Re: [reviewed] qsort comparator consistency checking

[Andrew Pinski <pinskia@gmail.com>]

On Fri, Sep 29, 2017 at 10:46 AM, Christophe Lyon
<christophe.lyon@linaro.org> wrote:
> Hi,
>
>
> On 29 September 2017 at 15:29, Alexander Monakov <amonakov@ispras.ru> wrote:
>> Hello,
>>
>> I'm going to install the following patch on trunk in the next few hours.
>> This revision doesn't offer per-callsite opt-out anymore as suggested by
>> Richi on the Cauldron (made possible by fixing all known issues on trunk).
>> Thus this patch has a few minor differences compared to the previous
>> revision that was ack'ed by Jeff.
>>
>> Tested on x86_64-linux, i686-linux and ppc64le-linux.
>>
>> Alexander
>>
>>         * genmodes.c (calc_wider_mode): Suppress qsort macro.
>>         * system.h [CHECKING_P] (qsort): Redirect to qsort_chk.
>>         (qsort_chk): Declare.
>>         * vec.c [CHECKING_P] (qsort_chk_error): New static function.
>>         (qsort_chk): New function.
>>
>
> This patch (r253295) breaks the gcc build for aarch64-linux-gnu:


I was just about to report the same thing.

Thanks,
Andrew

> libtool: compile:
> /tmp/3041688_6.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-aarch64-none-linux-gnu/gcc3/./gcc/xgcc
> -shared-libgcc -B/tmp/3041688_6.t
> mpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-aarch64-none-linux-gnu/gcc3/./gcc
> -nostdinc++ -L/tmp/3041688_6.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj
> -aarch64-none-linux-gnu/gcc3/aarch64-none-linux-gnu/libstdc++-v3/src
> -L/tmp/3041688_6.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-aarch64-none-linux-g
> nu/gcc3/aarch64-none-linux-gnu/libstdc++-v3/src/.libs
> -L/tmp/3041688_6.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-aarch64-none-linux-gnu/gcc3/aarch64
> -none-linux-gnu/libstdc++-v3/libsupc++/.libs
> -B/tmp/3041688_6.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/tools/aarch64-none-linux-gnu/bin/
> -B/tmp/3041688_6.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/tools/aarch64-none-linux-gnu/lib/
> -isystem /tmp/3041688_6.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/tools/aarch64-none-linux-gnu/include
> -isystem /tmp/3041688_6.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/tools/aarch64-none-linux-gnu/sys-include
> -I/tmp/3041688_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/libstdc++-v3/../libgcc
> -I/tmp/3041688_6.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-aarch64-none-linux-gnu/gcc3/aarch64-none-linux-gnu/libstdc++-v3/include/aarch64-none-linux-gnu
> -I/tmp/3041688_6.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-aarch64-none-linux-gnu/gcc3/aarch64-none-linux-gnu/libstdc++-v3/include
> -I/tmp/3041688_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/libstdc++-v3/libsupc++
> -D_GLIBCXX_SHARED -std=gnu++14 -Wall -Wextra -Wwrite-strings
> -Wcast-qual -Wabi -fdiagnostics-show-location=once -ffunction-sections
> -fdata-sections -frandom-seed=ops.lo -g -O2 -D_GNU_SOURCE -c
> /tmp/3041688_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/libstdc++-v3/src/filesystem/ops.cc
>  -fPIC -DPIC -D_GLIBCXX_SHARED -o ops.o
> In file included from
> /tmp/3041688_6.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-aarch64-none-linux-gnu/gcc3/aarch64-none-linux-gnu/libstdc++-v3/include/deque:66:0,
>                  from
> /tmp/3041688_6.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-aarch64-none-linux-gnu/gcc3/aarch64-none-linux-gnu/libstdc++-v3/include/stack:60,
>                  from
> /tmp/3041688_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/libstdc++-v3/src/filesystem/ops.cc:32:
> /tmp/3041688_6.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-aarch64-none-linux-gnu/gcc3/aarch64-none-linux-gnu/libstdc++-v3/include/bits/deque.tcc:
> In member function 'void std::deque<_Tp,
> _Alloc>::_M_range_insert_aux(std::deque<_Tp, _Alloc>::iterator,
> _ForwardIterator, _ForwardIterator, std::forward_iterator_tag) [with
> _ForwardIterator =
> std::experimental::filesystem::v1::__cxx11::path::iterator; _Tp =
> std::experimental::filesystem::v1::__cxx11::path; _Alloc =
> std::allocator<std::experimental::filesystem::v1::__cxx11::path>]':
> /tmp/3041688_6.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-aarch64-none-linux-gnu/gcc3/aarch64-none-linux-gnu/libstdc++-v3/include/bits/deque.tcc:626:7:
> error: qsort comparator non-negative on sorted output: 8
>        }
>        ^
> during RTL pass: sched2
> /tmp/3041688_6.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-aarch64-none-linux-gnu/gcc3/aarch64-none-linux-gnu/libstdc++-v3/include/bits/deque.tcc:626:7:
> internal compiler error: qsort checking failed
> 0x55f7a1 qsort_chk_error
>         /tmp/3041688_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/vec.c:222
> 0x15337d8 qsort_chk(void*, unsigned long, unsigned long, int (*)(void
> const*, void const*))
>         /tmp/3041688_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/vec.c:274
> 0x14360e0 ready_sort_real
>         /tmp/3041688_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/haifa-sched.c:3087
> 0x143de85 schedule_block(basic_block_def**, void*)
>         /tmp/3041688_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/haifa-sched.c:6749
> 0xd42132 schedule_region
>         /tmp/3041688_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/sched-rgn.c:3174
> 0xd42132 schedule_insns()
>         /tmp/3041688_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/sched-rgn.c:3513
> 0xd424ee rest_of_handle_sched2
>         /tmp/3041688_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/sched-rgn.c:3737
> 0xd424ee execute
>         /tmp/3041688_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/sched-rgn.c:3873
>
> Christophe
>
>> diff --git a/gcc/genmodes.c b/gcc/genmodes.c
>> index 97ed949c255..4eb8ee56d88 100644
>> --- a/gcc/genmodes.c
>> +++ b/gcc/genmodes.c
>> @@ -880,7 +880,7 @@ calc_wider_mode (void)
>>           for (i = 0, m = modes[c]; m; i++, m = m->next)
>>             sortbuf[i] = m;
>>
>> -         qsort (sortbuf, i, sizeof (struct mode_data *), cmp_modes);
>> +         (qsort) (sortbuf, i, sizeof (struct mode_data *), cmp_modes);
>>
>>           sortbuf[i] = 0;
>>           for (j = 0; j < i; j++)
>> diff --git a/gcc/system.h b/gcc/system.h
>> index 59449f1942b..f0664e93fc8 100644
>> --- a/gcc/system.h
>> +++ b/gcc/system.h
>> @@ -1181,4 +1181,14 @@ helper_const_non_const_cast (const char *p)
>>  /* Get definitions of HOST_WIDE_INT.  */
>>  #include "hwint.h"
>>
>> +/* qsort comparator consistency checking: except in release-checking compilers,
>> +   redirect 4-argument qsort calls to qsort_chk; keep 1-argument invocations
>> +   corresponding to vec::qsort (cmp): they use C qsort internally anyway.  */
>> +#if CHECKING_P
>> +#define PP_5th(a1, a2, a3, a4, a5, ...) a5
>> +#undef qsort
>> +#define qsort(...) PP_5th (__VA_ARGS__, qsort_chk, 3, 2, qsort, 0) (__VA_ARGS__)
>> +void qsort_chk (void *, size_t, size_t, int (*)(const void *, const void *));
>> +#endif
>> +
>>  #endif /* ! GCC_SYSTEM_H */
>> diff --git a/gcc/vec.c b/gcc/vec.c
>> index d612703184b..9a80f3421db 100644
>> --- a/gcc/vec.c
>> +++ b/gcc/vec.c
>> @@ -31,6 +31,12 @@ along with GCC; see the file COPYING3.  If not see
>>  #include "coretypes.h"
>>  #include "hash-table.h"
>>  #include "selftest.h"
>> +#ifdef GENERATOR_FILE
>> +#include "errors.h"
>> +#else
>> +#include "input.h"
>> +#include "diagnostic-core.h"
