Re: [PATCH v2 5/5] gdb/aarch64: Tests for fpmr

[Luis <luis.machado.foss@gmail.com>]

There seems to be a few whitespace issues with this patch. Please check 
them with "git diff --check" or "git show --check" and it should show you.

Also, running tclint on your exp files seems to point out these:

gdb/testsuite/gdb.arch/aarch64-fpmr-core.exp:22:5: expected braced word 
or word without substitutions in argument interpreted as expr [command-args]

gdb/testsuite/gdb.arch/aarch64-fpmr-core.exp:48:1: expected braced word 
or word without substitutions in argument interpreted as expr [command-args]

gdb/testsuite/gdb.arch/aarch64-fpmr-sighandler.exp:28:1: expected braced 
word or word without substitutions in argument interpreted as expr 
[command-args]

gdb/testsuite/gdb.arch/aarch64-fpmr-sighandler.exp:51:21: expression 
with substitutions should be enclosed by braces [unbraced-expr]

gdb/testsuite/gdb.arch/aarch64-fpmr.exp:26:1: expected braced word or 
word without substitutions in argument interpreted as expr [command-args]


On 07/10/2025 13:31, Ezra.Sitorus@arm.com wrote:
> From: Ezra Sitorus <ezra.sitorus@arm.com>
> 
> Add tests for FPMR support in gdb/gdbserver. These tests check
> availability of FPMR, reading/writing to FPMR, core file generation and
> preservation under sighandler frame unwinding.
> 
> A run of the full gdb testsuite has been done on aarch64-none-linux-gnu
> without FPMR support. I have run the gdb.arch tests on Shrinkwrap with
> FPMR support.
> ---
> Changes from v1->v2:
> * Removed fpmr modification functions to make the tests easier to
>    follow.
> * Test writing to fpmr in aarch64-fpmr.exp from outside the inferior
>    program.
> * Rewrite allow_aarch64_fpmr_tests to follow allow_aarch64_sve_tests.
> 
> Ezra
> 
>   gdb/testsuite/gdb.arch/aarch64-fpmr-core.c    |  40 ++++++
>   gdb/testsuite/gdb.arch/aarch64-fpmr-core.exp  |  97 +++++++++++++++
>   .../gdb.arch/aarch64-fpmr-sighandler.c        |  55 ++++++++
>   .../gdb.arch/aarch64-fpmr-sighandler.exp      |  77 ++++++++++++
>   gdb/testsuite/gdb.arch/aarch64-fpmr.c         | 117 ++++++++++++++++++
>   gdb/testsuite/gdb.arch/aarch64-fpmr.exp       |  72 +++++++++++
>   gdb/testsuite/lib/gdb.exp                     |  66 ++++++++++
>   7 files changed, 524 insertions(+)
>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-fpmr-core.c
>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-fpmr-core.exp
>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-fpmr-sighandler.c
>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-fpmr-sighandler.exp
>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-fpmr.c
>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-fpmr.exp
> 
> diff --git a/gdb/testsuite/gdb.arch/aarch64-fpmr-core.c b/gdb/testsuite/gdb.arch/aarch64-fpmr-core.c
> new file mode 100644
> index 00000000000..785fbd42d5c
> --- /dev/null
> +++ b/gdb/testsuite/gdb.arch/aarch64-fpmr-core.c
> @@ -0,0 +1,40 @@
> +/* This file is part of GDB, the GNU debugger.
> +
> +   Copyright 2008-2025 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/>.  */
> +
> +#include <stdint.h>
> +
> +uint64_t crash_address = 0;
> +
> +void
> +set_fpmr (uint64_t value)
> +{
> +  register uint64_t x0_val asm ("x0") = value;
> +  /* msr	fpmr, x0 */
> +  __asm__ volatile (".inst	0xd51b4440" : : );
> +}
> +
> +int
> +main (void)
> +{
> +  set_fpmr (0x3fff7fc049);
> +
> +  /* Check FPMR */
> +
> +  *((uint64_t *) crash_address) = 0xDEAD; /* crash point */
> +
> +  return 1;
> +}
> diff --git a/gdb/testsuite/gdb.arch/aarch64-fpmr-core.exp b/gdb/testsuite/gdb.arch/aarch64-fpmr-core.exp
> new file mode 100644
> index 00000000000..6f8ee996d27
> --- /dev/null
> +++ b/gdb/testsuite/gdb.arch/aarch64-fpmr-core.exp
> @@ -0,0 +1,97 @@
> +# Copyright (C) 2018-2025 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 generating and reading a core file with FPMR.
> +
> +proc check_fpmr_core_file { core_filename } {
> +    # Load the core file.
> +    if [gdb_test "core $core_filename" \
> +    [multi_line \
> +	    "Core was generated by .*" \
> +	    "Program terminated with signal SIGSEGV, Segmentation fault\\." \
> +	    "#0  ${::hex} in main \\(.*\\) at .*" \
> +	    ".* \\*\\(\\(uint64_t \\*\\) crash_address\\) = 0xDEAD.*"] \
> +	    "load core file"] {
> +	untested "failed to generate core file"
> +	return -1
> +	}
> +
> +    # Check the value of FPMR in the core file.
> +    gdb_test "print/x \$fpmr" " = 0x3fff7fc049" \
> +	     "fpmr contents from core file"
> +}
> +
> +require is_aarch64_target
> +require allow_aarch64_fpmr_tests
> +
> +standard_testfile
> +if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile}] } {
> +    return -1
> +}
> +
> +set binfile [standard_output_file ${testfile}]
> +
> +if ![runto_main] {
> +    untested "could not run to main"

