* asm (lidt) question
@ 2003-07-17 22:28 Randy.Dunlap
2003-07-17 22:36 ` Davide Libenzi
0 siblings, 1 reply; 12+ messages in thread
From: Randy.Dunlap @ 2003-07-17 22:28 UTC (permalink / raw)
To: lkml
In arch/i386/kernel, inline asm for loading IDT (lidt) is used a few
times, but with slightly different constraints and output/input
definitions. Are these OK, equivalent, or what?
[rddunlap@dragon kernel]$ findc lidt
./cpu/common.c:484: __asm__ __volatile__("lidt %0": "=m" (idt_descr));
./traps.c:783: __asm__ __volatile__("lidt %0": "=m" (idt_descr));
vs.
./reboot.c:186: __asm__ __volatile__ ("lidt %0" : : "m" (real_mode_idt));
./reboot.c:261: __asm__ __volatile__("lidt %0": :"m" (no_idt));
./suspend.c:95: asm volatile ("lidt %0" :: "m" (saved_context.idt_limit));
Thanks,
--
~Randy [yes, i've looked at the inline asm docs]
For Linux-2.6:
http://www.codemonkey.org.uk/post-halloween-2.5.txt
or http://lwn.net/Articles/39901/
http://www.kernel.org/pub/linux/kernel/people/rusty/modules/
^ permalink raw reply [flat|nested] 12+ messages in thread* Re: asm (lidt) question 2003-07-17 22:28 asm (lidt) question Randy.Dunlap @ 2003-07-17 22:36 ` Davide Libenzi 2003-07-17 23:18 ` Davide Libenzi 0 siblings, 1 reply; 12+ messages in thread From: Davide Libenzi @ 2003-07-17 22:36 UTC (permalink / raw) To: Randy.Dunlap; +Cc: lkml On Thu, 17 Jul 2003, Randy.Dunlap wrote: > > In arch/i386/kernel, inline asm for loading IDT (lidt) is used a few > times, but with slightly different constraints and output/input > definitions. Are these OK, equivalent, or what? > > [rddunlap@dragon kernel]$ findc lidt > ./cpu/common.c:484: __asm__ __volatile__("lidt %0": "=m" (idt_descr)); > ./traps.c:783: __asm__ __volatile__("lidt %0": "=m" (idt_descr)); > > vs. > > ./reboot.c:186: __asm__ __volatile__ ("lidt %0" : : "m" (real_mode_idt)); > ./reboot.c:261: __asm__ __volatile__("lidt %0": :"m" (no_idt)); > ./suspend.c:95: asm volatile ("lidt %0" :: "m" (saved_context.idt_limit)); I'd have said no looking at the syntax (input/output), but they indeed generate the same code (just checked). - Davide ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: asm (lidt) question 2003-07-17 22:36 ` Davide Libenzi @ 2003-07-17 23:18 ` Davide Libenzi 2003-07-17 23:31 ` Randy.Dunlap 2003-07-22 17:27 ` Jamie Lokier 0 siblings, 2 replies; 12+ messages in thread From: Davide Libenzi @ 2003-07-17 23:18 UTC (permalink / raw) To: Randy.Dunlap; +Cc: lkml On Thu, 17 Jul 2003, Davide Libenzi wrote: > On Thu, 17 Jul 2003, Randy.Dunlap wrote: > > > > > In arch/i386/kernel, inline asm for loading IDT (lidt) is used a few > > times, but with slightly different constraints and output/input > > definitions. Are these OK, equivalent, or what? > > > > [rddunlap@dragon kernel]$ findc lidt > > ./cpu/common.c:484: __asm__ __volatile__("lidt %0": "=m" (idt_descr)); > > ./traps.c:783: __asm__ __volatile__("lidt %0": "=m" (idt_descr)); > > > > vs. > > > > ./reboot.c:186: __asm__ __volatile__ ("lidt %0" : : "m" (real_mode_idt)); > > ./reboot.c:261: __asm__ __volatile__("lidt %0": :"m" (no_idt)); > > ./suspend.c:95: asm volatile ("lidt %0" :: "m" (saved_context.idt_limit)); > > I'd have said no looking at the syntax (input/output), but they indeed > generate the same code (just checked). Randy, I'd say that this : __asm__ __volatile__("lidt %0": "=m" (var)); is better then : __asm__ __volatile__("lidt %0": :"m" (var)); IMHO, since "var" is really an output parameter. - Davide ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: asm (lidt) question 2003-07-17 