* Why is -msoft-float used in Kernel compilation? @ 1999-02-13 14:37 Gavriel State 1999-02-13 16:19 ` Michael Meissner 1999-02-14 21:10 ` Michel Lanners 0 siblings, 2 replies; 5+ messages in thread From: Gavriel State @ 1999-02-13 14:37 UTC (permalink / raw) To: linuxppc-dev I can understand using -msoft-float if CONFIG__8xx is on, but why use it when compiling for 60x or 7x0 CPUs? -Gav -- Gavriel State Engineering Project Leader - Linux Apps Corel Corp gavriels@corel•com [[ This message was sent via the linuxppc-dev mailing list. Replies are ]] [[ not forced back to the list, so be sure to Cc linuxppc-dev if your ]] [[ reply is of general interest. To unsubscribe from linuxppc-dev, send ]] [[ the message 'unsubscribe' to linuxppc-dev-request@lists•linuxppc.org ]] ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Why is -msoft-float used in Kernel compilation? 1999-02-13 14:37 Why is -msoft-float used in Kernel compilation? Gavriel State @ 1999-02-13 16:19 ` Michael Meissner 1999-02-14 21:10 ` Michel Lanners 1 sibling, 0 replies; 5+ messages in thread From: Michael Meissner @ 1999-02-13 16:19 UTC (permalink / raw) To: Gavriel State; +Cc: linuxppc-dev On Sat, Feb 13, 1999 at 09:37:46AM -0500, Gavriel State wrote: > > I can understand using -msoft-float if CONFIG__8xx is on, > but why use it when compiling for 60x or 7x0 CPUs? I would imagine to prevent the compiler from using the FPU to move 64-bit aligned items via fp registers. -- Michael Meissner, Cygnus Solutions (Massachusetts office) 4th floor, 955 Massachusetts Avenue, Cambridge, MA 02139, USA meissner@cygnus•com, 617-354-5416 (office), 617-354-7161 (fax) [[ This message was sent via the linuxppc-dev mailing list. Replies are ]] [[ not forced back to the list, so be sure to Cc linuxppc-dev if your ]] [[ reply is of general interest. To unsubscribe from linuxppc-dev, send ]] [[ the message 'unsubscribe' to linuxppc-dev-request@lists•linuxppc.org ]] ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Why is -msoft-float used in Kernel compilation? 1999-02-13 14:37 Why is -msoft-float used in Kernel compilation? Gavriel State 1999-02-13 16:19 ` Michael Meissner @ 1999-02-14 21:10 ` Michel Lanners 1999-02-15 6:41 ` Troy Benjegerdes 1 sibling, 1 reply; 5+ messages in thread From: Michel Lanners @ 1999-02-14 21:10 UTC (permalink / raw) To: u497w7n9; +Cc: linuxppc-dev On 13 Feb, this message from Gavriel State echoed through cyberspace: > > I can understand using -msoft-float if CONFIG__8xx is on, > but why use it when compiling for 60x or 7x0 CPUs? I've heard something about a 'no floiting point in kernel' rule, and I've tried compiling without -msoft-float.... it does boot, but it's an ugly sight... fp warning messages all over! I have, however, never seen a clear explanation of why that rule exists... Any guru around? Michel ------------------------------------------------------------------------- Michel Lanners | " Read Philosophy. Study Art. 23, Rue Paul Henkes | Ask Questions. Make Mistakes. L-1710 Luxembourg | email mlan@cpu•lu | http://www.cpu.lu/~mlan | Learn Always. " [[ This message was sent via the linuxppc-dev mailing list. Replies are ]] [[ not forced back to the list, so be sure to Cc linuxppc-dev if your ]] [[ reply is of general interest. To unsubscribe from linuxppc-dev, send ]] [[ the message 'unsubscribe' to linuxppc-dev-request@lists•linuxppc.org ]] ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Why is -msoft-float used in Kernel compilation? 