Enable seccomp_bpf selftests on the Alpha architecture by providing
Alpha-specific register definitions and syscall accessors.

This allows the seccomp-bpf test suite to exercise syscall tracing,
seccomp filters, and user notification on Alpha.

Signed-off-by: Magnus Lindholm <[email protected]>
---
 tools/testing/selftests/seccomp/seccomp_bpf.c | 29 +++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c 
b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 32e2d4df397b..db2c81bb89b6 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -136,6 +136,8 @@ struct seccomp_data {
 #  define __NR_seccomp 354
 # elif defined(__x86_64__)
 #  define __NR_seccomp 317
+# elif defined(__alpha__)
+#  define __NR_seccomp 514
 # elif defined(__arm__)
 #  define __NR_seccomp 383
 # elif defined(__aarch64__)
@@ -1748,6 +1750,29 @@ TEST_F(TRACE_poke, getpid_runs_normally)
 # define ARCH_REGS             struct user_regs_struct
 # define SYSCALL_NUM(_regs)    (_regs).orig_eax
 # define SYSCALL_RET(_regs)    (_regs).eax
+#elif defined(__alpha__)
+#define ARCH_REGS struct pt_regs
+#define SYSCALL_NUM(_regs) ((_regs).r1)
+#define SYSCALL_NR_SET(_regs, _nr) \
+       ((_regs).r1 = (unsigned long)(_nr))
+#define SYSCALL_RET(_regs)     ((_regs).r0)
+/*
+ * Alpha syscall ABI:
+ *  - r0 holds return value (or positive errno on failure)
+ *  - r19 (a3) is 0 on success, 1 on failure
+ */
+#define SYSCALL_RET_SET(_regs, _val)                           \
+       do {                                                    \
+               long __v = (long)(_val);                        \
+               if (__v < 0) {                                  \
+                       (_regs).r0  = (unsigned long)(-__v);    \
+                       (_regs).r19 = 1;                        \
+               } else {                                        \
+                       (_regs).r0  = (unsigned long)__v;       \
+                       (_regs).r19 = 0;                        \
+               }                                               \
+       } while (0)
+
 #elif defined(__arm__)
 # define ARCH_REGS             struct pt_regs
 # define SYSCALL_NUM(_regs)    (_regs).ARM_r7
@@ -4643,6 +4668,10 @@ TEST(user_notification_wait_killable_pre_notification)
        pid_t pid;
        long ret;
        char c;
+
+       #if defined(__alpha__)
+               SKIP(return, "/proc/<pid>/syscall not available on Alpha");
+       #endif
        /* 100 ms */
        struct timespec delay = { .tv_nsec = 100000000 };
 
-- 
2.52.0


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