ptrace.2: Document struct ptrace_syscall_info

Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/ptrace.2

@@ -1026,7 +1026,56 @@ If the size of the data to be written by the kernel exceeds the size
 specified by the
 .I addr
 argument, the output data is truncated.
-.\" FIXME Document 'struct ptrace_syscall_info'
+.IP
+The
+.I ptrace_syscall_info
+structure contains the following fields:
+.IP
+.in
+.EX
+struct ptrace_syscall_info {
+    __u8 op;                    /* PTRACE_SYSCALL_INFO_* value
+                                   describing the kind
+                                   of system call stop,
+                                   see <linux/ptrace.h> */
+    __u32 arch;                 /* AUDIT_ARCH_* value,
+                                   see seccomp(2) */
+    __u64 instruction_pointer;  /* CPU instruction pointer */
+    __u64 stack_pointer;        /* CPU stack pointer */
+    union {
+        struct {
+            __u64 nr;           /* System call number */
+            __u64 args[6];      /* System call arguments */
+        } entry;                /* Information specific to
+                                   system call entry stops */
+        struct {
+            __s64 rval;         /* System call return value */
+            __u8 is_error;      /* System call error flag */
+        } exit;                 /* Information specific to
+                                   system call exit stops */
+        struct {
+            __u64 nr;           /* System call number */
+            __u64 args[6];      /* System call arguments */
+            __u32 ret_data;     /* The SECCOMP_RET_DATA portion
+                                   of SECCOMP_RET_TRACE return
+                                   value */
+        } seccomp;              /* Information specific to
+                                   PTRACE_EVENT_SECCOMP stops */
+    };
+};
+.EE
+.in
+.IP
+.IR op ,
+.IR arch ,
+.IR instruction_pointer ,
+and
+.I stack_pointer
+fields are defined for all kinds of ptrace system call stops.
+The rest of the structure is a union, one should read only those fields
+that are meaningful for the kind of system call stop specified by the
+.IR op
+field.
 .\"
 .SS Death under ptrace
 When a (possibly multithreaded) process receives a killing signal