[[!meta copyright="Copyright © 2010 Free Software Foundation, Inc."]] [[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable id="license" text="Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled [[GNU Free Documentation License|/fdl]]."]]"""]] Here's what's to be done for maintaining Boehm GC. This one does need Hurd-specific configuration. It is, for example, used by [[/GCC]] (which has its own fork), so any changes committed upstream should very like also be made there. # [[General information|/boehm_gc]] # [[Sources|source_repositories/boehm_gc]] # Configuration [[tschwinge]] reviewed its GNU/Hurd port's configuration on 2010-12-08, based on CVS HEAD sources from 2010-12-02, converted to [[Git, correspondingly 1c2455988a8f59a5f83b986b9156f03be395b3b6|source_repositories/boehm_gc]]. * `configure.ac` * `PARALLEL_MARK` is not enabled; doesn't make sense so far. * `*-*-kfreebsd*-gnu` defines `USE_COMPILER_TLS`. What's this, and why does not other config? * TODO [ if test "$enable_gc_debug" = "yes"; then AC_MSG_WARN("Should define GC_DEBUG and use debug alloc. in clients.") AC_DEFINE([KEEP_BACK_PTRS], 1, [Define to save back-pointers in debugging headers.]) keep_back_ptrs=true AC_DEFINE([DBG_HDRS_ALL], 1, [Define to force debug headers on all objects.]) case $host in x86-*-linux* | i586-*-linux* | i686-*-linux* | x86_64-*-linux* ) AC_DEFINE(MAKE_BACK_GRAPH) AC_MSG_WARN("Client must not use -fomit-frame-pointer.") AC_DEFINE(SAVE_CALL_COUNT, 8) ;; AM_CONDITIONAL([KEEP_BACK_PTRS], [test x"$keep_back_ptrs" = xtrue]) * `configure.host` Nothing. * `Makefile.am`, `include/include.am`, `cord/cord.am`, `doc/doc.am`, `tests/tests.am` Nothing. * `include/gc_config_macros.h` Should be OK. * `include/private/gcconfig.h` Hairy. But should be OK. Search for *HURD*, compare to *LINUX*, *I386* case. See `doc/porting.html` and `doc/README.macros` (and others) for documentation. *LINUX* has: * `#define LINUX_STACKBOTTOM` Defined instead of `STACKBOTTOM` to have the value read from `/proc/`. * `#define HEAP_START (ptr_t)0x1000` May want to define it for us, too? * `#ifdef USE_I686_PREFETCH`, `USE_3DNOW_PREFETCH` --- [...] Apparently these are optimization that we also could use. Have a look at *LINUX* for *X86_64*, which uses `__builtin_prefetch` (which Linux x86 could use, too?). * TODO #if defined(LINUX) && defined(USE_MMAP) /* The kernel may do a somewhat better job merging mappings etc. */ /* with anonymous mappings. */ # define USE_MMAP_ANON #endif * TODO #if defined(GC_LINUX_THREADS) && defined(REDIRECT_MALLOC) /* Nptl allocates thread stacks with mmap, which is fine. But it */ /* keeps a cache of thread stacks. Thread stacks contain the */ /* thread control blocks. These in turn contain a pointer to */ /* (sizeof (void *) from the beginning of) the dtv for thread-local */ /* storage, which is calloc allocated. If we don't scan the cached */ /* thread stacks, we appear to lose the dtv. This tends to */ /* result in something that looks like a bogus dtv count, which */ /* tends to result in a memset call on a block that is way too */ /* large. Sometimes we're lucky and the process just dies ... */ /* There seems to be a similar issue with some other memory */ /* allocated by the dynamic loader. */ /* This should be avoidable by either: */ /* - Defining USE_PROC_FOR_LIBRARIES here. */ /* That performs very poorly, precisely because we end up */ /* scanning cached stacks. */ /* - Have calloc look at its callers. */ /* In spite of the fact that it is gross and disgusting. */ /* In fact neither seems to suffice, probably in part because */ /* even with USE_PROC_FOR_LIBRARIES, we don't scan parts of stack */ /* segments that appear to be out of bounds. Thus we actually */ /* do both, which seems to yield the best results. */ # define USE_PROC_FOR_LIBRARIES #endif * TODO # if defined(GC_LINUX_THREADS) && defined(REDIRECT_MALLOC) \ && !defined(INCLUDE_LINUX_THREAD_DESCR) /* Will not work, since libc and the dynamic loader use thread */ /* locals, sometimes as the only reference. */ # define INCLUDE_LINUX_THREAD_DESCR # endif * TODO # if