[Qemu-devel] [PATCH] reduce magic numbers length to 16 bytes (qemu-binfmt-conf.sh)

[Qemu-devel] [PATCH] reduce magic numbers length to 16 bytes (qemu-binfmt-conf.sh)

[Anderson Lizardo]

[-- Attachment #1: Type: text/plain, Size: 600 bytes --]

Hi,

Any reason why the magic numbers from qemu-binfmt-conf.sh are not just
16 bytes long as those reported by "readelf --file-header"? For
example:

$ readelf --file-header /bin/true | grep Magic:
  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00

Using only the first 16 bytes avoids the need to have separate entries
for i386 and i486, given that they are emulated by the same program
(qemu-i386). The others still need separate entries because of
endianess.

Regards,
--
Anderson Lizardo
Embedded Linux Lab - 10LE
Nokia Institute of Technology - INdT
Manaus - Brazil

[-- Attachment #2: qemu-binfmt-conf-16bytes-magic.patch --]
[-- Type: text/x-patch, Size: 3719 bytes --]

--- qemu-binfmt-conf.sh.orig	2005-12-19 18:51:53.000000000 -0400
+++ qemu-binfmt-conf.sh	2006-03-10 22:51:01.000000000 -0400
@@ -20,20 +20,19 @@
 
 # register the interpreter for each cpu except for the native one
 if [ $cpu != "i386" ] ; then
-    echo ':i386:M::\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x03\x00:\xff\xff\xff\xff\xff\xfe\xfe\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff:/usr/local/bin/qemu-i386:' > /proc/sys/fs/binfmt_misc/register
-    echo ':i486:M::\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x06\x00:\xff\xff\xff\xff\xff\xfe\xfe\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff:/usr/local/bin/qemu-i386:' > /proc/sys/fs/binfmt_misc/register
+    echo ':i386:M::\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00:\xff\xff\xff\xff\xff\xfe\xfe\xff\xff\xff\xff\xff\xff\xff\xff\xff:/usr/local/bin/qemu-i386:' > /proc/sys/fs/binfmt_misc/register
 fi
 if [ $cpu != "arm" ] ; then
-    echo   ':arm:M::\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x28\x00:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff:/usr/local/bin/qemu-arm:' > /proc/sys/fs/binfmt_misc/register
-    echo   ':armeb:M::\x7fELF\x01\x02\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x28:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff:/usr/local/bin/qemu-armeb:' > /proc/sys/fs/binfmt_misc/register
+    echo ':arm:M::\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff:/usr/local/bin/qemu-arm:' > /proc/sys/fs/binfmt_misc/register
+    echo ':armeb:M::\x7fELF\x01\x02\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff:/usr/local/bin/qemu-armeb:' > /proc/sys/fs/binfmt_misc/register
 fi
 if [ $cpu != "sparc" ] ; then
-    echo   ':sparc:M::\x7fELF\x01\x02\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x02:\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff:/usr/local/bin/qemu-sparc:' > /proc/sys/fs/binfmt_misc/register
+    echo ':sparc:M::\x7fELF\x01\x02\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00:\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff:/usr/local/bin/qemu-sparc:' > /proc/sys/fs/binfmt_misc/register
 fi
 if [ $cpu != "ppc" ] ; then
-    echo   ':ppc:M::\x7fELF\x01\x02\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x14:\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff:/usr/local/bin/qemu-ppc:' > /proc/sys/fs/binfmt_misc/register
+    echo ':ppc:M::\x7fELF\x01\x02\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00:\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff:/usr/local/bin/qemu-ppc:' > /proc/sys/fs/binfmt_misc/register
 fi
 if [ $cpu != "mips" ] ; then
-    echo   ':mips:M::\x7fELF\x01\x02\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x08:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff:/usr/local/bin/qemu-mips:' > /proc/sys/fs/binfmt_misc/register
-    echo   ':mipsel:M::\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x08\x00:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff:/usr/local/bin/qemu-mipsel:' > /proc/sys/fs/binfmt_misc/register
+    echo ':mips:M::\x7fELF\x01\x02\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff:/usr/local/bin/qemu-mips:' > /proc/sys/fs/binfmt_misc/register
+    echo ':mipsel:M::\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff:/usr/local/bin/qemu-mipsel:' > /proc/sys/fs/binfmt_misc/register
 fi

