Use the _ attribute _ of gcc to compile the attribute section sub-item to construct the initialization function table. The gcc _ attribute _

Use the _ attribute _ of gcc to compile the attribute section sub-item to construct the initialization function table. The gcc _ attribute _

This article forwarded from: https://my.oschina.net/u/180497/blog/177206

It solves song Baohua's previousC language object-oriented (for larger software) ppt sharing and ppt annotationsMulti-module software initialization

Gcc's _ attribute _ compilation attribute has many sub-items, which are used to change the characteristics of the target object. The role of the section subitem is discussed here.

Use the section subitem of _ attribute _ as follows:

_ Attribute _ (section ("section_name ")))

The function is to put the function or data to a segment named "section_name.

Take a look at the following program snippets:

# Include <unistd. h>

# Include <stdint. h>

# Include <stdio. h>

Typedef void (* myown_call) (void );

Extern myown_call _ myown_start;

Extern myown_call _ myown_end;

# Define _ init _ attribute _ (unused, section (". mywn ")))

# Define func_init (func) myown_call _ fn _ # func _ init = func

Static void mspec1 (void)

{

Write (1, "aha! \ N ", 5 );

}

Static void mspec2 (void)

{

Write (1, "aloha! \ N ", 7 );

}

Static void mspec3 (void)

{

Write (1, "hello! \ N ", 7 );

}

Func_init (mspec1 );

Func_init (mspec2 );

Func_init (mspec3 );

/* Exactly like below:

Static myown_call mc1 _ attribute _ (unused, section (". mywn") = mspec1;

Static myown_call mc2 _ attribute _ (unused, section (". mywn") = mspec2;

Static myown_call mc3 _ attribute _ (unused, section (". mywn") = mspec3;

*/

Void do_initcils (void)

{

Myown_call * call_ptr = & _ myown_start;

Do {

Fprintf (stderr, "call_ptr: % p \ n", call_ptr );

(* Call_ptr )();

++ Call_ptr;

} While (call_ptr <& _ myown_end );

}

Int main (void)

{

Do_initcils ();

Return 0;

}

Fill in the UDF pointer of mspec1/mspec2/mspec3 in sequence in the custom. mywn segment, and call it in do_initcils to construct and call the initialization function list.

Two extern variables:

Extern myown_call _ myown_start;

Extern myown_call _ myown_end;

From the ld link script, you can use:

Ld -- verbose

Obtain the built-in lds script and go:

_ Bss_start = .;

Add the following content before:

_ Myown_start = .;

. Mywn: {* (. mywn)} = 0x90000000

_ Myown_end = .;

Code_segment: {* (code_segment )}

The. mywn segment and the _ myown_start/_ myown_end variable are defined (the value 0x90000000 may need to be adjusted ).

Save the modified linker script. If the program is s. c and the linker script is saved as s. lds, run the following command to compile the script:

Gcc s. c-Wl,-Ts. lds

Execution result:

[Root @ localhost] #./a. out

Call_ptr: 0x8049768

Aha!

Call_ptr: 0x804976c

Aloha!

Call_ptr: 0x8049770

Hello!

Have Fun!