Re: [patch 1/9]#2 Rename `enum target_signal' to target_signal_t

[Pedro Alves <pedro at codesourcery dot com>]

On Wednesday 01 September 2010 20:18:43, Jan Kratochvil wrote:
> On Wed, 01 Sep 2010 21:07:55 +0200, Pedro Alves wrote:
> > I wonder if switching on "-Wc++-compat" wouldn't catch these (at
> > least with recent enough gccs) and be more productive than
> > switching to a struct.  /me ducks.
> 
> I wanted to argue with this great point myself but during my tests (gcc-4.5)
> enum unfortunately IS compatible with int even in C++ (tried -Wall/-pedantic
> etc.).  I haven't checked the C++ spec.

I think "int signal = TARGET_SIGNAL_TRAP" would be valid C++, while
"enum gdb_signal signal = SIGTRAP" would not.  I thought the latter would
be the most common scenario to catch though.  Maybe not.

Anyway, personally, I'd just do a enum target_signal/enum gdb_signal
rename, and stay with that.

But, here's another idea of how to get compiler warnings/errors,
that I think is more transparent to code throughout:

/* An empty struct.  It's the instances we care about.  */
struct gdb_signal_1
{
};

/* An array of all defined gdb signals.  */
const struct gdb_signal_1 gdb_signals[NUM_GDB_SIGNALS];

/* gdb code uses gdb_signal, not gdb_signal_1.  gdb_signal is a
   pointer.  */
typedef struct gdb_signal_1 * gdb_signal;

/* Define the constants.  */
#define TARGET_SIGNAL_0 (&gdb_signals[0])
#define TARGET_SIGNAL_TRAP (&gdb_signals[5])
#define TARGET_SIGNAL_FOO (&gdb_signals[FOO])
...


Then, you can do this:

 gdb_signal signal = TARGET_SIGNAL_TRAP;

and still do this:

 for (gdb_signal foo = TARGET_SIGNAL_0; sig < TARGET_SIGNAL_LAST; sig++)
    do_things(foo);

... all as before.  But these:

int sig = TARGET_SIGNAL_TRAP;
gdb_signal sig = SIGTRAP;

gdb_signal sig = TARGET_SIGNAL_TRAP;
if (sig < SIGTRAP)
 do_things ();

... give out a warnings, fatal with -Werror.

Getting at the signal integer is simply:

#define GDB_SIGNAL_NUMBER(gdb_sig) \
  (((gdb_sig) - TARGET_SIGNAL_0) / sizeof (gdb_sig))


All the other macros TARGET_SIGNAL_EQ|NE|GT|... disappear.

Here's a compilable example:

$ cat sig.c
#include <signal.h>

struct gdb_signal_1 {};

typedef struct gdb_signal_1 * gdb_signal;

struct gdb_signal_1 signals[10];

#define TARGET_SIGNAL_TRAP (&signals[5])

int main ()
{
	gdb_signal sig = TARGET_SIGNAL_TRAP;
	int sig2 = SIGTRAP;

	if (sig == sig2)
	  {
	  }

	sig = sig2;
	sig2 = sig;

	return 0;
}

$ gcc sig.c -o sig.o -c -Wall
sig.c: In function âmainâ:
sig.c:16: warning: comparison between pointer and integer
sig.c:20: warning: assignment makes pointer from integer without a cast
sig.c:21: warning: assignment makes integer from pointer without a cast

-- 
Pedro Alves