[Bug symtab/30511] New: feature: set sysroot and file by default for attached containerized processes

[Bug symtab/30511] New: feature: set sysroot and file by default for attached containerized processes

[two at envs dot net]

https://sourceware.org/bugzilla/show_bug.cgi?id=30511

            Bug ID: 30511
           Summary: feature: set sysroot and file by default for attached
                    containerized processes
           Product: gdb
           Version: unknown
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: symtab
          Assignee: unassigned at sourceware dot org
          Reporter: two at envs dot net
  Target Milestone: ---

after starting gdb with `gdb --attach PID` for a process running in a different
root (such as a flatpak), it's necessary to do `set sysroot /proc/PID/root` and
`set file /proc/PID/exe` to get debug symbols. can this be done by default?

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[Bug symtab/30511] feature: set sysroot and file by default for attached containerized processes

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30511

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-06-05
                 CC|                            |tromey at sourceware dot org
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Tom Tromey <tromey at sourceware dot org> ---
FWIW it seems reasonable to me.
sysroot already defaults to "target:", so it's maybe just a matter of the
linux-nat target knowing how to do this under the hood.

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[Bug symtab/30511] feature: set sysroot and file by default for attached containerized processes

[mark at klomp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30511

Mark Wielaard <mark at klomp dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ahajkova at redhat dot com,
                   |                            |mark at klomp dot org

--- Comment #2 from Mark Wielaard <mark at klomp dot org> ---
This sounds like a good idea.

Adding myself and Sasha to CC to see how this is done (we would like something
similar for a "target valgrind", but then set sysroot / and set remote
exec-file ...).

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[Bug symtab/30511] feature: set sysroot and file by default for attached containerized processes

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30511

--- Comment #3 from Tom Tromey <tromey at sourceware dot org> ---
(In reply to Mark Wielaard from comment #2)
> This sounds like a good idea.
> 
> Adding myself and Sasha to CC to see how this is done (we would like
> something similar for a "target valgrind", but then set sysroot / and set
> remote exec-file ...).

Unfortunately this is a different situation.
Probably you should file a separate bug for that one.

For this bug, I don't really know how to implement it.
I don't know how to detect if a process needs this treatment.

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[Bug symtab/30511] feature: set sysroot and file by default for attached containerized processes

[two at envs dot net]

https://sourceware.org/bugzilla/show_bug.cgi?id=30511

--- Comment #4 from two at envs dot net <two at envs dot net> ---
(In reply to Tom Tromey from comment #3)
> I don't know how to detect if a process needs this treatment.

compare device and inode of / and /proc/PID/root/ to see if they're different?

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[Bug symtab/30511] feature: set sysroot and file by default for attached containerized processes

[sam at gentoo dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30511

Sam James <sam at gentoo dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sam at gentoo dot org

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[Bug symtab/30511] feature: set sysroot and file by default for attached containerized processes

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30511

--- Comment #5 from Tom Tromey <tromey at sourceware dot org> ---
linux-nat already seems to have code for this, at least somewhat,
so I wonder where the missing bit is.
See gdb/nat/linux-namespaces.c

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[Bug symtab/30511] feature: set sysroot and file by default for attached containerized processes

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30511

--- Comment #6 from Tom Tromey <tromey at sourceware dot org> ---
BTW which version of gdb are you using?
I'm not sure how to set up to try this out, but the code
seems to be there.
e.g., linux_proc_pid_to_exec_file does:

  xsnprintf (name, PATH_MAX, "/proc/%d/exe", pid);
  len = readlink (name, buf, PATH_MAX - 1);

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[Bug symtab/30511] feature: set sysroot and file by default for attached containerized processes

[two at envs dot net]

https://sourceware.org/bugzilla/show_bug.cgi?id=30511

--- Comment #7 from two at envs dot net <two at envs dot net> ---
(In reply to Tom Tromey from comment #6)
>   xsnprintf (name, PATH_MAX, "/proc/%d/exe", pid);
>   len = readlink (name, buf, PATH_MAX - 1);

readlink reads symbolic links.

```
$ readlink /proc/$(pidof epiphany)/exe
/app/bin/epiphany
$ file /app/bin/epiphany
/app/bin/epiphany: cannot open `/app/bin/epiphany' (No such file or directory)
```

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[Bug symtab/30511] feature: set sysroot and file by default for attached containerized processes

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30511

--- Comment #8 from Tom Tromey <tromey at sourceware dot org> ---
Yeah.  Funny, it's a symlink that can't be resolved?
Anyway, like I said, I don't know anything about flatpak,
someone else will have to figure this out.

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[Bug symtab/30511] feature: set sysroot and file by default for attached containerized processes

[mark at klomp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30511

--- Comment #9 from Mark Wielaard <mark at klomp dot org> ---
(In reply to Tom Tromey from comment #3)
> (In reply to Mark Wielaard from comment #2)
> > This sounds like a good idea.
> > 
> > Adding myself and Sasha to CC to see how this is done (we would like
> > something similar for a "target valgrind", but then set sysroot / and set
> > remote exec-file ...).
> 
> Unfortunately this is a different situation.
> Probably you should file a separate bug for that one.

Done: https://sourceware.org/bugzilla/show_bug.cgi?id=30541

> For this bug, I don't really know how to implement it.
> I don't know how to detect if a process needs this treatment.

Do you need any detection?
Can't you simply always set sysroot /proc/PID/root if it exists?

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[Bug symtab/30511] feature: set sysroot and file by default for attached containerized processes

[mark at klomp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30511

--- Comment #10 from Mark Wielaard <mark at klomp dot org> ---
(In reply to Tom Tromey from comment #8)
> Yeah.  Funny, it's a symlink that can't be resolved?
> Anyway, like I said, I don't know anything about flatpak,
> someone else will have to figure this out.

The symlink resolves "inside" the sysroot.
So the exe can be found as:
file /proc/$(pidof epiphany)/root$(readlink /proc/$(pidof epiphany)/exe)

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