136 lines
4.6 KiB
Plaintext
136 lines
4.6 KiB
Plaintext
See README.alpha for Linux on DEC AXP info.
|
|
|
|
This file applies mostly to Linux/Intel IA32. Ports to Linux on an M68K
|
|
and PowerPC are also integrated. They should behave similarly, except that
|
|
the PowerPC port lacks incremental GC support, and it is unknown to what
|
|
extent the Linux threads code is functional. See below for M68K specific
|
|
notes.
|
|
|
|
Incremental GC is supported on Intel IA32 and M68K.
|
|
|
|
Dynamic libraries are supported on an ELF system. A static executable
|
|
should be linked with the gcc option "-Wl,-defsym,_DYNAMIC=0".
|
|
|
|
The collector appears to work with Linux threads. We have seen
|
|
intermittent hangs in sem_wait. So far we have been unable to reproduce
|
|
these unless the process was being debugged or traced. Thus it's
|
|
possible that the only real issue is that the debugger loses
|
|
signals on rare occasions.
|
|
|
|
The garbage collector uses SIGPWR and SIGXCPU if it is used with
|
|
Linux threads. These should not be touched by the client program.
|
|
|
|
To use threads, you need to abide by the following requirements:
|
|
|
|
1) You need to use LinuxThreads (which are included in libc6).
|
|
|
|
The collector relies on some implementation details of the LinuxThreads
|
|
package. It is unlikely that this code will work on other
|
|
pthread implementations (in particular it will *not* work with
|
|
MIT pthreads).
|
|
|
|
2) You must compile the collector with -DGC_LINUX_THREADS and -D_REENTRANT
|
|
specified in the Makefile.
|
|
|
|
3a) Every file that makes thread calls should define GC_LINUX_THREADS and
|
|
_REENTRANT and then include gc.h. Gc.h redefines some of the
|
|
pthread primitives as macros which also provide the collector with
|
|
information it requires.
|
|
|
|
3b) A new alternative to (3a) is to build the collector and compile GC clients
|
|
with -DGC_USE_LD_WRAP, and to link the final program with
|
|
|
|
(for ld) --wrap read --wrap dlopen --wrap pthread_create \
|
|
--wrap pthread_join --wrap pthread_detach \
|
|
--wrap pthread_sigmask --wrap sleep
|
|
|
|
(for gcc) -Wl,--wrap -Wl,read -Wl,--wrap -Wl,dlopen -Wl,--wrap \
|
|
-Wl,pthread_create -Wl,--wrap -Wl,pthread_join -Wl,--wrap \
|
|
-Wl,pthread_detach -Wl,--wrap -Wl,pthread_sigmask \
|
|
-Wl,--wrap -Wl,sleep
|
|
|
|
In any case, _REENTRANT should be defined during compilation.
|
|
|
|
4) Dlopen() disables collection during its execution. (It can't run
|
|
concurrently with the collector, since the collector looks at its
|
|
data structures. It can't acquire the allocator lock, since arbitrary
|
|
user startup code may run as part of dlopen().) Under unusual
|
|
conditions, this may cause unexpected heap growth.
|
|
|
|
5) The combination of GC_LINUX_THREADS, REDIRECT_MALLOC, and incremental
|
|
collection fails in seemingly random places. This hasn't been tracked
|
|
down yet, but is perhaps not completely astonishing. The thread package
|
|
uses malloc, and thus can presumably get SIGSEGVs while inside the
|
|
package. There is no real guarantee that signals are handled properly
|
|
at that point.
|
|
|
|
6) Thread local storage may not be viewed as part of the root set by the
|
|
collector. This probably depends on the linuxthreads version. For the
|
|
time being, any collectable memory referenced by thread local storage should
|
|
also be referenced from elsewhere, or be allocated as uncollectable.
|
|
(This is really a bug that should be fixed somehow.)
|
|
|
|
|
|
M68K LINUX:
|
|
(From Richard Zidlicky)
|
|
The bad news is that it can crash every linux-m68k kernel on a 68040,
|
|
so an additional test is needed somewhere on startup. I have meanwhile
|
|
patches to correct the problem in 68040 buserror handler but it is not
|
|
yet in any standard kernel.
|
|
|
|
Here is a simple test program to detect whether the kernel has the
|
|
problem. It could be run as a separate check in configure or tested
|
|
upon startup. If it fails (return !0) than mprotect can't be used
|
|
on that system.
|
|
|
|
/*
|
|
* test for bug that may crash 68040 based Linux
|
|
*/
|
|
|
|
#include <sys/mman.h>
|
|
#include <signal.h>
|
|
#include <unistd.h>
|
|
#include <stdio.h>
|
|
#include <stdlib.h>
|
|
|
|
|
|
char *membase;
|
|
int pagesize=4096;
|
|
int pageshift=12;
|
|
int x_taken=0;
|
|
|
|
int sighandler(int sig)
|
|
{
|
|
mprotect(membase,pagesize,PROT_READ|PROT_WRITE);
|
|
x_taken=1;
|
|
}
|
|
|
|
main()
|
|
{
|
|
long l;
|
|
|
|
signal(SIGSEGV,sighandler);
|
|
l=(long)mmap(NULL,pagesize,PROT_READ,MAP_PRIVATE | MAP_ANON,-1,0);
|
|
if (l==-1)
|
|
{
|
|
perror("mmap/malloc");
|
|
abort();
|
|
}
|
|
membase=(char*)l;
|
|
*(long*)(membase+sizeof(long))=123456789;
|
|
if (*(long*)(membase+sizeof(long)) != 123456789 )
|
|
{
|
|
fprintf(stderr,"writeback failed !\n");
|
|
exit(1);
|
|
}
|
|
if (!x_taken)
|
|
{
|
|
fprintf(stderr,"exception not taken !\n");
|
|
exit(1);
|
|
}
|
|
fprintf(stderr,"vmtest Ok\n");
|
|
exit(0);
|
|
}
|
|
|
|
|