* Re: Bug in the _save_fp_context.
2001-03-19 15:43 ` Kevin D. Kissell
@ 2001-03-19 15:43 ` Kevin D. Kissell
2001-03-19 16:03 ` Kevin D. Kissell
` (2 subsequent siblings)
3 siblings, 0 replies; 8+ messages in thread
From: Kevin D. Kissell @ 2001-03-19 15:43 UTC (permalink / raw)
To: Carsten Langgaard, linux-mips
> I think there is a bug in the _save_fp_context function in
> arch/mips/kernel/r4k_fpu.S
>
> The problem is the following piece of code:
>
> jr ra
> .set nomacro
> EX(sw t0,SC_FPC_EIR(a0))
> nop
> .set macro
>
> First of all what should the ".set nomacro" do?
> If it means that the EX macro shouldn't be used then this entry wouldn't
> get into __ex_table, which would be wrong.
> But it look like it uses the macro anyway, regardless of the ".set
> nomacro", at least with the compiler I use.
Not surprising, really. "EX" is presumably a cpp macro
that gets expanded by gcc from the .S file, based on
some include file. .set directives affect only the assembler,
and would inhibit assembler-level macros only. I'm not
sure just what the definition of an assembler macro
would be - it may or may not include pseudo-instructions
like "la" or "li 32_bit_constant". I *think* that what the
author was trying to do here was to ensure that the
"sw" instruction in the EX expansion was really and
truly a single instruction.
> Never the less we do not handle entries in the __ex_table which is
> located in a branch delay.
> So we need to handle the situation where we take a page fault on an
> instruction which is located in a brach delay slot, or we don't put the
> "potential" faulting instruction in a delay slot.
>
> Any ideas, how we should handle this in a nice and clean way?
Is the __ex_table really ending up in the delay slot?
Just looking at the source, I have the impression
that the "sw t0,..." instruction should be in the delay
slot, followed by the __ex_table.
On another topic, now that I've patched the kernel to
turn off the stupid stuck interrupt on my Malta board,
I've realized that I can't just connect my old Atlas SCSI
disk. I'm torn between ordering a Tekram 390 PCI
SCSI card, which should be able to use our "MIPS
safe" NCR driver as-is (I hope) and buying an IDE
disk and going through the network install ritual.
Which do you recommend? One thing I really never
knew was just what kernel config options I need to
select to build a kernel that can do the NFS-root
bootstrap. Can you help me there?
Regards,
Kevin K.
^ permalink raw reply [flat|nested] 8+ messages in thread* Re: Bug in the _save_fp_context.
2001-03-19 15:43 ` Kevin D. Kissell
2001-03-19 15:43 ` Kevin D. Kissell
@ 2001-03-19 16:03 ` Kevin D. Kissell
2001-03-19 16:03 ` Kevin D. Kissell
2001-03-19 18:14 ` Jun Sun
2001-03-19 16:13 ` Carsten Langgaard
2001-03-19 18:10 ` SCSI card [Re: Bug in the _save_fp_context.] Jun Sun
3 siblings, 2 replies; 8+ messages in thread
From: Kevin D. Kissell @ 2001-03-19 16:03 UTC (permalink / raw)
To: linux-mips
Oops! I hadn't noticed that Carsten had copied the
Linux-MIPS mailing list on this, so I treated it as a
point-to-point communication. The rest of you can
ignore my last paragraph!
Kevin K.
----- Original Message -----
From: "Kevin D. Kissell" <kevink@mips.com>
To: "Carsten Langgaard" <carstenl@mips.com>; <linux-mips@oss.sgi.com>
Sent: Monday, March 19, 2001 4:43 PM
Subject: Re: Bug in the _save_fp_context.
> > I think there is a bug in the _save_fp_context function in
> > arch/mips/kernel/r4k_fpu.S
> >
> > The problem is the following piece of code:
> >
> > jr ra
> > .set nomacro
> > EX(sw t0,SC_FPC_EIR(a0))
> > nop
> > .set macro
> >
> > First of all what should the ".set nomacro" do?
> > If it means that the EX macro shouldn't be used then this entry wouldn't
> > get into __ex_table, which would be wrong.
> > But it look like it uses the macro anyway, regardless of the ".set
> > nomacro", at least with the compiler I use.
>
> Not surprising, really. "EX" is presumably a cpp macro
> that gets expanded by gcc from the .S file, based on
> some include file. .set directives affect only the assembler,
> and would inhibit assembler-level macros only. I'm not
> sure just what the definition of an assembler macro
> would be - it may or may not include pseudo-instructions
> like "la" or "li 32_bit_constant". I *think* that what the
> author was trying to do here was to ensure that the
> "sw" instruction in the EX expansion was really and
> truly a single instruction.
>
> > Never the less we do not handle entries in the __ex_table which is
> > located in a branch delay.
> > So we need to handle the situation where we take a page fault on an
> > instruction which is located in a brach delay slot, or we don't put the
> > "potential" faulting instruction in a delay slot.
> >
> > Any ideas, how we should handle this in a nice and clean way?
