"Illegal Instruction" error in grub_script_comments

"Illegal Instruction" error in grub_script_comments

[tedheadster]

[-- Attachment #1: Type: text/plain, Size: 1320 bytes --]

I am building the older grub2-1.98+20100804 under the similarly old Debian
'squeeze' distribution. However, I bet the error persists with newer
version. This is because I am building it on a true Intel 80486 and I don't
thing the compiler is building for the correct architecture. Here is the
output:

./config.status --file=-:tests/grub_script_dollar.in | sed -e
's,@pkglib_DATA@,efiemu32.o efiemu64.o moddep.lst command.lst fs.lst
partmap.lst parttool.lst handler.lst vi\
deo.lst crypto.lst terminal.lst,g' > grub_script_dollar
chmod +x grub_script_dollar

./config.status --file=-:tests/grub_script_comments.in | sed -e
's,@pkglib_DATA@,efiemu32.o efiemu64.o moddep.lst command.lst fs.lst
partmap.lst parttool.lst handler.lst \
video.lst crypto.lst terminal.lst,g' > grub_script_comments
chmod +x grub_script_comments

Illegal instruction

./grub_script_echo1: GRUB and BASH outputs did not match (see diff -u
/tmp/tmp.tP7l8uR3SD /tmp/tmp.wYCFOK2zor)
make[2]: *** [check] Error 1
make[2]: Leaving directory `/root/grub2-1.98+20100804/build/grub-pc'
dh_auto_test: make -j1 check returned exit code 2
make[1]: *** [build/stamps/build-grub-pc] Error 29
make[1]: Leaving directory `/root/grub2-1.98+20100804'
make: *** [build] Error 2

Is there a file I can modify to pass in -march=i486 or something similar?

- Matthew

[-- Attachment #2: Type: text/html, Size: 1771 bytes --]

Re: "Illegal Instruction" error in grub_script_comments

[Colin Watson]

On Mon, Oct 17, 2016 at 02:34:16PM -0400, tedheadster wrote:
> I am building the older grub2-1.98+20100804 under the similarly old Debian
> 'squeeze' distribution. However, I bet the error persists with newer
> version. This is because I am building it on a true Intel 80486 and I don't
> thing the compiler is building for the correct architecture.

If it is in fact the lack of an -march= option that's at fault, then
that was fixed in 2.02~beta1:

  http://git.savannah.gnu.org/cgit/grub.git/commit/?id=02663ee9d9cae806f90518bc4c89d31ae11b84e4

(You may be best simply setting TARGET_CFLAGS='-march=i386 -Os' in the
environment when running configure, rather than trying to regenerate
configure with that patch.)

If that doesn't do it, then it may be something more involved such as
hand-written non-486-compatible assembly somewhere, which won't be cured
by a compiler option.  GRUB is mostly in C, but something running at the
level of a boot loader does tend to need at least a little bit of
assembly to get itself going.

-- 
Colin Watson                                       [cjwatson@ubuntu.com]

Re: "Illegal Instruction" error in grub_script_comments

[Lennart Sorensen]

On Mon, Oct 17, 2016 at 02:34:16PM -0400, tedheadster wrote:
> I am building the older grub2-1.98+20100804 under the similarly old Debian
> 'squeeze' distribution. However, I bet the error persists with newer
> version. This is because I am building it on a true Intel 80486 and I don't
> thing the compiler is building for the correct architecture. Here is the
> output:
> 
> ./config.status --file=-:tests/grub_script_dollar.in | sed -e
> 's,@pkglib_DATA@,efiemu32.o efiemu64.o moddep.lst command.lst fs.lst
> partmap.lst parttool.lst handler.lst vi\
> deo.lst crypto.lst terminal.lst,g' > grub_script_dollar
> chmod +x grub_script_dollar
> 
> ./config.status --file=-:tests/grub_script_comments.in | sed -e
> 's,@pkglib_DATA@,efiemu32.o efiemu64.o moddep.lst command.lst fs.lst
> partmap.lst parttool.lst handler.lst \
> video.lst crypto.lst terminal.lst,g' > grub_script_comments
> chmod +x grub_script_comments
> 
> Illegal instruction
> 
> ./grub_script_echo1: GRUB and BASH outputs did not match (see diff -u
> /tmp/tmp.tP7l8uR3SD /tmp/tmp.wYCFOK2zor)
> make[2]: *** [check] Error 1
> make[2]: Leaving directory `/root/grub2-1.98+20100804/build/grub-pc'
> dh_auto_test: make -j1 check returned exit code 2
> make[1]: *** [build/stamps/build-grub-pc] Error 29
> make[1]: Leaving directory `/root/grub2-1.98+20100804'
> make: *** [build] Error 2
> 
> Is there a file I can modify to pass in -march=i486 or something similar?