defined(UNIX_LIKE) && defined(THREADS) && !defined(NO_CANCEL_SAFE) \ && !defined(PLATFORM_ANDROID) /* Make the code cancellation-safe. This basically means that we */ /* ensure that cancellation requests are ignored while we are in */ /* the collector. This applies only to Posix deferred cancellation;*/ /* we don't handle Posix asynchronous cancellation. */ /* Note that this only works if pthread_setcancelstate is */ /* async-signal-safe, at least in the absence of asynchronous */ /* cancellation. This appears to be true for the glibc version, */ /* though it is not documented. Without that assumption, there */ /* seems to be no way to safely wait in a signal handler, which */ /* we need to do for thread suspension. */ /* Also note that little other code appears to be cancellation-safe.*/ /* Hence it may make sense to turn this off for performance. */ # define CANCEL_SAFE # endif * `CAN_SAVE_CALL_ARGS` vs. -fomit-frame-pointer now being on by default for Linux x86 IIRC? (Which is an [[!taglink open_issue_gcc]] for not including us.) * TODO # if defined(REDIRECT_MALLOC) && defined(THREADS) && !defined(LINUX) # error "REDIRECT_MALLOC with THREADS works at most on Linux." # endif *HURD* has: * `#define STACK_GROWS_DOWN` * `#define HEURISTIC2` Defined instead of `STACKBOTTOM` to have the value probed. Linux also has this: #if defined(LINUX_STACKBOTTOM) && defined(NO_PROC_STAT) \ && !defined(USE_LIBC_PRIVATES) /* This combination will fail, since we have no way to get */ /* the stack base. Use HEURISTIC2 instead. */ # undef LINUX_STACKBOTTOM # define HEURISTIC2 /* This may still fail on some architectures like IA64. */ /* We tried ... */ #endif Being on [[glibc]], we could perhaps do similar as `USE_LIBC_PRIVATES` instead of `HEURISTIC2`. Pro: avoid `SIGSEGV` (and general fragility) during probing at startup (if I'm understanding this correctly). Con: rely on glibc internals. Or we instead add support to parse [[`/proc/`|hurd/translator/procfs]] (can even use the same as Linux?), or use some other interface. [[!tag open_issue_glibc]] * `#define SIG_SUSPEND SIGUSR1`, `#define SIG_THR_RESTART SIGUSR2` * We don't `#define MPROTECT_VDB` (WIP comment); but Linux neither. * Where does our `GETPAGESIZE` come from? Should we `#include <unistd.h>` like it is done for *LINUX*? * `include/gc_pthread_redirects.h` * TODO Cancellation stuff is Linux-only. In other places, too. * `mach_dep.c` * `#define NO_GETCONTEXT` [[!taglink open_issue_glibc]], but this is not a real problem here, because we can use the following GCC internal function without much overhead: * `GC_with_callee_saves_pushed` The `HAVE_BUILTIN_UNWIND_INIT` case is ours. * `os_dep.c` * `read` Sure that it doesn't internally (in [[glibc]]) use `malloc`. Probably only / mostly (?) a problem for `--enable-redirect-malloc` configurations? Linux with threads uses `readv`. * TODO. * `dyn_load.c` For `DYNAMIC_LOADING`. TODO. * `pthread_support.c`, `pthread_stop_world.c` TODO. * TODO. Other files also contain *LINUX* and other conditionals. * `libatomic_ops/` * `configure.ac` Nothing. * `Makefile`, `src/Makefile`, `src/atomic_ops/Makefile`, `src/atomic_ops/sysdeps/Makefile`, `doc/Makefile`, `tests/Makefile` Nothing. * `src/atomic_ops/sysdeps/gcc/x86.h` Nothing. # Testsuite There are different configurations possible, but in general, the testsuite restults of GNU/Linux and GNU/Hurd look very similar. It has last been run and compared on 2010-11-10, based on CVS HEAD sources from 2010-11-04, converted to [[Git, correspondingly 9abb37b2e581b415bb1f482085891a289c2c0be1|source_repositories/boehm_gc]]. ## `--enable-cplusplus --enable-gc-debug` * GNU/Hurd is missing *Call chain at allocation: [...] output*. `os_dep.c`:`GC_print_callers` # TODO * Port stuff to [[GCC]], and test it there. * What are other applications to test Boehm GC? Also especially in combination with [[/libpthread]] and dynamic loading of shared libraries? * There's been some talking about it on GNU guile mailing lists, and two Git branches (2010-12-15: last change 2009-09). * <http://www.hpl.hp.com/personal/Hans_Boehm/gc/#users>