8:27 p.m.
On 6/11/21 10:58 AM, Hyeonggon Yoo wrote:
On Thu, Jun 10, 2021, 8:43 PM Vlastimil Babka <vbabka(a)suse.cz
<mailto:vbabka@suse.cz>> wrote:
>> > void *kmalloc_node(size_t size, gfp_t flags, int node){
>> >
>> > if ( (__builtin_constant_p(
>> > !!(__builtin_constant_p(size)
>> > && size <= (1UL << ((11 + 12 - 1) <= 25 ?
(11 + 12 - 1) : 25))))
>> > ? (!!(__builtin_constant_p(size) && size <= (1UL
<< ((11 +
12 - 1) <= 25 ? (11 + 12 - 1) : 25))))
>
>
>> > if ( (__builtin_constant_p(!!((0 || 110000 >= 110000) &&
size_is_constant)) ? (!!((0 || 110000 >= 110000) && size_is_constant)) :
({
static struct ftrace_branch_data __attribute__((__aligned__(4)))
__attribute__((__section__("_ftrace_branch"))) __if_trace = { .func =
__func__, .file = "include/linux/slab.h", .line = 416, }; (!!((0 || 110000
>= 110000) && size_is_constant)) ? (__if_trace.miss_hit[1]++,1) :
(__if_trace.miss_hit[0]++,0); })) )
>> > do {
>> >
>> >
>> > extern void __compiletime_assert_131(void) ;
>> > // here - compiletime_assert_131 does NOTHING
>>
>> It doesn't seem to do nothing? see below
>>
>> > if ( (__builtin_constant_p(!!(!(!(1))))
>> > ? (!!(!(!(1))))
>> > : ({ static struct ftrace_branch_data
__attribute__((__aligned__(4)))
__attribute__((__section__("_ftrace_branch"))) __if_trace = { .func =
__func__, .file = "include/linux/slab.h", .line = 417, }; (!!(!(!(1)))) ?
(__if_trace.miss_hit[1]++,1) : (__if_trace.miss_hit[0]++,0); })) )
__compiletime_assert_131(); } while (0);
>>
>> The thing above seems to be exactly the "if (!(condition))
>> prefix ## suffix(); } while (0)" as the definition you posted below.
>>
>> Anyway, you can verify that clang works by commenting out the highest size
>> checks and passing a constant size that makes it reach the
BUILD_BUG_ON_MSG() ?
>>
>
> I verified as below.
> clang didn't make an error, gcc worked as expected.
>
> then I can explain why there is no error with clang:
> it just did nothing with BUILD_BUG_ON.
That might warrant a clang bug report too. We excluded clang 10 due to false
positives. If the BUILD_BUG_ON doesn't work at all in clang 11 we might have to
exclude clang completely.
After playing with clang more a bit, I got to know that compiletime_assert makes
weird link error (undefined reference to compiletime_assert_XXX), Not a compile
error.
Ah well that's much better than no error at all.
I think it's time to CC ClangBuiltLinux maintainers, who work on
clang/llvm
build support.
[+CC Nathan and Nick]
Good.
I assumeed that compiletime_assert (in linux/compiler.h) will make
compiler
error, but it makes no compile error, just makes weird link error.
I'm not sure it it works well with clang, or somewhat buggy status?
...
Yes. You could perhaps exclude CONFIG_PROFILE_ALL_BRANCHES for
now,
You do you mean by "exclude CONFIG_PROFILE_ALL_BRANCHES for now"?
Did you mean we don't need to fix it for now? (Anyway I have no idea what the
fix patch would be for now...)
I meant the the condition to use BUILD_BUG_ON instead of BUG_ON would include
!IS_ENABLED(CONFIG_PROFILE_ALL_BRANCHES)
and fill
official gcc bugzilla with the preprocessed file.
Bonus points if you can use cvise in a way that reduces the testcase but does
not remove any of the important parts. All we could get were degenerate cases
like this one
https://paste.opensuse.org/9320186 <https://paste.opensuse.org/9320186>
I'll try that and report it to gcc bugzilla soon!
I think I should let you know that I'm going to korean army next week, So I
can't access internet for next two months... (Because they don't allow internet
in military training period)
I'll be back after 2 months, But can I ask you (Vlastimil) to write follow up
patch if we can fix it before I'm back?
Sure, take care!
Sorry I didn't know compiler will bother us at that time I wrote
the patch :(