[Bug c++/114753] New: from_chars aborts with -m32 -ftrapv when passed -9223372036854775808

[Bug c++/114753] New: from_chars aborts with -m32 -ftrapv when passed -9223372036854775808

[gnu.ojxq8 at dralias dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114753

            Bug ID: 114753
           Summary: from_chars aborts with -m32 -ftrapv when passed
                    -9223372036854775808
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gnu.ojxq8 at dralias dot com
  Target Milestone: ---

std::from_chars may abort when used with -m32 -ftrapv on some values.

Without -m32, or without -ftrapv, or using clang, the code works correctly.

To reproduce:

$ cat a.cpp 
#include <charconv>
#include <cstdint>
#include <string_view>
int main() {
  int64_t result{};
  std::string_view str{"-9223372036854775808"};
  (void)std::from_chars(str.begin(), str.end(), result);
  return result != -9223372036854775807 - 1;
}


$  g++ -m32 -ftrapv -std=c++17 ./a.cpp && ./a.out 
Aborted (core dumped)

[Bug c++/114753] from_chars aborts with -m32 -ftrapv when passed -9223372036854775808

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114753

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2024-04-17
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The abort happens here:

                  if (__builtin_mul_overflow(__val, __sign, &__tmp))

With __val = 9223372036854775808LL __sign = -1LL

The libgcc2.c:__mulvdi3 function reaches the abort() on line 375

[Bug c++/114753] from_chars aborts with -m32 -ftrapv when passed -9223372036854775808

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114753

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #1)
> With __val = 9223372036854775808LL __sign = -1LL

Oops, that should be __val = 9223372036854775808ULL and __sign = -1

i.e.

int main()
{
  unsigned long long val = 9223372036854775808ULL;
  int sign = -1;
  long long res;
  return __builtin_mul_overflow(val, sign, &res);
}

This shouldn't trap.

[Bug middle-end/114753] from_chars aborts with -m32 -ftrapv when passed -9223372036854775808

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114753

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
          Component|c++                         |middle-end
            Version|unknown                     |14.0

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  .MUL_OVERFLOW expansion likely ends up calling expand_binop
which decides for itself whether the op traps based on the result type.

[Bug middle-end/114753] from_chars aborts with -m32 -ftrapv when passed -9223372036854775808

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114753

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
#0  expand_binop (mode=E_DImode, binoptab=smulv_optab, op0=0x7ffff71b53f0, 
    op1=0x7ffff71b85a0, target=0x0, unsignedp=0, methods=OPTAB_LIB_WIDEN)
    at /space/rguenther/src/gcc/gcc/optabs.cc:1497
#1  0x000000000116edf5 in expand_mult (mode=E_DImode, op0=0x7ffff71b53f0, 
    op1=0x7ffff71b85a0, target=0x0, unsignedp=0, no_libcall=false)
    at /space/rguenther/src/gcc/gcc/expmed.cc:3610
#2  0x00000000011a38e0 in expand_expr_real_2 (ops=0x7fffffffcef0, target=0x0, 
    tmode=E_DImode, modifier=EXPAND_NORMAL)
    at /space/rguenther/src/gcc/gcc/expr.cc:10275
#3  0x0000000001359608 in expand_mul_overflow (loc=2147483653, 
    lhs=<ssa_name 0x7ffff7016ee8 6>, arg0=<nop_expr 0x7ffff7181aa0>, 
    arg1=<nop_expr 0x7ffff7181a80>, unsr_p=false, uns0_p=false, uns1_p=true, 
    is_ubsan=false, datap=0x0)
    at /space/rguenther/src/gcc/gcc/internal-fn.cc:2359
#4  0x000000000135b7f7 in expand_arith_overflow (code=MULT_EXPR, 
    stmt=<gimple_call 0x7ffff7019f30>)
    at /space/rguenther/src/gcc/gcc/internal-fn.cc:2827
#5  0x000000000135b9c3 in expand_MUL_OVERFLOW (stmt=0x7ffff7019f30)
    at /space/rguenther/src/gcc/gcc/internal-fn.cc:2876

so a hack would be to reset flag_trapv around

2354                 For unsigned multiplication when high parts are both
non-zero
2355                 this overflows always.  */
2356              ops.code = MULT_EXPR;
2357              ops.op0 = make_tree (type, op0);
2358              ops.op1 = make_tree (type, op1);
2359              tem = expand_expr_real_2 (&ops, NULL_RTX, mode,
EXPAND_NORMAL);

in expand_mul_overflow.

[Bug middle-end/114753] from_chars aborts with -m32 -ftrapv when passed -9223372036854775808

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114753

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I wouldn't call it a hack, I'd say it is the right fix.
Though, we have tons of those in internal-fn.cc
          ops.code = MULT_EXPR;
              ops.code = MULT_EXPR;
          ops.code = MULT_EXPR;
              ops.code = MULT_EXPR;
              ops.code = MULT_EXPR;
          ops.code = WIDEN_MULT_EXPR;
          ops.code = MULT_HIGHPART_EXPR;
          ops.code = MULT_EXPR;
          ops.code = WIDEN_MULT_EXPR;
          ops.code = MULT_EXPR;
          ops.code = MULT_EXPR;
      ops.code = PLUS_EXPR;
          ops.code = TRUNC_DIV_EXPR;
              ops.code = TRUNC_MOD_EXPR;
plus some which reuse earlier set ops.code plus some which use just some
variable as ops.code.  Sure, I think WIDEN_MULT_EXPR/MULT_HIGHPART_EXPR and the
div/mod neither probably consider flag_trapv, but MULT_EXPR/PLUS_EXPR does
(though, perhaps the PLUS_EXPR is for vectors only).
So, the question is where to put that.
To cover everything, bet best would be to put it into expand_mul_overflow and
expand_arith_overflow and expand_vector_ubsan_overflow.