>
> Is the __ex_table really ending up in the delay slot?
> Just looking at the source, I have the impression
> that the "sw t0,..." instruction should be in the delay
> slot, followed by the __ex_table.
>
> On another topic, now that I've patched the kernel to
> turn off the stupid stuck interrupt on my Malta board,
> I've realized that I can't just connect my old Atlas SCSI
> disk. I'm torn between ordering a Tekram 390 PCI
> SCSI card, which should be able to use our "MIPS
> safe" NCR driver as-is (I hope) and buying an IDE
> disk and going through the network install ritual.
> Which do you recommend? One thing I really never
> knew was just what kernel config options I need to
> select to build a kernel that can do the NFS-root
> bootstrap. Can you help me there?
>
> Regards,
>
> Kevin K.
>
^ permalink raw reply [flat|nested] 8+ messages in thread* Re: Bug in the _save_fp_context.
2001-03-19 16:03 ` Kevin D. Kissell
@ 2001-03-19 16:03 ` Kevin D. Kissell
2001-03-19 18:14 ` Jun Sun
1 sibling, 0 replies; 8+ messages in thread
From: Kevin D. Kissell @ 2001-03-19 16:03 UTC (permalink / raw)
To: linux-mips
Oops! I hadn't noticed that Carsten had copied the
Linux-MIPS mailing list on this, so I treated it as a
point-to-point communication. The rest of you can
ignore my last paragraph!
Kevin K.
----- Original Message -----
From: "Kevin D. Kissell" <kevink@mips.com>
To: "Carsten Langgaard" <carstenl@mips.com>; <linux-mips@oss.sgi.com>
Sent: Monday, March 19, 2001 4:43 PM
Subject: Re: Bug in the _save_fp_context.
> > I think there is a bug in the _save_fp_context function in
> > arch/mips/kernel/r4k_fpu.S
> >
> > The problem is the following piece of code:
> >
> > jr ra
> > .set nomacro
> > EX(sw t0,SC_FPC_EIR(a0))
> > nop
> > .set macro
> >
> > First of all what should the ".set nomacro" do?
> > If it means that the EX macro shouldn't be used then this entry wouldn't
> > get into __ex_table, which would be wrong.
> > But it look like it uses the macro anyway, regardless of the ".set
> > nomacro", at least with the compiler I use.
>
> Not surprising, really. "EX" is presumably a cpp macro
> that gets expanded by gcc from the .S file, based on
> some include file. .set directives affect only the assembler,
> and would inhibit assembler-level macros only. I'm not
> sure just what the definition of an assembler macro
> would be - it may or may not include pseudo-instructions
> like "la" or "li 32_bit_constant". I *think* that what the
> author was trying to do here was to ensure that the
> "sw" instruction in the EX expansion was really and
> truly a single instruction.
>
> > Never the less we do not handle entries in the __ex_table which is
> > located in a branch delay.
> > So we need to handle the situation where we take a page fault on an
> > instruction which is located in a brach delay slot, or we don't put the
> > "potential" faulting instruction in a delay slot.
> >
> > Any ideas, how we should handle this in a nice and clean way?
>
> Is the __ex_table really ending up in the delay slot?
> Just looking at the source, I have the impression
> that the "sw t0,..." instruction should be in the delay
> slot, followed by the __ex_table.
>
> On another topic, now that I've patched the kernel to
> turn off the stupid stuck interrupt on my Malta board,
> I've realized that I can't just connect my old Atlas SCSI
> disk. I'm torn between ordering a Tekram 390 PCI
> SCSI card, which should be able to use our "MIPS
> safe" NCR driver as-is (I hope) and buying an IDE
> disk and going through the network install ritual.
> Which do you recommend? One thing I really never
> knew was just what kernel config options I need to
> select to build a kernel that can do the NFS-root
> bootstrap. Can you help me there?
>
> Regards,
>
> Kevin K.
>
^ permalink raw reply [flat|nested] 8+ messages in thread* Re: Bug in the _save_fp_context.
2001-03-19 16:03 ` Kevin D. Kissell
2001-03-19 16:03 ` Kevin D. Kissell
@ 2001-03-19 18:14 ` Jun Sun
1 sibling, 0 replies; 8+ messages in thread
From: Jun Sun @ 2001-03-19 18:14 UTC (permalink / raw)
To: Kevin D. Kissell; +Cc: linux-mips
"Kevin D. Kissell" wrote:
>
> Oops! I hadn't noticed that Carsten had copied the
> Linux-MIPS mailing list on this, so I treated it as a
> point-to-point communication. The rest of you can
> ignore my last paragraph!
>
> Kevin K.
>
Oops! Please ignore my previous reply too. :-)
Jun
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Bug in the _save_fp_context.
