Proposal: add more debugging symbols related to Node internal structures #46

mmarchini · 2017-08-16T15:30:00Z

Hello everyone!

I'm writing a command to llnode to print all Handles and Requests on the queue of a core dump (similar to what node::GetActiveHandles and node::GetActiveRequests do). While I was working I noticed that, although there's plenty of debugging symbols to help navigate V8 structures (v8dbg_ symbols, thanks to the postmortem-metadata action on V8 build), there are no symbols to describe Node internal structures.

Using as example the command I'm implementing, I need to get the current Environment, navigate to the corresponding queue (let's say, handle_wrap_queue_), and then iterate over this queue (which was created with ListHead) to be able to get the HandleWrap objects. All of this can be done easily on a node debug build, but it's not possible to do on a common build.

I thought about implementing something similar to V8 postmortem-metadata: a script that creates a .cc file with all wanted symbols prefixed with something like nodedbg_. Would that be acceptable? I could probably publish a draft patch at the end of this week. I think this would be useful for other debugging tools, not just llnode.

I'm opened to suggestions.

In the meantime, thank you so much for your attention and participation.

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Those changes are the first steps towards allowing debug tools to navigate some of Node's internals strucutres, giving more possibilities to developers doing post-mortem debugging. One example of what can be achieved with the symbols added is a new command being developed for llnode, which prints information about handles and requests on the queue for a core dump file. Ref: nodejs/post-mortem#46

rnchamberlain · 2017-08-18T10:47:23Z

This looks like a great step forward for post-mortem debugging of node internals (i.e. not just V8). The requirement raised here is typical: nodejs/llnode#100

Exposing the address of the Environment structure is a key step (as well as the offsets in that structure). You get that by setting a global symbol during node startup that you can then find in the debugger plugin?

Also you are wrapping this with NODE_POSTMORTEM_SUPPORT - is the intention to provide this in production builds of node? Thanks!

mhdawson · 2017-08-18T15:26:11Z

@mmarchini thanks for suggesting/working on this. Additional meta data would be greatly appreciated.

davepacheco · 2017-08-18T15:58:05Z

This sounds terrific. We already hardcode one Node offset in mdb_v8:
https://github.com/joyent/mdb_v8/blob/08571bf8d4ba1e7546b46e7d24011ca2f9be1f3d/src/mdb_v8_impl.h#L116

It would be great to incorporate this one into your new mechanism. And we'd love to use your proposed new metadata to provide an mdb_v8 dcmd to print active handles. As I'm sure you know, Node programs that don't exit when expected can be frustrating to debug, and that sort of problem is very amenable to debugging from a core file.

mmarchini · 2017-08-18T20:22:19Z

@rnchamberlain yes, the intention is to provide this in production builds too (I already removed those guards from the PR).

@davepacheco I'll add this offset to nodejs/node#14901, I'm just having trouble finding node_string.h, does it still exists on node's master branch?

Suggestions of other constants or offsets that can be added to this PR would be really appreciated!

Before these changes, only V8 added debug symbols to Node's binary, limiting the possibilities for debugger's developers to add some features that rely on investigating Node's internal structures. These changes are a first steps towards empowering debug tools to navigate Node's internals strucutres. One example of what can be achieved with this is shown at nodejs/llnode#122 (a command which prints information about handles and requests on the queue for a core dump file). Node debug symbols are prefixed with node_dbg_. Ref: nodejs/llnode#122 Ref: nodejs/post-mortem#46

Before these changes, only V8 added debug symbols to Node's binary, limiting the possibilities for debugger's developers to add some features that rely on investigating Node's internal structures. These changes are a first steps towards empowering debug tools to navigate Node's internals strucutres. One example of what can be achieved with this is shown at nodejs/llnode#122 (a command which prints information about handles and requests on the queue for a core dump file). Node debug symbols are prefixed with node_dbg_. Ref: nodejs/llnode#122 PR-URL: #14901 Refs: nodejs/post-mortem#46 Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>

