[Toybox] Stat %Z - What are valid values?

[Rich Felker]

On Tue, Jan 24, 2017 at 05:47:46PM -0600, Rob Landley wrote:
> 
> 
> On 01/21/2017 06:25 PM, Rich Felker wrote:
> > On Sat, Jan 21, 2017 at 03:18:28PM -0600, Rob Landley wrote:
> >>> Or if it's signed, that's -1346458162 which would be... sometime in the
> >>> 1930's? hmmm... "./date -D %s -d -1346458162" is failing under glibc,
> >>> and failing _differently_ under musl. (Wheee.)
> >>>
> >>> /me goes down tangent rathole debugging why.
> >> ....
> >>>
> >>> (Answer: musl doesn't implement %s at all, and glibc doesn't allow the
> >>> %s value it converts to be negative.)
> >>
> >> Query: does bionic strptime() handle %s, and if so does it handle
> >> negative input values? (If not I suppose I can try to special case this
> >> in toybox, but ew.)
> >>
> >> Also, Rich: any interest in adding this to musl?
> > 
> > strptime with %s? I suspect there are some nasty underspecified issues
> > with how it interacts with timezones.
> 
> I thought unix time was always UTS and the timezone just affected how it
> was displayed?

The problem is that strptime produces a struct tm. When the fields
it's parsing to produce this struct tm are "broken down time" fields,
strptime does not need to know/care whether the caller is going to
interpret the struct tm as UTC or local time; it's just a bunch of
numbers. But when strptime is going to take a unix time value (seconds
since epoch) and convert it to struct tm, it matters whether the
caller is supposed to treat that struct tm as UTC or local.

Rich