Re: I want to know the information about the function arguments

[David Malcolm <dmalcolm at redhat dot com>]

On Wed, 2018-06-06 at 13:04 +0200, Martin Jambor wrote:
> Hi,
> 
> On Wed, Jun 06 2018, 冠人 王 via gcc wrote:
> > When I modify the gcc source code, sometimes I do not know what
> > parameters does the function call.
> > For example, 
> > bool warn_if_unused_value(const tree exp,location_t locus){   
> > function declaration ...
> > }
> > I want to know what "exp" and "locus" are by using fprintf such as
> > fprintf(stderr,"%s\n%s\n",exp,locus) --> I know it does not work
> > since exp and locus is not strings
> > How should I do to know the content of variable "exp" and "locus" ?
> 
> For trees, look for example at:
> 
> - debug_tree (tree);
> - print_node (FILE *, const char *, tree, int);
> - print_node_brief (FILE *, const char *, const_tree, int);
> 
> For location_t, I *think* you need to expand it yourself first.  Look
> at
> how it is being done for example in tree-dump.c.
> 
> Generally speaking, for any given type, try searching for functions
> with
> "debug" or "dump" in their names that dump any particular type.

For a location_t, you can try adding a call to "inform" e.g.

  inform (locus, "some message");

This will emit a "note" diagnostic at the source location that "locus"
represents.

Alternatively, if you're already debugging the compiler in gdb, you can
call "inform" directly:

  (gdb) call inform (locus, "")

and it will emit a "note" diagnostic describing "locus".

FWIW, I've written some notes on debugging GCC here:
  https://dmalcolm.fedorapeople.org/gcc/newbies-guide/debugging.html


Hope this is helpful; good luck!
Dave