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Fix disabling of solib probes when LD_AUDITing

Message ID msuwfjx3reba8osb5p8dx-95-tl&8ve/ana-yjtsot75l&3imnt8@mail.bob131.so
State New
Headers show

Commit Message

George Barrett Dec. 14, 2019, 11:54 p.m. UTC
The SVR4 solib event handler determines whether an event is related to a
non-base link namespace by comparing the event's debug struct address
to the debug struct address of the initial program image. However, this
can fail when using LD_AUDIT as audit libraries are loaded before the
loader has initialised the initial program image's debug struct. When
the event handler fails to find the debug struct, the probe-based
debugger interface is disabled and a warning is flagged to the user.

This commit adds a fallback test to help determine whether an event is
for a foreign link namespace when the debug struct is unavailable.
 gdb/solib-svr4.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)
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diff --git a/gdb/solib-svr4.c b/gdb/solib-svr4.c
index de765576d0..f0c7769ac2 100644
--- a/gdb/solib-svr4.c
+++ b/gdb/solib-svr4.c
@@ -1942,7 +1942,27 @@  svr4_handle_solib_event (void)
     /* Always locate the debug struct, in case it moved.  */
     info->debug_base = 0;
     if (locate_base (info) == 0)
-      return;
+      {
+	/* It's possible for the reloc_complete probe to be triggered before
+	   the linker has set the DT_DEBUG pointer (for example, when the
+	   linker has finished relocating an LD_AUDIT library or its
+	   dependencies).  Since we can't yet handle libraries from other link
+	   namespaces, we don't lose anything by ignoring them here.  */
+	struct value *link_map_id_val;
+	try
+	  {
+	    link_map_id_val = pa->prob->evaluate_argument (0, frame);
+	  }
+	catch (const gdb_exception_error)
+	  {
+	    link_map_id_val = NULL;
+	  }
+	/* glibc and illumos' libc both define LM_ID_BASE as zero.  */
+	if (link_map_id_val != NULL && value_as_long (link_map_id_val) != 0)
+	  action = DO_NOTHING;
+	else
+	  return;
+      }
     /* GDB does not currently support libraries loaded via dlmopen
        into namespaces other than the initial one.  We must ignore