I don´t quite recall if we decided to not issue these untested/fail 
messages here. Looking at the overall testsuite, looks like we mostly 
just return -1.

> +    return -1
> +}
> +
> +set crash_breakpoint "crash point"
> +gdb_breakpoint [gdb_get_line_number $crash_breakpoint]
> +gdb_continue_to_breakpoint $crash_breakpoint
> +
> +gdb_test "print/x \$fpmr" " = 0x3fff7fc049" \
> +	     "fpmr contents from core file"
> +
> +gdb_test "continue" \
> +[multi_line \
> +	"Program received signal SIGSEGV, Segmentation fault\\." \
> +	"${::hex} in main \\(\\).* at .*" \
> +	".* \\*\\(\\(uint64_t \\*\\) crash_address\\) = 0xDEAD.*"] \
> +	"run to crash"
> +
> +# Generate the gcore core file.
> +set gcore_filename [standard_output_file "${testfile}.gcore"]
> +set gcore_generated [gdb_gcore_cmd "$gcore_filename" "generate gcore file"]
> +
> +# Generate a native core file.
> +set core_filename [core_find ${binfile}]
> +set core_generated [expr {$core_filename != ""}]
> +
> +# At this point we have a couple core files, the gcore one generated by GDB
> +# and the native one generated by the Linux Kernel.  Make sure GDB can read
> +# both correctly.
> +
> +if {$gcore_generated} {
> +	clean_restart
> +	gdb_load ${binfile}
> +	with_test_prefix "gcore corefile" {
> +		check_fpmr_core_file $gcore_filename
> +	}
> +} else {
> +	fail "gcore corefile not generated"
> +}
> +
> +if {$core_generated} {
> +	clean_restart
> +	gdb_load ${binfile}
> +	with_test_prefix "native corefile" {
> +		check_fpmr_core_file $core_filename
> +	}
> +} else {
> +	untested "native corefile not generated"
> +}
> diff --git a/gdb/testsuite/gdb.arch/aarch64-fpmr-sighandler.c b/gdb/testsuite/gdb.arch/aarch64-fpmr-sighandler.c
> new file mode 100644
> index 00000000000..bbdfbb0597c
> --- /dev/null
> +++ b/gdb/testsuite/gdb.arch/aarch64-fpmr-sighandler.c
> @@ -0,0 +1,55 @@
> +/* This file is part of GDB, the GNU debugger.
> +
> +   Copyright 2008-2025 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/>.  */
> +
> +#include <stdint.h>
> +#include <signal.h>
> +#include <unistd.h>
> +#include <stdlib.h>
> +
> +void
> +set_fpmr (uint64_t value)
> +{
> +  register uint64_t x0_val asm ("x0") = value;
> +  /* msr	fpmr, x0 */
> +  __asm__ volatile (".inst	0xd51b4440" : : );
> +}
> +
> +void
> +handler (int sig)
> +{
> +  set_fpmr (0xff008041);
> +  exit(0);
> +}
> +
> +int
> +main ()
> +{
> +  /* Ensure all the signals aren't blocked.  */

