https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71287
Bug ID: 71287
Summary: Possibly broken invocation of connect (and maybe
other) syscalls
Product: gcc
Version: 4.8.4
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: artpol84 at gmail dot com
Target Milestone: ---
Created attachment 38570
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=38570&action=edit
Change in SLURM sources that fixes the emmitted assembly code.
System type is Linux Mint 17.3. Was reproduced on RHEL 6.5 as well.
I'm facing the problem with the slurm compilation:
https://github.com/SchedMD/slurm
I'm building the master branch. And the problem I get is related to the
following construction:
https://github.com/SchedMD/slurm/blob/master/src/slurmd/slurmd/req.c#L6171:L6172
The problem I see is that "connect" returns "+1" instead of "-1". And I can't
reproduce this with the standalone code:
https://github.com/artpol84/poc/blob/master/linux-internals/syscalls/connect/cli_c1.c#L37
Here is what GDB shows for those 2 codes:
SLURM's req.c:
0x43e966 <_rpc_forward_data+326> lea 0x2(%rax),%edx
0x43e969 <_rpc_forward_data+329> lea -0x80(%rbp),%rcx
0x43e96d <_rpc_forward_data+333> mov -0xc4(%rbp),%eax
0x43e973 <_rpc_forward_data+339> mov %rcx,%rsi
0x43e976 <_rpc_forward_data+342> mov %eax,%edi
0x43e978 <_rpc_forward_data+344> callq 0x4287e0 <connect@plt>
# eax == -1
0x43e97d <_rpc_forward_data+349> shr $0x1f,%eax
# eax == 1
0x43e980 <_rpc_forward_data+352> movzbl %al,%eax
# eax == 1
0x43e983 <_rpc_forward_data+355> mov %eax,-0xc0(%rbp)
# (gdb) p $rbp
# $17 = (void *) 0x7fcb8e15ee60
# (gdb) p &rc
# $15 = (int *) 0x7fcb8e15eda0
# $rbp - 0xC0 == &rc
0x43e989 <_rpc_forward_data+361> cmpl $0x0,-0xc0(%rbp)
# if comparison
Standalone program:
0x400863 <usock_connect+198> mov %rcx,%rsi
0x400866 <usock_connect+201> mov %eax,%edi
0x400868 <usock_connect+203> callq 0x400690 <connect@plt>
# eax == -1
0x40086d <usock_connect+208> mov %eax,-0x94(%rbp)
# (gdb) p &rc
# $1 = (int *) 0x7fffffffdeac
# (gdb) p $rbp - 0x94
# $2 = (void *) 0x7fffffffdeac
# => we just move ( $eax == -1 ) to the rc.
0x400873 <usock_connect+214> cmpl $0x0,-0x94(%rbp)
0x40087a <usock_connect+221> jns 0x400888 <usock_connect+235>
So for some reasons the code issued by compiler for equal codes is different.
The compilation flags used was:
req.c:
gcc -DHAVE_CONFIG_H -I. -I../../.. -I../../../slurm
-DLIBSLURM_SO=\"/lxc-data/sandbox/slurm/lib/libslurm.so\" -I../../.. -g -O2
-pthread -Wall -g -O0 -fno-strict-aliasing -MT req.o -MD -MP -MF .deps/req.Tpo
-c -o req.o req.c
standalone (was trying to use the same flags):
gcc -g -O2 -pthread -Wall -g -O0 -fno-strict-aliasing -c -o cli_c1.o cli_c1.c
FIX that changes the situation in SLURM: if I apply attached patch to the SLURM
sources that shightly changes C construction:
- while ((rc = connect(fd, (struct sockaddr *)&sa, SUN_LEN(&sa)) < 0) &&
- (errno == EINTR));
+
+ do {
+ rc = connect(fd, (struct sockaddr *)&sa, SUN_LEN(&sa));
+ } while( (rc < 0) && (errno == EINTR) );
I'm getting correct code:
0x43e971 <_rpc_forward_data+337> mov %eax,%edi
0x43e973 <_rpc_forward_data+339> callq 0x4287e0 <connect@plt>
0x43e978 <_rpc_forward_data+344> mov %eax,-0xc0(%rbp)
0x43e97e <_rpc_forward_data+350> cmpl $0x0,-0xc0(%rbp)
