On 2022/05/27 11:22, HAGIO KAZUHITO(萩尾 一仁) wrote:
> Hi Lianbo,
>
> On 2022/05/26 16:07, Lianbo Jiang wrote:
>> Currently, the 'struct -o' command does not display the offsets
>> of struct fields like this:
>>
>> crash> struct page -ox ffffce98870a0d40
>> struct page {
>> [ffffce98870a0d40] unsigned long flags;
>> union {
>> struct {...};
>> struct {...};
>> struct {...};
>> struct {...};
>> struct {...};
>> struct {...};
>> struct {...};
>> [ffffce98870a0d48] struct callback_head callback_head;
>> };
>> ...
>> }
>> SIZE: 0x40
>
> Good catch!
>
>>
>> The gdb-10.2 added a new option '/o' for the 'ptype' command, which
>> prints the offsets and sizes of struct fields, let's use it now to
>> fix the above issue.
>
> but isn't there another gdb option or setting to show their details?
>
> (gdb) ptype struct page
> type = struct page {
> unsigned long flags;
> union {
> struct {...};
> struct {...};
> struct {...};
> ...
>
> If there is no setting other than '/o', it's a bit strange UI design,
> I think.. (although I cannot find so far..)
>
>
> Also the 'ptype /o' overdoes unfolding struct members,
> and extra spaces and lines are printed with the patch:
>
> * crash-7.3.2
>
> crash-7.3.2> struct address_space
> struct address_space {
> struct inode *host;
> struct xarray i_pages;
> atomic_t i_mmap_writable;
> struct rb_root_cached i_mmap;
> struct rw_semaphore i_mmap_rwsem;
> unsigned long nrpages;
> ...
> crash-7.3.2> struct -o address_space
> struct address_space {
> [0] struct inode *host;
> [8] struct xarray i_pages;
> [32] atomic_t i_mmap_writable;
> [40] struct rb_root_cached i_mmap;
> [56] struct rw_semaphore i_mmap_rwsem;
> [96] unsigned long nrpages;
>
> * With the patch
>
> crash-dev> struct address_space
> struct address_space {
> struct inode *host;
> struct xarray {
> spinlock_t xa_lock;
> gfp_t xa_flags;
> void *xa_head;
> size_t xarray_size_rh;
> struct xarray_rh {
> <no data fields>
>
>
> } _rh;
>
>
> } i_pages;
> atomic_t i_mmap_writable;
>
> struct rb_root_cached {
> struct rb_root {
> struct rb_node *rb_node;
> ...
> crash-dev> struct -o address_space
> struct address_space {
> [0] struct inode *host;
> struct xarray {
> spinlock_t xa_lock;
> gfp_t xa_flags;
> void *xa_head;
> size_t xarray_size_rh;
> struct xarray_rh {
> <no data fields>
>
>
> } _rh;
>
>
> [8] } i_pages;
> [32] atomic_t i_mmap_writable;
>
> struct rb_root_cached {
> struct rb_root {
> struct rb_node *rb_node;
> ...
>
>
> task_struct also looks wrong:
>
> crash-dev> struct -o task_struct
> struct task_struct {
> struct thread_info {
> [36] unsigned long flags;
> u32 status;
>
>
>
> [0] } thread_info;
> [16] volatile long state;
> [24] void *stack;
> ...
>
>
> If no another gdb setting, we will need to rewrite the parser.
> So first, I'd like to know whether there is no another setting.
Otherwise, maybe we can patch the gdb code...
That '{...}' is probably printed in c_type_print_base_struct_union().
And found a comment for c_type_print_base_1() in gdb/c-typeprint.c:
SHOW negative means just print the type name or struct tag if there
is one. If there is no name, print something sensible but concise
like "struct {...}".
Just an idea and clue.
Thanks,
Kazu
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