binutils: Be more forgiving of targets with large numbers of registers

binutils: Be more forgiving of targets with large numbers of registers

Currently if a target has a large ( > 1024 ) number of registers then
we get a warning when dumping the DWARF whenever a register over the
1024 limit is referenced, this occurs in dwarf.c:frame_need_space.

This check was initially introduced to guard against corrupted DWARF
referencing stupidly large numbers of registers.

The frame_need_space function already has a check in place so that, if
a target specifies a set of known DWARF register names then we must
only reference a register within this set, it is only after this check
that we check for the 1024 limit.

What this means is that if a target DOES NOT define a set of known
register names and if we reference more than 1024 registers
frame_need_space will give a warning.

If a target DOES define a set of known registers and there are more
than 1024 defined registers, and we try to reference a register beyond
1024 we will again get an error.

This second case feels wrong to me.  My thinking is that if a target
defines a set of registers then it is not unreasonable to assume the
tools can cope with that number of registers.  And so, if the target
defines 2000 named DWARF registers, frame_need_space should allow
access to all of these registers.

If a target does not define a set of named registers then the 1024
limit should remain.  This is pretty arbitrary, but we do need to have
some limit in place I think, so for now that seems as good as any.

This is an entirely theoretical fix - there are no targets that define
such large numbers of registers, but while experimenting with adding
support for RISC-V CSRs I ran into this issue and felt like it was a
good improvement.

binutils/ChangeLog:

	* dwarf.c (frame_need_space): Compare dwarf_regnames_count against
	0, and only warn about large numbers of registers if the number is
	more than the dwarf_regnames_count.

Change-Id: Ifac1a999ff0677676e81ee373c4c044b6a700827