Well I tried installing squeeze in a qemu VM emulating a 486.  It worked
fine there.

But qemu is emulating a 486DX4, which supports CPUID.  If your 486 is
older if probably does not have the CPUID instruction.  The place grub
is blowing up appears to be the test suite which uses qemu-system-i386.

So my suspicion is that it is actually qemu crashing, not grub, and
that your best bet would be to just not run the test suite.  The compile
almost certainly worked fine.

Simply uninstalling qemu whould make it not try to run the test based on
the debian/rules file, although debian/control considers qemu a built
dependancy.  So you probably have to use -d with dpkg-builcpackage to
make it ignore the missing dependancy.

Or edit debian/rules and simply set the with_check variable to no.

I can't find anything that says if qemu should run on an older 486,
probably since those usually didn't have enough memory to make that
worth the bother and they are too slow.  Maybe no one had ever tried
it before.

-- 
Len Sorensen

Re: "Illegal Instruction" error in grub_script_comments

[Matthew Whitehead]

[-- Attachment #1: Type: text/plain, Size: 2086 bytes --]

Lennart,
  I think I found the problem. I don't know what kernel.img does, but I'm guessing it is an essential part of grub2, loading after the 1st and 2nd stage loaders? I disassembled the binary using 'objdump -D -b binary -m i386 kernel.img' and found several cases both of rdtsc and cpuid. Both of these instructions do not exist on first generation 80486 cpus. Here they are, and I've attached the full disassembly output.

    53a0:       85 c0                   test   %eax,%eax
    53a2:       74 6f                   je     0x5413
    53a4:       b8 01 00 00 00          mov    $0x1,%eax
    53a9:       0f a2                   cpuid
    53ab:       80 e2 10                and    $0x10,%dl
    53ae:       74 63                   je     0x5413
    53b0:       31 c0                   xor    %eax,%eax
    53b2:       0f a2                   cpuid
    53b4:       0f 31                   rdtsc
    53b6:       a3 48 67 01 00          mov    %eax,0x16748
    53bb:       89 15 4c 67 01 00       mov    %edx,0x1674c
    53c1:       31 c0                   xor    %eax,%eax
    53c3:       0f a2                   cpuid
    53c5:       0f 31                   rdtsc
    53c7:       89 c6                   mov    %eax,%esi
    53c9:       b8 ff ff 00 00          mov    $0xffff,%eax
    53ce:       89 d7                   mov    %edx,%edi
    53d0:       e8 83 00 00 00          call   0x5458
    53d5:       31 c0                   xor    %eax,%eax
    53d7:       0f a2                   cpuid
    53d9:       0f 31                   rdtsc
    53db:       89 45 e0                mov    %eax,-0x20(%ebp)
    53de:       8b 4d e0                mov    -0x20(%ebp),%ecx
...
    5439:       31 c0                   xor    %eax,%eax
    543b:       0f a2                   cpuid
    543d:       0f 31                   rdtsc
    543f:       8b 0d 50 67 01 00       mov    0x16750,%ecx
    5445:       6a 00                   push   $0x0
    5447:       e8 8f dc ff ff          call   0x30db

How can we adjust the makefiles to include -march=i486 or something similar?

- Matthew


[-- Attachment #2: kernel.dis --]
[-- Type: application/vnd.mobius.dis, Size: 540582 bytes --]

Re: "Illegal Instruction" error in grub_script_comments

[Lennart Sorensen]

On Wed, Oct 19, 2016 at 11:32:08AM -0400, Matthew Whitehead wrote:
> Lennart,
>   I think I found the problem. I don't know what kernel.img does, but I'm guessing it is an essential part of grub2, loading after the 1st and 2nd stage loaders? I disassembled the binary using 'objdump -D -b binary -m i386 kernel.img' and found several cases both of rdtsc and cpuid. Both of these instructions do not exist on first generation 80486 cpus. Here they are, and I've attached the full disassembly output.
> 
>     53a0:       85 c0                   test   %eax,%eax
>     53a2:       74 6f                   je     0x5413
>     53a4:       b8 01 00 00 00          mov    $0x1,%eax
>     53a9:       0f a2                   cpuid
>     53ab:       80 e2 10                and    $0x10,%dl
>     53ae:       74 63                   je     0x5413
>     53b0:       31 c0                   xor    %eax,%eax
>     53b2:       0f a2                   cpuid
>     53b4:       0f 31                   rdtsc
>     53b6:       a3 48 67 01 00          mov    %eax,0x16748
>     53bb:       89 15 4c 67 01 00       mov    %edx,0x1674c
>     53c1:       31 c0                   xor    %eax,%eax
>     53c3:       0f a2                   cpuid
>     53c5:       0f 31                   rdtsc
>     53c7:       89 c6                   mov    %eax,%esi
>     53c9:       b8 ff ff 00 00          mov    $0xffff,%eax
>     53ce:       89 d7                   mov    %edx,%edi
>     53d0:       e8 83 00 00 00          call   0x5458
>     53d5:       31 c0                   xor    %eax,%eax
>     53d7:       0f a2                   cpuid
>     53d9:       0f 31                   rdtsc
>     53db:       89 45 e0                mov    %eax,-0x20(%ebp)
>     53de:       8b 4d e0                mov    -0x20(%ebp),%ecx
> ...
>     5439:       31 c0                   xor    %eax,%eax
>     543b:       0f a2                   cpuid
>     543d:       0f 31                   rdtsc
>     543f:       8b 0d 50 67 01 00       mov    0x16750,%ecx
>     5445:       6a 00                   push   $0x0
>     5447:       e8 8f dc ff ff          call   0x30db
> 
> How can we adjust the makefiles to include -march=i486 or something similar?

