linux-user: Add strace support for printing arguments of syscalls used to lock and unlock memory

This patch implements strace argument printing functionality for following syscalls:

    * mlock, munlock, mlockall, munlockall - lock and unlock memory

       int mlock(const void *addr, size_t len)
       int munlock(const void *addr, size_t len)
       int mlockall(int flags)
       int munlockall(void)
       man page: https://man7.org/linux/man-pages/man2/mlock.2.html

Implementation notes:

    Syscall mlockall() takes an argument that is composed of predefined values
    which represent flags that determine the type of locking operation that is
    to be performed. For that reason, a printing function "print_mlockall" was
    stated in file "strace.list". This printing function uses an already existing
    function "print_flags()" to print the "flags" argument.  These flags are stated
    inside an array "mlockall_flags" that contains values of type "struct flags".
    These values are instantiated using an existing macro "FLAG_TARGET()" that
    crates aproppriate target flag values based on those defined in files
    '/target_syscall.h'. These target flag values were changed from
    "TARGET_MLOCKALL_MCL*" to "TARGET_MCL_*" so that they can be aproppriately set
    and recognised in "strace.c" with "FLAG_TARGET()". Value for "MCL_ONFAULT"
    was added in this patch. This value was also added in "syscall.c" in function
    "target_to_host_mlockall_arg()". Because this flag value was added in kernel
    version 4.4, it is enwrapped in an #ifdef directive (both in "syscall.c" and
    in "strace.c") as to support older kernel versions.
    The other syscalls have only primitive argument types, so the
    rest of the implementation was handled by stating an appropriate
    printing format in file "strace.list". Syscall mlock2() is not implemented in
    "syscall.c" and thus it's argument printing is not implemented in this patch.

Signed-off-by: Filip Bozuta <Filip.Bozuta@syrmia.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20200811164553.27713-4-Filip.Bozuta@syrmia.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

1 files changed, 8 insertions, 2 deletions

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index ec71921..027dea3 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -6975,12 +6975,18 @@ static inline int target_to_host_mlockall_arg(int arg)
 {
     int result = 0;
 
-    if (arg & TARGET_MLOCKALL_MCL_CURRENT) {
+    if (arg & TARGET_MCL_CURRENT) {
         result |= MCL_CURRENT;
     }
-    if (arg & TARGET_MLOCKALL_MCL_FUTURE) {
+    if (arg & TARGET_MCL_FUTURE) {
         result |= MCL_FUTURE;
     }
+#ifdef MCL_ONFAULT
+    if (arg & TARGET_MCL_ONFAULT) {
+        result |= MCL_ONFAULT;
+    }
+#endif
+
     return result;
 }
 #endif