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Re: JIT debugging (Attach and speed)
- From: Pedro Alves <palves at redhat dot com>
- To: Yichao Yu <yyc1992 at gmail dot com>, gdb at sourceware dot org, Paul Pluzhnikov <ppluzhnikov at google dot com>
- Date: Tue, 22 Mar 2016 15:46:31 +0000
- Subject: Re: JIT debugging (Attach and speed)
- Authentication-results: sourceware.org; auth=none
- References: <CAMvDr+TKDYeECiUK7Kz7TGSRF826Vq24z_=CPQXz1vyxmMUm_w at mail dot gmail dot com>
On 03/22/2016 02:55 PM, Yichao Yu wrote:
Hi,
I've recently seen some issues when debugging julia JIT code with GDB.
Some of these might worth a bug report but I'd like to post here first
since the most blocking issue was discussed here a few years ago.
1. Registering JIT code to GDB is O(n^2) and this is very bad for
serious JIT users like julia. (I've seen 10k to 100k jit objects
generated in the test)
The issue was discussed on this list ~2011[1] but it seems that the
issue is still there. I was also told that lldb 3.8 should support the
same JIT debugging interface without the O(n^2) slow down[2].
I re-read the 2011 discussion, and it seems like we had an idea for a
fix:
https://sourceware.org/ml/gdb/2011-01/msg00011.html
Paul, did you ever manage to get that working?
2. JIT code registration on attach is broken.
When I set a breakpoint on `jit_inferior_init`[3] (i.e. lauching
gdb with `gdb --args gdb -p <pid_to_debug>`) which IIUC is what
responsible for walking the jit object list at init time, it seems
that the function is never called.
(I haven't seen a bug report about this yet)
Do you know whether this happens with 7.11 and master, and if so,
would it be possible for you to git bisect the culprit?
Thanks,
Pedro Alves