Before these changes, only V8 added debug symbols to Node's binary, limiting the possibilities for debugger's developers to add some features that rely on investigating Node's internal structures. These changes are a first steps towards empowering debug tools to navigate Node's internals strucutres. One example of what can be achieved with this is shown at nodejs/llnode#122 (a command which prints information about handles and requests on the queue for a core dump file). Node debug symbols are prefixed with node_dbg_. Ref: nodejs/llnode#122 Ref: nodejs/post-mortem#46

Before these changes, only V8 added debug symbols to Node's binary, limiting the possibilities for debugger's developers to add some features that rely on investigating Node's internal structures. These changes are a first steps towards empowering debug tools to navigate Node's internals strucutres. One example of what can be achieved with this is shown at nodejs/llnode#122 (a command which prints information about handles and requests on the queue for a core dump file). Node debug symbols are prefixed with node_dbg_. Ref: nodejs/llnode#122 PR-URL: #14901 Refs: nodejs/post-mortem#46 Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>

Before these changes, only V8 added postmortem metadata to Node's binary, limiting the possibilities for debugger's developers to add some features that rely on investigating Node's internal structures. These changes are first steps towards empowering debug tools to navigate Node's internal structures. One example of what can be achieved with this is shown at nodejs/llnode#122 (a command which prints information about handles and requests on the queue for a core dump file). Node postmortem metadata are prefixed with nodedbg_. This also adds tests to validate if all postmortem metadata are calculated correctly, plus some documentation on what is postmortem metadata and a few care to be taken to avoid breaking it. Ref: nodejs/llnode#122 Ref: nodejs/post-mortem#46

Before these changes, only V8 added postmortem metadata to Node's binary, limiting the possibilities for debugger's developers to add some features that rely on investigating Node's internal structures. These changes are first steps towards empowering debug tools to navigate Node's internal structures. One example of what can be achieved with this is shown at nodejs/llnode#122 (a command which prints information about handles and requests on the queue for a core dump file). Node postmortem metadata are prefixed with nodedbg_. This also adds tests to validate if all postmortem metadata are calculated correctly, plus some documentation on what is postmortem metadata and a few care to be taken to avoid breaking it. Ref: nodejs/llnode#122 Ref: nodejs/post-mortem#46 PR-URL: #14901 Refs: nodejs/post-mortem#46 Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

Before these changes, only V8 added postmortem metadata to Node's binary, limiting the possibilities for debugger's developers to add some features that rely on investigating Node's internal structures. These changes are first steps towards empowering debug tools to navigate Node's internal structures. One example of what can be achieved with this is shown at nodejs/llnode#122 (a command which prints information about handles and requests on the queue for a core dump file). Node postmortem metadata are prefixed with nodedbg_. This also adds tests to validate if all postmortem metadata are calculated correctly, plus some documentation on what is postmortem metadata and a few care to be taken to avoid breaking it. Ref: nodejs/llnode#122 Ref: nodejs/post-mortem#46 PR-URL: nodejs#14901 Refs: nodejs/post-mortem#46 Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

Before these changes, only V8 added postmortem metadata to Node's binary, limiting the possibilities for debugger's developers to add some features that rely on investigating Node's internal structures. These changes are first steps towards empowering debug tools to navigate Node's internal structures. One example of what can be achieved with this is shown at nodejs/llnode#122 (a command which prints information about handles and requests on the queue for a core dump file). Node postmortem metadata are prefixed with nodedbg_. This also adds tests to validate if all postmortem metadata are calculated correctly, plus some documentation on what is postmortem metadata and a few care to be taken to avoid breaking it. Ref: nodejs/llnode#122 Ref: nodejs/post-mortem#46 Backport-PR-URL: #18550 PR-URL: #14901 Refs: nodejs/post-mortem#46 Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

