On 03/09/2018 04:07 PM, Andrew Morton wrote: > On Fri, 9 Mar 2018 12:05:36 -0800 Kees Cook <keesc...@chromium.org> wrote: > >> When max() is used in stack array size calculations from literal values >> (e.g. "char foo[max(sizeof(struct1), sizeof(struct2))]", the compiler >> thinks this is a dynamic calculation due to the single-eval logic, which >> is not needed in the literal case. This change removes several accidental >> stack VLAs from an x86 allmodconfig build: >> >> $ diff -u before.txt after.txt | grep ^- >> -drivers/input/touchscreen/cyttsp4_core.c:871:2: warning: ISO C90 forbids >> variable length array ‘ids’ [-Wvla] >> -fs/btrfs/tree-checker.c:344:4: warning: ISO C90 forbids variable length >> array ‘namebuf’ [-Wvla] >> -lib/vsprintf.c:747:2: warning: ISO C90 forbids variable length array ‘sym’ >> [-Wvla] >> -net/ipv4/proc.c:403:2: warning: ISO C90 forbids variable length array >> ‘buff’ [-Wvla] >> -net/ipv6/proc.c:198:2: warning: ISO C90 forbids variable length array >> ‘buff’ [-Wvla] >> -net/ipv6/proc.c:218:2: warning: ISO C90 forbids variable length array >> ‘buff64’ [-Wvla] >> >> Based on an earlier patch from Josh Poimboeuf. > > v1, v2 and v3 of this patch all fail with gcc-4.4.4: > > ./include/linux/jiffies.h: In function 'jiffies_delta_to_clock_t': > ./include/linux/jiffies.h:444: error: first argument to > '__builtin_choose_expr' not a constant
I'm seeing that problem with > gcc --version gcc (SUSE Linux) 4.8.5 in mmotm. > That's with > > #define __max(t1, t2, x, y) \ > __builtin_choose_expr(__builtin_constant_p(x) && \ > __builtin_constant_p(y) && \ > __builtin_types_compatible_p(t1, t2), \ > (t1)(x) > (t2)(y) ? (t1)(x) : (t2)(y), \ > __single_eval_max(t1, t2, \ > __UNIQUE_ID(max1_), \ > __UNIQUE_ID(max2_), \ > x, y)) > /** > * max - return maximum of two values of the same or compatible types > * @x: first value > * @y: second value > */ > #define max(x, y) __max(typeof(x), typeof(y), x, y) > > > A brief poke failed to reveal a workaround - gcc-4.4.4 doesn't appear > to know that __builtin_constant_p(x) is a constant. Or something. > > Sigh. Wasn't there some talk about modernizing our toolchain > requirements? -- ~Randy
