[gdb/breakpoints] Workaround missing line-table entry

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.

gdb/ChangeLog:

2021-04-06  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:

2021-04-06  Tom de Vries  <tdevries@suse.de>

	PR breakpoints/25884
	* gdb.opt/inline-cmds.exp: Remove kfail.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 0abd3dd6df19ec466ad859c8f97a4234e1a1e373..bcd3786598f0c58d472f07042fe455e135f2e5ae 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2021-04-06  Tom de Vries  <tdevries@suse.de>
+
+       PR breakpoints/25884
+       * infcmd.c (prepare_one_step): Using inline frame info to narrow
+       stepping range.
+
 2021-04-06  Tom de Vries  <tdevries@suse.de>
 
        PR tui/27680

diff --git a/gdb/infcmd.c b/gdb/infcmd.c
index 9b0186dd391c4c3e89fbc9f5ba739b2e44782240..60f25d2468612770205705faede730772e39bc2b 100644 (file)
--- a/gdb/infcmd.c
+++ b/gdb/infcmd.c
@@ -1013,6 +1013,20 @@ 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/ChangeLog b/gdb/testsuite/ChangeLog
index f5fe029c049ab94a8a7af7f8d8497d407ae92000..c6063be383289abe22a67f4e813f056bddfb409f 100644 (file)
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2021-04-06  Tom de Vries  <tdevries@suse.de>
+
+       PR breakpoints/25884
+       * gdb.opt/inline-cmds.exp: Remove kfail.
+
 2021-04-06  Tom de Vries  <tdevries@suse.de>
 
        PR testsuite/27691

diff --git a/gdb/testsuite/gdb.opt/inline-cmds.exp b/gdb/testsuite/gdb.opt/inline-cmds.exp
index 17720c4679500f49c1eebf1f95e0929a3dbb5749..981dcbb4a29e9abc567d38b85ce5ff78ef6cb240 100644 (file)
--- 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"]