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

[Abhijit Nandy]

Hi Ian,

Thanks so much for the pointers. I was able to insert most of the lines 
except for the global extern declaration which is the following :

extern char _binary_ccu_start;


My current plugin code is as follows :

void insert_elfset_call()
{
    basic_block bb = ENTRY_BLOCK_PTR->next_bb;
    gimple_stmt_iterator gsi = gsi_start_bb(bb);

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

    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;                            //this does not 
cause var_decl to also be declared as extern globally
    rest_of_decl_compilation (var_decl, 1, 0);

    tree addr_var_decl = build_fold_addr_expr(var_decl);

    gimple assign = gimple_build_assign_stat (temp, addr_var_decl);
    gsi_insert_before(&gsi, assign, GSI_SAME_STMT);

    //Build a function call from the compiled molen_elfset() code first : 
function has unique attribute marked with __attribute__((user("replace"))) 
which helps pick it using elfset_decl
    gimple elfcall = gimple_build_call(elfset_decl,  1, temp);

    //gsi_insert_after (&gsi, elfcall, GSI_CONTINUE_LINKING);//can be used 
to insert the call after 1st statement, still needs function call graph edge
    gsi_insert_before(&gsi, elfcall, GSI_SAME_STMT);

    cgraph_create_edge(cgraph_node(current_function_decl),
            cgraph_node(elfset_decl), elfcall, bb->count,
            compute_call_stmt_bb_frequency(current_function_decl, bb), 
bb->loop_depth);
}


I get the following output from it :

;; Function main (main)

main ()
{
  char * p.1;

<bb 2>:
.....
  p.1 = &_binary_ccu_start;
  molen_elfset (p.1);
....
}
------------------------------------------------------------------------------------

To recall I am trying to insert the following in a C program :

extern char _binary_ccu_start;

int main (int argc, char **argv)
{
....
    char *p = &_binary_ccu_start;
    molen_elfset(p);
...
}


Thanks,
Abhi


-----Original Message----- 
From: Ian Lance Taylor
Sent: Tuesday, May 31, 2011 4:36 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:

> Thanks for the pointers. I have been trying to make a simple VAR_DECL
> using the following call :
>
> tree type_node = make_node(POINTER_TYPE);
> //TYPE_NAME(type_node) = type_id;
> tree var_decl = build0(VAR_DECL, type_node);

Use build_decl.

> testcode.c:33:1: internal compiler error: Segmentation fault

When you get a segmentation fault, your first step should be to use the
debugger to find out what went wrong.  That will normally point you in
the right direction.

Ian