Nit. Make it "Ensure no signals are blocked.". Makes it clearer.

> +  sigset_t newset;
> +  sigemptyset (&newset);
> +  sigprocmask (SIG_SETMASK, &newset, NULL);
> +
> +  signal (SIGILL, handler);
> +
> +  set_fpmr (0x3fff7fc049);
> +
> +  /* 0x06000000 : Cause an illegal instruction. Value undefined as per ARM

Formatting. Two spaces after period.

And maybe s/Cause/Causes or s/Cause/Execute, depending on what you meant.

> +     Architecture Reference Manual ARMv8, Section C4.1.  */
> +  __asm __volatile (".inst 0x06000000");
> +
> +  return 0;
> +}
> diff --git a/gdb/testsuite/gdb.arch/aarch64-fpmr-sighandler.exp b/gdb/testsuite/gdb.arch/aarch64-fpmr-sighandler.exp
> new file mode 100644
> index 00000000000..a776976eb7d
> --- /dev/null
> +++ b/gdb/testsuite/gdb.arch/aarch64-fpmr-sighandler.exp
> @@ -0,0 +1,77 @@
> +# Copyright 2018-2025 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 FPMR register set is properly preserved when unwiding sighandler frames.
> +
> +require is_aarch64_target
> +require allow_aarch64_fpmr_tests
> +
> +standard_testfile
> +if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile}] } {
> +    return -1
> +}
> +
> +if ![runto_main] {
> +    return -1
> +}
> +
> +set reg_main_value "0x3fff7fc049"
> +set reg_handler_value "0xff008041"
> +
> +proc check_fpmr {value} {
> +  gdb_test "print /x \$fpmr" \
> +    ".* = {?$value}?" \
> +    "check register \$fpmr has value $value"
> +}
> +
> +# Run until end of signal handler
> +
> +gdb_test "continue" \
> +    "Continuing.*Program received signal SIGILL.*" \
> +    "continue until signal"
> +
> +gdb_breakpoint [gdb_get_line_number "exit(0)"]
> +gdb_continue_to_breakpoint "exit" ".*exit.*"
> +
> +set handlerframe [get_current_frame_number]
> +set mainframe [expr $handlerframe + 2]
> +
> +# Check register values
> +
> +with_test_prefix "handler frame 1st" {
> +  check_fpmr $reg_handler_value
> +}
> +
> +# Switch to the frame for main(), and check register values
> +
> +gdb_test "frame $mainframe" \
> +      "#$mainframe.*main ().*" \
> +      "set to main frame"
> +
> +with_test_prefix "main frame" {
> +  check_fpmr $reg_main_value
> +}
> +
> +# Switch back to the signal handler frame, and check register values
> +
> +gdb_test "frame $handlerframe" \
> +      "#$handlerframe.*handler \\\(sig=4\\\).*" \
> +      "set to signal handler frame"
> +
> +with_test_prefix "handler frame 2nd" {
> +  check_fpmr $reg_handler_value
> +}
> diff --git a/gdb/testsuite/gdb.arch/aarch64-fpmr.c b/gdb/testsuite/gdb.arch/aarch64-fpmr.c
> new file mode 100644
> index 00000000000..f4bf889c3a8
> --- /dev/null
> +++ b/gdb/testsuite/gdb.arch/aarch64-fpmr.c
> @@ -0,0 +1,117 @@
> +/* This file is part of GDB, the GNU debugger.
> +
> +   Copyright 2008-2025 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/>.  */
> +
> +#include <stdint.h>
> +
> +enum FPM_FORMAT
> +{
> +  E5M2,
> +  E4M3,
> +};
> +
> +enum FPM_OVERFLOW
> +{
> +  INFNAN,
> +  SATURATE,
> +};
> +
> +void
> +set_fpmr (uint64_t value)
> +{
> +  register uint64_t x0_val asm ("x0") = value;
> +  __asm__ volatile (".inst	0xd51b4440" : : );

