[v4,1/3] gdb/aarch64: Disable displaced single-step for MOPS instructions

diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
index 8d0553f3d7cd..05ecd421cd0e 100644
--- a/gdb/aarch64-tdep.c
+++ b/gdb/aarch64-tdep.c
@@ -3808,10 +3808,12 @@  aarch64_displaced_step_copy_insn (struct gdbarch *gdbarch,
   if (aarch64_decode_insn (insn, &inst, 1, NULL) != 0)
     return NULL;
 
-  /* Look for a Load Exclusive instruction which begins the sequence.  */
-  if (inst.opcode->iclass == ldstexcl && bit (insn, 22))
+  /* Look for a Load Exclusive instruction which begins the sequence,
+     or for a MOPS instruction.  */
+  if ((inst.opcode->iclass == ldstexcl && bit (insn, 22))
+      || AARCH64_CPU_HAS_FEATURE (*inst.opcode->avariant, MOPS))
     {
-      /* We can't displaced step atomic sequences.  */
+      /* We can't displaced step atomic sequences nor MOPS instructions.  */
       return NULL;
     }
 
diff --git a/gdb/testsuite/gdb.arch/aarch64-mops-single-step.c b/gdb/testsuite/gdb.arch/aarch64-mops-single-step.c
new file mode 100644
index 000000000000..4a27867d4b57
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/aarch64-mops-single-step.c
@@ -0,0 +1,73 @@ 
+/* This file is part of GDB, the GNU debugger.
+
+   Copyright 2024 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#define TEST_STRING "Just a test string."
+#define BUF_SIZE sizeof(TEST_STRING)
+
+int
+main (void)
+{
+  char source[BUF_SIZE] = TEST_STRING;
+  char dest[BUF_SIZE];
+  char *p, *q;
+  long size, zero;
+
+  /* Note: The prfm instruction in the asm statements below is there just
+     to allow the testcase to recognize when the PC is at the instruction
+     right after the MOPS sequence.  */
+
+  p = dest;
+  size = sizeof (dest);
+  zero = 0;
+  /* Break memset.  */
+  /* memset implemented in MOPS instructions.  */
+  __asm__ volatile ("setp [%0]!, %1!, %2\n\t"
+		    "setm [%0]!, %1!, %2\n\t"
+		    "sete [%0]!, %1!, %2\n\t"
+		    "prfm pldl3keep, [%0, #0]\n\t"
+		    : "+&r"(p), "+&r"(size)
+		    : "r"(zero)
+		    : "memory");
+
+  p = dest;
+  q = source;
+  size = sizeof (dest);
+  /* Break memcpy.  */
+  /* memcpy implemented in MOPS instructions.  */
+  __asm__ volatile ("cpyfp [%0]!, [%1]!, %2!\n\t"
+		    "cpyfm [%0]!, [%1]!, %2!\n\t"
+		    "cpyfe [%0]!, [%1]!, %2!\n\t"
+		    "prfm pldl3keep, [%0, #0]\n\t"
+		    : "+&r" (p), "+&r" (q), "+&r" (size)
+		    :
+		    : "memory");
+
+  p = dest;
+  q = source;
+  size = sizeof (dest);
+  /* Break memmove.  */
+  /* memmove implemented in MOPS instructions.  */
+  __asm__ volatile ("cpyp [%0]!, [%1]!, %2!\n\t"
+		    "cpym [%0]!, [%1]!, %2!\n\t"
+		    "cpye [%0]!, [%1]!, %2!\n\t"
+		    "prfm pldl3keep, [%0, #0]\n\t"
+		    : "+&r" (p), "+&r" (q), "+&r" (size)
+		    :
+		    : "memory");
+
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.arch/aarch64-mops-single-step.exp b/gdb/testsuite/gdb.arch/aarch64-mops-single-step.exp
new file mode 100644
index 000000000000..2cb5fdcca36b
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/aarch64-mops-single-step.exp
@@ -0,0 +1,98 @@ 
+# Copyright 2024 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+# This file is part of the GDB testsuite.
+
+# Test single stepping through MOPS (memory operations) instruction sequences.
+
+require allow_aarch64_mops_tests
+
+standard_testfile
+if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile} \
+	  [list debug additional_flags=-march=armv9.3-a]] } {
+    return -1
+}
+
+# If the inferior is rescheduled to another CPU while a main or epilogue
+# instruction is executed, the OS resets the inferior back to the prologue
+# instruction, so we need to allow for that possibility.
+proc step_through_sequence { prefix } {
+    set count 0
+
+    while { [is_at_instruction ${prefix}p] == 1 && $count < 50 } {
+	incr count
+
+	# The stepi output isn't useful to detect whether we stepped over
+	# the instruction.
+	gdb_test "stepi" "\[^\r\n\]+" "step over ${prefix}p"
+	if { [is_at_instruction ${prefix}m] == 1 } {
+	    pass "stepped over ${prefix}p"
+	} else {
+	    fail "stepped over ${prefix}e"
+	    return 0
+	}
+
+	gdb_test "stepi" "\[^\r\n\]+" "step over ${prefix}m"
+	if { [is_at_instruction ${prefix}e] == 1 } {
+	    pass "stepped over ${prefix}m"
+	} elseif { [is_at_instruction ${prefix}p] == 1 } {
+	    # The inferior was rescheduled to another CPU.
+	    pass "${prefix}m: reset back to prologue"
+	    continue
+	} else {
+	    fail "stepped over ${prefix}m"
+	    return 0
+	}
+
+	gdb_test "stepi" "\[^\r\n\]+" "step over ${prefix}e"
+	if { [is_at_instruction prfm] == 1 } {
+	    pass "stepped over ${prefix}e"
+	    return 1
+	} elseif { [is_at_instruction ${prefix}p] == 1 } {
+	    # The inferior was rescheduled to another CPU.
+	    pass "${prefix}e: reset back to prologue"
+	    continue
+	}
+    }
+
+    fail "step through $prefix sequence"
+    return 0
+}
+
+if ![runto_main] {
+    return -1
+}
+
+gdb_breakpoint ${srcfile}:[gdb_get_line_number "Break memset"]
+gdb_breakpoint ${srcfile}:[gdb_get_line_number "Break memcpy"]
+gdb_breakpoint ${srcfile}:[gdb_get_line_number "Break memmove"]
+
+gdb_continue_to_breakpoint "memset breakpoint"
+
+if { [arrive_at_instruction setp] } {
+    step_through_sequence set
+}
+
+gdb_continue_to_breakpoint "memcpy breakpoint"
+
+if { [arrive_at_instruction cpyfp] } {
+    step_through_sequence cpyf
+}
+
+gdb_continue_to_breakpoint "memmove breakpoint"
+
+if { [arrive_at_instruction cpyp] } {
+    step_through_sequence cpy
+}
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index 55f6ab1fd8b9..762cf1cd5cf0 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -848,6 +848,44 @@  proc gdb_continue_to_breakpoint {name {location_pattern .*}} {
     }]
 }
 
