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