Re: FPU-intensive programs crashing with floating point exception on Cyrix MII

[Ondrej Zary <linux@rainbow-software.org>]

Linus Torvalds wrote:
> On Sun, 21 Aug 2005, Chuck Ebbert wrote:
>
> > > MATH ERROR: cwd = 0x37f, swd = 0x2800     <===========
> >
> > The error I marked has no exception flags set.  The rest are all (masked)
> > denormal exceptions.  Why your Cyrix MII would cause an FPU exception in these
> > cases is beyond me.  Could you try the statically-linked mprime program?

I use only the statically linked mprime.

> Also, please try this one, to see where it happens.
I did some modification to the code so it calls show_regs() in both 
cases where I get problems and also added the return so it does not 
crash. The code looks like this:
---
        printk("MATH ERROR: cwd = 0x%hx, swd = 0x%hx\n", cwd, swd);
        switch (((~cwd) & swd & 0x3f) | (swd & 0x240)) {
                case 0x000:
                case 0x200:
                        show_regs(regs);
                        return;
---
Here are the results.

MATH ERROR: cwd = 0x37f, swd = 0x1820

Pid: 1699, comm:               mprime
EIP: 0073:[<08181c73>] CPU: 0
EIP is at 0x8181c73
 ESP: 007b:bf927ab4 EFLAGS: 00010202    Not tainted  (2.6.12-pentium)
EAX: 00000001 EBX: 00000000 ECX: 0000808d EDX: b7f09480
ESI: b7455340 EDI: 080e01f0 EBP: bf927bf8 DS: 007b ES: 007b
CR0: 8005003b CR2: b7ed6058 CR3: 006f0000 CR4: 00000080
MATH ERROR: cwd = 0x37f, swd = 0x1020

Pid: 1699, comm:               mprime
EIP: 0073:[<0818ca5f>] CPU: 0
EIP is at 0x818ca5f
 ESP: 007b:bf927ab0 EFLAGS: 00010207    Not tainted  (2.6.12-pentium)
EAX: 00000005 EBX: 00000000 ECX: 00008407 EDX: b7f08140
ESI: b789aea0 EDI: b7f08200 EBP: bf927bf8 DS: 007b ES: 007b
CR0: 8005003b CR2: b75c6000 CR3: 006f0000 CR4: 00000080
MATH ERROR: cwd = 0x37f, swd = 0x2820

Pid: 1699, comm:               mprime
EIP: 0073:[<0818c4b1>] CPU: 0
EIP is at 0x818c4b1
 ESP: 007b:bf927ab0 EFLAGS: 00010247    Not tainted  (2.6.12-pentium)
EAX: 00000000 EBX: 00000000 ECX: 0000880f EDX: b7f09480
ESI: b741fc20 EDI: 080e0160 EBP: bf927bf8 DS: 007b ES: 007b
CR0: 8005003b CR2: b75c6000 CR3: 006f0000 CR4: 00000080
MATH ERROR: cwd = 0x37f, swd = 0x20

Pid: 1699, comm:               mprime
EIP: 0073:[<08181ca1>] CPU: 0
EIP is at 0x8181ca1
 ESP: 007b:bf927ab4 EFLAGS: 00010202    Not tainted  (2.6.12-pentium)
EAX: 00000002 EBX: 00000000 ECX: 00000084 EDX: b7f09480
ESI: b74f86c0 EDI: 080e01f0 EBP: bf927bf8 DS: 007b ES: 007b
CR0: 8005003b CR2: b75c6000 CR3: 006f0000 CR4: 00000080
MATH ERROR: cwd = 0x37f, swd = 0x1a20

Pid: 1699, comm:               mprime
EIP: 0073:[<08193c68>] CPU: 0
EIP is at 0x8193c68
 ESP: 007b:bf927ab8 EFLAGS: 00010206    Not tainted  (2.6.12-pentium)
EAX: 00000042 EBX: 00000000 ECX: 00154306 EDX: b7e3ba40
ESI: b7a1e680 EDI: b7e3be40 EBP: bf927bf8 DS: 007b ES: 007b
CR0: 8005003b CR2: b7499000 CR3: 006f0000 CR4: 00000080

MATH ERROR: cwd = 0x37f, swd = 0x20

Pid: 1699, comm:               mprime
EIP: 0073:[<0818de05>] CPU: 0
EIP is at 0x818de05
 ESP: 007b:bf927ab4 EFLAGS: 00010247    Not tainted  (2.6.12-pentium)
EAX: 00000004 EBX: 00000000 ECX: 0000880f EDX: b7f06b40
ESI: b7426400 EDI: 080e1960 EBP: bf927bf8 DS: 007b ES: 007b
CR0: 8005003b CR2: b7499000 CR3: 006f0000 CR4: 00000080
MATH ERROR: cwd = 0x37f, swd = 0x20

Pid: 1699, comm:               mprime
EIP: 0073:[<0818dfe4>] CPU: 0
EIP is at 0x818dfe4
 ESP: 007b:bf927ab4 EFLAGS: 00010247    Not tainted  (2.6.12-pentium)
EAX: 00000200 EBX: 00000000 ECX: 0000880f EDX: b7f06b40
ESI: b742a680 EDI: 080e1c60 EBP: bf927bf8 DS: 007b ES: 007b
CR0: 8005003b CR2: b7499000 CR3: 006f0000 CR4: 00000080

--
Ondrej Zary
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