linux-user: Add strace support for printing arguments for ioctls used for terminals and serial lines

Functions "print_ioctl()" and "print_syscall_ret_ioctl()" are used
to print arguments of "ioctl()" with "-strace". These functions
use "thunk_print()", which is defined in "thunk.c", to print the
contents of ioctl's third arguments that are not basic types.

However, this function doesn't handle ioctls of group ioctl_tty which
are used for terminals and serial lines. These ioctls use a type
"struct termios" which thunk type is defined in a non standard
way using "STRUCT_SPECIAL()". This means that this type is not decoded
regularly using "thunk_convert()" and uses special converting functions
"target_to_host_termios()" and "host_to_target_termios()", which are defined
in "syscall.c" to decode it's values.

For simillar reasons, this type is also not printed regularly using
"thunk_print()". That is the reason why a separate printing function
"print_termios()" is defined in file "strace.c". This function decodes
and prints flag values of the "termios" structure.

Implementation notes:

    Function "print_termios()" was implemented in "strace.c" using
    an existing function "print_flags()" to print flag values of
    "struct termios" fields. Also, recently implemented function
    "print_enums()" was also used to print enumareted values which
    are contained in the fields of 'struct termios'.

    These flag values were defined using an existing macro "FLAG_TARGET()"
    that generates aproppriate target flag values and string representations
    of these flags. Also, the recently defined macro "ENUM_TARGET()" was
    used to generate aproppriate enumarated values and their respective
    string representations.

    Function "print_termios()" was declared in "qemu.h" so that it can
    be accessed in "syscall.c". Type "StructEntry" defined in
    "exec/user/thunk.h" contains information that is used to decode
    structure values. Field "void print(void *arg)" was added in this
    structure as a special print function. Also, function "thunk_print()"
    was changed a little so that it uses this special print function
    in case it is defined. This printing function was instantiated with
    the defined "print_termios()" in "syscall.c" in "struct_termios_def".

Signed-off-by: Filip Bozuta <Filip.Bozuta@syrmia.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20200723210233.349690-4-Filip.Bozuta@syrmia.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

1 files changed, 14 insertions, 9 deletions

diff --git a/thunk.c b/thunk.c
index c5d9719747..0718325d86 100644
--- a/thunk.c
+++ b/thunk.c
@@ -404,19 +404,24 @@ const argtype *thunk_print(void *arg, const argtype *type_ptr)
             const int *arg_offsets;
 
             se = struct_entries + *type_ptr++;
-            a = arg;
 
-            field_types = se->field_types;
-            arg_offsets = se->field_offsets[0];
+            if (se->print != NULL) {
+                se->print(arg);
+            } else {
+                a = arg;
 
-            qemu_log("{");
-            for (i = 0; i < se->nb_fields; i++) {
-                if (i > 0) {
-                    qemu_log(",");
+                field_types = se->field_types;
+                arg_offsets = se->field_offsets[0];
+
+                qemu_log("{");
+                for (i = 0; i < se->nb_fields; i++) {
+                    if (i > 0) {
+                        qemu_log(",");
+                    }
+                    field_types = thunk_print(a + arg_offsets[i], field_types);
                 }
-                field_types = thunk_print(a + arg_offsets[i], field_types);
+                qemu_log("}");
             }
-            qemu_log("}");
         }
         break;
     default: