Re: [PATCH v 2/2] selftests: riscv: Add test for the Vector ptrace interface

[Charlie Jenkins <charlie@rivosinc.com>]

On Thu, Oct 02, 2025 at 12:53:13AM -0500, Andy Chiu wrote:
> Hi Yong-Xuan,
> 
> I found some issues which deserve a re-roll:
> 
> On Wed, Oct 1, 2025 at 6:15 AM Yong-Xuan Wang <yongxuan.wang@sifive.com> wrote:
> >
> > Add a test case that does some basic verification of the Vector ptrace
> > interface. This forks a child process then using ptrace to inspect and
> > manipulate the v31 register of the child.
> >
> > Signed-off-by: Yong-Xuan Wang <yongxuan.wang@sifive.com>
> > ---
> >  tools/testing/selftests/riscv/vector/Makefile |   5 +-
> >  .../selftests/riscv/vector/vstate_ptrace.c    | 132 ++++++++++++++++++
> >  2 files changed, 136 insertions(+), 1 deletion(-)
> >  create mode 100644 tools/testing/selftests/riscv/vector/vstate_ptrace.c
> >
> > diff --git a/tools/testing/selftests/riscv/vector/Makefile b/tools/testing/selftests/riscv/vector/Makefile
> > index 6f7497f4e7b3..45f25e9dd264 100644
> > --- a/tools/testing/selftests/riscv/vector/Makefile
> > +++ b/tools/testing/selftests/riscv/vector/Makefile
> > @@ -2,7 +2,7 @@
> >  # Copyright (C) 2021 ARM Limited
> >  # Originally tools/testing/arm64/abi/Makefile
> >
> > -TEST_GEN_PROGS := v_initval vstate_prctl
> > +TEST_GEN_PROGS := v_initval vstate_prctl vsate_ptrace
> 
> Please s/vsate_ptrace/vstate_ptrace
> 
> Otherwise we will not get the program compiled
> 
> >  TEST_GEN_PROGS_EXTENDED := vstate_exec_nolibc v_exec_initval_nolibc
> >
> >  include ../../lib.mk
> > @@ -26,3 +26,6 @@ $(OUTPUT)/v_initval: v_initval.c $(OUTPUT)/sys_hwprobe.o $(OUTPUT)/v_helpers.o
> >  $(OUTPUT)/v_exec_initval_nolibc: v_exec_initval_nolibc.c
> >         $(CC) -nostdlib -static -include ../../../../include/nolibc/nolibc.h \
> >                 -Wall $(CFLAGS) $(LDFLAGS) $^ -o $@ -lgcc
> > +
> > +$(OUTPUT)/vstate_ptrace: vstate_ptrace.c $(OUTPUT)/sys_hwprobe.o $(OUTPUT)/v_helpers.o
> > +       $(CC) -static -o$@ $(CFLAGS) $(LDFLAGS) $^
> > diff --git a/tools/testing/selftests/riscv/vector/vstate_ptrace.c b/tools/testing/selftests/riscv/vector/vstate_ptrace.c
> > new file mode 100644
> > index 000000000000..8a7bcf318e59
> > --- /dev/null
> > +++ b/tools/testing/selftests/riscv/vector/vstate_ptrace.c
> > @@ -0,0 +1,132 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +#include <stdio.h>
> > +#include <stdlib.h>
> > +#include <asm/ptrace.h>
> > +#include <linux/elf.h>
> > +#include <sys/ptrace.h>
> > +#include <sys/uio.h>
> > +#include <sys/wait.h>
> > +#include "../../kselftest.h"
> > +#include "v_helpers.h"
> > +
> > +int parent_set_val, child_set_val;
> > +
> > +static long do_ptrace(enum __ptrace_request op, pid_t pid, long type, size_t size, void *data)
> > +{
> > +       struct iovec v_iovec = {
> > +               .iov_len = size,
> > +               .iov_base = data
> > +       };
> > +
> > +       return ptrace(op, pid, type, &v_iovec);
> > +}
> > +
> > +static int do_child(void)
> > +{
> > +       int out;
> > +
> > +       if (ptrace(PTRACE_TRACEME, -1, NULL, NULL)) {
> > +               ksft_perror("PTRACE_TRACEME failed\n");
> > +               return EXIT_FAILURE;
> > +       }
> > +
> > +       asm volatile (".option push\n\t"
> > +               ".option        arch, +v\n\t"
> 
> As mentioned before, please use ".option arch, +v,-c\n\t" or ".option
> norvc\n\t" and +=4 when advancing the pc

arch -c should be avoided, there are cases when it does not always avoid
using all compressed instructions. norvc should always do the right
thing though. There is discussion at [1] about deprecating it (along with
all variants of -ext).