Re: [Qemu-devel] [PATCH] reduce magic numbers length to 16 bytes (qemu-binfmt-conf.sh)

[Paul Brook]

On Saturday 11 March 2006 02:58, Anderson Lizardo wrote:
> Hi,
>
> Any reason why the magic numbers from qemu-binfmt-conf.sh are not just
> 16 bytes long as those reported by "readelf --file-header"?

The first 16 bytes only tell you it's an ELF executable. ie. you've just 
removed the bits that tell you whether it's e.g an arm or a ppc executable.

You'll notice that after your patch all the be/le pattern matches are 
identical, which is obviously not going to work.

Paul

Re: [Qemu-devel] [PATCH] reduce magic numbers length to 16 bytes (qemu-binfmt-conf.sh)

[Andreas Schwab]

"Anderson Lizardo" <anderson.lizardo@gmail.com> writes:

> Any reason why the magic numbers from qemu-binfmt-conf.sh are not just
> 16 bytes long as those reported by "readelf --file-header"? For
> example:
>
> $ readelf --file-header /bin/true | grep Magic:
>   Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
>
> Using only the first 16 bytes avoids the need to have separate entries
> for i386 and i486, given that they are emulated by the same program
> (qemu-i386).

How would you distinguish it from an arm or mipsel binary?

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: [Qemu-devel] [PATCH] reduce magic numbers length to 16 bytes (qemu-binfmt-conf.sh)

[Anderson Lizardo]

On 3/11/06, Andreas Schwab <schwab@suse.de> wrote:
> "Anderson Lizardo" <anderson.lizardo@gmail.com> writes:
>
> > Any reason why the magic numbers from qemu-binfmt-conf.sh are not just
> > 16 bytes long as those reported by "readelf --file-header"? For
> > example:
> >
> > $ readelf --file-header /bin/true | grep Magic:
> >   Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
> >
> > Using only the first 16 bytes avoids the need to have separate entries
> > for i386 and i486, given that they are emulated by the same program
> > (qemu-i386).
>
> How would you distinguish it from an arm or mipsel binary?

Now I realize my mistake, sorry for the noise :/

To not make this thread completely useless: I find
/usr/share/misc/file/magic very useful to get machine patterns (as
detected by "file"). Search there for "magic for ELF executables" and
you will find a fairly complete list of machine magic numbers.

Regards,
--
Anderson Lizardo
Embedded Linux Lab - 10LE
Nokia Institute of Technology - INdT
Manaus - Brazil

Re: [Qemu-devel] [PATCH] reduce magic numbers length to 16 bytes (qemu-binfmt-conf.sh)

[Paul Brook]

> To not make this thread completely useless: I find
> /usr/share/misc/file/magic very useful to get machine patterns (as
> detected by "file"). Search there for "magic for ELF executables" and
> you will find a fairly complete list of machine magic numbers.

Or you could just use the official list in the gABI spec:

http://www.thescogroup.com/developers/gabi/latest/ch4.eheader.html

Paul

Re: [Qemu-devel] [PATCH] reduce magic numbers length to 16 bytes (qemu-binfmt-conf.sh)

[Johannes Schindelin]

Hi,

On Sat, 11 Mar 2006, Paul Brook wrote:

> > To not make this thread completely useless: I find
> > /usr/share/misc/file/magic very useful to get machine patterns (as
> > detected by "file"). Search there for "magic for ELF executables" and
> > you will find a fairly complete list of machine magic numbers.
> 
> Or you could just use the official list in the gABI spec:
> 
> http://www.thescogroup.com/developers/gabi/latest/ch4.eheader.html

... but be aware they might sue you for using it ;-)

Ciao,
Dscho