gdb: skip objfiles with no BFD in DWARF unwinder

While playing with JIT reader I experienced GDB to crash on null-pointer
dereference when stepping through non-jitted code.

The problem was that dwarf2_frame_find_fde () assumed that all objfiles
have BFD but that's not always true. To address this problem, this
commit skips such objfiles.

To test the fix we put breakpoint in jit_function_add (). The JIT reader
does not know how unwind this function so unwinding eventually falls
back to DWARF unwinder which in turn iterates over objfiles. Since the
the code is jitted, it is guaranteed it would eventually process JIT
objfile.

Approved-By: Simon Marchi <simon.marchi@efficios.com>

diff --git a/gdb/dwarf2/frame.c b/gdb/dwarf2/frame.c
index 3f884abe1d5813f386e88fad2e9e82745eb0f141..54a0912ebc60e63b9b682214fd1c302e61a794a9 100644 (file)
--- a/gdb/dwarf2/frame.c
+++ b/gdb/dwarf2/frame.c
@@ -1560,6 +1560,9 @@ dwarf2_frame_find_fde (CORE_ADDR *pc, dwarf2_per_objfile **out_per_objfile)
       CORE_ADDR offset;
       CORE_ADDR seek_pc;
 
+      if (objfile->obfd == nullptr)
+       continue;
+
       comp_unit *unit = find_comp_unit (objfile);
       if (unit == NULL)
        {

diff --git a/gdb/objfiles.h b/gdb/objfiles.h
index 9a152cbc3879c616499798d55e81d0ece37045bd..0d887ce112fe8bfcddb70f6d9e15764974fbb1e4 100644 (file)
--- a/gdb/objfiles.h
+++ b/gdb/objfiles.h
@@ -646,7 +646,9 @@ public:
   struct compunit_symtab *compunit_symtabs = nullptr;
 
   /* The object file's BFD.  Can be null if the objfile contains only
-     minimal symbols, e.g. the run time common symbols for SunOS4.  */
+     minimal symbols (e.g. the run time common symbols for SunOS4) or
+     if the objfile is a dynamic objfile (e.g. created by JIT reader
+     API).  */
 
   gdb_bfd_ref_ptr obfd;
 

diff --git a/gdb/testsuite/gdb.base/jit-reader.exp b/gdb/testsuite/gdb.base/jit-reader.exp
index 69bf721d90aaf4e9163ab3e68c02b1a90267ea5c..a66896dda67e1ff084a8bc5218791c4ab2c82ba7 100644 (file)
--- a/gdb/testsuite/gdb.base/jit-reader.exp
+++ b/gdb/testsuite/gdb.base/jit-reader.exp
@@ -277,6 +277,19 @@ proc jit_reader_test {} {
            "True" \
            "at least one file-based objfile"
     }
+
+    with_test_prefix "test dwarf unwinder" {
+       # Check that the DWARF unwinder does not crash in presence of
+       # JIT objfiles.
+       gdb_test "up"
+       gdb_breakpoint "*function_add" temporary
+       gdb_test "cont" ".*Temporary breakpoint ${any} in jit_function_add .*"
+       gdb_test "bt" \
+           [multi_line \
+                "#0 ${any} in jit_function_add ${any}" \
+                "#1 ${any} in main ${any}" \
+               ]
+    }
 }
 
 jit_reader_test