Add the following here as well?

/* msr	fpmr, x0 */

> +}
> +
> +uint64_t
> +modify_src1_fmt (uint64_t fpmr, uint64_t fmt)
> +{
> +  return (fpmr & ~(0x7)) | (fmt & 0x7);
> +}
> +
> +uint64_t
> +modify_src2_fmt (uint64_t fpmr, uint64_t fmt)
> +{
> +  return (fpmr & ~((0x7) << 3)) | ((fmt & 0x7) << 3);
> +}
> +
> +uint64_t
> +modify_dst_fmt (uint64_t fpmr, uint64_t fmt)
> +{
> +  return (fpmr & ~((0x7) << 6)) | ((fmt & 0x7) << 6);
> +}
> +
> +uint64_t
> +modify_osm (uint64_t fpmr, uint64_t overflow)
> +{
> +  return (fpmr & ~((0x1) << 14)) | ((overflow & 0x1) << 14);
> +}
> +
> +uint64_t
> +modify_osc (uint64_t fpmr, uint64_t overflow)
> +{
> +  return (fpmr & ~((0x1) << 15)) | ((overflow & 0x1) << 15);
> +}
> +
> +uint64_t
> +modify_lscale (uint64_t fpmr, uint64_t scale)
> +{
> +  return (fpmr & ~((0x7f) << 16)) | ((scale & 0x7f) << 16);
> +}
> +
> +uint64_t
> +modify_nscale (uint64_t fpmr, uint64_t scale)
> +{
> +  return (fpmr & ~((0xff) << 24)) | ((scale & 0xff) << 24);
> +}
> +
> +uint64_t
> +modify_lscale2 (uint64_t fpmr, uint64_t scale)
> +{
> +  return (fpmr & ~((uint64_t)(0x3f) << 32)) | ((uint64_t)(scale & 0x3f) << 32);
> +}
> +
> +int
> +main (void)
> +{
> +  uint64_t fpmr = 0;
> +
> +  fpmr = modify_src1_fmt (fpmr, E4M3);
> +  set_fpmr (fpmr); /* MODIFY SRC1 */
> +
> +  fpmr = modify_src2_fmt (fpmr, E4M3);
> +  set_fpmr (fpmr); /* MODIFY SRC2 */
> +
> +  fpmr = modify_dst_fmt (fpmr, E4M3);
> +  set_fpmr (fpmr); /* MODIFY DST */
> +
> +  fpmr = modify_osm (fpmr, SATURATE);
> +  set_fpmr (fpmr); /* MODIFY OSM */
> +
> +  fpmr = modify_osc (fpmr, SATURATE);
> +  set_fpmr (fpmr); /* MODIFY OSC */
> +
> +  fpmr = modify_lscale (fpmr, -1);
> +  set_fpmr (fpmr); /* MODIFY LSCALE */
> +
> +  fpmr = modify_nscale (fpmr, -1);
> +  set_fpmr (fpmr); /* MODIFY NSCALE */
> +
> +  fpmr = modify_lscale2 (fpmr, -1);
> +  set_fpmr (fpmr); /* MODIFY LSCALE2 */
> +
> +  return 1;
> +}
> diff --git a/gdb/testsuite/gdb.arch/aarch64-fpmr.exp b/gdb/testsuite/gdb.arch/aarch64-fpmr.exp
> new file mode 100644
> index 00000000000..947d47e981d
> --- /dev/null
> +++ b/gdb/testsuite/gdb.arch/aarch64-fpmr.exp
> @@ -0,0 +1,72 @@
> +# Copyright 2023-2025 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/>.  */
> +
> +# Exercise reading/writing FPMR when it is present.
> +
> +require is_aarch64_target
> +require allow_aarch64_fpmr_tests
> +
> +standard_testfile
> +if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile}] } {
> +    return -1
> +}
> +
> +if ![runto_main] {
> +    untested "could not run to main"

