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Re: allowed uses of non-baseline CPU extensions

Philipp Kern wrote:
> I think that's a very important observation. I don't think you can
> necessarily conclude that the system where the package is initially
> installed is the system were the code is executed.
> In many kinds of image-based environments the machines the image is
> shipped to have very likely a different instruction capability than the
> machine where the image is built on.
> You argued in #873733[1] that you'd rather see the package installation
> fail. I see the appeal of that, especially to alert the admin. But there
> needs to be some kind of switch to flip to ignore these. Right now it
> seems that switch is IGNORE_ISA in the environment. But given the
> attempts to get a cleaner environment for dpkg, I'm not sure that's the
> best file. I.e. it'd be better to also have a flag file.

As with others in this thread, I'd prefer to have apt understand the
concept of architecture variations and instruction set features, as a
variation on multiarch. (apt could potentially have a command-line
option to override that and install a package onto a system that didn't
understand the instruction set features, but that would potentially
require delaying the execution of any code from the package, which could
include maintainer scripts, until runtime, much like debootstrap's cross

> As a side note I'm also amazed that there's literally a uuencoded blob
> in the preinst that contains binary code that is unpacked and executed,
> just like any malware would do. :)

You can, in fact, simply ship a binary preinst.

~$ file /var/lib/dpkg/info/bash.preinst
/var/lib/dpkg/info/bash.preinst: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=09642c1eb0869e8a9c075d0e8109f7ef1f62b320, with debug_info, not stripped

- Josh Triplett

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