2023-05-22 14:48:31

by Mark Brown

Subject: [PATCH v2] kselftest/arm64: Add a smoke test for ptracing hardware break/watch points

There was a report that the hardware breakpoints and watch points weren't
reporting the debug architecture version as expected, they were reporting
a version of 0 which is not defined in the architecture. This happens
when running in a KVM guest if the host has a debug architecture version
not supported by KVM, it in turn confuses GDB which rejects any debug
architecture version it does not know about.

Add a test that covers that situation and while we're at it reports the
debug architecture version and number of slots available to aid with
figuring out problems that may arise.

Signed-off-by: Mark Brown <[email protected]>
---
Changes in v2:
- Rebase onto v6.4-rc3.
- Link to v1: https://lore.kernel.org/r/[email protected]
---
tools/testing/selftests/arm64/abi/ptrace.c | 32 +++++++++++++++++++++++++++++-
1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/arm64/abi/ptrace.c b/tools/testing/selftests/arm64/abi/ptrace.c
index be952511af22..abe4d58d731d 100644
--- a/tools/testing/selftests/arm64/abi/ptrace.c
+++ b/tools/testing/selftests/arm64/abi/ptrace.c
@@ -20,7 +20,7 @@

#include "../../kselftest.h"

-#define EXPECTED_TESTS 7
+#define EXPECTED_TESTS 11

#define MAX_TPIDRS 2

@@ -132,6 +132,34 @@ static void test_tpidr(pid_t child)
}
}

+static void test_hw_debug(pid_t child, int type, const char *type_name)
+{
+ struct user_hwdebug_state state;
+ struct iovec iov;
+ int slots, arch, ret;
+
+ iov.iov_len = sizeof(state);
+ iov.iov_base = &state;
+
+ /* Should be able to read the values */
+ ret = ptrace(PTRACE_GETREGSET, child, type, &iov);
+ ksft_test_result(ret == 0, "read_%s\n", type_name);
+
+ if (ret == 0) {
+ /* Low 8 bits is the number of slots, next 4 bits the arch */
+ slots = state.dbg_info & 0xff;
+ arch = (state.dbg_info >> 8) & 0xf;
+
+ ksft_print_msg("%s version %d with %d slots\n", type_name,
+ arch, slots);
+
+ /* Zero is not currently architecturally valid */
+ ksft_test_result(arch, "%s_arch_set\n", type_name);
+ } else {
+ ksft_test_result_skip("%s_arch_set\n");
+ }
+}
+
static int do_child(void)
{
if (ptrace(PTRACE_TRACEME, -1, NULL, NULL))
@@ -207,6 +235,8 @@ static int do_parent(pid_t child)
ksft_print_msg("Parent is %d, child is %d\n", getpid(), child);

test_tpidr(child);
+ test_hw_debug(child, NT_ARM_HW_WATCH, "NT_ARM_HW_WATCH");
+ test_hw_debug(child, NT_ARM_HW_BREAK, "NT_ARM_HW_BREAK");

ret = EXIT_SUCCESS;


---
base-commit: 44c026a73be8038f03dbdeef028b642880cf1511
change-id: 20230414-arm64-test-hw-breakpoint-83fe02f607fc

Best regards,
--
Mark Brown <[email protected]>

2023-05-26 10:10:09

by Catalin Marinas

Subject: Re: [PATCH v2] kselftest/arm64: Add a smoke test for ptracing hardware break/watch points

On Mon, 22 May 2023 15:28:00 +0100, Mark Brown wrote:
> There was a report that the hardware breakpoints and watch points weren't
> reporting the debug architecture version as expected, they were reporting
> a version of 0 which is not defined in the architecture. This happens
> when running in a KVM guest if the host has a debug architecture version
> not supported by KVM, it in turn confuses GDB which rejects any debug
> architecture version it does not know about.
>
> [...]

Applied to arm64 (for-next/kselftest), thanks!

[1/1] kselftest/arm64: Add a smoke test for ptracing hardware break/watch points
https://git.kernel.org/arm64/c/cb5aa6379438

--
Catalin