[1] https://inbox.sourceware.org/binutils/7ecdc846-0822-4666-957f-ff818786fb44@iscas.ac.cn/T/#t

- Charlie

> 
> > +               "vsetivli       x0, 1, e32, m1, ta, ma\n\t"
> > +               "vmv.s.x        v31, %[in]\n\t"
> > +               "ebreak\n\t"
> > +               "vmv.x.s        %[out], v31\n\t"
> > +               ".option pop\n\t"
> > +               : [out] "=r" (out)
> > +               : [in] "r" (child_set_val));
> > +
> > +       if (out != parent_set_val)
> > +               return EXIT_FAILURE;
> > +
> > +       return EXIT_SUCCESS;
> > +}
> > +
> > +static void do_parent(pid_t child)
> > +{
> > +       int status;
> > +       void *data = NULL;
> > +
> > +       /* Attach to the child */
> > +       while (waitpid(child, &status, 0)) {
> > +               if (WIFEXITED(status)) {
> > +                       ksft_test_result(WEXITSTATUS(status) == 0, "SETREGSET vector\n");
> > +                       goto out;
> > +               } else if (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGTRAP)) {
> > +                       size_t size, t;
> 
> unused variable t
> 
> > +                       void *data, *v31;
> > +                       struct __riscv_v_regset_state *v_regset_hdr;
> > +                       struct user_regs_struct *gpreg;
> > +
> > +                       size = sizeof(*v_regset_hdr);
> > +                       data = malloc(size);
> > +                       if (!data)
> > +                               goto out;
> > +                       v_regset_hdr = (struct __riscv_v_regset_state *)data;
> > +
> > +                       if (do_ptrace(PTRACE_GETREGSET, child, NT_RISCV_VECTOR, size, data))
> > +                               goto out;
> > +
> > +                       ksft_print_msg("vlenb %ld\n", v_regset_hdr->vlenb);
> > +                       data = realloc(data, size + v_regset_hdr->vlenb * 32);
> 
> realloc may give a new pointer so v_regset_hdr has to be updated here
> before the next use
> 
> > +                       if (!data)
> > +                               goto out;
> > +                       v31 = (void *)(data + size + v_regset_hdr->vlenb * 31);
> > +                       size += v_regset_hdr->vlenb * 32;
> > +
> > +                       if (do_ptrace(PTRACE_GETREGSET, child, NT_RISCV_VECTOR, size, data))
> > +                               goto out;
> > +
> > +                       ksft_test_result(*(int *)v31 == child_set_val, "GETREGSET vector\n");
> > +
> > +                       *(int *)v31 = parent_set_val;
> > +                       if (do_ptrace(PTRACE_SETREGSET, child, NT_RISCV_VECTOR, size, data))
> > +                               goto out;
> > +
> > +                       /* move the pc forward */
> > +                       size = sizeof(*gpreg);
> > +                       data = realloc(data, size);
> > +                       gpreg = (struct user_regs_struct *)data;
> > +
> > +                       if (do_ptrace(PTRACE_GETREGSET, child, NT_PRSTATUS, size, data))
> > +                               goto out;
> > +
> > +                       gpreg->pc += 2;
> > +                       if (do_ptrace(PTRACE_SETREGSET, child, NT_PRSTATUS, size, data))
> > +                               goto out;
> > +               }
> > +
> > +               ptrace(PTRACE_CONT, child, NULL, NULL);
> > +       }
> > +
> > +out:
> > +       free(data);
> > +}
> > +
> > +int main(void)
> > +{
> > +       pid_t child;
> > +
> > +       ksft_set_plan(2);
> > +       if (!is_vector_supported() && !is_xtheadvector_supported())
> > +               ksft_exit_skip("Vector not supported\n");
> > +
> > +       srandom(getpid());
> > +       parent_set_val = rand();
> > +       child_set_val = rand();
> > +
> > +       child = fork();
> > +       if (child < 0)
> > +               ksft_exit_fail_msg("Fork failed %d\n", child);
> > +
> > +       if (!child)
> > +               return do_child();
> > +
> > +       do_parent(child);
> > +
> > +       ksft_finished();
> > +}
> > --
> > 2.43.0
> >
> 
> Thanks,
> Andy