Re: Attribute alloc__size use and clang 5.0.1 vs. gcc7 (e.g.): __builtin_object_size(p,1) and __builtin_object_size(p,3) disagreements result

2018-01-20 Thread Pedro Giffuni 

Very interesting , thanks for running such tests ...


On 01/20/18 18:59, Mark Millard wrote:

[Noting a typo in the program source, and
so in the output text: the 2nd occurance of: "my_calloc_alt0
should have been: "my_calloc_alt1
. Hand edited corrections below for clarity.]

On 2018-Jan-20, at 3:27 PM, Mark Millard  wrote:


[Bugzilla 225197 indirectly lead to this.
Avoiding continuing there.]

I decided to compare some alternate uses of
__attribute__((alloc_size(. . .))) compiled
and run under clang 5.0.1 and gcc7. I did not
get what I expected based on prior discussion
material.

This is an FYI since I do not know how important
the distinctions that I found are.

Here is the quick program:

# more alloc_size_attr_test.c
#include 
#include 

__attribute__((alloc_size(1,2)))
void* my_calloc_alt0(size_t n, size_t s)
{
   void* p = calloc(n,s);
   printf("calloc __builtin_object_size 0,1,2,3: %ld, %ld, %ld, %ld\n"
 ,(long) __builtin_object_size(p, 0)
 ,(long) __builtin_object_size(p, 1)
 ,(long) __builtin_object_size(p, 2)
 ,(long) __builtin_object_size(p, 3)
 );
   return p;
}

__attribute__((alloc_size(1))) __attribute__((alloc_size(2)))
void* my_calloc_alt1(size_t n, size_t s)
{
   void* p = calloc(n,s);
   printf("calloc __builtin_object_size 0,1,2,3: %ld, %ld, %ld, %ld\n"
 ,(long) __builtin_object_size(p, 0)
 ,(long) __builtin_object_size(p, 1)
 ,(long) __builtin_object_size(p, 2)
 ,(long) __builtin_object_size(p, 3)
 );
   return p;
}

int main()
{
   void* p = my_calloc_alt0(2,7);
   printf("my_calloc_alt0 __builtin_object_size 0,1,2,3: %ld, %ld, %ld, %ld\n"
 ,(long) __builtin_object_size(p, 0)
 ,(long) __builtin_object_size(p, 1)
 ,(long) __builtin_object_size(p, 2)
 ,(long) __builtin_object_size(p, 3)
 );
   void* q = my_calloc_alt1(2,7);
   printf("my_calloc_alt0 __builtin_object_size 0,1,2,3: %ld, %ld, %ld, %ld\n"

The above line should have been:

printf("my_calloc_alt1 __builtin_object_size 0,1,2,3: %ld, %ld, %ld, %ld\n"


 ,(long) __builtin_object_size(q, 0)
 ,(long) __builtin_object_size(q, 1)
 ,(long) __builtin_object_size(q, 2)
 ,(long) __builtin_object_size(q, 3)
 );
}

# uname -apKU
FreeBSD FBSDFSSD 12.0-CURRENT FreeBSD 12.0-CURRENT  r327485M  amd64 amd64 
1200054 1200054

The system-clang 5.0.1 result was:

# clang -O2 alloc_size_attr_test.c

The later outputs are edited for clarity:


# ./a.out
calloc __builtin_object_size 0,1,2,3: 14, 14, 14, 0
my_calloc_alt0 __builtin_object_size 0,1,2,3: 14, 14, 14, 0
calloc __builtin_object_size 0,1,2,3: 14, 14, 14, 0

my_calloc_alt1 __builtin_object_size 0,1,2,3: 14, 14, 14, 0

The lang/gcc7 result was:

# gcc7 -O2 alloc_size_attr_test.c

# ./a.out
calloc __builtin_object_size 0,1,2,3: -1, -1, 0, 0
my_calloc_alt0 __builtin_object_size 0,1,2,3: 14, 14, 14, 14
calloc __builtin_object_size 0,1,2,3: -1, -1, 0, 0

my_calloc_alt1 __builtin_object_size 0,1,2,3: 14, 7, 14, 14

I'll ignore that gcc does not provide actual sizes
via __builtin_object_size for calloc use.

