Messages in this thread | | | Date | Mon, 12 Mar 2012 13:05:56 +0100 | From | Denys Vlasenko <> | Subject | Re: Extending coredump note section to contain filenames |
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On 03/09/2012 06:29 PM, Jan Kratochvil wrote: > On Fri, 09 Mar 2012 18:13:49 +0100, Denys Vlasenko wrote: >> gdb retrieves loaded library names by examining dynamic loader's >> data stored in the coredump's data segments. It uses intimate >> knowledge how and where dynamic loader keeps the list of loaded >> libraries. > > this is the backward compatible way and it is no longer the right one with > build-ids. > > GDB should scan the address space for mapped build-ids and map symbol files > accordingly.
Build-ids are useful, but they still don't map directly to the names of loaded files. You need to rely on /usr/lib/debug/.build-id/XX/YYYYYYYYYY symlinks to translate build-ids to names.
For example, on my home machine (linux-from-scratch style) I don't have /usr/lib/debug/.build-id/* directory at all. So build-ids can't be used to find the binary and libraries there.
Why we don't save library names in coredump? I see no logical reason not to do so. Even if those names sometimes won't be reliable ("deleted files" problem), it's not a good reason to shoot ourself in the food and deprive ourself from this information 100% of the time.
>> Another question is detection of deleted files. >> If /usr/lib/xulrunner-2/libmozjs.so was updated while program ran >> and now file mapped into process address space does not correspond >> to the same-named file on disk, can we help users to detect this? How? >> By saving maj/min/inode? Hash thereof? >> File size? >> File's md5sum (probably not, way too expensive. But nicely robust...)? > > build-id is already being saved. This is all that matters. Filename does not > say anything - as you noticed it can be even already deleted,
Yes, the file can be deleted/updated-via-rename. That's the case I want to be possible to detect.
> it can have unknown content etc.
I don't understand. *What* can have unknown content?
> I do not see what problems you target here.
I'm thinking whether we should supply some mechanism for detecting "deleted/updated file" problem. Even if this would be a heuristic. I'll be satisfied with 99.9999% success rate instead of 100% :)
-- vda
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