I don't think that's likely to make a difference.

The cpuid and rdtsc instructions are supposed to be protected by a check
for whether cpuid is a valid instruction, so it should never try to run
them unless that isn't working.

Would be interesting to see the failing test run under gdb in case it
can point to what instruction is illegal and on what line.

-- 
Len Sorensen

Re: "Illegal Instruction" error in grub_script_comments

[Matthew Whitehead]

Lennart,
  tell me how can I run this under gdb and I'll find where the exception is. I'm pretty sure I cannot do it while the system is booting from disk, but is there a userland way to do it?

- Matthew

Re: "Illegal Instruction" error in grub_script_comments

[Andrei Borzenkov]

19.10.2016 18:32, Matthew Whitehead пишет:
> Lennart,
>   I think I found the problem. I don't know what kernel.img does, but I'm guessing it is an essential part of grub2, loading after the 1st and 2nd stage loaders? I disassembled the binary using 'objdump -D -b binary -m i386 kernel.img' and found several cases both of rdtsc and cpuid. Both of these instructions do not exist on first generation 80486 cpus. Here they are, and I've attached the full disassembly output.
> 
>     53a0:       85 c0                   test   %eax,%eax
>     53a2:       74 6f                   je     0x5413
>     53a4:       b8 01 00 00 00          mov    $0x1,%eax
>     53a9:       0f a2                   cpuid
>     53ab:       80 e2 10                and    $0x10,%dl
>     53ae:       74 63                   je     0x5413
>     53b0:       31 c0                   xor    %eax,%eax
>     53b2:       0f a2                   cpuid
>     53b4:       0f 31                   rdtsc
>     53b6:       a3 48 67 01 00          mov    %eax,0x16748
>     53bb:       89 15 4c 67 01 00       mov    %edx,0x1674c
>     53c1:       31 c0                   xor    %eax,%eax
>     53c3:       0f a2                   cpuid
>     53c5:       0f 31                   rdtsc
>     53c7:       89 c6                   mov    %eax,%esi
>     53c9:       b8 ff ff 00 00          mov    $0xffff,%eax
>     53ce:       89 d7                   mov    %edx,%edi
>     53d0:       e8 83 00 00 00          call   0x5458
>     53d5:       31 c0                   xor    %eax,%eax
>     53d7:       0f a2                   cpuid
>     53d9:       0f 31                   rdtsc
>     53db:       89 45 e0                mov    %eax,-0x20(%ebp)
>     53de:       8b 4d e0                mov    -0x20(%ebp),%ecx
> ...
>     5439:       31 c0                   xor    %eax,%eax
>     543b:       0f a2                   cpuid
>     543d:       0f 31                   rdtsc
>     543f:       8b 0d 50 67 01 00       mov    0x16750,%ecx
>     5445:       6a 00                   push   $0x0
>     5447:       e8 8f dc ff ff          call   0x30db
> 
> How can we adjust the makefiles to include -march=i486 or something similar?
> 

This code is likely grub_cpu_is_tsc_supported() (see
include/grub/i386/tsc.h) which *is* protected by
grub_cpu_is_cpuid_supported(). Can you test if this function yields
wrong result in your case (just compile it separately)?

> - Matthew
> 
> 
> 
> _______________________________________________
> Grub-devel mailing list
> Grub-devel@gnu.org
> https://lists.gnu.org/mailman/listinfo/grub-devel
> 

Re: "Illegal Instruction" error in grub_script_comments

[Matthew Whitehead]

Lennart,
  I was able to make some progress installing GRUB and Legacy GRUB onto my ancient 80486 computer. Right now I have Legacy GRUB installed as the primary boot loader on the MBR. From there I can boot GRUB via 'kernel /grub2/core.img'. 

However, once I try to load a kernel it reports "cannot allocate real mode pages".  lsmmap reports "base_addr - 0x100000, length = 0x3fffc00, type = 0x1".

What can I do to debug this further?

- Matthew