[Bug tdep/34198] New: Z80: "break main" crashes in z80_skip_prologue when SAL has no symtab

[ronald.hecht at gmx dot de]

https://sourceware.org/bugzilla/show_bug.cgi?id=34198

            Bug ID: 34198
           Summary: Z80: "break main" crashes in z80_skip_prologue when
                    SAL has no symtab
           Product: gdb
           Version: HEAD
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: tdep
          Assignee: unassigned at sourceware dot org
          Reporter: ronald.hecht at gmx dot de
  Target Milestone: ---

Created attachment 16743
  --> https://sourceware.org/bugzilla/attachment.cgi?id=16743&action=edit
Small example used to test setting breakpoints.

With a Z80 ELF binary, "break main" crashes GDB internally.
"break *main" works.

The crash happens in z80_skip_prologue after find_sal_for_pc returns
a symtab_and_line whose symtab is NULL.  The code unconditionally calls:

  prologue_sal.symtab->compunit()->debugformat()

----- Backtrace -----
0x6385f3c7fc41 gdb_internal_backtrace_1
        ../../gdb/bt-utils.c:122
0x6385f3c7fc41 _Z22gdb_internal_backtracev
        ../../gdb/bt-utils.c:173
0x6385f3dd2313 handle_fatal_signal
        ../../gdb/event-top.c:1008
0x6385f3dd28b9 handle_sigsegv
        ../../gdb/event-top.c:1085
0x757e7704532f ???
        ./signal/../sysdeps/unix/sysv/linux/x86_64/libc_sigaction.c:0
0x6385f40f8207 _ZNK15compunit_symtab11debugformatEv
        ../../gdb/symtab.h:1857
0x6385f40f8207 z80_skip_prologue
        ../../gdb/z80-tdep.c:499
0x6385f3c250bc _Z30gdbarch_skip_prologue_noexceptP7gdbarchm
        ../../gdb/arch-utils.c:1046
0x6385f3ff46f5 _Z17skip_prologue_salP15symtab_and_line
        ../../gdb/symtab.c:3765
0x6385f3ff4bba find_function_start_sal_1
        ../../gdb/symtab.c:3538
0x6385f3ff4c83 _Z23find_function_start_salmP11obj_sectionb
        ../../gdb/symtab.c:3549
0x6385f3e73c9e minsym_found
        ../../gdb/linespec.c:4078
0x6385f3e73c9e convert_linespec_to_sals
        ../../gdb/linespec.c:2290
0x6385f3e755f8 parse_linespec
        ../../gdb/linespec.c:2655
0x6385f3e76d35 location_spec_to_sals
        ../../gdb/linespec.c:3053
0x6385f3e771b0
_Z16decode_line_fullP13location_speciP13program_spaceP6symtabiP15linespec_resultPKcS8_
        ../../gdb/linespec.c:3129
0x6385f3c671d3 parse_breakpoint_sals
        ../../gdb/breakpoint.c:9084
0x6385f3c6b490
_Z17create_breakpointP7gdbarchP13location_specPKciiS4_bii6bptypei12auto_booleanPK14breakpoint_opsiiij
        ../../gdb/breakpoint.c:9319
0x6385f3c6be42 break_command_1
        ../../gdb/breakpoint.c:9478
0x6385f3cbe834 _Z8cmd_funcP16cmd_list_elementPKci
        ../../gdb/cli/cli-decode.c:2810
0x6385f4047c44 _Z15execute_commandPKci
        ../../gdb/top.c:632
0x6385f3dd3158 _Z15command_handlerPKc
        ../../gdb/event-top.c:611
0x6385f3dd4b60
_Z20command_line_handlerOSt10unique_ptrIcN3gdb13xfree_deleterIcEEE
        ../../gdb/event-top.c:844
0x6385f3dd3d74 gdb_rl_callback_handler
        ../../gdb/event-top.c:288
0x6385f41173e8 rl_callback_read_char
        ../../../readline/readline/callback.c:302
0x6385f3dd3eed gdb_rl_callback_read_char_wrapper_sjlj
        ../../gdb/event-top.c:197
0x6385f3dd40b3 gdb_rl_callback_read_char_wrapper_noexcept
        ../../gdb/event-top.c:240
0x6385f3dd40b3 gdb_rl_callback_read_char_wrapper
        ../../gdb/event-top.c:252
0x6385f4085c8f stdin_event_handler
        ../../gdb/ui.c:161
0x6385f41d7f85 gdb_wait_for_event
        ../../gdbsupport/event-loop.cc:694
0x6385f41d87e1 _Z16gdb_do_one_eventi
        ../../gdbsupport/event-loop.cc:263
0x6385f3e8be39 _ZN6interp12do_one_eventEi
        ../../gdb/interps.h:90
0x6385f3e8be39 start_event_loop
        ../../gdb/main.c:400
0x6385f3e8be39 captured_command_loop
        ../../gdb/main.c:465
0x6385f3e8e2c4 captured_main
        ../../gdb/main.c:1373
0x6385f3e8e2c4 _Z8gdb_mainP18captured_main_args
        ../../gdb/main.c:1392
0x6385f3bbf5bb main
        ../../gdb/gdb.c:38
---------------------
A fatal error internal to GDB has been detected, further
debugging is not possible.  GDB will now terminate.

How to reproduce:
  z80-...-gdb hello.elf
  (gdb) break main

Expected:
GDB should either set the breakpoint or fall back gracefully.

Actual:
GDB terminates with an internal segmentation fault.

Tested fix:
Adding null checks for prologue_sal.symtab and compunit prevents the crash.

diff --git a/gdb/z80-tdep.c b/gdb/z80-tdep.c
index f7e207d0..f2e9b09e 100644
--- a/gdb/z80-tdep.c
+++ b/gdb/z80-tdep.c
@@ -495,12 +495,17 @@ z80_skip_prologue (struct gdbarch *gdbarch, CORE_ADDR pc)
   if (prologue_end != 0)
     {
       struct symtab_and_line prologue_sal = find_sal_for_pc (func_addr, 0);
-      struct compunit_symtab *compunit = prologue_sal.symtab->compunit ();
-      const char *debug_format = compunit->debugformat ();
-
-      if (debug_format != NULL &&
-         !strncasecmp ("dwarf", debug_format, strlen("dwarf")))
-       return std::max (pc, prologue_end);
+      if (prologue_sal.symtab != nullptr)
+       {
+         struct compunit_symtab *compunit = prologue_sal.symtab->compunit ();
+         if (compunit != nullptr)
+           {
+             const char *debug_format = compunit->debugformat ();
+             if (debug_format != nullptr
+                 && !strncasecmp ("dwarf", debug_format, strlen ("dwarf")))
+               return std::max (pc, prologue_end);
+           }
+       }
     }

   return pc;

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