Re: [PATCH] riscv: selftests: Add signal handling vector tests

[Vineet Gupta <vineetg@xxxxxxxxxxxx>]

On 4/3/24 16:50, Charlie Jenkins wrote:
> Add two tests to check vector save/restore when a signal is received
> during a vector routine. One test ensures that a value is not clobbered
> during signal handling. The other verifies that vector registers
> modified in the signal handler are properly reflected when the signal
> handling is complete.

Hmm, isn't this testing two contradictory things ?

We do want V regs to be not clobbered across a handled signal, o/w V
enabled code would just not work at all.
That implies that anything done by signal handler should just be
discarded - no ?

Am I missing something.

-Vineet

>
> Signed-off-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>
> ---
> These tests came about to highlight the bug fixed in
> https://lore.kernel.org/lkml/20240403072638.567446-1-bjorn@xxxxxxxxxx/
> and will only pass with that fix applied.
> ---
>  tools/testing/selftests/riscv/Makefile             |  2 +-
>  tools/testing/selftests/riscv/sigreturn/.gitignore |  1 +
>  tools/testing/selftests/riscv/sigreturn/Makefile   | 12 ++++
>  .../testing/selftests/riscv/sigreturn/sigreturn.c  | 82 ++++++++++++++++++++++
>  4 files changed, 96 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/riscv/Makefile b/tools/testing/selftests/riscv/Makefile
> index 4a9ff515a3a0..7ce03d832b64 100644
> --- a/tools/testing/selftests/riscv/Makefile
> +++ b/tools/testing/selftests/riscv/Makefile
> @@ -5,7 +5,7 @@
>  ARCH ?= $(shell uname -m 2>/dev/null || echo not)
>  
>  ifneq (,$(filter $(ARCH),riscv))
> -RISCV_SUBTARGETS ?= hwprobe vector mm
> +RISCV_SUBTARGETS ?= hwprobe vector mm sigreturn
>  else
>  RISCV_SUBTARGETS :=
>  endif
> diff --git a/tools/testing/selftests/riscv/sigreturn/.gitignore b/tools/testing/selftests/riscv/sigreturn/.gitignore
> new file mode 100644
> index 000000000000..35002b8ae780
> --- /dev/null
> +++ b/tools/testing/selftests/riscv/sigreturn/.gitignore
> @@ -0,0 +1 @@
> +sigreturn
> diff --git a/tools/testing/selftests/riscv/sigreturn/Makefile b/tools/testing/selftests/riscv/sigreturn/Makefile
> new file mode 100644
> index 000000000000..eb8bac9279a8
> --- /dev/null
> +++ b/tools/testing/selftests/riscv/sigreturn/Makefile
> @@ -0,0 +1,12 @@
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (C) 2021 ARM Limited
> +# Originally tools/testing/arm64/abi/Makefile
> +
> +CFLAGS += -I$(top_srcdir)/tools/include
> +
> +TEST_GEN_PROGS := sigreturn
> +
> +include ../../lib.mk
> +
> +$(OUTPUT)/sigreturn: sigreturn.c
> +	$(CC) -static -o$@ $(CFLAGS) $(LDFLAGS) $^
> diff --git a/tools/testing/selftests/riscv/sigreturn/sigreturn.c b/tools/testing/selftests/riscv/sigreturn/sigreturn.c
> new file mode 100644
> index 000000000000..62397d5934f1
> --- /dev/null
> +++ b/tools/testing/selftests/riscv/sigreturn/sigreturn.c
> @@ -0,0 +1,82 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +#include <signal.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <ucontext.h>
> +#include <linux/ptrace.h>
> +#include "../../kselftest_harness.h"
> +
> +#define RISCV_V_MAGIC		0x53465457
> +#define DEFAULT_VALUE		2
> +#define SIGNAL_HANDLER_OVERRIDE	3
> +
> +static void simple_handle(int sig_no, siginfo_t *info, void *vcontext)
> +{
> +	ucontext_t *context = vcontext;
> +
> +	context->uc_mcontext.__gregs[REG_PC] = context->uc_mcontext.__gregs[REG_PC] + 4;
> +}
> +
> +static void vector_override(int sig_no, siginfo_t *info, void *vcontext)
> +{
> +	ucontext_t *context = vcontext;
> +
> +	// vector state
> +	struct __riscv_extra_ext_header *ext;
> +	struct __riscv_v_ext_state *v_ext_state;
> +
> +	/* Find the vector context. */
> +	ext = (void *)(&context->uc_mcontext.__fpregs);
> +	if (ext->hdr.magic != RISCV_V_MAGIC) {
> +		fprintf(stderr, "bad vector magic: %x\n", ext->hdr.magic);
> +		abort();
> +	}
> +
> +	v_ext_state = (void *)((char *)(ext) + sizeof(*ext));
> +
> +	*(int *)v_ext_state->datap = SIGNAL_HANDLER_OVERRIDE;
> +
> +	context->uc_mcontext.__gregs[REG_PC] = context->uc_mcontext.__gregs[REG_PC] + 4;
> +}
> +
> +static int vector_sigreturn(int data, void (*handler)(int, siginfo_t *, void *))
> +{
> +	int after_sigreturn;
> +	struct sigaction sig_action = {
> +		.sa_sigaction = handler,
> +		.sa_flags = SA_SIGINFO
> +	};
> +
> +	sigaction(SIGSEGV, &sig_action, 0);
> +
> +	asm(".option push				\n\
> +		.option		arch, +v		\n\
> +		vsetivli	x0, 1, e32, ta, ma	\n\
> +		vmv.s.x		v0, %1			\n\
> +		# Generate SIGSEGV			\n\
> +		lw		a0, 0(x0)		\n\
> +		vmv.x.s		%0, v0			\n\
> +		.option pop" : "=r" (after_sigreturn) : "r" (data));
> +
> +	return after_sigreturn;
> +}
> +
> +TEST(vector_restore)
> +{
> +	int result;
> +
> +	result = vector_sigreturn(DEFAULT_VALUE, &simple_handle);
> +
> +	EXPECT_EQ(DEFAULT_VALUE, result);
> +}
> +
> +TEST(vector_restore_signal_handler_override)
> +{
> +	int result;
> +
> +	result = vector_sigreturn(DEFAULT_VALUE, &vector_override);
> +
> +	EXPECT_EQ(SIGNAL_HANDLER_OVERRIDE, result);
> +}
> +
> +TEST_HARNESS_MAIN
>
> ---
> base-commit: 4cece764965020c22cff7665b18a012006359095
> change-id: 20240403-vector_sigreturn_tests-8118f0ac54fa