[binutils-gdb] Implement gdbarch_stack_frame_destroyed_p for aarch64

[binutils-gdb] Implement gdbarch_stack_frame_destroyed_p for aarch64

[Tom Tromey]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=da729c5ccde6eeccae539cbe51a285bc84769b3d

commit da729c5ccde6eeccae539cbe51a285bc84769b3d
Author: Tom Tromey <tromey@adacore.com>
Date:   Mon Mar 7 14:06:09 2022 -0700

    Implement gdbarch_stack_frame_destroyed_p for aarch64
    
    The internal AdaCore testsuite has a test that checks that an
    out-of-scope watchpoint is deleted.  This fails on some aarch64
    configurations, reporting an extra stop:
    
        (gdb) continue
        Continuing.
    
        Thread 3 hit Watchpoint 2: result
    
        Old value = 64
        New value = 0
        0x0000000040021648 in pck.get_val (seed=0, off_by_one=false) at [...]/pck.adb:13
        13     end Get_Val;
    
    I believe what is happening here is that the variable is stored at:
    
        <efa>   DW_AT_location    : 2 byte block: 91 7c     (DW_OP_fbreg: -4)
    
    and the extra stop is reported just before a return, when the ldp
    instruction is executed:
    
       0x0000000040021644 <+204>:   ldp     x29, x30, [sp], #48
       0x0000000040021648 <+208>:   ret
    
    This instruction modifies the frame base calculation, and so the test
    picks up whatever memory is pointed to in the callee frame.
    
    Implementing the gdbarch hook gdbarch_stack_frame_destroyed_p fixes
    this problem.
    
    As usual with this sort of patch, it has passed internal testing, but
    I don't have a good way to try it with dejagnu.  So, I don't know
    whether some existing test covers this.  I suspect there must be one,
    but it's also worth noting that this test passes for aarch64 in some
    configurations -- I don't know what causes one to fail and another to
    succeed.

Diff:
---
 gdb/aarch64-tdep.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
index 3f3a65240c0..b714f6194b6 100644
--- a/gdb/aarch64-tdep.c
+++ b/gdb/aarch64-tdep.c
@@ -3396,6 +3396,25 @@ aarch64_cannot_store_register (struct gdbarch *gdbarch, int regnum)
 	  || regnum == AARCH64_PAUTH_CMASK_REGNUM (tdep->pauth_reg_base));
 }
 
+/* Implement the stack_frame_destroyed_p gdbarch method.  */
+
+static int
+aarch64_stack_frame_destroyed_p (struct gdbarch *gdbarch, CORE_ADDR pc)
+{
+  CORE_ADDR func_start, func_end;
+  if (!find_pc_partial_function (pc, NULL, &func_start, &func_end))
+    return 0;
+
+  enum bfd_endian byte_order_for_code = gdbarch_byte_order_for_code (gdbarch);
+  uint32_t insn = read_memory_unsigned_integer (pc, 4, byte_order_for_code);
+
+  aarch64_inst inst;
+  if (aarch64_decode_insn (insn, &inst, 1, nullptr) != 0)
+    return 0;
+
+  return streq (inst.opcode->name, "ret");
+}
+
 /* Initialize the current architecture based on INFO.  If possible,
    re-use an architecture from ARCHES, which is a list of
    architectures already created during this debugging session.
@@ -3602,6 +3621,9 @@ aarch64_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
   set_gdbarch_long_double_format (gdbarch, floatformats_ia64_quad);
   set_gdbarch_type_align (gdbarch, aarch64_type_align);
 
+  /* Detect whether PC is at a point where the stack has been destroyed.  */
+  set_gdbarch_stack_frame_destroyed_p (gdbarch, aarch64_stack_frame_destroyed_p);
+
   /* Internal <-> external register number maps.  */
   set_gdbarch_dwarf2_reg_to_regnum (gdbarch, aarch64_dwarf_reg_to_regnum);