Question about instrumenting gimple

[Erick Ochoa]

Hi,

I am trying to instrument gimple so that "hello world" is printed after 
each call to malloc. I've tried instrumenting using the following code

static void
// G points to the gcall which corresponds to malloc
call_hello_world(gimple* g)
{
  gimple_stmt_iterator gsi = gsi_start(g);

  // create string constant "hello world\n"
  const char* _string = "hello world\n";
  // plus 1 for the null char
  const unsigned _size = strlen(_string) + 1;
  tree _string_cst = build_string (_size, _string);

  // create char*
  tree _char_ptr = build_pointer_type(char_type_node);

  // create variable hello_string
  tree _var_decl = build_decl(UNKNOWN_LOCATION, VAR_DECL, 
get_identifier("hellostring"), _char_ptr);

  // char* hello_string = "hello world\n";
  gassign *assign_stmt = gimple_build_assign(_var_decl, _string_cst);
  gsi_insert_after(&gsi, assign_stmt, GSI_NEW_STMT);
  update_stmt(assign_stmt);

  gcall *call_stmt = 
gimple_build_call(builtin_decl_explicit(BUILT_IN_PRINTF), 1, _var_decl);
  gsi_insert_after(&gsi, call_stmt, GSI_NEW_STMT);

  update_stmt(call_stmt);
}

but when GCC is compiled with these changes it segfaults in the 
following place:


0xcca9ff crash_signal
        /home/eochoa/code/ipa-dlo/gcc/gcc/toplev.c:327
0x9b99c0 useless_type_conversion_p(tree_node*, tree_node*)
        /home/eochoa/code/ipa-dlo/gcc/gcc/gimple-expr.c:71
0xd1a5a7 verify_gimple_assign_single
        /home/eochoa/code/ipa-dlo/gcc/gcc/tree-cfg.c:4440
0xd1a5a7 verify_gimple_assign
        /home/eochoa/code/ipa-dlo/gcc/gcc/tree-cfg.c:4667
0xd1a5a7 verify_gimple_stmt
        /home/eochoa/code/ipa-dlo/gcc/gcc/tree-cfg.c:4932
0xd2126b verify_gimple_in_cfg(function*, bool)
        /home/eochoa/code/ipa-dlo/gcc/gcc/tree-cfg.c:5418
0xbd6ca3 execute_function_todo
        /home/eochoa/code/ipa-dlo/gcc/gcc/passes.c:1992
0xbd7a63 do_per_function
        /home/eochoa/code/ipa-dlo/gcc/gcc/passes.c:1647
0xbd7ae3 execute_todo
        /home/eochoa/code/ipa-dlo/gcc/gcc/passes.c:2046

This tells me that gimple was ill formed and that there's likely a bad 
type conversion... and that the type conversion was ill formed during 
the assign statement... but nothing is immediately obvious why the 
assignment statement is ill formed. Do I have to update something or 
make sure to have push_cfun the function that I'm modifying?

Thanks!