Re: unwind support for Linux 2.6 vsyscall DSO

[Roland McGrath <roland at redhat dot com>]

> > There should be an iterator over the entries in the /proc/pid/auxv
> > file with a callback that processes each entry. So that the iterator
> > could be used not just for finding the AT_SYSINFO_EHDR entry. 
> 
> Ok, an iterator interface is fine with me, just marginally less efficient
> than the searcher when only one tag is actually used (and more efficient if
> many tags are used).  (I had not proposed any function that would be useful
> solely for AT_SYSINFO_EHDR, though that was one of Jim's early
> suggestions.)  If others agree this is the right interface for a target_ops
> addition, I will write that patch.

Actually, I think this is not as useful an interface as one that fetches
the whole block for you.  There is another use for this call besides the
Linux-specific AT_SYSINFO_EHDR check: gcore.  We want gcore to produce
NT_AUXV notes in core dumps so that those core dumps can be used to extract
whatever AT_* information we could extract from core dumps written by a kernel.

This is easy to add either way, but is cleaner, simpler, and more efficient
if it just writes the whole block uninterpreted than if it dissects and
reassembles it.