bug#54458: 27.2; erc-dcc-get: Re-entering top level after C stack overflow

[J.P.]

Hi Fernando,

Fernando de Morais <fernandodemorais.jf@gmail.com> writes:

> If FILE is larger than 120~150 MB, `erc-dcc' cannot handle the
> download process. Transfers of such files causes "Re-entering top
> level after C stack overflow" and, sometimes, crash.

Unfortunately, I was unable to reproduce the error message or the crash
using the same ArchLinux Emacs package. See attached logs.

> If I transfer multiple files (three or four), sometimes with sizes
> smaller than those mentioned above, the C stack overflow hits way
> earlier.

I neglected to try this variant but certainly can.

> If I reduce the `max-specpdl-size', the process stop and I don't get
> the file properly.

No luck here either. I couldn't get any transfers to terminate
prematurely by lowering this value significantly.

One thing I found somewhat curious was that all the receiver's "length
acks" were clumped together in batches. These are those 4-byte messages
containing the length of the last chunk received. (The raw traffic log
only shows the first of many repeating instances.) I'd have to double
check on the protocol, but I'm guessing this is normal and thus
unrelated. If not, I can try again using a different client on the
sending side.

I also tried starving Emacs of resources to provoke some kind of related
response. While I could get it to crash during transfers, most of the
info printed ended up being metadata relevant to the supervisor (systemd
cgroups) rather than anything revealing from Emacs itself.

Anyway, since you're able to manifest this consistently, what about
seeing if any insights can be found by attaching a debugger? Not sure
what a sensible break point would be (handle_sigsegv perhaps?). As might
be obvious, I'm rather useless in this department. Hopefully an expert
will chime in at some point. Thanks.

bookends.log
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configuration.log
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misc.log
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pcap.log
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