As mentioned above, we should just drop this and return -1 here.

> +    return -1
> +}
> +
> +gdb_test_multiple "info register \$fpmr" "Test FPMR SRC1 E5M2" {
> +    -re ".*\r\n.*\[ F8S1=E5M2 F8S2=E5M2 F8D=E5M2 OSM=Inf OSC=Inf/NaN LSCALE=0 NSCALE=0 LSCALE2=0 \]" {
> +        pass "FPMR SRC1 matches E5M2"
> +    }
> +}
> +
> +set breakpoints [list "MODIFY SRC1" "MODIFY SRC2" "MODIFY DST" "MODIFY OSM" "MODIFY OSC" "MODIFY LSCALE" "MODIFY NSCALE" "MODIFY LSCALE2"]

Nit. For simplicity, you might want to drop the "MODIFY" from all of 
these and just use the field name, as all of them modify something. And 
then update the source file accordingly.

> +set reg_values [list \
> +    ".*\r\n.*\[ F8S1=E4M3 F8S2=E5M2 F8D=E5M2 OSM=Inf OSC=Inf/NaN LSCALE=0 NSCALE=0 LSCALE2=0 \]" \
> +    ".*\r\n.*\[ F8S1=E4M3 F8S2=E4M3 F8D=E5M2 OSM=Inf OSC=Inf/NaN LSCALE=0 NSCALE=0 LSCALE2=0 \]" \
> +    ".*\r\n.*\[ F8S1=E4M3 F8S2=E4M3 F8D=E4M3 OSM=Inf OSC=Inf/NaN LSCALE=0 NSCALE=0 LSCALE2=0 \]" \
> +    ".*\r\n.*\[ F8S1=E4M3 F8S2=E4M3 F8D=E4M3 OSM=MaxNormal OSC=Inf/NaN LSCALE=0 NSCALE=0 LSCALE2=0 \]" \
> +    ".*\r\n.*\[ F8S1=E4M3 F8S2=E4M3 F8D=E4M3 OSM=MaxNormal OSC=MaxNormal LSCALE=0 NSCALE=0 LSCALE2=0 \]" \
> +    ".*\r\n.*\[ F8S1=E4M3 F8S2=E4M3 F8D=E4M3 OSM=MaxNormal OSC=MaxNormal LSCALE=127 NSCALE=0 LSCALE2=0 \]" \
> +    ".*\r\n.*\[ F8S1=E4M3 F8S2=E4M3 F8D=E4M3 OSM=MaxNormal OSC=MaxNormal LSCALE=127 NSCALE=255 LSCALE2=0 \]" \
> +    ".*\r\n.*\[ F8S1=E4M3 F8S2=E4M3 F8D=E4M3 OSM=MaxNormal OSC=MaxNormal LSCALE=127 NSCALE=255 LSCALE2=63 \]" \
> +]
> +set pass_messages [list "FPMR SRC1 matches E4M3" "FPMR SRC2 matches E4M3" "FPMR DST matches E4M3" "FPMR OSM matches MaxNormal" "FPMR OSC matches MaxNormal" "FPMR LSCALE matches" "FPMR NSCALE matches" "FPMR LSCALE2 matches"]
> +
> +for {set i 0} {$i < 8} {incr i} {
> +    set bp [lindex $breakpoints $i]
> +    gdb_breakpoint [gdb_get_line_number $bp]
> +    gdb_continue_to_breakpoint $bp
> +
> +    gdb_test_multiple "info register \$fpmr" "" {
> +        -re [lindex $reg_values $i] {
> +            pass [lindex $pass_messages $i]
> +        }
> +    }
> +}
> +
> +gdb_test_multiple "set \$fpmr=0x0" "" {
> +    -re ".*\r\n.*\[ F8S1=E5M2 F8S2=E5M2 F8D=E5M2 OSM=Inf OSC=Inf/NaN LSCALE=0 NSCALE=0 LSCALE2=0 \]" {
> +        pass "Reset FPMR to 0 from GDB"
> +    }
> +}
> +
> +gdb_test_multiple "set \$fpmr=0x3f007f4008" "" {
> +    -re ".*\r\n.*\[ F8S1=E5M2 F8S2=E4M3 F8D=E5M2 OSM=MaxNormal OSC=Inf/NaN LSCALE=127 NSCALE=0 LSCALE2=63 \]" {
> +        pass "Write to FPMR from GDB"
> +    }
> +}
> diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
> index 930462f63fa..0d0369511bb 100644
> --- a/gdb/testsuite/lib/gdb.exp
> +++ b/gdb/testsuite/lib/gdb.exp
> @@ -5201,6 +5201,72 @@ proc aarch64_supports_sme_svl { length } {
>       return 1
>   }
>   
> +# Run a test on the target to see if it supports AArch64 FPMR hardware.

