[binutils-gdb] [gdb/tdep] Fix reverse execution of LDR(immediate) T4

[Tom de Vries <vries@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=7e4208a3f5d60f43b4a8f02e583fa950b599cd00

commit 7e4208a3f5d60f43b4a8f02e583fa950b599cd00
Author: Tom de Vries <tdevries@suse.de>
Date:   Tue Feb 13 09:10:54 2024 +0100

    [gdb/tdep] Fix reverse execution of LDR(immediate) T4
    
    When running test-case gdb.reverse/func-map-to-same-line.exp on arm-linux with
    target board unix/-mthumb, we run into:
    ...
    (gdb) reverse-step
    func2 () at func-map-to-same-line.c:26
    26      {
    (gdb) FAIL: gdb.reverse/func-map-to-same-line.exp: \
      column_info_flag=column-info: step-test: reverse-step into func2
    ...
    
    The FAIL is caused by incorrect recording of this insn:
    ...
    4f6:   f85d 7b04       ldr.w   r7, [sp], #4
    ...
    
    The insn updates the sp, but we don't record this:
    ...
    $ gdb -q -batch func-map-to-same-line \
      -ex "b *func2+8" \
      -ex run \
      -ex record \
      -ex "set debug record 2" \
      -ex stepi
    Breakpoint 1 at 0x4f6: file func-map-to-same-line.c, line 27.
    
    Breakpoint 1, 0xaaaaa4f6 in func2 () at func-map-to-same-line.c:27
    27      } /* END FUNC2 */
    Process record: arm_process_record addr = 0xaaaaa4f6
    Process record: add register num = 15 to record list.
    Process record: record_full_arch_list_add 0xabc6c460.
    Process record: add register num = 7 to record list.
    Process record: record_full_arch_list_add 0xabc3b868.
    Process record: add register num = 25 to record list.
    ...
    [ Note that sp is r13, and we see here only r15 (pc), r7, and r25 (ps). ]
    
    The problem is that the specific insn, an LDR(immediate) T4, is not handled in
    thumb2_record_ld_word.
    
    Fix this by detecting the insn in thumb2_record_ld_word, and recording the
    updated base register.
    
    Tested on arm-linux.
    
    Reported-By: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
    Approved-By: Luis Machado <luis.machado@arm.com>
    
    PR tdep/31278
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31278

Diff:
---
 gdb/arm-tdep.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
index 861d50a6a3b..081e934cf86 100644
--- a/gdb/arm-tdep.c
+++ b/gdb/arm-tdep.c
@@ -14184,6 +14184,14 @@ thumb2_record_ld_word (arm_insn_decode_record *thumb2_insn_r)
   record_buf[1] = ARM_PS_REGNUM;
   thumb2_insn_r->reg_rec_count = 2;
 
+  if ((thumb2_insn_r->arm_insn & 0xfff00900) == 0xf8500900)
+    {
+      /* Detected LDR(immediate), T4, with write-back bit set.  Record Rn
+	 update.  */
+      record_buf[2] = bits (thumb2_insn_r->arm_insn, 16, 19);
+      thumb2_insn_r->reg_rec_count++;
+    }
+
   REG_ALLOC (thumb2_insn_r->arm_regs, thumb2_insn_r->reg_rec_count,
 	    record_buf);
   return ARM_RECORD_SUCCESS;