How to insert external global variable declarations and pointer assignment statements through GCC plugin GIMPLE pass

[Abhijit Nandy]

Hi Ian,

Thanks. Yes it was a basic mistake. I assumed that the undefined reference 
was due to the extern declaration not being inserted.

So I guess DECL_EXTERNAL(var_decl) = 1 causes the var_decl to be set as an 
external declaration in the following code  :

tree var_decl = build_decl(UNKNOWN_LOCATION, VAR_DECL, 
get_identifier("_binary_ccu_start"), char_type_node);
TREE_STATIC(var_decl) = 1;
DECL_EXTERNAL(var_decl) = 1;


I have another question. Right now I create the following declaration
char *p;

using :
tree temp = create_tmp_var(TREE_TYPE(TREE_TYPE(elfset_decl)), "p");

where elfset_decl is set to be char* in a separate function.

However is there another way to create a pointer to char, especially if I 
want the exact identifier 'p' instead of
char * p.1;

which the gimple pass dump is showing me.

I tried to do it as follows :
tree var_decl1 = build_decl(UNKNOWN_LOCATION, VAR_DECL, get_identifier("p"), 
char_type_node);
TREE_STATIC(var_decl1) = 0;
DECL_EXTERNAL(var_decl1) = 0;
rest_of_decl_compilation (var_decl1, 1, 0);

But nothing appears in the gimple pass dump. I think this may be due to not 
actually inserting the declaration in the tree using a gimple function.

Thanks,
Abhi


-----Original Message----- 
From: Ian Lance Taylor
Sent: Tuesday, June 14, 2011 7:38 PM
To: Abhijit Nandy
Cc: gcc
Subject: Re: How to insert external global variable declarations and pointer 
assignment statements through GCC plugin GIMPLE pass

"Abhijit Nandy" <abhijit.nandy@gmail.com> writes:

> My C input file is testcode.c and after I compile with the plugin
> enabled as :
>
> gcc -fplugin=./test_plugin.so -Wall -fdump-tree-gimple -fdump-tree-all
> testcode.c molen_htx.c -o testcode
>
> The molen_htx.c has the molen_elfset()
>
> I get the following linker error :
>
> root@slax:/mnt/f/Thesis/gcc-pluginelf# make testcode
> cc -I/usr/lib/gcc/i486-slackware-linux/4.5.2/plugin/include -fPIC
> -Wall   -c
> -o test_plugin.o test_plugin.c
> gcc -shared test_plugin.o -o test_plugin.so
> gcc -fplugin=./test_plugin.so -Wall -fdump-tree-gimple -fdump-tree-all
> testcode.c molen_htx.c -o testcode
> plugin init test_plugin
> testcode.c: In function 'main':
> testcode.c:26:7: warning: unused variable 'q'
> plugin init test_plugin
> /tmp/ccLUccsU.o: In function `main':
> testcode.c:(.text+0x82): undefined reference to `_binary_ccu_start'
> <---------------
> collect2: ld returned 1 exit status
> make: *** [testcode] Error 1
>
>
> A dump file called testcode.c.220t.replace is produced which does not
> show the global declaration(if it is being inserted at all)
>
> But the undefined reference implies that the global extern declaration
> was not inserted.

A global extern declaration is not a definition.  The variable needs to
be defined somewhere.

If your .c file has "extern char _binary_ccu_start;" you still need to
have some .c file which has "char _binary_ccu_start;", right?

Ian