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

[HAGIO KAZUHITO(萩尾 一仁)]

(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 at fujitsu.com>

Acked-by: Kazuhito Hagio <k-hagio-ab at nec.com>

Lianbo, this is also needed for RHEL9 crash before GA.

Thanks,
Kazu

> ---
>  defs.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/defs.h b/defs.h
> index e9e8143..b63741c 100644
> --- a/defs.h
> +++ b/defs.h
> @@ -1013,7 +1013,6 @@ 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 *);
> @@ -1063,6 +1062,7 @@ struct machdep_table {
>          void (*get_irq_affinity)(int);
>          void (*show_interrupts)(int, ulong *);
>  	int (*is_page_ptr)(ulong, physaddr_t *);
> +	int (*get_cpu_reg)(int, int, const char *, int, void *);
>  };
> 
>  /*
> --
> 2.31.1
> 
> 
> 
> 
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