[Bug gdb/27159] New: maintenance command to ignore probes

["vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=27159

            Bug ID: 27159
           Summary: maintenance command to ignore probes
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

On f.i. current openSUSE, libs like libgcc and glibc contain probes, which gdb
uses for various things.

There may be a fallback scenario for the case when probes are not present. 
F.i., for installing a master exception breakpoint, if the libgcc/unwind probe
is not present, the libgcc hook _Unwind_DebugHook is used instead.

It may be interesting or necessary (to test a fix) to test the fallback
scenario, but AFAICT it's not possible to do this without modifying sources. 
There is a command to disable individual probes, but for the libgcc/unwind one,
I get:
...
(gdb) disable probes libgcc unwind
Probe libgcc:unwind cannot be disabled.
...

F.i., I did this to disable all probes:
...
diff --git a/gdb/elfread.c b/gdb/elfread.c
index ce63d6b4b56..6667b6799e7 100644
--- a/gdb/elfread.c
+++ b/gdb/elfread.c
@@ -1404,10 +1404,12 @@ elf_get_probes (struct objfile *objfile)
     {
       probes_per_bfd = probe_key.emplace (objfile->obfd);

+#if 0
       /* Here we try to gather information about all types of probes from the
         objfile.  */
       for (const static_probe_ops *ops : all_static_probe_ops)
        ops->get_probes (probes_per_bfd, objfile);
+#endif
     }

   return *probes_per_bfd;
...
to be able to test whether the code using _Unwind_DebugHook still worked.

So perhaps a command "maintenance probes-disable" could be convenient.

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