[PATCH] gdb/record-full: disable range stepping when resuming threads

[Simon Marchi <simon.marchi@efficios.com>]

I see these failures, when running with the native-gdbserver of
native-extended-gdbserver boards:

    Running /home/smarchi/src/binutils-gdb/gdb/testsuite/gdb.reverse/finish-reverse-next.exp ...
    FAIL: gdb.reverse/finish-reverse-next.exp: reverse next 1 LEP from function body
    FAIL: gdb.reverse/finish-reverse-next.exp: reverse next 2 at b = 5, from function body
    FAIL: gdb.reverse/finish-reverse-next.exp: reverse next 1 GEP call from function body
    FAIL: gdb.reverse/finish-reverse-next.exp: reverse next 2 at b = 50 from function body

Let's use this simpler program to illustrate the problem:

    int main()
    {
      int a = 362;
      a = a * 17;
      return a;
    }

It compiles down to:

    int a = 362;
    401689:       c7 45 fc 6a 01 00 00    movl   $0x16a,-0x4(%rbp)
    a = a * 17;
    401690:       8b 55 fc                mov    -0x4(%rbp),%edx
    401693:       89 d0                   mov    %edx,%eax
    401695:       c1 e0 04                shl    $0x4,%eax
    401698:       01 d0                   add    %edx,%eax
    40169a:       89 45 fc                mov    %eax,-0x4(%rbp)
    return a;
    40169d:       8b 45 fc                mov    -0x4(%rbp),%eax

When single stepping these lines, debugging locally, while recording,
these are the recorded instructions (basically one for each instruction
shown above):

    (gdb) maintenance print record-instruction 0
    4 bytes of memory at address 0x00007fffffffdc5c changed from: 6a 01 00 00
    Register rip changed: (void (*)()) 0x40169a <main+21>
    (gdb) maintenance print record-instruction -1
    Register rax changed: 5792
    Register eflags changed: [ PF AF IF ]
    Register rip changed: (void (*)()) 0x401698 <main+19>
    (gdb) maintenance print record-instruction -2
    Register rax changed: 362
    Register eflags changed: [ PF ZF IF ]
    Register rip changed: (void (*)()) 0x401695 <main+16>
    (gdb) maintenance print record-instruction -3
    Register rax changed: 4200069
    Register rip changed: (void (*)()) 0x401693 <main+14>
    (gdb) maintenance print record-instruction -4
    Register rdx changed: 140737488346696
    Register rip changed: (void (*)()) 0x401690 <main+11>
    (gdb) maintenance print record-instruction -5
    4 bytes of memory at address 0x00007fffffffdc5c changed from: 00 00 00 00
    Register rip changed: (void (*)()) 0x401689 <main+4>
    (gdb) maintenance print record-instruction -6
    Not enough recorded history

But when debugging remotely:

    (gdb) maintenance print record-instruction 0
    Register rdx changed: 140737488346728
    Register rip changed: (void (*)()) 0x401690 <main+11>
    (gdb) maintenance print record-instruction -1
    4 bytes of memory at address 0x00007fffffffdc7c changed from: 00 00 00 00
    Register rip changed: (void (*)()) 0x401689 <main+4>
    (gdb) maintenance print record-instruction -2
    Not enough recorded history

In this list, we only have entries for the beginning of each line.  This
is because of the remote target's support for range stepping.  The
record-full layer can only record instructions when the underlying
process target reports a stop.  With range stepping, the remote target
single-steps multiple instructions at a time, so the record-full target
doesn't get to see and record them all.

Fix this by making the record-full layer disable range-stepping
before handing the resume request to the beneath layer, forcing the
remote target to report stops for each instruction.

Change-Id: Ia95ea62720bbcd0b6536a904360ffbf839eb823d
---
 gdb/record-full.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/gdb/record-full.c b/gdb/record-full.c
index 15c5b7d682ed..026c309b674c 100644
--- a/gdb/record-full.c
+++ b/gdb/record-full.c
@@ -1094,6 +1094,13 @@ record_full_target::resume (ptid_t ptid, int step, enum gdb_signal signal)
       /* Make sure the target beneath reports all signals.  */
       target_pass_signals ({});
 
+      /* Disable range-stepping, forcing the process target to report stops for
+	 all executed instructions, so we can record them all.  */
+      process_stratum_target *proc_target
+	= current_inferior ()->process_target ();
+      for (thread_info *thread : all_non_exited_threads (proc_target, ptid))
+	thread->control.may_range_step = 0;
+
       this->beneath ()->resume (ptid, step, signal);
     }
 }
-- 
2.40.0