Hi,

i proposed as test for modern released grub-mkrescue binary:

...

strings /usr/bin/grub-mkrescue | grep '^--usage'

Leslie Zhai wrote:

My local is grub2-XXX so strings /usr/bin/grub2-mkrescue | grep '^--usage' --usage

So this test (or an equivalent one) would tell whether a binary grub-mkrescue needs no argument "--" between its own options and the user provided options for xorriso's mkisofs emulation.

Your proposed patch compensates for the effect of "--" on the modern released version of grub-mkrescue. But i would rather propose to suppress the "--" in this case and to stay in mkisofs emulation mode and option -f. Mixing both modes of xorriso is well possible, but might lead to unexpected results for people who are only used to the behavior of mkisofs.

So the next step propose is to find out which arguments are handed to grub-mkrescue and from where in the Perl code the argument "--" stems. This code part would have to become conditional depending on the detected binary version of grub-mkrescue.

The old script grub-mkrescue needs no argument "--" at the start of the xorriso -as mkisofs options. So it is compatible with the expectations of the modern released binary version. I.e. the current state of Grub.pm could be incompatible with the old script, too.

Have a nice day :)

Thomas

pretty cool :)

在 2017年05月31日 17:46, Thomas Schmitt 写道:

Hi,

i am now pondering over function grub2_mkisofs in Grub.pm (lacking much experience with Perl, i fear).

Do i get it right that this code looks for the shell script variant of grub-mkrescue and prepares for having xorriso re-start mkisofs emulation after it was ended by the "--" part of "--$opt -f" ?

my $opt = ''; open(A, $fp) && do { $opt = " -as mkisofs" if <A> =~ /^#! +/.+sh/; close A; }; my $cmd = "$mkr --output="$isofilename" $dir ". join(' ', @morefiles)." --$opt -f";

If the script is detected, then grub-mkrescue will get arguments equivalent to this pseudo shellcode:

--output="$isofilename" "$dir" -- -as mkisofs -f

whereas the binary grub-mkrescue gets

--output="$isofilename" "$dir" -- -f

which is wrong in case of the modern released binary version.

Although i really do not like the gesture "-- -as mkisofs", this would be the place to test for the modern released binary and to treat it like the old shell script variant.

My proposal is nevertheless to issue "--" only for the intermediate incompatible binary version. I.e. something like

my $opt = '--'; open(A, $fp) && do { $opt = "" if <A> =~ /^#! +/.+sh/; close A; };

# >>> test for modern released binary version and if so: $opt = ""

my $cmd = "$mkr --output="$isofilename" $dir ". join(' ', @morefiles)." $opt -f";

or

my $opt = ''

# >>> test for intermediate unreleased binary version and if so: $opt = "--"

my $cmd = "$mkr --output="$isofilename" $dir ". join(' ', @morefiles)." $opt -f";

Testing for the unreleased version might be more reliable, because this one is not supposed to change its signatures any more.

I understand that the programmer of Grub.pm expected grub-mkrescue to go on with its incompatible CLI change, whereas GRUB developers decided to rather fix the unintended incompatibility before next release. This release has happened meanwile. So _now_ the behavior is supposed to be stable and deviations are to be considered bugs.

Have a nice day :)

Thomas

Hi,

i tested with the intermediate grub-mkrescue version of Debian 8.

$ grub-mkrescue --version grub-mkrescue (GRUB) 2.02~beta2-22

Test case is to pack up the grub-mkrescue program as payload of a bootable ISO. grub-mkrescue insists in some payload. One could as well use some /tmp/dummy file instead of $(which grub-mkrescue).

One can see that it is neither the script nor the released binary, because it fails without "--" before option -f :

$ grub-mkrescue --output=/dev/null $(which grub-mkrescue) -f grub-mkrescue: invalid option -- 'f' Try 'grub-mkrescue --help' or 'grub-mkrescue --usage' for more information. $ echo $? 64 $

So the way to operate it is with "--":

$ grub-mkrescue --output=/dev/null $(which grub-mkrescue) -- -f GNU xorriso 1.4.7 : RockRidge filesystem manipulator, libburnia project. ... Written to medium : 4421 sectors at LBA 0 Writing to 'stdio:/dev/null' completed successfully.

$ echo $? 0 $

But the --help text describes the behavior of script and released binary:

$ grub-mkrescue --help ... Generates a bootable CD/USB/floppy image. Arguments other than options to this program are passed to xorriso, and indicate source files, source directories, or any of the mkisofs options listed by the output of `xorriso -as mkisofs -help'.

Option -- switches to native xorriso command mode. ...

The intermediate binary consumes the first "--" and thus does not let xorriso switch to native command mode. The script and the released binary forward all "--" arguments to xorriso, This causes the error message which Leslie experiences, because -f is not a native xorriso command.

Given the pitfalls of program analysis, i deem above direct experiment the most reliable way to determine the need for "--".

Have a nice day :)

Thomas