How can I assess compatibility of a statically linked binary?

How can I assess compatibility of a statically linked binary?

[Oliver Schneider]

Hi,

when I have a file linked against glibc the file(1) utility will usually
tell me something like this:

ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked
(uses shared libs), for GNU/Linux 2.6.15, stripped

However, when I run this on a statically linked binary that uses musl, I
get

ELF 64-bit LSB executable, x86-64, version 1 (SYSV), statically linked,
stripped

which gives no indication of the minimum expected kernel. Does that mean
that this binary will also run on, say, a 2.4.x kernel? I guess not?

How can I tell which kernel interface a certain binary requires? After
all the system call numbers on which the libc relies change every once
in a while.

Thanks,

// Oliver

Re: How can I assess compatibility of a statically linked binary?

[Justin Cormack]

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On 20 Feb 2014 17:51, "Oliver Schneider" <musl-mailinglist@f-prot.com>
wrote:
>
> Hi,
>
> when I have a file linked against glibc the file(1) utility will usually
> tell me something like this:
>
> ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked
> (uses shared libs), for GNU/Linux 2.6.15, stripped
>
> However, when I run this on a statically linked binary that uses musl, I
> get
>
> ELF 64-bit LSB executable, x86-64, version 1 (SYSV), statically linked,
> stripped
>
> which gives no indication of the minimum expected kernel. Does that mean
> that this binary will also run on, say, a 2.4.x kernel? I guess not?
>
> How can I tell which kernel interface a certain binary requires? After
> all the system call numbers on which the libc relies change every once
> in a while.
>

The Musl docs say which the earliest supported release is. From memory it
is late 2.4 but I don't recall the exact version. If you don't use some
functionality things might work on an earlier version of course.

Justin

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Re: How can I assess compatibility of a statically linked binary?

[Oliver Schneider]

Hey Justin,

> The Musl docs say which the earliest supported release is. From
> memory it is late 2.4 but I don't recall the exact version. If you
> don't use some functionality things might work on an earlier version
> of course.
thanks for the swift response, found it in the Wiki now thanks to your
pointer:

> Musl is built on the Linux syscall layer. Linux kernel >=2.6.39 is
> necessary for POSIX conformant behaviour, older kernels will work
> with varying degrees of non-conformance, 2.4 kernels will only work
> for simple single-threaded applications.


I had mistakenly expected it under

  <http://wiki.musl-libc.org/wiki/Compatibility>

when it was of course to be found under:

  <http://wiki.musl-libc.org/wiki/Supported_Platforms>

Thanks,

// Oliver

Re: How can I assess compatibility of a statically linked binary?

[Rich Felker]

On Thu, Feb 20, 2014 at 06:20:51PM +0000, Oliver Schneider wrote:
> > Musl is built on the Linux syscall layer. Linux kernel >=2.6.39 is
> > necessary for POSIX conformant behaviour, older kernels will work
> > with varying degrees of non-conformance, 2.4 kernels will only work
> > for simple single-threaded applications.
> 
> 
> I had mistakenly expected it under
> 
>   <http://wiki.musl-libc.org/wiki/Compatibility>
> 
> when it was of course to be found under:
> 
>   <http://wiki.musl-libc.org/wiki/Supported_Platforms>

This will also be documented more formally in the official manual to
be released in conjunction with musl 1.0. For this we should clarify
what version is really needed. I don't think 2.6.39 is necessary;
something like 2.6.32 should be sufficient for POSIX 2008, barring any
arch-specific bugs (or just general bugs that need to be patched to
avoid having an unstable/insecure kernel). I know glibc is planning on
requiring at least 2.6.32 in the next release, so it would be nice if
we could just state the same requirement.

As for older kernels, somewhere down to 2.6.22 works if you don't care
about atomic close-on-exec working atomically (musl has fallback for
kernels that lack it, but the fallback is of course non-atomic). Then
there are also ranges going all the way back to 2.6.0 or even 2.5.x
that work if you don't care about certain POSIX signal semantics
(mainly, wrongly-generated EINTR where a syscall should have
restarted) and don't need *at() functions (note that musl presently
does not emulate these, even though it could do so using /proc). And
if in addition you don't need threads, even 2.4.x will work. It would
also be nice to get these version ranges documented in detail, in case
anyone has need to use musl binaries with such old kernels (some users
adding new software to existing embedded systems may care; otherwise
it's probably a non-issue).

Rich