Re: Possible issue around utime() and symlinks on at least MIPS64

[Rich Felker <dalias@libc.org>]

On Wed, Apr 18, 2018 at 04:51:31PM -0500, A. Wilcox wrote:
> On 04/18/18 15:00, Rich Felker wrote:
> > On Thu, Jul 06, 2017 at 02:50:16PM +0100, Adam Hill wrote:
> >> Hi,
> >> 
> >> Not carried out ANY investigation around this... unfortunately I
> >> don't have any time atm. Could also have been mentioned already or
> >> actually be a bug in tar itself etc. but I couldn't find anything
> >> with my quick search. Just thought I'd mention it in case anyone
> >> does feel inclined to investigate.
> >> 
> >> I compiled OpenWrt using pretty much default build settings for an
> >> octeon chip... it uses musl-1.1.16. The only real change I made was
> >> to use GNU tar rather than busybox. The resulting tar binary can't
> >> fix the modification/access times on any extracted symbolic links,
> >>  resulting in for example:
> >> 
> >> tar: usr/share/zoneinfo/Africa: Cannot utime: Invalid argument
> >> 
> >> I didn't have strace available so can't even be sure tar's using
> >> utime()... just going by the error message alone.
> >> 
> >> I recompiled OpenWrt changing only the C library ( to GCC ) and the
> >> resulting tar binary worked fine... so I can only *assume* it's
> >> something to do with musl.
> > 
> > Did anyone ever get a chance to look further into this? It's been on 
> > my todo for a long time, but without sufficient information to 
> > reproduce I don't know where to begin. I spent about 20 minutes 
> > looking at the musl and kernel code now and it does not seem likely 
> > that this is mips64-specific.
> > 
> > Rich
> > 
> 
> This really sounds like broken cross-compiling.  When we cross-compile
> cp, it's unable to handle xattrs until it's re-compiled on native
> hardware.  I'd suggest poking around at autoconf for GNU tar and seeing
> what it is 'guessing' the environment is like, and perhaps overriding
> some with ac_*={yes,no} on the configure line.

That's a good thought and would probably explain why we haven't hit a
similar issue elsewhere. It probably also indicates a bug in
gnulib/tar rather than musl.

Rich