how can I combine two different gdb commands “info symbol” and “ptype” into single one？ - nginx

Question

in other words，Is there a command that can find the symbol at an address meanwhile use ptype show this symbol‘s detail info ？
or if there is not， how can i write a user-define command meet this needs ？
for example， now i can firstly get data struct‘s name (ngx_errlog_module_ctx) in a address use “info symbol” command， than use ptype show the data struct’s detail info like this：
(gdb) info symbol 0x80b4568
ngx_errlog_module_ctx in section .data of /usr/local/nginx/sbin/nginx
(gdb) ptype ngx_errlog_module_ctx
type = struct {
ngx_str_t name;
void *(*create_conf)(ngx_cycle_t *);
char *(*init_conf)(ngx_cycle_t *, void *);
}
but now， how can i write a user-difined command (ptype_with_address) that i can use like this :
ptype_with_address 0x80b4568
ngx_errlog_module_ctx in section .data of /usr/local/nginx/sbin/nginx
type = struct {
ngx_str_t name;
void *(*create_conf)(ngx_cycle_t *);
char *(*init_conf)(ngx_cycle_t *, void *);
}
i want to do this because i am research nginx’s code，i want write a user-defined command to show all ngx_modules's detail info, include each module's ctx member variable.

Answer 1

can i write a user-define command meet this need
If you have a reasonably recent version of GDB, you should be able to use built-in Python interpreter to achieve your goal.
Unfortunately, it doesn't look like you can get the gdb.Symbol from its address, you need the symbol name. In other words, it doesn't look like info symbol is currently exposed to Python interpreter in GDB.
I suggest filing a feature request in bugzilla to extend gdb.lookup_global_symbol to also accept an address.
Googling for "gdb python info symbol" revealed this thread, in which Tom Tromey (gdb developer) also asked to file a bugzilla issue, and suggested a workaround.