svn commit: r259080 - in head/sys: dev/iicbus geom/cache geom/journal

[Justin Hibbits]

On Sun, 8 Dec 2013 13:53:30 +1100 (EST)
Bruce Evans <brde at optusnet.com.au> wrote:

> On Sat, 7 Dec 2013, Justin Hibbits wrote:
> 
> > Log:
> >  Fix some integer signs.  These unsigned integers should all be
> > signed.
> >
> >  Found by:	clang (powerpc64)
> 
> Unsigned integers are indeed used excessively.  They should only be
> used if values larger than INT_MAX need to be represented, but values
> larger than UINT_MAX need not be represented.  This is a very small
> target (just 1 more bit).
> 
> > Modified: head/sys/dev/iicbus/max6690.c
> > ==============================================================================
> > --- head/sys/dev/iicbus/max6690.c	Sat Dec  7 19:39:38
> > 2013	(r259079) +++ head/sys/dev/iicbus/max6690.c	Sat
> > Dec  7 19:55:34 2013	(r259080) @@ -362,7 +362,7 @@
> > max6690_sensor_sysctl(SYSCTL_HANDLER_ARG struct max6690_softc *sc;
> > 	struct max6690_sensor *sens;
> > 	int error;
> > -	unsigned int temp;
> > +	int temp;
> >
> > 	dev = arg1;
> > 	sc = device_get_softc(dev);
> >
> 
> This fixes one style bug (non-use of the BSD spelling u_int) but adds
> another (int declarations not grouped together).
> 
> > Modified: head/sys/geom/cache/g_cache.c
> > ==============================================================================
> > --- head/sys/geom/cache/g_cache.c	Sat Dec  7 19:39:38
> > 2013	(r259079) +++ head/sys/geom/cache/g_cache.c	Sat
> > Dec  7 19:55:34 2013	(r259080) @@ -67,7 +67,7 @@ static
> > u_int g_cache_used_hi = 20; static int
> > sysctl_handle_pct(SYSCTL_HANDLER_ARGS)
> > {
> > -	u_int val = *(u_int *)arg1;
> > +	int val;
> > 	int error;
> >
> > 	error = sysctl_handle_int(oidp, &val, 0, req);
> >
> 
> This adds the larger non-style bug that val is used uninitialized.
> Compilers should warn about this.  This results in stack garbage
> being copied out instead of the "old" value.
> 
> sysctl_handle_u_int() doesn't exist, so sysctl_handle_int() os often
> abused to handle u_int's and worse (sometimes "opaque" types, where
> it usually works accidentally if the type is 32 bits, and sometimes
> even works accidentally if the type is larger).  clang seems to be
> complaining about this abuse.  Why does it only complain here?  Ah,
> maybe it is not smart enough to complain about this, but is just
> complaining about the (val < 0) range check.
> 
> This adds 2 (lexical) style bugs:
> - the int declarations are not grouped together
> 
> This misses fixing nearby bogus unsigned variables.  The cast for
> these is more bogus than before.  Indeed, the whole function is
> horrible, and this change is sort of backwards since it gives a sign
> mismatch with the underlying variables:
> 
> % static u_int g_cache_used_lo = 5;
> % static u_int g_cache_used_hi = 20;
> 
> Example of excessive use of unsigned types.  These variables only need
> to handle percentages between 0 and 100.
> 
> % static int
> 
> Style bug (missing blank line);
> 
> % sysctl_handle_pct(SYSCTL_HANDLER_ARGS)
> % {
> % 	u_int val = *(u_int *)arg1;
> 
> This is the old version.  It has another style bug (initialization in
> declaration).  The initialization wouldn't have been lost so easily
> if it had been in the correct place.
> 
> But the type was correct, since it is bug-for-bug constent with the
> underlying variables.
> 
> % 	int error;
> % 
> % 	error = sysctl_handle_int(oidp, &val, 0, req);
> 
> sysctl_handle_int() was abused to handle the u_int (arg1 points to
> one of the above 2 variables).
> 
> % 	if (error || !req->newptr)
> % 		return (error);
> 
> 2 style bugs (2 boolean comparisions of non-booleans).  Strict KNF
> doesn't even use the ! operator to test booleansl; it uses an
> explicit " == 0" test for this, though it sometimes doesn't write out
> "!= 0" for the reverse test.
> 
> % 	if (val < 0 || val > 100)
> % 		return (EINVAL);
> 
> The first test in this is redundant,  This is apparently what clang
> was complaining about.  The warning for that can be fixed by removing
> the test.  However, I don't like this fix.  It depends on the type
> being unsigned.  The code becomes more fragile, and would break if
> the type were changed to the correct one (signed).
> 
> % 	if ((arg1 == &g_cache_used_lo && val > g_cache_used_hi) ||
> % 	    (arg1 == &g_cache_used_hi && g_cache_used_lo > val))
