Re: [PATCH 2/3] Simplify and inline get_uleb128 and get_sleb128

[Petr Machata <pmachata at redhat dot com>]

Richard Henderson <rth@redhat.com> writes:

> On 04/23/2014 03:17 AM, Petr Machata wrote:
>> Wouldn't something like this get us off the hook as well?
>> 
>> -	(var) |= (typeof (var)) __s.i << ((nth) * 7);			      \
>> +	(var) |= (typeof (var))						      \
>> +	  (((uint64_t) (typeof (var)) __s.i) << ((nth) * 7));		      \
>> 
>> We are really only using the bitfield trick to avoid having to
>> sign-extend by hand, but we can shift unsigned without losing anything.
>
> It gets us off the hook, but might introduce a 64-bit shift where
> only a 32-bit shift was required.

Good point, but get_sleb128_step is only used from __libdw_get_sleb128,
where the type is int64_t.  This macro is not safe for outside use
anyway, as it uses its parameters more than once.

Hmm, should we maybe #undef it after __libdw_get_sleb128, so that it's
clear that it's for local use only?

Thanks,
PM