Hi dmtcp folks,
I am running dmtcp 2.4.5 release on a red hat 6.6 (see detailed in in appendix
below) and run into the following problem:
* the vdso section is re-located after mtcp_check_vdso is executed in
mtcp_restart
- personality flag ADDR_NO_RANDOMIZE is not set when mtcp_restart is
executed
* leads mtcp_restart to set ADDR_NO_RANDOMIZE and re-exec mtcp_restart in
mtcp_check_vdso
* after the re-exec the vdso section is in a different location
-> in turn this breaks restore for some processes as the new vdso overlaps
with the location where mtcp_restart wants to re-locate itself to
I didn't really tried newer dmtcp-* releases as the corresponding code seem the
same in master.
I tried to reconstruct the whole scenario without dmtcp as in the c file test.c
(see appendix below).
Surprisingly to me the vdso section was not relocated when running this test
program.
I wanted to ask the following:
* Do you have any experience or explanation why the vdso section moves in
mtcp_restart after setting ADDR_NO_RANDOMIZE and re-execing but not in the test
program?
Is the re-location maybe not related to setting ADDR_NO_RANDOMIZE?
* Generally, do we need to set ADDR_NO_RANDOMIZE in mtcp_check_vdso if ASLR
is turned off globally (/proc/sys/kernel/randomize_va_space == 0)?
Thanks a lot for any feedback or thoughts.
Cheers
Johannes
Appendix:
[test.c]:
===============================================================
#include <sys/personality.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
int main() {
int pers = personality (0xfffffffful);
printf("personality=0x%x, ADDR_NO_RANDOMIZE=%d, ADDR_COMPAT_LAYOUT=%d\n",
pers, (pers&ADDR_NO_RANDOMIZE?1:0), (pers&ADDR_COMPAT_LAYOUT?1:0));
personality ((pers | ADDR_NO_RANDOMIZE) & ~ADDR_COMPAT_LAYOUT);
pers = personality (0xfffffffful);
printf("personality=0x%x, ADDR_NO_RANDOMIZE=%d, ADDR_COMPAT_LAYOUT=%d\n",
pers, (pers&ADDR_NO_RANDOMIZE?1:0), (pers&ADDR_COMPAT_LAYOUT?1:0));
{
FILE* f = fopen("/proc/self/maps", "r");
int c;
while ((c = getc(f)) != EOF) {
printf("%c", c);
}
}
if (!getenv("REEXEC")) {
char* envp[] = { "REEXEC=1", 0};
execve("./test",0,envp);
}
return 0;
}
===============================================================
[env]:
===============================================================
DMTCP version: 2.4.5
Date built: Tue Mar 19 08:47:01 CET 2019
config.log: ./configure --prefix=<PATH>/dmtcp-gcc-6.2.0/2.4.5 CXXFLAGS=-g3
-O0 -DDEBUG CFLAGS=-g3 -O0 -DDEBUG --enable-debug --disable-m32
--disable-pthread-mutex-wrappers --d
isable-openmp --disable-infiniband-support --disable-forked-checkpointing
--disable-fast-restart --disable-delta-compression
Description: CentOS release 6.6 (Final)
Codename: Final
Linux 2.6.32-696.30.1.el6.x86_64 #1 SMP Tue May 22 03:28:18 UTC 2018 x86_64
x86_64 x86_64 GNU/Linux
Compiler: gcc
Using built-in specs.
COLLECT_GCC=/SDR/main/linux64/bin/gcc
COLLECT_LTO_WRAPPER=/SDR/linux64/gcc/6.2.0/bin/../libexec/gcc/x86_64-pc-linux-gnu/6.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /sdrsandbox/linux64/gcc520/src/gcc-6.2.0/configure
--disable-nls --enable-languages=c++,fortran --with-gnu-as --with-gnu-ld
--enable-__cxa_atexit --with-cpu=generic --prefix=/SDR/linux64/
gcc/6.2.0
Thread model: posix
gcc version 6.2.0 (GCC)
CFLAGS: -DDEBUG -g -O0 -Wall
CXXFLAGS: -DDEBUG -g -O0 -Wall
CPPFLAGS:
LDFLAGS:
openjdk version "1.8.0_171"
OpenJDK Runtime Environment (build 1.8.0_171-b10)
OpenJDK 64-Bit Server VM (build 25.171-b10, mixed mode)
lrwxrwxrwx 1 root root 12 Apr 12 2018 /lib64/libc.so.6 -> libc-2.12.so
lrwxrwxrwx 1 root root 12 Apr 12 2018 /lib/libc.so.6 -> libc-2.12.so
-rw------- 1 root root 217016 Mar 19 08:46 /var/db/nscd/hosts
-rw-r--r-- 1 root root 5 Dec 8 10:22 /var/run/nscd/nscd.pid
srw-rw-rw- 1 root root 0 Dec 8 10:22 /var/run/nscd/socket
===============================================================
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