June 2005 - Darwin-dev - lists.apple.com

Re: setjmp/longjmp changed in Tiger
by David N. Williams 01 Jun '05

01 Jun '05

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Organization: University of Michigan User-agent: Mozilla/5.0 (Macintosh; U; PPC Mac OS X Mach-O; en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 You might consider trying your code on other systems to see what they do. Here's what I get on FreeBSD, for instance: % ./a.out rounding direction before setjmp is 0 rounding direction changed to 1024 status = 15 rounding direction after longjmp is 0 The only other OS I have easy access to is linux. There I get the same behavior as Panther: arkanoid% gcc -v Reading specs from /usr/lib/gcc-lib/i686-pc-linux-gnu/3.3.1/specs Configured with: ./configure --prefix=/usr --enable-shared --enable-languages=all --enable-threads=posix --with-slibdir=/lib --enable-__cxa_atexit --enable-clocale=gnu Thread model: posix gcc version 3.3.1 arkanoid% gcc -lm -o testsetjmp testsetjmp.c arkanoid% testsetjmp rounding direction before setjmp is 0 rounding direction changed to 1024 status = 15 rounding direction after longjmp is 1024 -- David _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… Matt Watson wrote: If you find that other OS's do the same thing, I suggest adapting your code to work with this behavior. This email sent to site_archiver(a)lists.apple.com

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Re: fsevents oddities (was Re: EVFILT_VNODES?)
by Mike Smith 01 Jun '05

01 Jun '05

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com

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Re: setjmp/longjmp changed in Tiger
by Matt Watson 01 Jun '05

01 Jun '05

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Here's what I get on FreeBSD, for instance: % ./a.out rounding direction before setjmp is 0 rounding direction changed to 1024 status = 15 rounding direction after longjmp is 0 matt. _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… You might consider trying your code on other systems to see what they do. If you find that other OS's do the same thing, I suggest adapting your code to work with this behavior. This email sent to site_archiver(a)lists.apple.com

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Re: setjmp/longjmp changed in Tiger
by David N. Williams 01 Jun '05

01 Jun '05

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Organization: University of Michigan User-agent: Mozilla/5.0 (Macintosh; U; PPC Mac OS X Mach-O; en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 On May 28, 2005, Matt Watson wrote: > On May 28, 2005, at 7:47 PM, David N. Williams wrote: > > >>Is the Tiger behavior a bug? If so, I'll file a bug report. >>Please let me know what you think. > > > This is not a bug. longjmp() should restore the environment at the > time of the setjmp() and floating-point rounding mode is part of the > environment, so Tiger does this correctly. I'm going to argue below that it's not so clear that the rounding mode is part of the environment for this purpose, basically because the spec for setjmp() is silent about that. > As to the "for example, floating-point status flags" part of the man > page, floating-point status flags are not floating-point control > modes. See the distinction here: > > http://www.opengroup.org/onlinepubs/009695399/basedefs/fenv.h.html > > [...] > > A floating-point status flag is a system variable whose value is > set (but never cleared) when a > floating-point exception is raised, which occurs as a side > effect of exceptional floating-point > arithmetic to provide auxiliary information. A floating-point > control mode is a system variable > whose value may be set by the user to affect the subsequent > behavior of floating-point arithmetic. I much appreciate your going to the trouble to locate this reference. But your conclusion that longjmp() should restore the rounding mode part of the floating-point environment doesn't seem that obvious to me. While it doesn't say anything explicit about setjmp/longjmp, it seems to me that the spirit of what it does say would allow the programmer to change the rounding mode between the two. It says: Certain application programming conventions support the intended model of use for the floating-point environment: * A function call does not alter its caller's floating-point control modes, clear its caller's floating-point status flags, nor depend on the state of its caller's floating-point status flags unless the function is so documented. * A function call is assumed to require default floating-point control modes, unless its documentation promises otherwise. * A function call is assumed to have the potential for raising floating-point exceptions, unless its documentation promises otherwise. With these conventions, an application can safely assume default floating-point control modes (or be unaware of them). The responsibilities associated with accessing the floating-point environment fall on the application that does so explicitly. So for ordinary function calls, the programmer is allowed to change the mode between functions as long as he documents it; and I don't see anything that should be interpreted as disallowing that between setjmp() and longjmp(). Moreover, couldn't the fact that the two are typically embedded in different functions be taken as an argument that they *should* be treated that way? The spec for longjmp/setjmp also doesn't say that any part of the floating point environment except for status flags should be restored. It says "for example" floating-point status flags should not be restored; and indeed, the floating point control modes seem to me sort of analogous to file open/close modes, and might even be seen in the spirit of "accessible objects" (except I was unable to find the definition of those in Single Unix 3). I am really not an expert on this kind of thing; but it seems to me that the meaning of the "environment saved" by setjmp() which longjmp() is supposed to restore, which I take to be the contents of jmp_buf, is plain ambiguous according to the setjmp() spec. In that situation, I'd prefer a conservative approach, restoring the "minimum necessary", whatever *that* might mean. :-( In fact, it makes me nervous that /usr/include/ppc/setjmp.h doesn't mention any qualifications about saving r13-r31 and fr14-fr31, which would conflict with the gcc spec if any of those were to be declared a global register variable. I can work around this by avoiding setjmp/longjmp -- maybe that's even good for the soul! -- David _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com

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pdisk vs pdisk.8
by Walt Pawley 01 Jun '05

01 Jun '05

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Is it just me or does the actual behavior of "pdisk" differ almost entirely from what it's man page says? -- Walter M. Pawley <walt(a)wump.org> Wump Research & Company 676 River Bend Road, Roseburg, OR 97470 541-672-8975 _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com

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Re: bless command and target mode
by Stéphane Thiell 01 Jun '05

01 Jun '05

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com On 31 mai 05, at 19:37, Kevin Van Vechten wrote: OK thanks for the info. I use the bless command from the G5 like this: %s being the mount point of the PowerBook in target mode. Thanks, Stéphane Thiell _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… The --setBoot argument (which used to be called --setOF) does not change the on-disk representation at all, but instead changes the boot-device open firmware variable (`nvram boot-device`). It's not possible (as far as I know) to modify an open firmware variable on a machine that is in target disk mode. Thus, I don't think your problem has any relation to the bootx.bootinfo file, but instead is due to the open firmware variable not being set on the PowerBook (until you set it via the option key and clicking the icon at boot). The thing is, the disk doesn't even appear when I boot the PowerBook with the option key. I need to select it on the startup disk preferences pane to make it work (so another boot volume is needed on the PowerBook). bless -folder "%s/System/Library/CoreServices" -bootinfo "/usr/ standalone/ppc/bootx.bootinfo" -label "%@" This email sent to site_archiver(a)lists.apple.com

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