Pairing the other lines for easy comparison, with
some notes mixed in:

__attribute__((alloc_size(1,2))) style:
my_calloc_alt0 __builtin_object_size 0,1,2,3: 14, 14, 14, 0  (system clang)
my_calloc_alt0 __builtin_object_size 0,1,2,3: 14, 14, 14, 14 (gcc7)

__attribute__((alloc_size(1))) __attribute__((alloc_size(2))) style:

my_calloc_alt1 __builtin_object_size 0,1,2,3: 14, 14, 14, 0  (system clang)
my_calloc_alt1 __builtin_object_size 0,1,2,3: 14, 7, 14, 14  (gcc7)

So on GCC7 it appears
 __attribute__((alloc_size(1,2))) != __attribute__((alloc_size(1))) 
__attribute__((alloc_size(2)))


This is not good as it was the base for r280801 .. related to the old 
discussion about deprecating old compilers that don't accept VA_ARGS.


I am unsure if its a regression but it appears that for clang it is the 
same thing though.



Thus. . .

For __attribute__((alloc_size(1))) __attribute__((alloc_size(2))):
__builtin_object_size(p,1) is not equivalent (clang vs. gcc7)

For both of the alloc_size usage styles:
__builtin_object_size(p,3) is not equivalent (clang vs. gcc7)

This means that the two style of alloc_size use are not
equivalent across some major compilers/toolchains.


This is actually not a surprise: GCC and clang implementation of 
__alloc_size__ has differences due to limitations on the LLVM IR (or the 
fact there is one).


The alloc_size attribute is basically only used for the so-called 
FORTIFY_SOURCE feature that depends on GCC with some support from the 
C-library: last time I looked clang didn't support the compile-time 
checks very well. The attributes are mostly unused in FreeBSD at this 
time but, GCC7 -Walloc-size-larger-than=size depends on them (I have 
never tested that though).


FWIW, we had an unfinished GSoC that attempted to implement 
FORTIFY_SOURCE but we got stuck on the lack of

Re: Attribute alloc__size use and clang 5.0.1 vs. gcc7 (e.g.): __builtin_object_size(p,1) and __builtin_object_size(p,3) disagreements result

2018-01-20 Thread Mark Millard via freebsd-toolchain 
[Noting a typo in the program source, and
so in the output text: the 2nd occurance of: "my_calloc_alt0
should have been: "my_calloc_alt1
. Hand edited corrections below for clarity.]

On 2018-Jan-20, at 3:27 PM, Mark Millard  wrote:

> [Bugzilla 225197 indirectly lead to this.
> Avoiding continuing there.]
> 
> I decided to compare some alternate uses of
> __attribute__((alloc_size(. . .))) compiled
> and run under clang 5.0.1 and gcc7. I did not
> get what I expected based on prior discussion
> material.
> 
> This is an FYI since I do not know how important
> the distinctions that I found are.
> 
> Here is the quick program:
> 
> # more alloc_size_attr_test.c 
> #include 
> #include 
> 
> __attribute__((alloc_size(1,2)))
> void* my_calloc_alt0(size_t n, size_t s)
> {
>   void* p = calloc(n,s);
>   printf("calloc __builtin_object_size 0,1,2,3: %ld, %ld, %ld, %ld\n"
> ,(long) __builtin_object_size(p, 0)
> ,(long) __builtin_object_size(p, 1)
> ,(long) __builtin_object_size(p, 2)
> ,(long) __builtin_object_size(p, 3)
> );
>   return p;
> }
> 
> __attribute__((alloc_size(1))) __attribute__((alloc_size(2)))
> void* my_calloc_alt1(size_t n, size_t s)
> {
>   void* p = calloc(n,s);
>   printf("calloc __builtin_object_size 0,1,2,3: %ld, %ld, %ld, %ld\n"
> ,(long) __builtin_object_size(p, 0)
> ,(long) __builtin_object_size(p, 1)
> ,(long) __builtin_object_size(p, 2)
> ,(long) __builtin_object_size(p, 3)
> );
>   return p;
> }
> 
> int main()
> {
>   void* p = my_calloc_alt0(2,7);
>   printf("my_calloc_alt0 __builtin_object_size 0,1,2,3: %ld, %ld, %ld, %ld\n"
> ,(long) __builtin_object_size(p, 0)
> ,(long) __builtin_object_size(p, 1)
> ,(long) __builtin_object_size(p, 2)
> ,(long) __builtin_object_size(p, 3)
> );
>   void* q = my_calloc_alt1(2,7);
>   printf("my_calloc_alt0 __builtin_object_size 0,1,2,3: %ld, %ld, %ld, %ld\n"