+# Check whether GDB is stopped at the given instruction.
+# INSTRUCTION should be just its mnemonic, without any arguments.
+
+proc is_at_instruction { instruction } {
+    global gdb_prompt hex
+
+    set test "pc points to $instruction"
+    gdb_test_multiple {x/i $pc} $test {
+	-re -wrap "=> $hex \[^\r\n\]+:\t$instruction\t\[^\r\n\]+" {
+	    return 1
+	}
+	-re "\r\n$gdb_prompt $" {
+	    return 0
+	}
+    }
+
+    return 0
+}
+
+# Single-steps GDB until it arrives at the given instruction.
+# INSTRUCTION should be just its mnemonic, without any arguments.
+
+proc arrive_at_instruction { instruction } {
+    set count 0
+
+    while { [is_at_instruction $instruction] != 1 } {
+	gdb_test -nopass "stepi" "\[^\r\n\]+" \
+	    "stepi #$count to reach $instruction"
+	incr count
+
+	if { $count > 50 } {
+	    fail "didn't reach $instruction"
+	    return 0
+	}
+    }
+
+    return 1
+}
 
 # gdb_internal_error_resync:
 #
@@ -4497,6 +4535,67 @@  proc aarch64_supports_sme_svl { length } {
     return 1
 }
 
+# Run a test on the target to see if it supports AArch64 MOPS (Memory
+# Operations) extensions.  Return 1 if so, 0 if it does not.  Note this
+# causes a restart of GDB.
+
+gdb_caching_proc allow_aarch64_mops_tests {} {
+    global srcdir subdir gdb_prompt inferior_exited_re
+
+    set me "allow_aarch64_mops_tests"
+
+    if { ![is_aarch64_target]} {
+	return 0
+    }
+
+    # ARMv9.3-A contains the MOPS extension.  The test program doesn't use it,
+    # but take the opportunity to check whether the toolchain knows about MOPS.
+    set compile_flags "{additional_flags=-march=armv9.3-a}"
+
+    # Compile a program that tests the MOPS feature.
+    set src {
+	#include <stdbool.h>
+	#include <sys/auxv.h>
+
+	#ifndef HWCAP2_MOPS
+	#define HWCAP2_MOPS (1UL << 43)
+	#endif
+
+	int main() {
+	    bool mops_supported = getauxval (AT_HWCAP2) & HWCAP2_MOPS;
+
+	    return !mops_supported;
+	}
+    }
+
+    if {![gdb_simple_compile $me $src executable $compile_flags]} {
+	return 0
+    }
+
+    # Compilation succeeded so now run it via gdb.
+    clean_restart $obj
+    gdb_run_cmd
+    gdb_expect {
+	-re ".*$inferior_exited_re with code 01.*${gdb_prompt} $" {
+	    verbose -log "\n$me mops support not detected"
+	    set allow_mops_tests 0
+	}
+	-re ".*$inferior_exited_re normally.*${gdb_prompt} $" {
+	    verbose -log "\n$me: mops support detected"
+	    set allow_mops_tests 1
+	}
+	default {
+	  warning "\n$me: default case taken"
+	    set allow_mops_tests 0
+	}
+    }
+    gdb_exit
+    remote_file build delete $obj
+
+    verbose "$me:  returning $allow_mops_tests" 2
+    return $allow_mops_tests
+}
+
 # A helper that compiles a test case to see if __int128 is supported.
 proc gdb_int128_helper {lang} {
     return [gdb_can_simple_compile "i128-for-$lang" {