maintain compatibility of data structures shared among > > extension modules. > > > > For example, as the result, crash gcore command results in unexpected > > behavior: > > > > crash> gcore -v 7 > > GETBUF(168 -> 0) > > <readmem: ffff8b267dd28020, KVADDR, "task_struct.stack", 8, (FOE), 7fffaef8afa8> > > <read_kdump: addr: ffff8b267dd28020 paddr: 7dd28020 cnt: 8> > > read_netdump: addr: ffff8b267dd28020 paddr: 7dd28020 cnt: 8 offset: 767ec020 > > <readmem: ffffa3f740abff58, KVADDR, "genregs_get: pt_regs", 168, (FOE), e71f80> > > gcore: invalid kernel virtual address: ffffa3f740abff58 type: "genregs_get: pt_regs" > > vma hit rate: 0% (0 of 274308) > > > > crash gcore uses machdep->get_stacktop() to retrieve registers saved > > at the bottom of a given user-space task's kernel stack: > > > > static int genregs_get(struct task_context *target, > > const struct user_regset *regset, > > unsigned int size, void *buf) > > { > > ...snip... > > pt_regs_buf = GETBUF(SIZE(pt_regs)); > > > > readmem(machdep->get_stacktop(target->task) - SIZE(pt_regs), KVADDR, > > pt_regs_buf, SIZE(pt_regs), "genregs_get: pt_regs", > > gcore_verbose_error_handle()); > > > > As seen above, the position of get_stacktop in struct machdep_table is > > behind the position where get_cpu_reg was added: > > > > int (*uvtop)(struct task_context *, ulong, physaddr_t *, int); > > int (*kvtop)(struct task_context *, ulong, physaddr_t *, int); > > int (*get_cpu_reg)(int, int, const char *, int, void *); ulong (*get_task_pgd)(ulong); > > void (*dump_irq)(int); > > void (*get_stack_frame)(struct bt_info *, ulong *, ulong *); > > ulong (*get_stackbase)(ulong); > > ulong (*get_stacktop)(ulong); > > > > Signed-off-by: HATAYAMA Daisuke <d.hatayama(a)fujitsu.com&gt; > > Acked-by: Kazuhito Hagio <k-hagio-ab(a)nec.com&gt; >