[Bug middle-end/114753] from_chars aborts with -m32 -ftrapv when passed -9223372036854775808

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114753

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |jakub at gcc dot gnu.org

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 57972
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57972&action=edit
gcc14-pr114753.patch

Untested fix.

[Bug middle-end/114753] from_chars aborts with -m32 -ftrapv when passed -9223372036854775808

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114753

--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:6c152c9db3b5b9d43e12846fb7a44977c0b65fc2

commit r14-10012-g6c152c9db3b5b9d43e12846fb7a44977c0b65fc2
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Apr 18 09:45:14 2024 +0200

    internal-fn: Temporarily disable flag_trapv during .{ADD,SUB,MUL}_OVERFLOW
etc. expansion [PR114753]

    __builtin_{add,sub,mul}_overflow{,_p} builtins are well defined
    for all inputs even for -ftrapv, and the -fsanitize=signed-integer-overflow
    ifns shouldn't abort in libgcc but emit the desired ubsan diagnostics
    or abort depending on -fsanitize* setting regardless of -ftrapv.
    The expansion of these internal functions uses expand_expr* in various
    places (e.g. MULT_EXPR at least in 2 spots), so temporarily disabling
    flag_trapv in all those spots would be hard.
    The following patch disables it around the bodies of 3 functions
    which can do the expand_expr calls.
    If it was in the C++ FE, I'd use some RAII sentinel, but I don't think
    we have one in the middle-end.

    2024-04-18  Jakub Jelinek  <jakub@redhat.com>

            PR middle-end/114753
            * internal-fn.cc (expand_mul_overflow): Save flag_trapv and
            temporarily clear it for the duration of the function, then
            restore previous value.
            (expand_vector_ubsan_overflow): Likewise.
            (expand_arith_overflow): Likewise.

            * gcc.dg/pr114753.c: New test.

[Bug middle-end/114753] from_chars aborts with -m32 -ftrapv when passed -9223372036854775808

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114753

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed.

[Bug middle-end/114753] from_chars aborts with -m32 -ftrapv when passed -9223372036854775808

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114753

--- Comment #9 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:33bf8e5385099c2963f278bff38e4f917eddf1d8

commit r14-10041-g33bf8e5385099c2963f278bff38e4f917eddf1d8
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Apr 19 18:15:39 2024 +0200

    internal-fn: Fix up expand_arith_overflow [PR114753]

    During backporting I've noticed I've missed one return spot for the
    restoration of the original flag_trapv flag value.

    2024-04-19  Jakub Jelinek  <jakub@redhat.com>

            PR middle-end/114753
            * internal-fn.cc (expand_arith_overflow): Add one missing restore
            of flag_trapv before return.

[Bug middle-end/114753] from_chars aborts with -m32 -ftrapv when passed -9223372036854775808

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114753

--- Comment #10 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-13 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:10f689596ad1633f4f5de1852c8f82a993fe948e

commit r13-8635-g10f689596ad1633f4f5de1852c8f82a993fe948e
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Apr 18 09:45:14 2024 +0200

    internal-fn: Temporarily disable flag_trapv during .{ADD,SUB,MUL}_OVERFLOW
etc. expansion [PR114753]

    __builtin_{add,sub,mul}_overflow{,_p} builtins are well defined
    for all inputs even for -ftrapv, and the -fsanitize=signed-integer-overflow
    ifns shouldn't abort in libgcc but emit the desired ubsan diagnostics
    or abort depending on -fsanitize* setting regardless of -ftrapv.
    The expansion of these internal functions uses expand_expr* in various
    places (e.g. MULT_EXPR at least in 2 spots), so temporarily disabling
    flag_trapv in all those spots would be hard.
    The following patch disables it around the bodies of 3 functions
    which can do the expand_expr calls.
    If it was in the C++ FE, I'd use some RAII sentinel, but I don't think
    we have one in the middle-end.

    2024-04-18  Jakub Jelinek  <jakub@redhat.com>

            PR middle-end/114753
            * internal-fn.cc (expand_mul_overflow): Save flag_trapv and
            temporarily clear it for the duration of the function, then
            restore previous value.
            (expand_vector_ubsan_overflow): Likewise.
            (expand_arith_overflow): Likewise.

            * gcc.dg/pr114753.c: New test.

    (cherry picked from commit 6c152c9db3b5b9d43e12846fb7a44977c0b65fc2)

[Bug middle-end/114753] from_chars aborts with -m32 -ftrapv when passed -9223372036854775808

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114753

--- Comment #11 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed for 13.3 too.