[PING][PATCH][gdb/breakpoints] Workaround missing line-table entry

[Tom de Vries <tdevries@suse.de>]

On 1/22/21 10:15 AM, Tom de Vries wrote:
> Hi,
> 
> When running test-case gdb.opt/inline-cmds.exp, we run into this KFAIL with
> gcc:
> ...
> Breakpoint 7, main () at gdb.opt/inline-cmds.c:71^M
> 71        result = 0; /* set breakpoint 3 here */^M
> (gdb) PASS: gdb.opt/inline-cmds.exp: continue to breakpoint: consecutive func1
> next^M
> 73        func1 (); /* first call */^M
> (gdb) PASS: gdb.opt/inline-cmds.exp: next to first func1
> next^M
> 75        marker ();^M
> (gdb) KFAIL: gdb.opt/inline-cmds.exp: next to second func1 (PRMS: gdb/25884)
> ...
> while with clang we have instead:
> ...
> next^M
> 74        func1 (); /* second call */^M
> (gdb) PASS: gdb.opt/inline-cmds.exp: next to second func1
> ...
> 
> The relevant bit of the test source is here in inline-cmds.c:
> ...
>     71    result = 0; /* set breakpoint 3 here */
>     72
>     73    func1 (); /* first call */
>     74    func1 (); /* second call */
>     75    marker ();
> ...
> with func1 defined as:
> ...
>     33  inline __attribute__((always_inline)) int func1(void)
>     34  {
>     35    bar ();
>     36    return x * y;
>     37  }
> ...
> 
> The corresponding insns are:
> ...
>   40050b:       movl   $0x0,0x200b1f(%rip)        # 601034 <result>
>   400515:       callq  40057b <bar>
>   40051a:       callq  40057b <bar>
>   40051f:       callq  400596 <marker>
> ...
> and the line number info is:
> ...
> Line number    Starting address    View    Stmt
>          71            0x40050b               x
>          35            0x400515               x
>          75            0x40051f               x
> ...
> 
> The line number info is missing an entry for the insn at 40051a, and that is
> causing the FAIL.  This is a gcc issue, filed as PR gcc/98780 -" Missing line
> table entry for inlined stmt at -g -O0".
> 
> [ For contrast, with clang we have an extra entry:
> ...
> Line number    Starting address    View    Stmt
>          71            0x40050b               x
>          35            0x400515               x
>          35            0x40051a
>          75            0x40051f               x
> ...
> though it appears to be missing the start-of-statement marker. ]
> 
> However, there is debug info that indicates that the insn at 40051a is not
> part of the line table entry for the insn at 400515:
> ...
> <2><1c4>: Abbrev Number: 8 (DW_TAG_inlined_subroutine)
>     <1c5>   DW_AT_abstract_origin: <0x2a2>
>     <1c9>   DW_AT_low_pc      : 0x400515
>     <1d1>   DW_AT_high_pc     : 0x5
>     <1d9>   DW_AT_call_file   : 1
>     <1da>   DW_AT_call_line   : 73
>  <2><1db>: Abbrev Number: 8 (DW_TAG_inlined_subroutine)
>     <1dc>   DW_AT_abstract_origin: <0x2a2>
>     <1e0>   DW_AT_low_pc      : 0x40051a
>     <1e8>   DW_AT_high_pc     : 0x5
>     <1f0>   DW_AT_call_file   : 1
>     <1f1>   DW_AT_call_line   : 74
> ...
> and indeed lldb manages to "next" from line 73 to line 74.
> 
> Work around the missing line table entry, by using the inline frame info to
> narrow the stepping range in prepare_one_step.
> 
> Tested on x86_64-linux.
> 
> Any comments?
> 
> Thanks,
> - Tom
> 
> [gdb/breakpoints] Workaround missing line-table entry
> 
> gdb/ChangeLog:
> 
> 2021-01-22  Tom de Vries  <tdevries@suse.de>
> 
> 	PR breakpoints/25884
> 	* infcmd.c (prepare_one_step): Using inline frame info to narrow
> 	stepping range.
> 
> gdb/testsuite/ChangeLog:
> 
> 2021-01-22  Tom de Vries  <tdevries@suse.de>
> 
> 	PR breakpoints/25884
> 	* gdb.opt/inline-cmds.exp: Remove kfail.
> 
> ---
>  gdb/infcmd.c                          | 14 ++++++++++++++
>  gdb/testsuite/gdb.opt/inline-cmds.exp | 17 +----------------
>  2 files changed, 15 insertions(+), 16 deletions(-)
> 
> diff --git a/gdb/infcmd.c b/gdb/infcmd.c
> index 6f0ed952de6..ecb3de31879 100644
> --- a/gdb/infcmd.c
> +++ b/gdb/infcmd.c
> @@ -1009,6 +1009,20 @@ prepare_one_step (thread_info *tp, struct step_command_fsm *sm)
>  				 &tp->control.step_range_start,
>  				 &tp->control.step_range_end);
>  
> +	  /* There's a problem in gcc (PR gcc/98780) that causes missing line
> +	     table entries, which results in a too large stepping range.
> +	     Use inlined_subroutine info to make the range more narrow.  */
> +	  if (inline_skipped_frames (tp) > 0)
> +	    {
> +	      symbol *sym = inline_skipped_symbol (tp);
> +	      if (SYMBOL_CLASS (sym) == LOC_BLOCK)
> +		{
> +		  const block *block = SYMBOL_BLOCK_VALUE (sym);
> +		  if (BLOCK_END (block) < tp->control.step_range_end)
> +		    tp->control.step_range_end = BLOCK_END (block);
> +		}
> +	    }
> +
>  	  tp->control.may_range_step = 1;
>  
>  	  /* If we have no line info, switch to stepi mode.  */
> diff --git a/gdb/testsuite/gdb.opt/inline-cmds.exp b/gdb/testsuite/gdb.opt/inline-cmds.exp
> index 17720c46795..981dcbb4a29 100644
> --- a/gdb/testsuite/gdb.opt/inline-cmds.exp
> +++ b/gdb/testsuite/gdb.opt/inline-cmds.exp
> @@ -222,22 +222,7 @@ gdb_breakpoint $line3
>  gdb_continue_to_breakpoint "consecutive func1"
>  
>  gdb_test "next" ".*func1 .*first call.*" "next to first func1"
> -set msg "next to second func1"
> -gdb_test_multiple "next" $msg {
> -    -re ".*func1 .*second call.*$gdb_prompt $" {
> -	pass $msg
> -    }
> -    -re ".*marker .*$gdb_prompt $" {
> -	# This assembles to two consecutive call instructions.
> -	# Both appear to be at the same line, because they're
> -	# in the body of the same inlined function.  This is
> -	# reasonable for the line table.  GDB should take the
> -	# containing block and/or function into account when
> -	# deciding how far to step.  The single line table entry
> -	# is actually two consecutive instances of the same line.
> -	kfail gdb/25884 $msg
> -    }
> -}
> +gdb_test "next" ".*func1 .*second call.*" "next to second func1"
>  
>  # It is easier when the two inlined functions are not on the same line.
>  set line4 [gdb_get_line_number "set breakpoint 4 here"]
>