1999-02-14 21:10 ` Michel Lanners @ 1999-02-15 6:41 ` Troy Benjegerdes 1999-02-15 11:49 ` Gary Thomas 0 siblings, 1 reply; 5+ messages in thread From: Troy Benjegerdes @ 1999-02-15 6:41 UTC (permalink / raw) To: Michel Lanners; +Cc: u497w7n9, linuxppc-dev On Sun, 14 Feb 1999, Michel Lanners wrote: > > On 13 Feb, this message from Gavriel State echoed through cyberspace: > > > > I can understand using -msoft-float if CONFIG__8xx is on, > > but why use it when compiling for 60x or 7x0 CPUs? > > I've heard something about a 'no floiting point in kernel' rule, and > I've tried compiling without -msoft-float.... it does boot, but it's an > ugly sight... fp warning messages all over! > > I have, however, never seen a clear explanation of why that rule > exists... I'm not sure, but I believe it's an optimization to allow the kernel to not have to save floating point registers on every context switch. -------------------------------------------------------------------------- | Troy Benjegerdes | troy@microux•com | hozer@drgw•net | | Unix is user friendly... You just have to be friendly to it first. | | This message composed with 100% free software. http://www.gnu.org | -------------------------------------------------------------------------- [[ This message was sent via the linuxppc-dev mailing list. Replies are ]] [[ not forced back to the list, so be sure to Cc linuxppc-dev if your ]] [[ reply is of general interest. To unsubscribe from linuxppc-dev, send ]] [[ the message 'unsubscribe' to linuxppc-dev-request@lists•linuxppc.org ]] ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Why is -msoft-float used in Kernel compilation? 1999-02-15 6:41 ` Troy Benjegerdes @ 1999-02-15 11:49 ` Gary Thomas 0 siblings, 0 replies; 5+ messages in thread From: Gary Thomas @ 1999-02-15 11:49 UTC (permalink / raw) To: Troy Benjegerdes; +Cc: linuxppc-dev, u497w7n9, Michel Lanners On 15-Feb-99 Troy Benjegerdes wrote: > > On Sun, 14 Feb 1999, Michel Lanners wrote: > >> >> On 13 Feb, this message from Gavriel State echoed through cyberspace: >> > >> > I can understand using -msoft-float if CONFIG__8xx is on, >> > but why use it when compiling for 60x or 7x0 CPUs? >> >> I've heard something about a 'no floiting point in kernel' rule, and >> I've tried compiling without -msoft-float.... it does boot, but it's an >> ugly sight... fp warning messages all over! >> >> I have, however, never seen a clear explanation of why that rule >> exists... > > I'm not sure, but I believe it's an optimization to allow the kernel to > not have to save floating point registers on every context switch. > More importantly it is to keep GCC from trying to use FP registers to do structure copies. Without this option, GCC will try to use the FP registers to perform high[er] performance copying of structures. This would mean that the kernel would have to save/restore some number of FP registers on every context change, not just the switch from user to kernel mode, because these registers are considered totally volatile by the compiler. ------------------------------------------------------------------------ Gary Thomas | email: gdt@linuxppc•org | "Fine wine is a necessity of ... opinions expressed here are mine | life for me" and no one else would claim them! | | Thomas Jefferson ------------------------------------------------------------------------ [[ This message was sent via the linuxppc-dev mailing list. Replies are ]] [[ not forced back to the list, so be sure to Cc linuxppc-dev if your ]] [[ reply is of general interest. To unsubscribe from linuxppc-dev, send ]] [[ the message 'unsubscribe' to linuxppc-dev-request@lists•linuxppc.org ]] ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~1999-02-15 11:49 UTC | newest] Thread overview: 5+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 1999-02-13 14:37 Why is -msoft-float used in Kernel compilation? Gavriel State 1999-02-13 16:19 ` Michael Meissner 1999-02-14 21:10 ` Michel Lanners 1999-02-15 6:41 ` Troy Benjegerdes 1999-02-15 11:49 ` Gary Thomas
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