[Bug c/101925] New: reversed storage order when compiling with -O3 only
george.thopas at gmail dot com
gcc-bugzilla@gcc.gnu.org
Sun Aug 15 23:43:34 GMT 2021
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101925
Bug ID: 101925
Summary: reversed storage order when compiling with -O3 only
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: george.thopas at gmail dot com
Target Milestone: ---
/*
reversed storage order when compiling with -O3 only.
this time sets up an all big-endian struct
from an all little-endian one
no warnings
Target: x86_64-pc-linux-gnu
gcc versie 11.1.0 (Gentoo 11.1.0-r2 p3)
gcc-trunk too
$ gcc -Wall -Wextra -O3 test.c
$ ./a.out
Abort
*/
#define BIG_ENDIAN __attribute__((scalar_storage_order("big-endian")))
/* host order version (little endian)*/
struct _ip6_addr {
union {
char addr8[16];
int addr32[4];
} u;
};
typedef struct _ip6_addr t_ip6_addr;
struct _net_addr {
char is_v4;
union {
int addr;
t_ip6_addr addr6;
} u;
};
typedef struct _net_addr t_net_addr;
/* big endian version */
struct _be_ip6_addr {
union {
char addr8[16];
} BIG_ENDIAN u;
} BIG_ENDIAN;
typedef struct _be_ip6_addr t_be_ip6_addr;
struct _be_net_addr {
char is_v4;
union {
t_be_ip6_addr addr6;
int addr;
} BIG_ENDIAN u;
} BIG_ENDIAN;
typedef struct _be_net_addr t_be_net_addr;
/* convert */
t_be_ip6_addr be_ip6_addr(const t_ip6_addr ip6)
{
t_be_ip6_addr rc = {
.u.addr8[0] = ip6.u.addr8[0],
.u.addr8[1] = ip6.u.addr8[1],
.u.addr8[2] = ip6.u.addr8[2],
.u.addr8[3] = ip6.u.addr8[3],
.u.addr8[4] = ip6.u.addr8[4],
.u.addr8[5] = ip6.u.addr8[5],
.u.addr8[6] = ip6.u.addr8[6],
.u.addr8[7] = ip6.u.addr8[7],
.u.addr8[8] = ip6.u.addr8[8],
.u.addr8[9] = ip6.u.addr8[9],
.u.addr8[10] = ip6.u.addr8[10],
.u.addr8[11] = ip6.u.addr8[11],
.u.addr8[12] = ip6.u.addr8[12],
.u.addr8[13] = ip6.u.addr8[13],
.u.addr8[14] = ip6.u.addr8[14],
.u.addr8[15] = ip6.u.addr8[15],
};
return rc;
}
t_be_net_addr be_net_addr(const t_net_addr ip)
{
t_be_net_addr rc = {.is_v4 = ip.is_v4 };
if (ip.is_v4) {
rc.u.addr = ip.u.addr;
} else {
rc.u.addr6 = be_ip6_addr(ip.u.addr6);
}
return rc;
}
int main(void)
{
t_be_net_addr out = { };
t_net_addr in = {
.is_v4 = 0,
.u.addr6.u.addr8 =
{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 }
};
out = be_net_addr(in);
// actually first 4 bytes are swapped
if (in.u.addr6.u.addr8[0] != out.u.addr6.u.addr8[0])
__builtin_abort();
return 0;
}
More information about the Gcc-bugs
mailing list