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Re: [RFA] Enhance stabs reader to better deal with forward references

From: Pedro Alves <pedro_alves at portugalmail dot pt>
To: Joel Brobecker <brobecker at adacore dot com>
Cc: gdb-patches at sourceware dot org
Date: Sat, 31 Mar 2007 21:41:56 +0100
Subject: Re: [RFA] Enhance stabs reader to better deal with forward references
References: <20070209194107.GA3365@adacore.com> <20070227165003.GB31729@caradoc.them.org> <20070228201201.GH13140@adacore.com> <20070327162947.GC3452@caradoc.them.org> <20070329183609.GA3737@adacore.com>

Hi,

Joel Brobecker wrote:

2007-02-08 Joel Brobecker <brobecker@adacore.com>

        * stabsread.c (add_undefined_type): Add extra parameter.
        Now handles nameless types separately.
        (struct nat): New type.
        (noname_undefs, noname_undefs_allocated, noname_undefs_length):
        New static variables.
        (read_type): Update calls to add_undefined_type.
        (add_undefined_type_noname): New function.
        (add_undefined_type_1): Renames from add_undefined_type.
        (cleanup_undefined_types_noname): New function.
        (cleanup_undefined_types_1): Renames cleanup_undefined_types.
        (cleanup_undefined_types): New handles nameless types separately.
        (_initialize_stabsread): Initialize our new static constants.

Unfortunatelly, this patch broke Cygwin, which still uses stabs by default.

I am getting a SIGSEGV while issuing a breakpoint.
Here is a backtrace showing the problem.

(current_objfile is NULL on the SIGSEGV)

(I love these gdb in gdb in gdb in gdb thingies :) )

>/usr/bin/gdb --args /usr/local/bin/gdb --args /usr/local/bin/gdb ./main.exe 5404 GNU gdb 6.5.50.20060706-cvs (cygwin-special) Copyright (C) 2006 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "i686-pc-cygwin"... (gdb) r Starting program: /usr/local/bin/gdb.exe --args /usr/local/bin/gdb ./main.exe 5404 Loaded symbols for /cygdrive/c/WINDOWS/system32/ntdll.dll Loaded symbols for /cygdrive/c/WINDOWS/system32/kernel32.dll Loaded symbols for /usr/bin/cygwin1.dll Loaded symbols for /cygdrive/c/WINDOWS/system32/advapi32.dll Loaded symbols for /cygdrive/c/WINDOWS/system32/rpcrt4.dll Loaded symbols for /usr/bin/cygexpat-0.dll Loaded symbols for /usr/bin/cygiconv-2.dll Loaded symbols for /usr/bin/cygintl-8.dll Loaded symbols for /usr/bin/cygncurses-8.dll Loaded symbols for /cygdrive/c/WINDOWS/system32/user32.dll Loaded symbols for /cygdrive/c/WINDOWS/system32/gdi32.dll GNU gdb 6.6.50.20070329-cvs Copyright (C) 2007 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "i686-pc-cygwin"... (gdb) b win32_attach

Program received signal SIGSEGV, Segmentation fault. 0x004e003f in dbx_lookup_type (typenums=0x22c110) at ../../gdb-server_submit/src/gdb/stabsread.c:293 293 if (real_filenum >= N_HEADER_FILES (current_objfile)) (gdb) #0 0x004e003f in dbx_lookup_type (typenums=0x22c110) at ../../gdb-server_submit/src/gdb/stabsread.c:293 #1 0x004e7769 in cleanup_undefined_types_noname () at ../../gdb-server_submit/src/gdb/stabsread.c:4259 #2 0x004e7933 in cleanup_undefined_types () at ../../gdb-server_submit/src/gdb/stabsread.c:4346 #3 0x00539e5b in end_symtab (end_addr=4269324, objfile=0x10075fe0, section=0) at ../../gdb-server_submit/src/gdb/buildsym.c:896 #4 0x00502334 in read_ofile_symtab (pst=0x1014e258) at ../../gdb-server_submit/src/gdb/dbxread.c:2625 #5 0x00501ceb in dbx_psymtab_to_symtab_1 (pst=0x1014e258) at ../../gdb-server_submit/src/gdb/dbxread.c:2380 #6 0x00501c62 in dbx_psymtab_to_symtab_1 (pst=0x100f0058) at ../../gdb-server_submit/src/gdb/dbxread.c:2366 #7 0x00501e0e in dbx_psymtab_to_symtab (pst=0x100f0058) at ../../gdb-server_submit/src/gdb/dbxread.c:2431 #8 0x004044fe in psymtab_to_symtab (pst=0x100f0058) at ../../gdb-server_submit/src/gdb/symfile.c:287 #9 0x004667a5 in lookup_symbol_aux_psymtabs (block_index=1, name=0x22c400 "win32_attach", linkage_name=0x0, domain=VAR_DOMAIN, symtab=0x0) at ../../gdb-server_submit/src/gdb/symtab.c:1368 #10 0x004664c7 in lookup_symbol_aux (name=0x22c400 "win32_attach", linkage_name=0x0, block=0x0, domain=VAR_DOMAIN, language=language_c, is_a_field_of_this=0x0, symtab=0x0) at ../../gdb-server_submit/src/gdb/symtab.c:1227 #11 0x004662fe in lookup_symbol_in_language (name=0x22c400 "win32_attach", block=0x0, domain=VAR_DOMAIN, lang=language_c, is_a_field_of_this=0x0, symtab=0x0) at ../../gdb-server_submit/src/gdb/symtab.c:1133 #12 0x00466367 in lookup_symbol (name=0x22c400 "win32_attach", block=0x0, domain=VAR_DOMAIN, is_a_field_of_this=0x0, symtab=0x0) at ../../gdb-server_submit/src/gdb/symtab.c:1154 #13 0x004c6579 in find_imps (symtab=0x0, block=0x0, method=0x10033f3a "win32_attach", syms=0x0, nsym=0x22c49c, ndebug=0x22c498) at ../../gdb-server_submit/src/gdb/objc-lang.c:1438 #14 0x0048fb17 in decode_objc (argptr=0x22c750, funfirstline=1, file_symtab=0x0, canonical=0x22c6dc, saved_arg=0x10033f3a "win32_attach") at ../../gdb-server_submit/src/gdb/linespec.c:1103 #15 0x0048f377 in decode_line_1 (argptr=0x22c750, funfirstline=1, default_symtab=0x0, default_line=0, canonical=0x22c6dc, not_found_ptr=0x22c6ac) at ../../gdb-server_submit/src/gdb/linespec.c:728 #16 0x0044118e in parse_breakpoint_sals (address=0x22c750, sals=0x22c720, addr_string=0x22c6dc, not_found_ptr=0x22c6ac) at ../../gdb-server_submit/src/gdb/breakpoint.c:5185 #17 0x0044129e in do_captured_parse_breakpoint (ui=0x100696e0, data=0x22c6c0) at ../../gdb-server_submit/src/gdb/breakpoint.c:5247 #18 0x00412d7c in catch_exception (uiout=0x100696e0, func=0x441267 <do_captured_parse_breakpoint>, func_args=0x22c6c0, mask=6) at ../../gdb-server_submit/src/gdb/exceptions.c:469 #19 0x00441362 in break_command_1 (arg=0x10033f3a "win32_attach", flag=0, from_tty=1, pending_bp=0x0) at ../../gdb-server_submit/src/gdb/breakpoint.c:5292 #20 0x00441fb5 in break_command (arg=0x10033f3a "win32_attach", from_tty=1) at ../../gdb-server_submit/src/gdb/breakpoint.c:5660 #21 0x0042ca8b in do_cfunc (c=0x10049ca8, args=0x10033f3a "win32_attach", from_tty=1) at ../../gdb-server_submit/src/gdb/cli/cli-decode.c:62 #22 0x0042ef7d in cmd_func (cmd=0x10049ca8, args=0x10033f3a "win32_attach", from_tty=1) at ../../gdb-server_submit/src/gdb/cli/cli-decode.c:1666 #23 0x004025b8 in execute_command (p=0x10033f45 "h", from_tty=1) at ../../gdb-server_submit/src/gdb/top.c:451 #24 0x00424422 in command_handler (command=0x10033f38 "b win32_attach") at ../../gdb-server_submit/src/gdb/event-top.c:519 #25 0x00424be4 in command_line_handler (rl=0x1012e3d0 "") at ../../gdb-server_submit/src/gdb/event-top.c:804 #26 0x00424d38 in gdb_readline2 (client_data=0x0) at ../../gdb-server_submit/src/gdb/event-top.c:884 #27 0x004242cc in stdin_event_handler (error=0, client_data=0x0) at ../../gdb-server_submit/src/gdb/event-top.c:432 #28 0x004394be in handle_file_event (event_file_desc=0) at ../../gdb-server_submit/src/gdb/event-loop.c:730 #29 0x00438d42 in process_event () at ../../gdb-server_submit/src/gdb/event-loop.c:343 #30 0x00438d8b in gdb_do_one_event (data=0x0) at ../../gdb-server_submit/src/gdb/event-loop.c:380 #31 0x00412f9b in catch_errors (func=0x438d57 <gdb_do_one_event>, func_args=0x0, errstring=0x649101 "", mask=6) at ../../gdb-server_submit/src/gdb/exceptions.c:515 #32 0x004a2f2b in tui_command_loop (data=0x0) at ../../gdb-server_submit/src/gdb/tui/tui-interp.c:151 #33 0x0041c96a in current_interp_command_loop () at ../../gdb-server_submit/src/gdb/interps.c:278 #34 0x004010cb in captured_command_loop (data=0x0) at ../../gdb-server_submit/src/gdb/main.c:101 #35 0x00412f9b in catch_errors (func=0x4010c0 <captured_command_loop>, func_args=0x0, errstring=0x61a139 "", mask=6) at ../../gdb-server_submit/src/gdb/exceptions.c:515 #36 0x00402110 in captured_main (data=0x22cc70) at ../../gdb-server_submit/src/gdb/main.c:867 #37 0x00412f9b in catch_errors (func=0x401102 <captured_main>, func_args=0x22cc70, errstring=0x61a139 "", mask=6) at ../../gdb-server_submit/src/gdb/exceptions.c:515 #38 0x00402146 in gdb_main (args=0x22cc70) at ../../gdb-server_submit/src/gdb/main.c:876 #39 0x004010ba in main (argc=5, argv=0x10033c40) at ../../gdb-server_submit/src/gdb/gdb.c:35

