Re: ecos hal symbol table creation mechanism

[Sergei Gavrikov <sergei dot gavrikov at gmail dot com>]

On Mon, 16 Nov 2015, Robert H wrote:

>  Hello all,
>
> I have some questions concerning the ecos hal symbol table creation in
> hal_tables.h
>
> How is it possible to export a symbol which is in the ecos image into
> some object file for it being able to call it?
>
> I know that test_mods.c uses some defines the object file - that the
> application programer wants to load - uses some defines:
> e.g.
> CYG_LDR_TABLE_ENTRY(cyg_alarm_create_entry,"cyg_alarm_create",cyg_alarm_create);
>
> which then gets replaced by
>
> cyg_ldr_table_entry __name CYG_HAL_TABLE_ENTRY(ldr_table) = {
> __symbol_name, __handler };    // line 141 in objelf.h
> // with __name being a struct of
> // { char *__symbol_name , void *__handler };
> // where is the definition of ldr_table? I can't seem to find it anywhere
>
> and then again gets replaced by
>
> cyg_ldr_table_entry __name
> __attribute__((section(".ecos.table.ldr_table.data")) = {
> __symbol_name , __handler };
> // line 103 in hal_tables.h
>
> Does the section attribute here tell the compiler to put a struct
> cyg_ldr_tables_entry entry (in this example: {"cyg_alarm_create" ,
> cyg_alarm_create} )
> into the ecos image's section .ecos.table.ldr_table.data?

Correct. Look on HAL arch. linker script(s). E.g. for ARM architecture

  https://sourceware.org/viewvc/ecos/packages/hal/arm/arch/current/src/arm.ld?revision=1.23&view=markup#l329

> Then again, I wonder then how the ecos is able to get the adress of
> the function/symbol cyg_alarm_create into the handler
> cyg_alarm_create.
>
> 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


Sergei

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