Ping...
On 11/2/19 7:49 AM, Bernd Edlinger wrote: > Ping... > > On 10/27/19 9:14 AM, Bernd Edlinger wrote: >> Ping... >> >> I'd like to ping for this patch: >> https://gcc.gnu.org/ml/gcc-patches/2019-10/msg01459.html >> >> >> Thanks >> Bernd. >> >> On 10/20/19 9:58 PM, Bernd Edlinger wrote: >>> Hi, >>> >>> this fixes an issue with the gdb step-over aka. "n" command. >>> >>> It can be seen when you debug an optimized stage-3 cc1 >>> it does not affect -O0 code, though. >>> >>> This example debug session will explain the effect. >>> >>> (gdb) b get_alias_set >>> Breakpoint 5 at 0xa099f0: file ../../gcc-trunk/gcc/alias.c, line 837. >>> (gdb) r >>> Breakpoint 5, get_alias_set (t=t@entry=0x7ffff7ff7ab0) at >>> ../../gcc-trunk/gcc/alias.c:837 >>> 837 if (t == error_mark_node >>> (gdb) n >>> 839 && (TREE_TYPE (t) == 0 || TREE_TYPE (t) == error_mark_node))) >>> (gdb) n >>> 3382 return __t; <-- now we have a problem: wrong line info here >>> (gdb) bt >>> #0 get_alias_set (t=t@entry=0x7ffff7ff7ab0) at >>> ../../gcc-trunk/gcc/tree.h:3382 >>> #1 0x0000000000b25dfe in set_mem_attributes_minus_bitpos >>> (ref=0x7ffff746f990, t=0x7ffff7ff7ab0, objectp=1, bitpos=...) >>> at ../../gcc-trunk/gcc/emit-rtl.c:1957 >>> #2 0x0000000001137a55 in make_decl_rtl (decl=0x7ffff7ff7ab0) at >>> ../../gcc-trunk/gcc/varasm.c:1518 >>> #3 0x000000000113b6e8 in assemble_variable (decl=0x7ffff7ff7ab0, >>> top_level=<optimized out>, at_end=<optimized out>, >>> dont_output_data=0) at ../../gcc-trunk/gcc/varasm.c:2246 >>> #4 0x000000000113f0ea in varpool_node::assemble_decl (this=0x7ffff745b000) >>> at ../../gcc-trunk/gcc/varpool.c:584 >>> #5 0x000000000113fa17 in varpool_node::assemble_decl (this=0x7ffff745b000) >>> at ../../gcc-trunk/gcc/varpool.c:750 >>> >>> >>> There are at least two problems here: >>> >>> First you did not want to step into the TREE_TYPE, but it happens all >>> the time, even if you use "n" to step over it. >>> >>> And secondly, from the call stack, you don't know where you are in >>> get_alias_set. >>> But the code that is executing at this point is actually the x == 0 || x == >>> error_mark_node >>> from alias.c, line 839, which contains the inlined body of the TREE_TYPE, >>> but >>> the rest of the if. So there is an inconsistency in the >>> >>> Contents of the .debug_info section: >>> >>> <2><4f686>: Abbrev Number: 12 (DW_TAG_inlined_subroutine) >>> <4f687> DW_AT_abstract_origin: <0x53d4e> >>> <4f68b> DW_AT_entry_pc : 0x7280 >>> <4f693> DW_AT_GNU_entry_view: 1 >>> <4f695> DW_AT_ranges : 0xb480 >>> <4f699> DW_AT_call_file : 8 <- alias.c >>> <4f69a> DW_AT_call_line : 839 >>> <4f69c> DW_AT_call_column : 8 >>> <4f69d> DW_AT_sibling : <0x4f717> >>> >>> The File Name Table (offset 0x253): >>> 8 2 0 0 alias.c >>> 10 2 0 0 tree.h >>> >>> Contents of the .debug_ranges section: >>> >>> 0000b480 0000000000007280 0000000000007291 >>> 0000b480 0000000000002764 000000000000277e >>> 0000b480 <End of list> >>> >>> The problem is at pc=0x7291 in the Line Number Section: >>> >>> Line Number Statements: >>> >>> [0x00008826] Special opcode 61: advance Address by 4 to 0x7284 and Line >>> by 0 to 3380 >>> [0x00008827] Set is_stmt to 1 >>> [0x00008828] Special opcode 189: advance Address by 13 to 0x7291 and >>> Line by 2 to 3382 (*) >>> [0x00008829] Set is_stmt to 0 (**) >>> [0x0000882a] Copy (view 1) >>> [0x0000882b] Set File Name to entry 8 in the File Name Table <- back to >>> alias.c >>> [0x0000882d] Set column to 8 >>> [0x0000882f] Advance Line by -2543 to 839 >>> [0x00008832] Copy (view 2) >>> [0x00008833] Set column to 27 >>> [0x00008835] Special opcode 61: advance Address by 4 to 0x7295 and Line >>> by 0 to 839 >>> [0x00008836] Set column to 3 >>> [0x00008838] Set is_stmt to 1 <-- next line info counts: alias.c:847 >>> [0x00008839] Special opcode 153: advance Address by 10 to 0x729f and >>> Line by 8 to 847 >>> [0x0000883a] Set column to 7 >>> >>> (*) this line is tree.h:3382, but the program counter is *not* within the >>> subroutine, >>> but exactly at the first instruction *after* the subroutine according to >>> the debug_ranges. >>> >>> What makes it worse, is that (**) makes gdb ignore the new location info >>> alias.c:839, >>> which means, normally the n command would have continued to pc=0x729f, >>> which is at alias.c:847. >>> >>> >>> The problem happens due to a block with only var >>> This patch fixes this problem by moving (**) to the first statement with a >>> different line number. >>> >>> In alias.c.316r.final this looks like that: >>> >>> (note 2884 2883 1995 31 0x7f903a931ba0 NOTE_INSN_BLOCK_BEG) >>> (note 1995 2884 2885 31 ../../gcc-trunk/gcc/tree.h:3377 >>> NOTE_INSN_INLINE_ENTRY) >>> (note 2885 1995 1996 31 0x7f903a931c00 NOTE_INSN_BLOCK_BEG) >>> [...] >>> (note 50 39 59 32 [bb 32] NOTE_INSN_BASIC_BLOCK) >>> (note 59 50 60 32 NOTE_INSN_DELETED) >>> (note 60 59 1997 32 NOTE_INSN_DELETED) >>> (note 1997 60 2239 32 ../../gcc-trunk/gcc/tree.h:3382 NOTE_INSN_BEGIN_STMT) >>> (note 2239 1997 2240 32 (var_location __tD.143911 (nil)) >>> NOTE_INSN_VAR_LOCATION) >>> (note 2240 2239 2241 32 (var_location __sD.143912 (nil)) >>> NOTE_INSN_VAR_LOCATION) >>> (note 2241 2240 2242 32 (var_location __fD.143913 (nil)) >>> NOTE_INSN_VAR_LOCATION) >>> (note 2242 2241 2243 32 (var_location __lD.143914 (nil)) >>> NOTE_INSN_VAR_LOCATION) >>> (note 2243 2242 2886 32 (var_location __gD.143915 (nil)) >>> NOTE_INSN_VAR_LOCATION) >>> (note 2886 2243 2887 32 0x7f903a931c00 NOTE_INSN_BLOCK_END) >>> (note 2887 2886 57 32 0x7f903a931ba0 NOTE_INSN_BLOCK_END) >>> (insn:TI 57 2887 61 32 (set (reg/f:DI 0 ax [orig:87 _7 ] [87]) >>> (mem/f/j:DI (plus:DI (reg/f:DI 5 di [orig:83 t.85_2 ] [83]) >>> (const_int 8 [0x8])) [0 t.85_2->typedD.91322.typeD.90828+0 >>> S8 A64])) "../../gcc-trunk/gcc/alias.c":839:108 66 {*movdi_internal} >>> (nil)) >>> >>> So this patch detects the NOTE_INSN_VAR_LOCATION and makes the next location >>> with a different file&line info a statement location, which is hopefully >>> a real instruction, thus either part of the subroutine, or the first >>> instruction after the subroutine, which should have the correct location. >>> Once the same address has a second statement-type .loc info, gdb will ignore >>> the first one, and the stepping works as expected. >>> >>> So this is a bit of a heuristic, but it appears to work quite well. >>> >>> The test case g++.dg/guality/pr55541.C is the only test where this >>> change had an effect. But it is not a regression, since previously >>> the test case was "unsupported" on any optimization mode, since there >>> was no breakpoint at line 11, now the breakpoint works, but the variable >>> value is wrong, but basically this was not working before. >>> >>> I don't know how to make this test xfail when compiled with optimization, >>> but the do-skip-if is probably good enough for this kind of test case. >>> >>> >>> Bootstrapped and reg-tested on x86_64-pc-linux-gnu. >>> Is it OK for trunk? >>> >>> >>> Thanks >>> Bernd. >>>