23:18 ` Davide Libenzi @ 2003-07-17 23:31 ` Randy.Dunlap 2003-07-17 23:36 ` Davide Libenzi 2003-07-22 17:27 ` Jamie Lokier 1 sibling, 1 reply; 12+ messages in thread From: Randy.Dunlap @ 2003-07-17 23:31 UTC (permalink / raw) To: Davide Libenzi; +Cc: linux-kernel On Thu, 17 Jul 2003 16:18:06 -0700 (PDT) Davide Libenzi <davidel@xmailserver.org> wrote: | On Thu, 17 Jul 2003, Davide Libenzi wrote: | | > On Thu, 17 Jul 2003, Randy.Dunlap wrote: | > | > > | > > In arch/i386/kernel, inline asm for loading IDT (lidt) is used a few | > > times, but with slightly different constraints and output/input | > > definitions. Are these OK, equivalent, or what? | > > | > > [rddunlap@dragon kernel]$ findc lidt | > > ./cpu/common.c:484: __asm__ __volatile__("lidt %0": "=m" (idt_descr)); | > > ./traps.c:783: __asm__ __volatile__("lidt %0": "=m" (idt_descr)); | > > | > > vs. | > > | > > ./reboot.c:186: __asm__ __volatile__ ("lidt %0" : : "m" (real_mode_idt)); | > > ./reboot.c:261: __asm__ __volatile__("lidt %0": :"m" (no_idt)); | > > ./suspend.c:95: asm volatile ("lidt %0" :: "m" (saved_context.idt_limit)); | > | > I'd have said no looking at the syntax (input/output), but they indeed | > generate the same code (just checked). | | Randy, I'd say that this : | | __asm__ __volatile__("lidt %0": "=m" (var)); | | is better then : | | __asm__ __volatile__("lidt %0": :"m" (var)); | | IMHO, since "var" is really an output parameter. Yes, I agree, var is output and should be listed after the first ':' IMHO also. Thanks for checking that they generate the same code, though. I'll buy you a beer... No, wait, I already did that. :) -- ~Randy ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: asm (lidt) question 2003-07-17 23:31 ` Randy.Dunlap @ 2003-07-17 23:36 ` Davide Libenzi 0 siblings, 0 replies; 12+ messages in thread From: Davide Libenzi @ 2003-07-17 23:36 UTC (permalink / raw) To: Randy.Dunlap; +Cc: Linux Kernel Mailing List On Thu, 17 Jul 2003, Randy.Dunlap wrote: > | Randy, I'd say that this : > | > | __asm__ __volatile__("lidt %0": "=m" (var)); > | > | is better then : > | > | __asm__ __volatile__("lidt %0": :"m" (var)); > | > | IMHO, since "var" is really an output parameter. > > Yes, I agree, var is output and should be listed after the first ':' > IMHO also. BF (Brain Farting) is contagious ;) I need a vacation, a long one (and you too so maybe OSDL will hire someone else meanwhile :) - Davide ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: asm (lidt) question 2003-07-17 23:18 ` Davide Libenzi 2003-07-17 23:31 ` Randy.Dunlap @ 2003-07-22 17:27 ` Jamie Lokier 2003-07-22 17:31 ` Davide Libenzi 1 sibling, 1 reply; 12+ messages in thread From: Jamie Lokier @ 2003-07-22 17:27 UTC (permalink / raw) To: Davide Libenzi; +Cc: Randy.Dunlap, lkml Davide Libenzi wrote: > IMHO, since "var" is really an output parameter. "var" is read, not written. I think you are confusing "lidt" with "sidt". Therefore > __asm__ __volatile__("lidt %0": :"m" (var)); is the better choice, and that's why I wrote it in reboot.c :) -- Jamie ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: asm (lidt) question 2003-07-22 17:27 ` Jamie Lokier @ 2003-07-22 17:31 ` Davide Libenzi 2003-07-22 17:50 ` Richard B. Johnson 2003-07-22 18:58 ` Randy.Dunlap 0 siblings, 2 replies; 12+ messages in thread From: Davide Libenzi @ 2003-07-22 17:31 UTC (permalink / raw) To: Jamie Lokier; +Cc: Randy.Dunlap, lkml On Tue, 22 Jul 2003, Jamie Lokier wrote: > Davide Libenzi wrote: > > IMHO, since "var" is really an output parameter. > > "var" is