scripts/gdb: fix lx-version string output

A bug is present in GDB which causes early string termination when
parsing variables. This has been reported [0], but we should ensure
that we can support at least basic printing of the core kernel strings.

For current gdb version (has been tested with 7.3 and 8.1), 'lx-version'
only prints one character.

(gdb) lx-version
L(gdb)

This can be fixed by casting 'linux_banner' as (char *).

(gdb) lx-version
Linux version 4.19.0-rc1+ (changbin@acer) (gcc version 7.3.0 (Ubuntu 7.3.0-16ubuntu3)) #21 SMP Sat Sep 1 21:43:30 CST 2018

[0] https://sourceware.org/bugzilla/show_bug.cgi?id=20077

[[e-mail]: add detail to commit message]
Link: http://lkml.kernel.org/r/[e-mail]
Fixes: 2d061d999424 ("scripts/gdb: add version command")
Signed-off-by: Du Changbin <[e-mail]>
Signed-off-by: Kieran Bingham <[e-mail]>
Acked-by: Jan Kiszka <[e-mail]>
Cc: Jan Kiszka <[e-mail]>
Cc: Jason Wessel <[e-mail]>
Cc: Daniel Thompson <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

scripts/gdb/linux/proc.py

···
 
     def invoke(self, arg, from_tty):
         # linux_banner should contain a newline
-        gdb.write(gdb.parse_and_eval("linux_banner").string())
+        gdb.write(gdb.parse_and_eval("(char *)linux_banner").string())
 
 LxVersion()