* dwarf2 - multiple DW_TAG_variable for global variable @ 2010-01-05 7:34 Nenad Vukicevic 2010-01-09 20:40 ` Nenad Vukicevic 0 siblings, 1 reply; 6+ messages in thread From: Nenad Vukicevic @ 2010-01-05 7:34 UTC (permalink / raw) To: gcc I installed gcc-4.5-20091224 snapshot and noticed that for simple variable declaration I get two DW_TAG_variable dies in the object file. For example, the following code int xxxxx; main() {xxxxx=1;} generates (with -g -gdwarf2 -O0 switches): <1><54>: Abbrev Number: 4 (DW_TAG_variable) <55> DW_AT_name : (indirect string, offset: 0x36): xxxxx <59> DW_AT_decl_file : 1 <5a> DW_AT_decl_line : 1 <5b> DW_AT_type : <0x4d> <5f> DW_AT_external : 1 <60> DW_AT_declaration : 1 <1><61>: Abbrev Number: 5 (DW_TAG_variable) <62> DW_AT_name : (indirect string, offset: 0x36): xxxxx <66> DW_AT_decl_file : 1 <67> DW_AT_decl_line : 1 <68> DW_AT_type : <0x4d> <6c> DW_AT_external : 1 <6d> DW_AT_location : 9 byte block: 3 0 0 0 0 0 0 0 0 (DW_OP_addr: 0) Is the above normal? 4.3.2 compiler generates only one die, the second one with DW_AT_location attribute, which is correct. I also noticed that this example (were variable is not used): int xxxxx; main() {} generates only one DW_TAG_variable, the one with DW_AT_location, which again should be correct. I ran into this problem by porting some GDB code that uses DWARF2 and got surprised to see this change from the previous version of gcc (4.3). Thanks, Nenad ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: dwarf2 - multiple DW_TAG_variable for global variable 2010-01-05 7:34 dwarf2 - multiple DW_TAG_variable for global variable Nenad Vukicevic @ 2010-01-09 20:40 ` Nenad Vukicevic 2010-01-09 21:02 ` Gary Funck 0 siblings, 1 reply; 6+ messages in thread From: Nenad Vukicevic @ 2010-01-09 20:40 UTC (permalink / raw) To: gcc; +Cc: jan.kratochvil, Gary Funck This dwarf code started appearing since this patch: ------------------------------------------------------------------------ r145293 | jakub | 2009-03-30 14:35:03 +0000 (Mon, 30 Mar 2009) | 11 lines PR debug/39563 * c-decl.c (struct c_binding): Add locus field. (bind): Add locus argument, set locus field from it. (pop_scope): For b->nested VAR_DECL or FUNCTION_DECL, add a DECL_EXTERNAL copy of b->decl to current BLOCK_VARS. (push_file_scope, pushtag, pushdecl, pushdecl_top_level, implicitly_declare, undeclared_variable, lookup_label, declare_label, c_make_fname_decl, c_builtin_function, c_builtin_function_ext_scope, store_parm_decls_newstyle): Adjust bind callers. Jan, can you confirm that this is indeed the correct DWARF that is being generated. Thank you, Nenad On 1/4/10 11:34 PM, Nenad Vukicevic wrote: > I installed gcc-4.5-20091224 snapshot and noticed that for simple > variable declaration > I get two DW_TAG_variable dies in the object file. For example, the > following > code > > int xxxxx; > main() > {xxxxx=1;} > > generates (with -g -gdwarf2 -O0 switches): > > <1><54>: Abbrev Number: 4 (DW_TAG_variable) > <55> DW_AT_name : (indirect string, offset: 0x36): xxxxx > <59> DW_AT_decl_file : 1 > <5a> DW_AT_decl_line : 1 > <5b> DW_AT_type : <0x4d> > <5f> DW_AT_external : 1 > <60> DW_AT_declaration : 1 > <1><61>: Abbrev Number: 5 (DW_TAG_variable) > <62> DW_AT_name : (indirect string, offset: 0x36): xxxxx > <66> DW_AT_decl_file : 1 > <67> DW_AT_decl_line : 1 > <68> DW_AT_type : <0x4d> > <6c> DW_AT_external : 1 > <6d> DW_AT_location : 9 byte block: 3 0 0 0 0 0 0 0 0 > (DW_OP_addr: 0) > > Is the above normal? 4.3.2 compiler generates only one die, the second > one with > DW_AT_location attribute, which is correct. > > I also noticed that this example (were variable is not used): > > int xxxxx; > main() > {} > > generates only one DW_TAG_variable, the one with DW_AT_location, > which again > should be correct. > > I ran into this problem by porting some GDB code that uses DWARF2 and > got surprised > to see this change from the previous version of gcc (4.3). > > Thanks, > Nenad > ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: dwarf2 - multiple DW_TAG_variable for global variable 2010-01-09 20:40 ` Nenad Vukicevic @ 2010-01-09 21:02 ` Gary Funck 2010-01-09 21:18 ` Jan Kratochvil 0 siblings, 1 reply; 6+ messages in thread From: Gary Funck @ 2010-01-09 21:02 UTC (permalink / raw) To: jan.kratochvil; +Cc: GCC List On 01/09/10 12:39:55, Nenad Vukicevic wrote: > This dwarf code started appearing since this patch: Here's the GCC bug report that led to this patch: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39563 It references a GDB fix as well: http://sourceware.org/ml/gdb-patches/2009-03/threads.html#00595 http://sourceware.org/ml/gdb-patches/2009-04/threads.html#00040 http://sourceware.org/ml/gdb-cvs/2009-04/msg00021.html ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: dwarf2 - multiple DW_TAG_variable for global variable 2010-01-09 21:02 ` Gary Funck @ 2010-01-09 21:18 ` Jan Kratochvil 2010-01-09 23:32 ` Nenad Vukicevic 0 siblings, 1 reply; 6+ messages in thread From: Jan Kratochvil @ 2010-01-09 21:18 UTC (permalink / raw) To: Gary Funck; +Cc: GCC List On Sat, 09 Jan 2010 22:01:54 +0100, Gary Funck wrote: > On 01/09/10 12:39:55, Nenad Vukicevic wrote: > > This dwarf code started appearing since this patch: > > Here's the GCC bug report that led to this patch: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39563 Such DIEs duplicities are being tracked at: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39524 (Unaware how/if any were caused by the PR 39563.) Regards, Jan ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: dwarf2 - multiple DW_TAG_variable for global variable 2010-01-09 21:18 ` Jan Kratochvil @ 2010-01-09 23:32 ` Nenad Vukicevic 2010-01-10 8:43 ` Jan Kratochvil 0 siblings, 1 reply; 6+ messages in thread From: Nenad Vukicevic @ 2010-01-09 23:32 UTC (permalink / raw) To: Jan Kratochvil; +Cc: Gary Funck, GCC List We used GCC regression testing to pin point PR39563 when multiple (but not equal) definitions started appearing in dwarf code. We used the head version of GCC, gcc-4.5.20091224 to be precise, for testing this abnormally. I also saw appearance of DIEs duplicates you mention in PR 39524 in the following example: extern int xxxxx; int main(){xxxxx=1;} gcc 4.3.2 - does NOT have duplicates gcc 4..4.1 20090725 (REDHAT 4.4.1-2) - does have duplicates gcc 4.4.2 - does NOT have duplicates gcc 4.5.20091224 - does have duplicates Duplicates are in the form described in PR39524. In the case of this code: int xxxxx; int main(){xxxxx=1;} I see duplicates in the form of: <1><54>: Abbrev Number: 4 (DW_TAG_variable) <55> DW_AT_name : (indirect string, offset: 0x38): xxxxx <59> DW_AT_decl_file : 1 <5a> DW_AT_decl_line : 1 <5b> DW_AT_type : <0x4d> <5f> DW_AT_external : 1 <60> DW_AT_declaration : 1 <1><61>: Abbrev Number: 5 (DW_TAG_variable) <62> DW_AT_name : (indirect string, offset: 0x38): xxxxx <66> DW_AT_decl_file : 1 <67> DW_AT_decl_line : 1 <68> DW_AT_type : <0x4d> <6c> DW_AT_external : 1 <6d> DW_AT_location : 9 byte block: 3 0 0 0 0 0 0 0 0 (DW_OP_addr: 0) in 4.4.1 and 4.5 releases. Any idea if this is a correct dwarf? Or must be treated as a duplicate somehow? Thanks, Nenad On 1/9/10 1:18 PM, Jan Kratochvil wrote: > On Sat, 09 Jan 2010 22:01:54 +0100, Gary Funck wrote: > >> On 01/09/10 12:39:55, Nenad Vukicevic wrote: >> >>> This dwarf code started appearing since this patch: >>> >> Here's the GCC bug report that led to this patch: >> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39563 >> > Such DIEs duplicities are being tracked at: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39524 > > (Unaware how/if any were caused by the PR 39563.) > > > Regards, > Jan > ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: dwarf2 - multiple DW_TAG_variable for global variable 2010-01-09 23:32 ` Nenad Vukicevic @ 2010-01-10 8:43 ` Jan Kratochvil 0 siblings, 0 replies; 6+ messages in thread From: Jan Kratochvil @ 2010-01-10 8:43 UTC (permalink / raw) To: Nenad Vukicevic; +Cc: Gary Funck, GCC List On Sun, 10 Jan 2010 00:31:56 +0100, Nenad Vukicevic wrote: ... > <1><54>: Abbrev Number: 4 (DW_TAG_variable) > <55> DW_AT_name : (indirect string, offset: 0x38): xxxxx > <59> DW_AT_decl_file : 1 > <5a> DW_AT_decl_line : 1 > <5b> DW_AT_type : <0x4d> > <5f> DW_AT_external : 1 > <60> DW_AT_declaration : 1 > <1><61>: Abbrev Number: 5 (DW_TAG_variable) > <62> DW_AT_name : (indirect string, offset: 0x38): xxxxx > <66> DW_AT_decl_file : 1 > <67> DW_AT_decl_line : 1 > <68> DW_AT_type : <0x4d> > <6c> DW_AT_external : 1 > <6d> DW_AT_location : 9 byte block: 3 0 0 0 0 0 0 0 0 (DW_OP_addr: 0) > > in 4.4.1 and 4.5 releases. > > Any idea if this is a correct dwarf? Or must be treated as a > duplicate somehow? It does not hurt much GDB - if the debugger ignores the second definition it looks as a declaration of external symbol and it gets correctly looked up through the ELF (not DWARF) .symtab symbol without using DW_AT_location. PR 39524 mentions a special scope case which gets broken by it but in common cases it works fine. Regards, Jan ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2010-01-10 8:43 UTC | newest] Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2010-01-05 7:34 dwarf2 - multiple DW_TAG_variable for global variable Nenad Vukicevic 2010-01-09 20:40 ` Nenad Vukicevic 2010-01-09 21:02 ` Gary Funck 2010-01-09 21:18 ` Jan Kratochvil 2010-01-09 23:32 ` Nenad Vukicevic 2010-01-10 8:43 ` Jan Kratochvil
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