Before these changes, only V8 added postmortem metadata to Node's binary, limiting the possibilities for debugger's developers to add some features that rely on investigating Node's internal structures. These changes are first steps towards empowering debug tools to navigate Node's internal structures. One example of what can be achieved with this is shown at nodejs/llnode#122 (a command which prints information about handles and requests on the queue for a core dump file). Node postmortem metadata are prefixed with nodedbg_. This also adds tests to validate if all postmortem metadata are calculated correctly, plus some documentation on what is postmortem metadata and a few care to be taken to avoid breaking it. Ref: nodejs/llnode#122 Ref: nodejs/post-mortem#46 PR-URL: nodejs#14901 Refs: nodejs/post-mortem#46 Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

mmarchini · 2018-03-21T12:35:17Z

I'm closing because nodejs/node#14901 landed and is shipped on v9.7.0+, but feel free to reopen if you think there's something else to discuss here.

Before these changes, only V8 added postmortem metadata to Node's binary, limiting the possibilities for debugger's developers to add some features that rely on investigating Node's internal structures. These changes are first steps towards empowering debug tools to navigate Node's internal structures. One example of what can be achieved with this is shown at nodejs/llnode#122 (a command which prints information about handles and requests on the queue for a core dump file). Node postmortem metadata are prefixed with nodedbg_. This also adds tests to validate if all postmortem metadata are calculated correctly, plus some documentation on what is postmortem metadata and a few care to be taken to avoid breaking it. Ref: nodejs/llnode#122 Ref: nodejs/post-mortem#46 PR-URL: nodejs#14901 Refs: nodejs/post-mortem#46 Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

Before these changes, only V8 added postmortem metadata to Node's binary, limiting the possibilities for debugger's developers to add some features that rely on investigating Node's internal structures. These changes are first steps towards empowering debug tools to navigate Node's internal structures. One example of what can be achieved with this is shown at nodejs/llnode#122 (a command which prints information about handles and requests on the queue for a core dump file). Node postmortem metadata are prefixed with nodedbg_. This also adds tests to validate if all postmortem metadata are calculated correctly, plus some documentation on what is postmortem metadata and a few care to be taken to avoid breaking it. Ref: nodejs/llnode#122 Ref: nodejs/post-mortem#46 PR-URL: #14901 Refs: nodejs/post-mortem#46 Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

Before these changes, only V8 added postmortem metadata to Node's binary, limiting the possibilities for debugger's developers to add some features that rely on investigating Node's internal structures. These changes are first steps towards empowering debug tools to navigate Node's internal structures. One example of what can be achieved with this is shown at nodejs/llnode#122 (a command which prints information about handles and requests on the queue for a core dump file). Node postmortem metadata are prefixed with nodedbg_. This also adds tests to validate if all postmortem metadata are calculated correctly, plus some documentation on what is postmortem metadata and a few care to be taken to avoid breaking it. Ref: nodejs/llnode#122 Ref: nodejs/post-mortem#46 Backport-PR-URL: #19176 PR-URL: #14901 Refs: nodejs/post-mortem#46 Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

This was referenced Aug 17, 2017

src, test: node internals' postmortem metadata nodejs/node#14901

Closed

src: add commands to inspect the workqueue nodejs/llnode#122

Closed

mmarchini closed this as completed Mar 21, 2018

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Proposal: add more debugging symbols related to Node internal structures #46

Proposal: add more debugging symbols related to Node internal structures #46

mmarchini commented Aug 16, 2017

rnchamberlain commented Aug 18, 2017

mhdawson commented Aug 18, 2017

davepacheco commented Aug 18, 2017

mmarchini commented Aug 18, 2017

mmarchini commented Mar 21, 2018

Proposal: add more debugging symbols related to Node internal structures #46

Proposal: add more debugging symbols related to Node internal structures #46

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mmarchini commented Aug 16, 2017

rnchamberlain commented Aug 18, 2017

mhdawson commented Aug 18, 2017

davepacheco commented Aug 18, 2017

mmarchini commented Aug 18, 2017

mmarchini commented Mar 21, 2018