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Re: Re: ecos hal symbol table creation mechanism
- From: Sergei Gavrikov <sergei dot gavrikov at gmail dot com>
- To: Robert H <robert dot huem at gmail dot com>
- Cc: ecos-discuss at ecos dot sourceware dot org
- Date: Wed, 18 Nov 2015 18:59:48 +0300 (MSK)
- Subject: Re: Re: ecos hal symbol table creation mechanism
- Authentication-results: sourceware.org; auth=none
- References: <CAJMZFXfLoHo7N_iNckj_Mxzoo0z4ER1BP8uNZvECov84LuuKcQ at mail dot gmail dot com>
On Wed, 18 Nov 2015, Robert H wrote:
> 2015-11-17 Sergei Gavrikov wrote:
> > On Mon, 16 Nov 2015, Robert H wrote:
[snip]
> >> I would be very pleased to know more about how the mechanism to get
> >> ecos symbols works in hal_tables.h
> >
> > Generally and particularly (objloader case) the table boundaries are
> > known
> >
> > https://sourceware.org/viewvc/ecos/packages/services/objloader/current/src/objelf.c?view=markup#l62
> >
> > Look up example, objelf.c:cyg_ldr_external_address():
> >
> > https://sourceware.org/viewvc/ecos/packages/services/objloader/current/src/objelf.c?view=markup#l219
> I probably still don't get it by looking at the source code how
> entry->handler gets filled with the address of the symbol_name in the
> ecos image.
>
> cyg_ldr_external_address is for accessing the symbol table in that
> section until the entry-pointer reached the cyg_ldr_table_end-pointer,
> but to me that still doesn't explain how entry->handler gets filled by
> the right address.
Notice, that eCos table macros is a quite smart way to declare the
arrays of some C structure and keep them in a special memory region.
For your case the array's item (or "row" of the table) is C struct
cyg_ldr_table_entry:
https://sourceware.org/viewvc/ecos/packages/services/objloader/current/include/objelf.h?revision=1.7&view=markup#l133
Similar in plain C
extern int bar();
extern int foo();
struct s {
char *name;
void *call;
};
struct s table[] = { { "bar", bar }, {"foo", foo}, };
struct s *table_end = &table[sizeof table / sizeof table[0]];
struct s *entry = table;
while(entry != table_end) {
if(strcmp(entry->name, "foo") == 0) {
return entry->call;
}
entry++;
}
Hope, that no magic anymore.
Sergei
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