> % 		return (EINVAL);
> % 	*(u_int *)arg1 = val;
> 
> There are only 2 variables handled by this function, so we use arg1 
> to set the correct one.  However, the previous statement has decided
> which of the variables is being set, and we could use that to set it.
> Or better, convert arg1 from void * to u_int * up front, and use that
> throughout instead of several casts of arg1.
> 
> % 	return (0);
> % }
> % SYSCTL_PROC(_kern_geom_cache, OID_AUTO, used_lo,
> CTLTYPE_UINT|CTLFLAG_RW,
> 
> Style bugs:
> - missing blank line.  This is intentional for grouping the function
> with its variables, as above, but still ugly.
> - missing spaces around binary operator '|'.  This bug is too common
> for this operator, and for CTLFLAG*.  But the spaces are even more
> needed for '|' than for '+' or '*', since '|' looks more like an
> alphanumeric character.
> 
> % 	&g_cache_used_lo, 0, sysctl_handle_pct, "IU", "");
> % SYSCTL_PROC(_kern_geom_cache, OID_AUTO, used_hi,
> CTLTYPE_UINT|CTLFLAG_RW, % 	&g_cache_used_hi, 0,
> sysctl_handle_pct, "IU", "");
> 
> Style bugs:
> - non-KNF continuation indent.  This bug is too common for SYSCTL*(),
>    although someone once did a fairly global sweep to fix it for them.
> - no description.
> 
> This sysctl is over-engineered.  A simple SYSCTL_UINT() is enough.
> There are many more-critical sysctls that don't have any range
> checking. The fix is not to bloat the kernel by adding range checking
> to them all.  With several thousand sysctls, the range checking code
> could easily be over-engineered enough to double the size of an
> already massively bloated kernel.  OTOH, there may still be runtime
> errors from sloppy caclulations using the percentage variables.  The
> calculations are of the form (x * pct / 100) and not the more robust
> but fuzzier (x / 100 * pct).  pct will normally be promoted to the
> type of x in these expressions (often to 64 bits, and then overflow
> is far off).  Overflow is only affected by pct being unsigned if x is
> int or shorter.
> 
> > Modified: head/sys/geom/journal/g_journal.c
> > ==============================================================================
> > --- head/sys/geom/journal/g_journal.c	Sat Dec  7 19:39:38
> > 2013	(r259079) +++ head/sys/geom/journal/g_journal.c
> > Sat Dec  7 19:55:34 2013	(r259080) @@ -168,7 +168,7 @@
> > SYSCTL_UINT(_kern_geom_journal_cache, OI static int
> > g_journal_cache_switch_sysctl(SYSCTL_HANDLER_ARGS)
> > {
> > -	u_int cswitch;
> > +	int cswitch;
> > 	int error;
> >
> > 	cswitch = g_journal_cache_switch;
> >
> 
> 2 style bugs (int variables not grouped; int variables not sorted).
> 
> This sysctl is missing most of the style bugs discussed above:
> - the transfer variable cswitch is not initialized in its declaration.
>    Its initialization didn't get deleted.
> - the comparisons of the non-booleans are non-boolean.
> - the percentage variable is used in the robust way (x / 100 * pct).
> - the SYSCTL()s use KNF continuation indentation
> - there are spaces around the binary operator '|'
> - the SYSCTL()s have descriptions.
> 
> This leaves mainly type errors (excessive use of unsigned variables).
> There is a different inconsistency: the u_int g_journal_cache_switch
> has formatting data "I" instead of "IU".  Both will work due to the
> range checking and assumptions that the machine is not exotic, but
> there is no reason to not to use a consistent format.
> 
> Another common style bug/API design error visible here is using
> sysctl_handle_int() on generic variables.  You have to know that the
> variable type is int to use it or u_int, int32_t or uint32_t to abuse
> it.  The width of the variable is in the sysctl data and is usually
> correct.  sysctl_handle_opaque() is usable on generic variables but
> doesn't work so well (it prevents type checking and has more locking
> overheads).  When sysctl_handle_int() is used, the width in the sysctl
> data should be used to detect size mismatches.  It is used, but there
> are bugs in the error handling for this (something like ignoring size
> mismatches for short i/o's in only 1 direction).
> 
> Bruce

I just reverted these two changes in r259096.  Rather than fix what I
did and change the rest of the files, I'm leaving them for another day,
and reverted my changes so they're at least back to the working order
from before.

- Justin