[m-rev.] for the record: GC & stack scanning
Fergus Henderson
fjh at cs.mu.OZ.AU
Tue Apr 10 12:00:24 AEST 2001
I spent some time working on getting the Boehm collector to only scan the
live parts of the LLDS back-end stacks. But I ran into a problem where
gcc wouldn't compile the Boehm collector if global register declarations
were included.
It might be possible to work around this by hacking the Boehm collector,
but those changes couldn't be folded back into the main distribution of
the Boehm collector, so they'd cause us continuing maintenance difficulty.
In the long term, I think the right approach is either to fix gcc (also
a lot of work, most likely), or to abandon the use of global register
variables (e.g. by switching to the MLDS back-end).
In the mean time, I think we'll just have to live with the GC scanning
the whole of the LLDS stacks.
Because of the problems mentioned, I won't commit this change.
----------
Estimated hours taken: 6
Branches: none
Get the Boehm collector to only scan the live parts of the Mercury stacks.
XXX This change is incomplete:
XXX - need to conditionalize so that it only does this for the LLDS back-end
XXX - need to deal with transient registers on SPARC
XXX - need to fix the XXXs below
boehm_gc/Makefile:
Ensure that the boehm_gc directory gets compiled with the
GNU C global register variable declarations visible,
XXX With recent versions of gcc, this change stops the
collector compiling, because gcc doesn't support global
register variables; it gets an "internal error / impossible asm"
error.
runtime/mercury_engine.h:
Add a comment.
runtime/mercury_memory.c:
runtime/mercury_wrapper.c:
Move MR_init_conservative_GC() from mercury_wrapper.c to
mercury_memory.c, because the latter is more a appropriate place,
and to match where it is declared (mercury_memory.h).
runtime/mercury_memory.c:
Add new function MR_push_other_roots() to push the live parts of
the Mercury stacks onto the GC mark stack.
Change MR_init_conservative_GC() so that it registers the
MR_push_other_roots callback with the GC.
runtime/mercury_memory_zones.c:
Don't scan the zones allocated with memalign(), even if
conservative GC is enabled. These should now be handled
by MR_push_other_roots() instead.
runtime/Mmakefile:
Compile mercury_memory.c with -Wno-strict-prototypes,
to avoid spurious warnings in gc_priv.h.
(XXX this is wrong for compilers other than gcc)
Index: runtime/Mmakefile
===================================================================
RCS file: /home/mercury1/repository/mercury/runtime/Mmakefile,v
retrieving revision 1.70
diff -u -d -u -r1.70 Mmakefile
--- runtime/Mmakefile 2001/03/16 01:40:39 1.70
+++ runtime/Mmakefile 2001/04/08 08:46:51
@@ -24,6 +24,10 @@
MGNUCFLAGS = --no-ansi
MOD2C = $(SCRIPTS_DIR)/mod2c
+# mercury_memory.c #includes gc_priv.h,
+# which has lots of unprototyped functions
+MGNUCFLAGS-mercury_memory = -Wno-strict-prototypes
+
#-----------------------------------------------------------------------------#
# All the headers in $(HDRS) should be syntactically well-formed
Index: runtime/mercury_engine.h
===================================================================
RCS file: /home/mercury1/repository/mercury/runtime/mercury_engine.h,v
retrieving revision 1.21
diff -u -d -u -r1.21 mercury_engine.h
--- runtime/mercury_engine.h 2000/12/04 18:28:39 1.21
+++ runtime/mercury_engine.h 2001/04/06 08:02:30
@@ -220,6 +220,11 @@
#endif
jmp_buf *e_jmp_buf;
MR_Word *e_exception;
+ /*
+ ** Note: if you add any new memory zones, you may need to modify
+ ** MR_push_other_roots() to register these with the conservative
+ ** garbage collector.
+ */
#ifndef CONSERVATIVE_GC
MR_MemoryZone *heap_zone;
MR_MemoryZone *solutions_heap_zone;
Index: runtime/mercury_memory.c
===================================================================
RCS file: /home/mercury1/repository/mercury/runtime/mercury_memory.c,v
retrieving revision 1.24
diff -u -d -u -r1.24 mercury_memory.c
--- runtime/mercury_memory.c 2000/11/24 06:03:37 1.24
+++ runtime/mercury_memory.c 2001/04/06 07:59:59
@@ -96,6 +96,8 @@
#include "mercury_trace_base.h"
#include "mercury_memory_handlers.h"
+#include "gc_priv.h" /* for GC_push_other_roots() and GC_push_all() */
+
/*---------------------------------------------------------------------------*/
#if defined(HAVE_SYSCONF) && defined(_SC_PAGESIZE)
@@ -362,5 +364,90 @@
return ptr;
}
+
+/*---------------------------------------------------------------------------*/
+/*
+** Support routines for use of the conservative garbage collector.
+*/
+
+#ifdef CONSERVATIVE_GC
+
+static void (*orig_push_other_roots)(void);
+
+/*
+** This function registers the Mercury stacks with the
+** conservative garbage collector.