I didn't look much into the code, but the attached works for me.

Cheers,
Pedro Alves

2007-03-31  Pedro Alves  <pedro_alves@portugalmail.pt>

	* dbxread.c (read_ofile_symtab): Move current_objfile
	clearing to after end_stabs.
---
 gdb/dbxread.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Index: src/gdb/dbxread.c
===================================================================
--- src.orig/gdb/dbxread.c	2005-12-17 21:34:00.000000000 +0000
+++ src/gdb/dbxread.c	2007-03-31 21:31:42.000000000 +0100
@@ -2608,8 +2608,6 @@ read_ofile_symtab (struct partial_symtab
 	}
     }
 
-  current_objfile = NULL;
-
   /* In a Solaris elf file, this variable, which comes from the
      value of the N_SO symbol, will still be 0.  Luckily, text_offset,
      which comes from pst->textlow is correct. */
@@ -2625,6 +2623,8 @@ read_ofile_symtab (struct partial_symtab
   pst->symtab = end_symtab (text_offset + text_size, objfile, SECT_OFF_TEXT (objfile));
 
   end_stabs ();
+
+  current_objfile = NULL;
 }

References:
- Re: [RFA] Enhance stabs reader to better deal with forward references
  - From: Daniel Jacobowitz
- Re: [RFA] Enhance stabs reader to better deal with forward references
  - From: Joel Brobecker

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