tty compile warnings

tty compile warnings

[Robert Reif]

I have been getting these compile warnings on sparc32 for a few weeks now:

CC drivers/char/n_tty.o
drivers/char/n_tty.c: In function ‘normal_poll’:
drivers/char/n_tty.c:1555: warning: array subscript is above array bounds
drivers/char/n_tty.c:1564: warning: array subscript is above array bounds
drivers/char/n_tty.c: In function ‘read_chan’:
drivers/char/n_tty.c:1269: warning: array subscript is above array bounds
CC drivers/char/tty_ioctl.o
drivers/char/tty_ioctl.c: In function ‘set_termios’:
drivers/char/tty_ioctl.c:533: warning: array subscript is above array bounds
drivers/char/tty_ioctl.c:537: warning: array subscript is above array bounds
drivers/char/tty_ioctl.c: In function ‘tty_mode_ioctl’:
drivers/char/tty_ioctl.c:662: warning: array subscript is above array bounds
drivers/char/tty_ioctl.c:892: warning: array subscript is above array bounds
drivers/char/tty_ioctl.c:896: warning: array subscript is above array bounds
drivers/char/tty_ioctl.c:577: warning: array subscript is above array bounds
drivers/char/tty_ioctl.c:928: warning: array subscript is above array bounds
drivers/char/tty_ioctl.c:934: warning: array subscript is above array bounds

Re: tty compile warnings

[Alan Cox]

On Mon, 01 Sep 2008 09:27:14 -0400
Robert Reif <reif@earthlink.net> wrote:

> I have been getting these compile warnings on sparc32 for a few weeks now:

gcc is complaining about some nasty hacks the sparc32 tree does with
termios.

        cc_t c_cc[NCCS];                /* control characters */
#ifdef __KERNEL__
#define SIZEOF_USER_TERMIOS sizeof (struct termios) - (2*sizeof (cc_t))
        cc_t _x_cc[2];                  /* We need them to hold
vmin/vtime */ #endif


struct ktermios {
        tcflag_t c_iflag;               /* input mode flags */
        tcflag_t c_oflag;               /* output mode flags */
        tcflag_t c_cflag;               /* control mode flags */
        tcflag_t c_lflag;               /* local mode flags */
        cc_t c_line;                    /* line discipline */  
        cc_t c_cc[NCCS];                /* control characters */
        cc_t _x_cc[2];                  /* We need them to hold
vmin/vtime */ speed_t c_ispeed;               /* input speed */
        speed_t c_ospeed;               /* output speed */
};



You could try removing _x_cc[2] and changing [NCCS] to [NCCS+2] which
might work depending upon the alignment you get.

Re: tty compile warnings

[Robert Reif]

[-- Attachment #1: Type: text/plain, Size: 517 bytes --]

Alan Cox wrote:
> You could try removing _x_cc[2] and changing [NCCS] to [NCCS+2] which
> might work depending upon the alignment you get.
>   
The following patch compiles without error but I'm a bit confused
about the sizes.  VMIN is 16 and VTIME is 17 so user NCCS should
be 16 and kernel NCCS 18 unless there are padding or some legacy
issues here. 17 + 2 + one for c_line = 20 bytes which makes sense for
padding but NCCS is used to copy the control characters which means
an unused control character is copied.

[-- Attachment #2: tty.diff.txt --]
[-- Type: text/plain, Size: 1493 bytes --]

diff --git a/arch/sparc/include/asm/termbits.h b/arch/sparc/include/asm/termbits.h
index d6ca3e2..c154288 100644
--- a/arch/sparc/include/asm/termbits.h
+++ b/arch/sparc/include/asm/termbits.h
@@ -29,10 +29,11 @@ struct termios {
 	tcflag_t c_cflag;		/* control mode flags */
 	tcflag_t c_lflag;		/* local mode flags */
 	cc_t c_line;			/* line discipline */
+#ifndef __KERNEL__
 	cc_t c_cc[NCCS];		/* control characters */
-#ifdef __KERNEL__
+#else
+	cc_t c_cc[NCCS+2];	/* kernel needs 2 more to hold vmin/vtime */
 #define SIZEOF_USER_TERMIOS sizeof (struct termios) - (2*sizeof (cc_t))
-	cc_t _x_cc[2];                  /* We need them to hold vmin/vtime */
 #endif
 };
 
@@ -42,8 +43,7 @@ struct termios2 {
 	tcflag_t c_cflag;		/* control mode flags */
 	tcflag_t c_lflag;		/* local mode flags */
 	cc_t c_line;			/* line discipline */
-	cc_t c_cc[NCCS];		/* control characters */
-	cc_t _x_cc[2];                  /* padding to match ktermios */
+	cc_t c_cc[NCCS+2];		/* control characters */
 	speed_t c_ispeed;		/* input speed */
 	speed_t c_ospeed;		/* output speed */
 };
@@ -54,8 +54,7 @@ struct ktermios {
 	tcflag_t c_cflag;		/* control mode flags */
 	tcflag_t c_lflag;		/* local mode flags */
 	cc_t c_line;			/* line discipline */
-	cc_t c_cc[NCCS];		/* control characters */
-	cc_t _x_cc[2];                  /* We need them to hold vmin/vtime */
+	cc_t c_cc[NCCS+2];		/* control characters */
 	speed_t c_ispeed;		/* input speed */
 	speed_t c_ospeed;		/* output speed */
 };

Re: tty compile warnings

[David Miller]

From: Alan Cox <alan@lxorguk.ukuu.org.uk>
Date: Mon, 1 Sep 2008 14:57:29 +0100

> You could try removing _x_cc[2] and changing [NCCS] to [NCCS+2] which
> might work depending upon the alignment you get.

We can't do that kind of change for the "struct termios" case as
changing the array size would change the size of the structure in
userspace.  Here, the _x_cc[] thing is only present when __KERNEL__.

I've looked at this issue before, and so far my conclusion is that
ignoring the warnings and teaching other people to do so as well is so
much easier than trying to make this palatable to the compiler and
checking tools.