Re: [PATCH 0/7] Fix race in DWARF reader

[John Baldwin <jhb@FreeBSD.org>]

On 4/3/24 11:16 AM, Tom Tromey wrote:
>>>>>> "Tom" == Tom Tromey <tom@tromey.com> writes:
> 
> Tom> The background DWARF reader turns out to have a few races.  This
> Tom> series fixes one that occurs when the indexer runs at the same time as
> Tom> DWARF relocation.
> 
> Tom> Most of the series is just cleanup / preparation.
> 
> Tom> The main patch affects MIPS16.  I can't test this -- I tried on a MIPS
> Tom> machine in the GCC compile farm, but unfortunately the relevant
> Tom> gdb.arch test says that the processor doesn't support MIPS16.  It's
> Tom> possible this code is simply dead; I do not know.
> 
> Elsewhere I mentioned that I had a different idea for this series.
> 
> It seems to me that most (or maybe even all) the calls to
> dwarf2_per_objfile::adjust aren't really needed.  Many of them only
> affect lookup tables, where the adjustment isn't needed.  This includes
> all calls made by the indexer.
> 
> Some of the calls (like the one in read_attribute_value) even seem to be
> wrong.
> 
> So, I wrote a short series to remove these.  Unfortunately, though, it's
> hard to know for sure if the result is correct, given that I don't know
> how to test MIPS16.
> 
> I could probably test some simple things ("break") by debugging gdb
> while examining (but not running) a MIPS16 program.  I'm not sure if
> that's really sufficient though.
> 
> I'd appreciate some insight if you have any.

I haven't seen anyone active with submitting MIPS patches in several years.
I no longer make use of MIPS myself (and we've removed it from FreeBSD
entirely, though I know it's still present in Linux distros).  Even when I
was working with MIPS I never tested microMIPS / MIPS16.

OTOH, I think MIPS16 is similar to Thumb on ARM, and it might even be
using a similar trick from reading your series (setting the LSB to enter
"compressed decoding mode" vs "regular decoding mode").  I think ARM uses
special mapping symbols to mark Thumb vs non-Thumb code though instead of
depending on the LSB?  That is, I wonder why Thumb doesn't trip over this
issue the way MIPS16 does?

-- 
John Baldwin