From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 13439 invoked by alias); 8 Jan 2009 10:25:41 -0000 Received: (qmail 13403 invoked by uid 22791); 8 Jan 2009 10:25:40 -0000 X-SWARE-Spam-Status: No, hits=-2.3 required=5.0 tests=AWL,BAYES_00 X-Spam-Check-By: sourceware.org Received: from outdoor.onevision.de (HELO outdoor.onevision.de) (212.77.172.51) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Thu, 08 Jan 2009 10:25:34 +0000 Received: from sanders.onevision.de (moonrace [212.77.172.62]) by outdoor.onevision.de (8.14.3/8.13.7/ROSCH/DDB) with ESMTP id n08APQ9R021622; Thu, 8 Jan 2009 11:25:31 +0100 In-Reply-To: <20090108101911.GQ3664@adacore.com> To: Joel Brobecker Cc: gdb-patches@sourceware.org, Mark Kettenis Subject: Re: [RFC] convert a host address to a string MIME-Version: 1.0 Message-ID: From: Kai Tietz Date: Thu, 08 Jan 2009 10:25:00 -0000 Content-Type: text/plain; charset="US-ASCII" X-IsSubscribed: yes 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/msg00139.txt.bz2 gdb-patches-owner@sourceware.org wrote on 08.01.2009 11:19:11: > > Probably not, but there's a problem with %p. While it is specified by > > C90 and almost certainly implemented in the C library of all systems > > we care about, it is implemented how exactly the pointer will be > > printed. On OpenBSD and Linux it is something like 0xNNNNNNNN, but > > Solaris generates NNNNNNNN (without the initial 0x). That's > > undesirable I think. > > I agree. > > > 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. > > 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). > > 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. > > 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. > > 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 > > For completeness' sake, I also investigate the use of the PRIxPTR > macro, but we still have the problem of casting the address to > the right integer type: If PRIxPTR resolves to "lx", then we should > cast to "long", otherwise, we should cas to "long long". > > 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. Perhaps we could avoid that > using an extra "if (sizeof (void *) != sizeof (long))" but then > the code becomes increasingly complex. My next favorite would > probably be option 2 because I'm lazy, but it's really not elegant. > Option 1 looks like a fair amount of work, but would give us access > to a predicatable printf. > > Thoughts? > > -- > Joel > Why not simply use stdint.h (gstdint.h) for this? Cheers, Kai | (\_/) This is Bunny. Copy and paste Bunny | (='.'=) into your signature to help him gain | (")_(") world domination.