The above line should have been:

printf("my_calloc_alt1 __builtin_object_size 0,1,2,3: %ld, %ld, %ld, %ld\n"

> ,(long) __builtin_object_size(q, 0)
> ,(long) __builtin_object_size(q, 1)
> ,(long) __builtin_object_size(q, 2)
> ,(long) __builtin_object_size(q, 3)
> );
> }
> 
> # uname -apKU
> FreeBSD FBSDFSSD 12.0-CURRENT FreeBSD 12.0-CURRENT  r327485M  amd64 amd64 
> 1200054 1200054
> 
> The system-clang 5.0.1 result was:
> 
> # clang -O2 alloc_size_attr_test.c

The later outputs are edited for clarity:

> # ./a.out
> calloc __builtin_object_size 0,1,2,3: 14, 14, 14, 0
> my_calloc_alt0 __builtin_object_size 0,1,2,3: 14, 14, 14, 0
> calloc __builtin_object_size 0,1,2,3: 14, 14, 14, 0
my_calloc_alt1 __builtin_object_size 0,1,2,3: 14, 14, 14, 0
> 
> The lang/gcc7 result was:
> 
> # gcc7 -O2 alloc_size_attr_test.c
> 
> # ./a.out
> calloc __builtin_object_size 0,1,2,3: -1, -1, 0, 0
> my_calloc_alt0 __builtin_object_size 0,1,2,3: 14, 14, 14, 14
> calloc __builtin_object_size 0,1,2,3: -1, -1, 0, 0
my_calloc_alt1 __builtin_object_size 0,1,2,3: 14, 7, 14, 14
> 
> I'll ignore that gcc does not provide actual sizes
> via __builtin_object_size for calloc use.
> 
> Pairing the other lines for easy comparison, with
> some notes mixed in:
> 
> __attribute__((alloc_size(1,2))) style:
> my_calloc_alt0 __builtin_object_size 0,1,2,3: 14, 14, 14, 0  (system clang)
> my_calloc_alt0 __builtin_object_size 0,1,2,3: 14, 14, 14, 14 (gcc7)
> 
> __attribute__((alloc_size(1))) __attribute__((alloc_size(2))) style:
my_calloc_alt1 __builtin_object_size 0,1,2,3: 14, 14, 14, 0  (system clang)
my_calloc_alt1 __builtin_object_size 0,1,2,3: 14, 7, 14, 14  (gcc7)
> 
> Thus. . .
> 
> For __attribute__((alloc_size(1))) __attribute__((alloc_size(2))):
> __builtin_object_size(p,1) is not equivalent (clang vs. gcc7)
> 
> For both of the alloc_size usage styles:
> __builtin_object_size(p,3) is not equivalent (clang vs. gcc7)
> 
> This means that the two style of alloc_size use are not
> equivalent across some major compilers/toolchains.
> 
> But I do not know if either of the differences is a problem or
> not.
> 
> 
> Note: without a sufficient -O all the figures can be
> the mix of -1's and 0's.


===
Mark Millard
marklmi at yahoo.com
( markmi at dsl-only.net is
going away in 2018-Feb, late)

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[Bug 225330] clang bug can incorrectly enable or disable interrupts on amd64

2018-01-20 Thread bugzilla-noreply 
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=225330

Dimitry Andric  changed:

   What|Removed |Added

 CC||d...@freebsd.org

--- Comment #1 from Dimitry Andric  ---
It would be much better to take this issue upstream.  We would not want to
carry patches like this without them having been checked over first.

-- 
You are receiving this mail because:
You are the assignee for the bug.
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