Suggestions on good first bugs

Robert O'Callahan robert at ocallahan.org
Thu Mar 5 16:29:34 PST 2015


On Fri, Mar 6, 2015 at 11:25 AM, Robert O'Callahan <robert at ocallahan.org>
wrote:

> On Fri, Mar 6, 2015 at 8:53 AM, Daniel Näslund <dannas at dannas.name> wrote:
>
> Other suggestions? ===
>>
>> rocallahan said in [2]:
>>
>>     "Even just installing an unrelated package could cause problems.
>>     Probably we should always just copy /etc/ld.so.cache into the trace so
>>     that you can do Unrelated package changes without invalidating
>> traces."
>>
>>     Is that something that is feasible? Needed?
>>
>
> I think it would definitely be worth doing this if it allows unrelated
> packages to be installed/removed without breaking replayability of existing
> traces. It's really easy to do; see should_copy_mmap_region.
>

If you look into this, it's also worth trying to figure out why we have a
problem with /etc/ld.so.cache. Many tools that overwrite files actually
write a new file and then rename it over the old file, to ensure atomicity
and to avoid breaking processes that already have the file open, and I'd
expect /etc/ld.so.cache to be updated in the same way. When we choose not
to copy file data into the trace, we instead make a hardlink to the file
and use that; then if the file is replaced using the write-rename
technique, the hardlink continues to point to the old file and rr is fine.
So it's worth figuring out how/why /etc/ld.so.cache is being overwritten in
a way that causes problems for rr. stracing ldconfig might show us.

Rob
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