Date: Sun, 8 Dec 2013 01:36:14 -0800 From: Justin Hibbits <chmeeedalf@gmail.com> To: Bruce Evans <brde@optusnet.com.au> Cc: svn-src-head@freebsd.org, Justin Hibbits <jhibbits@freebsd.org>, src-committers@freebsd.org, svn-src-all@freebsd.org Subject: Re: svn commit: r259080 - in head/sys: dev/iicbus geom/cache geom/journal Message-ID: <20131208013614.6dc63ef9@zhabar.gateway.2wire.net> In-Reply-To: <20131208123144.U883@besplex.bde.org> References: <201312071955.rB7JtYNH001792@svn.freebsd.org> <20131208123144.U883@besplex.bde.org>
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On Sun, 8 Dec 2013 13:53:30 +1100 (EST)
Bruce Evans <brde@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
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