From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 25999 invoked by alias); 8 Jan 2009 13:26:47 -0000 Received: (qmail 25990 invoked by uid 22791); 8 Jan 2009 13:26:47 -0000 X-SWARE-Spam-Status: No, hits=-2.5 required=5.0 tests=AWL,BAYES_00 X-Spam-Check-By: sourceware.org Received: from sibelius.xs4all.nl (HELO sibelius.xs4all.nl) (82.92.89.47) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Thu, 08 Jan 2009 13:26:40 +0000 Received: from brahms.sibelius.xs4all.nl (kettenis@localhost.sibelius.xs4all.nl [127.0.0.1]) by brahms.sibelius.xs4all.nl (8.14.3/8.14.3) with ESMTP id n08DQF6w022694; Thu, 8 Jan 2009 14:26:15 +0100 (CET) Received: (from kettenis@localhost) by brahms.sibelius.xs4all.nl (8.14.3/8.14.3/Submit) id n08DQEgY002357; Thu, 8 Jan 2009 14:26:15 +0100 (CET) Date: Thu, 08 Jan 2009 13:26:00 -0000 Message-Id: <200901081326.n08DQEgY002357@brahms.sibelius.xs4all.nl> From: Mark Kettenis To: brobecker@adacore.com CC: gdb-patches@sourceware.org In-reply-to: <20090108101911.GQ3664@adacore.com> (message from Joel Brobecker on Thu, 8 Jan 2009 14:19:11 +0400) Subject: Re: [RFC] convert a host address to a string References: <20090107121908.GH1751@adacore.com> <200901071616.n07GGXtu029119@brahms.sibelius.xs4all.nl> <20090108101911.GQ3664@adacore.com> Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org X-SW-Source: 2009-01/txt/msg00156.txt.bz2 > Date: Thu, 8 Jan 2009 14:19:11 +0400 > From: Joel Brobecker > > > An option would be to use the strategy used by phex_nz() to print host > > addresses. Or we could use PRINTF_HAS_LONG_LONG, and always use %llx > > if it's available. > > Unfortunately, I don't know how this could be made to work. > The problem is that GCC insists that the integer type that we > use to cast the host address to must have the same size. > At one point, hoping that GCC would kill the wrong branch, > I even tried: > > if (sizeof (void *) == sizeof (long)) > printf ("0x%lx", (long) address); > else > printf ("0x%llx", (long long) address); > > But this didn't work, because GCC complained about the cast > in the "if" branch. Ah, GCC is being a bit too helpful here. Damn! > Actually, it's only after writing the entire email that I realized > that we have another option. See option (3) below. > > > I'd really like to avoid introducing another macro dealing with > > type-size issues if possible. I especially dislike HOST_IS_LLP64 > > since I fear its existence encourages people to write unportable code. > > I can see several solutions: > > 1. Use %p. To overcome the problem with 0x, we could use > two alternatives: > > a. Import printf from gnulib. I looked at this a while ago, > for some other issue, and I immediately stopped, as it > looked like it might be a lot of work to do so (printf > doesn't come alone, there's a bunch of other routines > that printf uses which we probably want). I'm not very excited about this option. And if the gnulib printf doesn't actually implement the Microsoft-invented non-standard format specifiers it may even cause us more grief. > b. Strip the leading "0x" if %p already provides it. In other > words: > > fprintf (buf, "0x%p", address); > if (buf[2] == '0' && buf[3] == 'x') > buf = buf + 2; > return buf; > > There is no memory management issue in this case, because > the buffer we return is more or less static. It's part > of a bunch of buffers we cycle through each time we call > this routine. The caller never frees the memory we return. Ugh, this is a bit ugly. And we can't even be sure that there are even more variations on the format that %p generates. I wouldn't be surprised at all if some platforms would use upper case for the hex digits for example. > 2. Avoid the HOST_IS_LLP64 macro, but still do something similar > inside host_address_to_string. Something like: > > #if defined(WIN64_) > fprintf (buf, "0x%llx", (unsigned long long) address); > #else > fprintf (buf, "0x%lx", (unsigned long) address); > #endif > > This eliminates the likeliness of re-using the HOST_IS_LLP64 > macro to write non-portable code. Not really excited about this one either. > 3. Work through uintptr_t. > > #ifdef PRINTF_HAS_LONG_LONG > fprintf (buf, "0x%llx", (unsigned long long) (uintptr_t) address); > #else > fprintf (buf, "0x%lx", (unsigned long) (uintptr_t) address); > #endif This wouldn't be the first place where we'd use a double cast in connection with intptr_t/uintptr_t. So I'd say that while this is a bit ugly, it's certainly acceptable. It's by far the simplest way to fix things. > I kinda like option 1b as being simple and avoiding the need to > cast the address to an integer. Option (3) is my next favorite, > but I don't like the fact that we end up doing an unnecessary > integer promotion on the 32bit targets. I'm not really worried about the integer promotion. Printing host addresses is a fairly rare operation, and certainly not time critical.