+*/
+static void
+MR_push_other_roots(void)
+{
+#if defined(__sparc__) && defined(USE_GCC_GLOBAL_REGISTERS)
+ MR_restore_transient_stack_ptrs();
+#endif
+
+ GC_push_all(MR_CONTEXT(detstack_zone)->min, MR_sp + 1);
+ GC_push_all(MR_CONTEXT(nondetstack_zone)->min, MR_maxfr + 1);
+#ifdef MR_USE_TRAIL
+ GC_push_all(MR_trail_zone->min, MR_trail_ptr + 1);
+#endif
+#ifdef MR_USE_MINIMAL_MODEL
+ /* XXX handle cutstack and generatorstack */
+#endif
+
+ if (orig_push_other_roots != NULL) (*orig_push_other_roots)();
+}
+
+void
+MR_init_conservative_GC(void)
+{
+ /*
+ ** sometimes mercury apps fail the GC_is_visible() test.
+ ** dyn_load.c traverses the entire address space and registers
+ ** all segments that could possibly have been written to, which
+ ** makes us suspect that &MR_runqueue_head is not in the registered
+ ** roots. So we force a write to that address, which seems to make
+ ** the problem go away.
+ */
+ MR_runqueue_head = NULL;
+
+ GC_quiet = TRUE;
+
+ /*
+ ** Call GC_INIT() to tell the garbage collector about this DLL.
+ ** (This is necessary to support Windows DLLs using gnu-win32.)
+ */
+ GC_INIT();
+
+ /*
+ ** call the init_gc() function defined in <foo>_init.c,
+ ** which calls GC_INIT() to tell the GC about the main program.
+ ** (This is to work around a Solaris 2.X (X <= 4) linker bug,
+ ** and also to support Windows DLLs using gnu-win32.)
+ */
+ (*MR_address_of_init_gc)();
+
+ /*
+ ** Double-check that the garbage collector knows about
+ ** global variables in shared libraries.
+ */
+ GC_is_visible(&MR_runqueue_head);
+
+ /* The following code is necessary to tell the conservative */
+ /* garbage collector that we are using tagged pointers */
+ {
+ int i;
+
+ for (i = 1; i < (1 << TAGBITS); i++) {
+ GC_REGISTER_DISPLACEMENT(i);
+ }
+ }
+
+ /*
+ ** Ensure that the GC will scan the Mercury stacks properly.
+ */
+ orig_push_other_roots = GC_push_other_roots;
+ GC_push_other_roots = MR_push_other_roots;
+}
+#endif /* CONSERVATIVE_GC */
/*---------------------------------------------------------------------------*/
Index: runtime/mercury_wrapper.c
===================================================================
RCS file: /home/mercury1/repository/mercury/runtime/mercury_wrapper.c,v
retrieving revision 1.87
diff -u -d -u -r1.87 mercury_wrapper.c
--- runtime/mercury_wrapper.c 2001/03/28 08:18:11 1.87
+++ runtime/mercury_wrapper.c 2001/04/06 07:58:59
@@ -399,54 +399,6 @@
} /* end runtime_mercury_init() */
-#ifdef CONSERVATIVE_GC
-void
-MR_init_conservative_GC(void)
-{
- /*
- ** sometimes mercury apps fail the GC_is_visible() test.
- ** dyn_load.c traverses the entire address space and registers
- ** all segments that could possibly have been written to, which
- ** makes us suspect that &MR_runqueue_head is not in the registered
- ** roots. So we force a write to that address, which seems to make
- ** the problem go away.
- */
- MR_runqueue_head = NULL;
-
- GC_quiet = TRUE;
-
- /*
- ** Call GC_INIT() to tell the garbage collector about this DLL.
- ** (This is necessary to support Windows DLLs using gnu-win32.)
- */
- GC_INIT();
-
- /*
- ** call the init_gc() function defined in <foo>_init.c,
- ** which calls GC_INIT() to tell the GC about the main program.
- ** (This is to work around a Solaris 2.X (X <= 4) linker bug,
- ** and also to support Windows DLLs using gnu-win32.)
- */
- (*MR_address_of_init_gc)();
-
- /*
- ** Double-check that the garbage collector knows about
- ** global variables in shared libraries.
- */
- GC_is_visible(&MR_runqueue_head);
-
- /* The following code is necessary to tell the conservative */
- /* garbage collector that we are using tagged pointers */
- {
- int i;
-
- for (i = 1; i < (1 << TAGBITS); i++) {
- GC_REGISTER_DISPLACEMENT(i);
- }
- }
-}
-#endif /* CONSERVATIVE_GC */
-
void
MR_do_init_modules(void)
{
Index: runtime/mercury_memory_zones.c
===================================================================
RCS file: /home/mercury1/repository/mercury/runtime/mercury_memory_zones.c,v
retrieving revision 1.16
diff -u -d -r1.16 mercury_memory_zones.c
--- runtime/mercury_memory_zones.c 2001/03/13 18:02:26 1.16
+++ runtime/mercury_memory_zones.c 2001/04/10 01:55:22
@@ -129,14 +129,8 @@
(unsigned long) GetLastError());
}
- #ifdef CONSERVATIVE_GC
- if (ptr != NULL)
- GC_add_roots((char *)ptr, (char *)ptr + size);
- #endif
return ptr;
}
-#elif defined(CONSERVATIVE_GC)
- #define memalign(a,s) GC_MALLOC_UNCOLLECTABLE(s)
#elif defined(HAVE_MEMALIGN)
extern void *memalign(size_t, size_t);
#else
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--
Fergus Henderson <fjh at cs.mu.oz.au> | "I have always known that the pursuit
| of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh> | -- the last words of T. S. Garp.
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