From 6053cecf4a4ffd19d1ac0a3bb3ffef100ab83fda Mon Sep 17 00:00:00 2001
From: "Frank Ch. Eigler" <fche@redhat.com>
Date: Tue, 28 Jan 2020 15:48:42 -0500
Subject: [PATCH] RHBZ1795196: tolerate partial elf + missing dwarf vmlinuz for
 -d kernel

Previous code in dump_symbol_tables() couldn't tolerate the case where
new elfutils opened /boot/vmlinuz* as an elf file for the kernel, and
could not extract a symbol table from that (nor an absent -debuginfo).
New code instead emits a warning and moves on.  A special error code
triggers return to the dump_kallsyms() path that prior elfutils/stap
versions rely on.
---
 testsuite/systemtap.base/kallsyms.exp |  3 +++
 translate.cxx                         | 12 +++++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/testsuite/systemtap.base/kallsyms.exp b/testsuite/systemtap.base/kallsyms.exp
index 8ee52422d..13ca4adec 100644
--- a/testsuite/systemtap.base/kallsyms.exp
+++ b/testsuite/systemtap.base/kallsyms.exp
@@ -5,7 +5,10 @@ if {![installtest_p]} {untested $test; return}
 set script {"probe timer.profile {print_stack(backtrace()); exit()}"}
 set passed 0
 
+# don't let stap find kernel debuginfo!
 setenv SYSTEMTAP_DEBUGINFO_PATH $srcdir
+setenv DEBUGINFOD_URLS ""
+setenv DEBUGINFOD_CACHE_PATH "/dev/null"
 
 eval spawn stap --all-modules -e $script
 expect {
diff --git a/translate.cxx b/translate.cxx
index f14266702..9e3042742 100644
--- a/translate.cxx
+++ b/translate.cxx
@@ -6786,7 +6786,17 @@ dump_symbol_tables (Dwfl_Module *m,
   dwfl_module_info (m, NULL, NULL, &end, NULL, NULL, NULL, NULL);
 
   int syments = dwfl_module_getsymtab(m);
-  DWFL_ASSERT (_F("Getting symbol table for %s", modname), syments >= 0);
+  if (syments < 0) // RHBZ1795196: elfutils 0.178+ can open vmlinuz as elf.main but fail here
+    {
+      c->session.print_warning(_F("libdwfl failure getting symbol table for %s: %s",
+                                  modname, dwfl_errmsg(-1)));
+      return DWARF_CB_ABORT;
+
+      // signal to dump_unwindsyms() to not let things proceed all the way to
+      // dump_unwindsym_cxt(), which then believes it has all the info for a
+      // complete record about this module.  In the kernel's case, this allows
+      // PR17921 fallback to /proc/kallsyms via dump_kallsyms().
+    }
 
   // Look up the relocation basis for symbols
   int n = dwfl_module_relocations (m);
-- 
2.43.5