2001-03-19 15:43 ` Kevin D. Kissell
2001-03-19 15:43 ` Kevin D. Kissell
2001-03-19 16:03 ` Kevin D. Kissell
@ 2001-03-19 16:13 ` Carsten Langgaard
2001-03-19 18:10 ` SCSI card [Re: Bug in the _save_fp_context.] Jun Sun
3 siblings, 0 replies; 8+ messages in thread
From: Carsten Langgaard @ 2001-03-19 16:13 UTC (permalink / raw)
To: Kevin D. Kissell; +Cc: linux-mips
"Kevin D. Kissell" wrote:
> > I think there is a bug in the _save_fp_context function in
> > arch/mips/kernel/r4k_fpu.S
> >
> > The problem is the following piece of code:
> >
> > jr ra
> > .set nomacro
> > EX(sw t0,SC_FPC_EIR(a0))
> > nop
> > .set macro
> >
> > First of all what should the ".set nomacro" do?
> > If it means that the EX macro shouldn't be used then this entry wouldn't
> > get into __ex_table, which would be wrong.
> > But it look like it uses the macro anyway, regardless of the ".set
> > nomacro", at least with the compiler I use.
>
> Not surprising, really. "EX" is presumably a cpp macro
> that gets expanded by gcc from the .S file, based on
> some include file. .set directives affect only the assembler,
> and would inhibit assembler-level macros only. I'm not
> sure just what the definition of an assembler macro
> would be - it may or may not include pseudo-instructions
> like "la" or "li 32_bit_constant". I *think* that what the
> author was trying to do here was to ensure that the
> "sw" instruction in the EX expansion was really and
> truly a single instruction.
>
> > Never the less we do not handle entries in the __ex_table which is
> > located in a branch delay.
> > So we need to handle the situation where we take a page fault on an
> > instruction which is located in a brach delay slot, or we don't put the
> > "potential" faulting instruction in a delay slot.
> >
> > Any ideas, how we should handle this in a nice and clean way?
>
> Is the __ex_table really ending up in the delay slot?
> Just looking at the source, I have the impression
> that the "sw t0,..." instruction should be in the delay
> slot, followed by the __ex_table.
The problem is that the address of the delay slot is put in the __ex_table
and then we take a page fault EPC is pointing at the jr instruction and not
the delay slot.
This result in a miss match when we try to lookup in __ex_table, resulting in
a kernel crash.
The faulting situation look like this:
EPC = address of delay slot
entry in __ex_table = address of delay slot - 4
Hopes that clarify it a bit more.
>
> On another topic, now that I've patched the kernel to
> turn off the stupid stuck interrupt on my Malta board,
> I've realized that I can't just connect my old Atlas SCSI
> disk. I'm torn between ordering a Tekram 390 PCI
> SCSI card, which should be able to use our "MIPS
> safe" NCR driver as-is (I hope) and buying an IDE
> disk and going through the network install ritual.
> Which do you recommend? One thing I really never
> knew was just what kernel config options I need to
> select to build a kernel that can do the NFS-root
> bootstrap. Can you help me there?
>
> Regards,
>
> Kevin K.
--
_ _ ____ ___ Carsten Langgaard Mailto:carstenl@mips.com
|\ /|||___)(___ MIPS Denmark Direct: +45 4486 5527
| \/ ||| ____) Lautrupvang 4B Switch: +45 4486 5555
TECHNOLOGIES 2750 Ballerup Fax...: +45 4486 5556
Denmark http://www.mips.com
^ permalink raw reply [flat|nested] 8+ messages in thread* SCSI card [Re: Bug in the _save_fp_context.]
2001-03-19 15:43 ` Kevin D. Kissell
` (2 preceding siblings ...)
2001-03-19 16:13 ` Carsten Langgaard
@ 2001-03-19 18:10 ` Jun Sun
3 siblings, 0 replies; 8+ messages in thread
From: Jun Sun @ 2001-03-19 18:10 UTC (permalink / raw)
To: Kevin D. Kissell; +Cc: Carsten Langgaard, linux-mips
"Kevin D. Kissell" wrote:
> On another topic, now that I've patched the kernel to
> turn off the stupid stuck interrupt on my Malta board,
> I've realized that I can't just connect my old Atlas SCSI
> disk. I'm torn between ordering a Tekram 390 PCI
> SCSI card, which should be able to use our "MIPS
> safe" NCR driver as-is (I hope) and buying an IDE
> disk and going through the network install ritual.
> Which do you recommend? One thing I really never
> knew was just what kernel config options I need to
> select to build a kernel that can do the NFS-root
> bootstrap. Can you help me there?
>
Kevin,
If you store your kernel image on flash and boots from there, using a local
hard disk is not a bad idea. I recently used a SCSI card based on NCR
53C895A. I have to turn off some optimization in the driver in order to get
it work. See some related configs below.
CONFIG_SCSI_NCR53C8XX=y
# CONFIG_SCSI_SYM53C8XX is not set
CONFIG_SCSI_NCR53C8XX_DEFAULT_TAGS=0
CONFIG_SCSI_NCR53C8XX_MAX_TAGS=32
CONFIG_SCSI_NCR53C8XX_SYNC=0
In general NFS root is always easier to get kernel going. Many defconfigs
under arch/mips/ already have NFS root fs configured as default, at least in
the two I put in, DDB5476 and ocelot.
Jun
^ permalink raw reply [flat|nested] 8+ messages in thread