diff options
Diffstat (limited to 'gc/doc/README.linux')
| -rw-r--r-- | gc/doc/README.linux | 135 |
1 files changed, 0 insertions, 135 deletions
diff --git a/gc/doc/README.linux b/gc/doc/README.linux deleted file mode 100644 index efd0a26..0000000 --- a/gc/doc/README.linux +++ /dev/null @@ -1,135 +0,0 @@ -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); -} - - |