Nit. s/AArch64 FPMR hardware/the AArch64 FPMR feature.

> +# Return 1 if so, 0 if it does not.  Note this causes a restart of GDB.
> +
> +gdb_caching_proc allow_aarch64_fpmr_tests {} {
> +    global srcdir subdir gdb_prompt inferior_exited_re
> +
> +    set me "allow_aarch64_fpmr_tests"
> +
> +    if { ![is_aarch64_target]} {
> +	return 0
> +    }
> +
> +    set compile_flags "{additional_flags=-march=armv8-a}"
> +
> +    # Compile a test program that writes to FPMR.

Here it says "writes"...

> +    set src {
> +	int main() {
> +	    asm volatile ("msr x0, fpmr");
> +	    return 0;
> +	}
> +    }
> +    if {![gdb_simple_compile $me $src executable $compile_flags]} {
> +	# Try again, but with a raw hex instruction so we don't rely on
> +	# assembler support for FPMR.
> +
> +	set compile_flags "{additional_flags=-march=armv8-a}"
> +
> +	# Compile a test program reading FPMR.

... but here it says reading. Which one is it?
> +	set src {
> +	    int main() {
> +		asm volatile (".word 0xD51B4440");
> +		return 0;
> +	    }
> +	}
> +
> +	if {![gdb_simple_compile $me $src executable $compile_flags]} {
> +	    return 0
> +	}
> +    }
> +
> +    # Compilation succeeded so now run it via gdb.
> +    clean_restart
> +    gdb_load $obj
> +    gdb_run_cmd
> +
> +    gdb_expect {
> +        -re ".*Illegal instruction.*${gdb_prompt} $" {
> +            verbose -log "\n$me fpmr support not detected"
> +            set allow_fpmr_tests 0
> +        }
> +        -re ".*$inferior_exited_re normally.*${gdb_prompt} $" {
> +            verbose -log "\n$me: fpmr support detected"
> +            set allow_fpmr_tests 1
> +        }
> +        default {
> +          warning "\n$me: default case taken"
> +            set allow_fpmr_tests 0
> +        }
> +    }
> +    gdb_exit
> +    remote_file build delete $obj
> +
> +    verbose "$me:  returning $allow_fpmr_tests" 2
> +    return $allow_fpmr_tests
> +}
> +
>   # 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.