char[] chars; void main() { string lok = "Something"; chars = "Anything".dup; } compiled dmd -g mk@bid:~/work/pokus/debug$ gdb ./locals GNU gdb (GDB) 7.8.50.20141030-cvs (gdb) b 6 Breakpoint 1 at 0x8064e88: file locals.d, line 6. (gdb) r Starting program: /home/mk/work/pokus/debug/locals Breakpoint 1, D main () at locals.d:6 6 chars = "Anything".dup; (gdb) info locals lok = <error reading variable> This is with Ian's patched gdb on linux x86 dmd 2.066 works and 2.067a -gc works too. Debug info (2.066 vs 2.067a) looks the same. I haven't tested patched gdb + x86_64 I suspect this may be a gdb problem or something botched up on my side, but I don't have time for more testing now.
Introduced by https://github.com/D-Programming-Language/druntime/commit/5a5d1c5c4d9f27785422191178fc4e2876a0a097
Small correction: -gc doesn't make it work. Also the problem is not limited to recent gdb version, 7.4.1-debian is affected too for example.
Pull request in question: https://github.com/D-Programming-Language/druntime/pull/1031
Confirmed, doesn't depend on ld.bfd vs. ld.gold. Neither dwarfdump nor readelf --debug-dump report any error.
.debug_frame and .debug_ranges changed and look indeed weird. There is an overlapping PC range. 000000c0 0000000000000024 00000000 FDE cie=00000000 pc=0000000000000000..0000000000000084 DW_CFA_advance_loc: 1 to 0000000000000001 DW_CFA_def_cfa_offset: 16 DW_CFA_offset: r6 (rbp) at cfa-16 DW_CFA_advance_loc: 2 to 0000000000000003 DW_CFA_def_cfa_register: r6 (rbp) DW_CFA_advance_loc: 6 to 0000000000000009 DW_CFA_offset: r1 (rdx) at cfa-80 DW_CFA_nop DW_CFA_nop DW_CFA_nop DW_CFA_nop DW_CFA_nop 000000e8 0000000000000024 00000000 FDE cie=00000000 pc=0000000000000000..0000000000000053 DW_CFA_advance_loc: 1 to 0000000000000001 DW_CFA_def_cfa_offset: 16 DW_CFA_offset: r6 (rbp) at cfa-16 DW_CFA_advance_loc: 2 to 0000000000000003 DW_CFA_def_cfa_register: r6 (rbp) DW_CFA_advance_loc: 6 to 0000000000000009 DW_CFA_offset: r1 (rdx) at cfa-24 DW_CFA_nop DW_CFA_nop DW_CFA_nop DW_CFA_nop DW_CFA_nop 00000000 0000000000000000 0000000000000084 00000000 0000000000000000 0000000000000053 Further investigation tomorrow ;).
Any news?
For yet unknown reason gdb reads an incorrect sizeof for the .length variable of the string. This only applies to the arrays in main not the ones passed to the dup functions. It also works in lldb. It would be more optimal if dmd cached and emitted only a single instance per array type. Will try to implement that and see if it helps before spending more hours debugging gdb.
(In reply to Martin Nowak from comment #7) > It would be more optimal if dmd cached and emitted only a single instance > per array type. Will try to implement that and see if it helps before > spending more hours debugging gdb. Indeed, fixing the type repetition of debug infos for arrays fixes the issue. The code is pretty ugly and needs some refactoring before fixing the incorrect hashing, but that'd be my preferred fix as it get's rid of a lot of unnecessary debug info.
(In reply to Martin Nowak from comment #8) > Indeed, fixing the type repetition of debug infos for arrays fixes the issue. > The code is pretty ugly and needs some refactoring before fixing the > incorrect hashing, but that'd be my preferred fix as it get's rid of a lot > of unnecessary debug info. What is the prospect of this being done in time for 2.067?
(In reply to Walter Bright from comment #9) > What is the prospect of this being done in time for 2.067? I'm working on that, but dwarf.c is a mess. So far everything I tried had to touch too much code, likely resulting in a regression. I think the simplest solution is to throw out DW_AT_siblings, it's not that useful anyhow.
OK, found it. For TYref we set the pointer byte_size to -1. Wondering why we're emitting TYref for arrays though.
https://github.com/D-Programming-Language/dmd/pull/4494
Commits pushed to master at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/c89d666984b74bcd6d50afbdf2d478370f3c52a9 fix Issue 14225 - GDB: error reading variable (string + dup) - tysize(t->Tty) for TYref was -1 - fixed by omitting the explicit byte_size for pointers - the debugger will use the address_size for the compilation unit instead https://github.com/D-Programming-Language/dmd/commit/7cb0b4fe2a56d187b4ef8c6416446dc15e1218cf Merge pull request #4494 from MartinNowak/fix14225 fix Issue 14225 - GDB: error reading variable (string + dup)
Commit pushed to 2.067 at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/c4a2d7c74897c0114e1c4c1896620abec65c91a0 Merge pull request #4494 from MartinNowak/fix14225 fix Issue 14225 - GDB: error reading variable (string + dup)
Commit pushed to master at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/c4a2d7c74897c0114e1c4c1896620abec65c91a0 Merge pull request #4494 from MartinNowak/fix14225
Commits pushed to stable at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/c89d666984b74bcd6d50afbdf2d478370f3c52a9 fix Issue 14225 - GDB: error reading variable (string + dup) https://github.com/D-Programming-Language/dmd/commit/7cb0b4fe2a56d187b4ef8c6416446dc15e1218cf Merge pull request #4494 from MartinNowak/fix14225