[Bug c++/111436] New: Wrong code when bit-casting struct through pointer
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111436
Bug ID: 111436
Summary: Wrong code when bit-casting struct through pointer
Product: gcc
Version: 12.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: josopait at goopax dot com
Target Milestone: ---
Does gcc produce wrong code here? The program below is part of a bitwise
conversion mechanism, similar to std::bit_cast, but for more general types.
The output should be:
from=17,23
to=17,23
But with -O2 or higher the output is:
from=17,23
to=0,0
I tried with gcc 12, 13, and 14 on x86_64 linux.
#include
#include
#include
using namespace std;
template
inline void reinterpret_switch3(TO& to, const FROM& from)
{
to = *reinterpret_cast(&from);
}
template
inline void reinterpret_switch2(TO& to, const FROM& from)
{
reinterpret_switch3(to, array({ { from } }));
}
template
inline void reinterpret_switch(TO& to, const FROM& from)
{
array tmp;
reinterpret_switch2(tmp, from);
to = tmp[0];
}
int main(int argc, char** argv)
{
pair from = {17, 23};
pair to;
reinterpret_switch(to, from);
cout << "from=" << from.first << "," << from.second << endl;
cout << "to=" << to.first << "," << to.second << endl;
}
[Bug libbacktrace/112322] New: std::stacktrace fails
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112322
Bug ID: 112322
Summary: std::stacktrace fails
Product: gcc
Version: 12.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libbacktrace
Assignee: unassigned at gcc dot gnu.org
Reporter: josopait at goopax dot com
CC: ian at gcc dot gnu.org
Target Milestone: ---
I installed gcc on gentoo linux:
EXTRA_ECONF="--enable-libstdcxx-backtrace=yes" emerge gcc
and compiled the following program:
#include
#include
int main()
{
std::cout << std::stacktrace::current() << std::endl;
}
$ g++-13 -g -std=c++23 a.cpp -o a -lstdc++_libbacktrace
When compiled with GCC 13 or GCC 14, the program output is weird:
$ ./a
0# at :32764
1# at :32764
2# at :32764
3# at :32764
4#
The number 32764 changes randomly between program calls, in the range 32764 ..
32767.
When compiled with GCC 12, the program crashes with a segmentation fault:
(gdb) bt
#0 0x in ?? ()
#1 0xad41 in elf_nodebug (state=, pc=, callback=, data=, error_callback=) at elf.c:585
#2 elf_nodebug (state=, pc=, callback=, error_callback=, data=) at elf.c:565
#3 0x7c0f in std::stacktrace_entry::_M_get_info
(this=0x5557e2b0, __desc=0x7fffdb60, __file=0x7fffdb80,
__line=0x7fffdb5c) at
/usr/lib/gcc/x86_64-pc-linux-gnu/12/include/g++-v12/stacktrace:191
#4 0x7db2 in std::operator<< (__os=..., __f=...) at
/usr/lib/gcc/x86_64-pc-linux-gnu/12/include/g++-v12/stacktrace:722
#5 0x85ce in std::operator<<
> (__os=..., __st=...) at
/usr/lib/gcc/x86_64-pc-linux-gnu/12/include/g++-v12/stacktrace:737
#6 0x7492 in main () at a.cpp:8
Here, parameter `state` of function elf_nodebug points to:
(gdb) p *__state
$10 = {filename = 0x0, threaded = 1, lock = 0x0, fileline_fn = 0xa5f0
, fileline_data = 0x0, syminfo_fn = 0xa5d0 ,
syminfo_data = 0x0, fileline_initialization_failed = 0, lock_alloc = 0,
freelist = 0x77fc4048}
and error_callback is NULL, which causes the segmentation fault.
[Bug libstdc++/112498] New: std::is_convertible::value returns false
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112498
Bug ID: 112498
Summary: std::is_convertible::value returns
false
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: josopait at goopax dot com
Target Milestone: ---
If I am not mistaken, this should succeed:
#include
int main()
{
static_assert(std::is_convertible::value); // ok
static_assert(std::is_convertible::value); // fails
}
[Bug c++/112498] std::is_convertible::value returns false
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112498 --- Comment #2 from Ingo Josopait --- Yes, you are right. It is confusing, though. Maybe the warning message should mention that it is actually invalid code. It looked more like a suggestion to me.