>> +#endif
>>
>>  /* vNULL is an empty type with a template cast operation that returns
>>     a zero-initialized vec<T, A, L> instance.  Use this when you want
>> @@ -190,6 +196,93 @@ dump_vec_loc_statistics (void)
>>    vec_mem_desc.dump (VEC_ORIGIN);
>>  }
>>
>> +#if CHECKING_P
>> +/* Report qsort comparator CMP consistency check failure with P1, P2, P3 as
>> +   witness elements.  */
>> +ATTRIBUTE_NORETURN ATTRIBUTE_COLD
>> +static void
>> +qsort_chk_error (const void *p1, const void *p2, const void *p3,
>> +                int (*cmp) (const void *, const void *))
>> +{
>> +  if (!p3)
>> +    {
>> +      int r1 = cmp (p1, p2), r2 = cmp (p2, p1);
>> +      error ("qsort comparator not anti-commutative: %d, %d", r1, r2);
>> +    }
>> +  else if (p1 == p2)
>> +    {
>> +      int r = cmp (p1, p3);
>> +      error ("qsort comparator non-negative on sorted output: %d", r);
>> +    }
>> +  else
>> +    {
>> +      int r1 = cmp (p1, p2), r2 = cmp (p2, p3), r3 = cmp (p1, p3);
>> +      error ("qsort comparator not transitive: %d, %d, %d", r1, r2, r3);
>> +    }
>> +  internal_error ("qsort checking failed");
>> +}
>> +
>> +/* Wrapper around qsort with checking that CMP is consistent on given input.
>> +
>> +   Strictly speaking, passing invalid (non-transitive, non-anti-commutative)
>> +   comparators to libc qsort can result in undefined behavior.  Therefore we
>> +   should ideally perform consistency checks prior to invoking qsort, but in
>> +   order to do that optimally we'd need to sort the array ourselves beforehand
>> +   with a sorting routine known to be "safe".  Instead, we expect that most
>> +   implementations in practice will still produce some permutation of input
>> +   array even for invalid comparators, which enables us to perform checks on
>> +   the output array.  */
>> +void
>> +qsort_chk (void *base, size_t n, size_t size,
>> +          int (*cmp)(const void *, const void *))
>> +{
>> +  (qsort) (base, n, size, cmp);
>> +#if 0
>> +#define LIM(n) (n)
>> +#else
>> +  /* Limit overall time complexity to O(n log n).  */
>> +#define LIM(n) ((n) <= 16 ? (n) : 12 + floor_log2 (n))
>> +#endif
>> +#define ELT(i) ((const char *) base + (i) * size)
>> +#define CMP(i, j) cmp (ELT (i), ELT (j))
>> +#define ERR2(i, j) qsort_chk_error (ELT (i), ELT (j), NULL, cmp)
>> +#define ERR3(i, j, k) qsort_chk_error (ELT (i), ELT (j), ELT (k), cmp)
>> +  size_t i1, i2, i, j;
>> +  /* This outer loop iterates over maximum spans [i1, i2) such that
>> +     elements within each span compare equal to each other.  */
>> +  for (i1 = 0; i1 < n; i1 = i2)
>> +    {
>> +      /* Position i2 one past last element that compares equal to i1'th.  */
>> +      for (i2 = i1 + 1; i2 < n; i2++)
>> +       if (CMP (i1, i2))
>> +         break;
>> +       else if (CMP (i2, i1))
>> +         return ERR2 (i1, i2);
>> +      size_t lim1 = LIM (i2 - i1), lim2 = LIM (n - i2);
>> +      /* Verify that other pairs within current span compare equal.  */
>> +      for (i = i1 + 1; i + 1 < i2; i++)
>> +       for (j = i + 1; j < i1 + lim1; j++)
>> +         if (CMP (i, j))
>> +           return ERR3 (i, i1, j);
>> +         else if (CMP (j, i))
>> +           return ERR2 (i, j);
>> +      /* Verify that elements within this span compare less than
>> +         elements beyond the span.  */
>> +      for (i = i1; i < i2; i++)
>> +       for (j = i2; j < i2 + lim2; j++)
>> +         if (CMP (i, j) >= 0)
>> +           return ERR3 (i, i1, j);
>> +         else if (CMP (j, i) <= 0)
>> +           return ERR2 (i, j);
>> +    }
>> +#undef ERR3
>> +#undef ERR2
>> +#undef CMP
>> +#undef ELT
>> +#undef LIM
>> +}
>> +#endif /* #if CHECKING_P */
>> +
>>  #ifndef GENERATOR_FILE
>>  #if CHECKING_P
>>