read, not written. > I think you are confusing "lidt" with "sidt". Actually I don't even know what I was confusing, since L and S are not there for nothing ;) And yes, the form with =m as input parameter should be corrected, even if it generates the same code. - Davide ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: asm (lidt) question 2003-07-22 17:31 ` Davide Libenzi @ 2003-07-22 17:50 ` Richard B. Johnson 2003-07-22 17:54 ` Davide Libenzi 2003-07-22 18:58 ` Randy.Dunlap 1 sibling, 1 reply; 12+ messages in thread From: Richard B. Johnson @ 2003-07-22 17:50 UTC (permalink / raw) To: Davide Libenzi; +Cc: Jamie Lokier, Randy.Dunlap, lkml On Tue, 22 Jul 2003, Davide Libenzi wrote: > On Tue, 22 Jul 2003, Jamie Lokier wrote: > > > Davide Libenzi wrote: > > > IMHO, since "var" is really an output parameter. > > > > "var" is read, not written. > > I think you are confusing "lidt" with "sidt". > > Actually I don't even know what I was confusing, since L and S are not > there for nothing ;) And yes, the form with =m as input parameter should > be corrected, even if it generates the same code. > > > > - Davide LIDT is "load interrupt descriptor table". SIDT is "store interrupt descriptor table". Only SIDT modifies memory. LIDT reads from memory and puts the result into a special CPU register, therefore doesn't modify memory. Cheers, Dick Johnson Penguin : Linux version 2.4.20 on an i686 machine (797.90 BogoMips). Note 96.31% of all statistics are fiction. ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: asm (lidt) question 2003-07-22 17:50 ` Richard B. Johnson @ 2003-07-22 17:54 ` Davide Libenzi 0 siblings, 0 replies; 12+ messages in thread From: Davide Libenzi @ 2003-07-22 17:54 UTC (permalink / raw) To: Richard B. Johnson; +Cc: Jamie Lokier, Randy.Dunlap, lkml On Tue, 22 Jul 2003, Richard B. Johnson wrote: > LIDT is "load interrupt descriptor table". SIDT is "store interrupt > descriptor table". Only SIDT modifies memory. LIDT reads from memory > and puts the result into a special CPU register, therefore doesn't > modify memory. Indeed, that why this is not really correct : __asm__ __volatile__("lidt %0": "=m" (var)); even if it generates the same code of : __asm__ __volatile__("lidt %0": : "m" (var)); - Davide ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: asm (lidt) question 2003-07-22 17:31 ` Davide Libenzi 2003-07-22 17:50 ` Richard B. Johnson @ 2003-07-22 18:58 ` Randy.Dunlap 2003-07-22 18:58 ` Davide Libenzi 1 sibling, 1 reply; 12+ messages in thread From: Randy.Dunlap @ 2003-07-22 18:58 UTC (permalink / raw) To: Davide Libenzi; +Cc: jamie, linux-kernel On Tue, 22 Jul 2003 10:31:37 -0700 (PDT) Davide Libenzi <davidel@xmailserver.org> wrote: | On Tue, 22 Jul 2003, Jamie Lokier wrote: | | > Davide Libenzi wrote: | > > IMHO, since "var" is really an output parameter. | > | > "var" is read, not written. | > I think you are confusing "lidt" with "sidt". | | Actually I don't even know what I was confusing, since L and S are not | there for nothing ;) And yes, the form with =m as input parameter should | be corrected, even if it generates the same code. Yes, less confusion is better, so here's a patch to use the same reasonable syntax in all places. Look OK? Generates the same code, as Davide pointed out. -- ~Randy patch_name: lidt_norm.patch patch_version: 2003-07-22.11:47:21 author: Randy.Dunlap <rddunlap@osdl.org> description: normalize lidt/lgdt syntax usage product: Linux product_versions: 2.6.0-test1 diffstat: = arch/i386/kernel/cpu/common.c | 4 ++-- arch/i386/kernel/traps.c | 2 +- 2 files changed, 3 insertions(+), 3 deletions(-) diff -Naur ./arch/i386/kernel/cpu/common.c~lidt ./arch/i386/kernel/cpu/common.c --- ./arch/i386/kernel/cpu/common.c~lidt 2003-07-13 20:29:29.000000000 -0700 +++ ./arch/i386/kernel/cpu/common.c 2003-07-22 11:41:05.000000000 -0700 @@ -480,8 +480,8 @@ */ memcpy(thread->tls_array, cpu_gdt_table[cpu], GDT_ENTRY_TLS_ENTRIES * 8); - __asm__ __volatile__("lgdt %0": "=m" (cpu_gdt_descr[cpu])); - __asm__ __volatile__("lidt %0": "=m" (idt_descr)); + __asm__ __volatile__("lgdt %0": :"m" (cpu_gdt_descr[cpu])); + __asm__ __volatile__("lidt %0": :"m" (idt_descr)); /* * Delete NT diff -Naur ./arch/i386/kernel/traps.c~lidt ./arch/i386/kernel/traps.c --- ./arch/i386/kernel/traps.c~lidt 2003-07-13 20:31:20.000000000 -0700 +++ ./arch/i386/kernel/traps.c 2003-07-22 11:39:31.000000000 -0700 @@ -780,7 +780,7 @@ * it uses the read-only mapped virtual address. */ idt_descr.address = fix_to_virt(FIX_F00F_IDT); - __asm__ __volatile__("lidt %0": "=m" (idt_descr)); + __asm__ __volatile__("lidt %0": :"m" (idt_descr)); } #endif ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: asm (lidt) question 2003-07-22 18:58 ` Randy.Dunlap @ 2003-07-22 18:58 ` Davide Libenzi 2003-07-22 19:04 ` Randy.Dunlap 0 siblings, 1 reply; 12+ messages in thread From: Davide Libenzi @ 2003-07-22 18:58 UTC (permalink / raw) To: Randy.Dunlap; +Cc: jamie, Linux Kernel Mailing List On Tue, 22 Jul 2003, Randy.Dunlap wrote: > On Tue, 22 Jul 2003 10:31:37 -0700 (PDT) Davide Libenzi <davidel@xmailserver.org> wrote: > > | On Tue, 22 Jul 2003, Jamie Lokier wrote: > | > | > Davide Libenzi wrote: > | > > IMHO, since "var" is really an output parameter. > | > > | > "var" is read, not written. > | > I think you are confusing "lidt" with "sidt". > | > | Actually I don't even know what I was confusing, since L and S are not > | there for nothing ;) And yes, the form with =m as input parameter should > | be corrected, even if it generates the same code. > > Yes, less confusion is better, so here's a patch to use the > same reasonable syntax in all places. > > Look OK? Generates the same code, as Davide pointed out. Yep, that's the right syntax (pls push to Andrew or Linus) ;) - Davide ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: asm (lidt) question 2003-07-22 18:58 ` Davide Libenzi @ 2003-07-22 19:04 ` Randy.Dunlap 0 siblings, 0 replies; 12+ messages in thread From: Randy.Dunlap @ 2003-07-22 19:04 UTC (permalink / raw) To: Davide Libenzi; +Cc: jamie, linux-kernel On Tue, 22 Jul 2003 11:58:16 -0700 (PDT) Davide Libenzi <davidel@xmailserver.org> wrote: | > Yes, less confusion is better, so here's a patch to use the | > same reasonable syntax in all places. | > | > Look OK? Generates the same code, as Davide pointed out. | | Yep, that's the right syntax (pls push to Andrew or Linus) ;) | Yes, planning to. ~Randy ^ permalink raw reply [flat|nested] 12+ messages in thread
end of thread, other threads:[~2003-07-22 18:52 UTC | newest] Thread overview: 12+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2003-07-17 22:28 asm (lidt) question Randy.Dunlap 2003-07-17 22:36 ` Davide Libenzi 2003-07-17 23:18 ` Davide Libenzi 2003-07-17 23:31 ` Randy.Dunlap 2003-07-17 23:36 ` Davide Libenzi 2003-07-22 17:27 ` Jamie Lokier 2003-07-22 17:31 ` Davide Libenzi 2003-07-22 17:50 ` Richard B. Johnson 2003-07-22 17:54 ` Davide Libenzi 2003-07-22 18:58 ` Randy.Dunlap 2003-07-22 18:58 ` Davide Libenzi 2003-07-22 19:04 ` Randy.Dunlap
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