From 5a8e6c4183a30f3b10de22fa5ba80950dfb2adea Mon Sep 17 00:00:00 2001
From: Patrik Nyblom <pan@erlang.org>
Date: Mon, 7 Dec 2009 15:25:32 +0100
Subject: Fit all heap data into the 32-bit address range

This is the first step in the implementation of the half-word emulator,
a 64-bit emulator where all pointers to heap data will be stored
in 32-bit words. Code specific for this emulator variant is
conditionally compiled when the HALFWORD_HEAP define has
a non-zero value.

First force all pointers to heap data to fall into a single 32-bit range,
but still store them in 64-bit words.

Temporary term data stored on C stack is moved into scheduler specific
storage (allocated as heaps) and macros are added to make this
happen only in emulators where this is needed. For a vanilla VM the
temporary terms are still stored on the C stack.
---
 erts/emulator/sys/common/erl_mseg.c | 56 +++++++++++++++++++++++++++++++++++--
 1 file changed, 54 insertions(+), 2 deletions(-)

(limited to 'erts/emulator/sys')

diff --git a/erts/emulator/sys/common/erl_mseg.c b/erts/emulator/sys/common/erl_mseg.c
index f4e21bc05f..c859b192f7 100644
--- a/erts/emulator/sys/common/erl_mseg.c
+++ b/erts/emulator/sys/common/erl_mseg.c
@@ -87,11 +87,22 @@ static int is_cache_check_requested;
 /* Mmap ... */
 
 #define MMAP_PROT		(PROT_READ|PROT_WRITE)
+
+#if HALFWORD_HEAP
+# ifdef MAP_32BIT
+#  define RANGE_FLAG            (MAP_32BIT)
+# else
+#  error "Cannot have halfword heap if unable to restrict mmap areas
+# endif
+#else
+# define RANGE_FLAG             (0)
+#endif
+
 #ifdef MAP_ANON
-#  define MMAP_FLAGS		(MAP_ANON|MAP_PRIVATE)
+#  define MMAP_FLAGS		(MAP_ANON|MAP_PRIVATE|RANGE_FLAG)
 #  define MMAP_FD		(-1)
 #else
-#  define MMAP_FLAGS		(MAP_PRIVATE)
+#  define MMAP_FLAGS		(MAP_PRIVATE|RANGE_FLAG)
 #  define MMAP_FD		mmap_fd
 static int mmap_fd;
 #endif
@@ -310,6 +321,12 @@ mseg_create(Uint size)
 			MMAP_PROT, MMAP_FLAGS, MMAP_FD, 0);
     if (seg == (void *) MAP_FAILED)
 	seg = NULL;
+#if HALFWORD_HEAP
+    if ((unsigned long) seg & CHECK_POINTER_MASK) {
+	erts_fprintf(stderr,"Pointer mask failure (0x%08lx)\n",(unsigned long) seg);
+	return NULL;
+    }
+#endif
 #else
 #error "Missing mseg_create() implementation"
 #endif
@@ -1300,6 +1317,37 @@ erts_mseg_unit_size(void)
 {
     return page_size;
 }
+#if HAVE_MMAP && HALFWORD_HEAP
+#ifdef MAP_NORESERVE
+#define RESERVE_FLAGS (MMAP_FLAGS | MAP_NORESERVE)
+#else
+#define RESERVE_FLAGS (MMAP_FLAGS)
+#endif
+static void halfword_reserve(void)
+{
+#if 0
+    void *ptr, *understack;
+    unsigned long x = 0x80000000;
+    long i = 0;
+
+    understack = mmap(NULL,GET_PAGE_SIZE, PROT_NONE, RESERVE_FLAGS,
+		      MMAP_FD, 0);
+    while (x < (unsigned long) understack) {
+	ptr = mmap((void *) x, GET_PAGE_SIZE, PROT_NONE, RESERVE_FLAGS,
+		   MMAP_FD, 0);
+	if ((unsigned long) ptr < 0x80000000) {
+	    munmap(ptr, GET_PAGE_SIZE);
+	} else {
+	    ++i;
+	}
+	x += GET_PAGE_SIZE;
+    }
+    erts_fprintf(stderr,"Reserved %ld pages [%d MB]...\n",i, (i*GET_PAGE_SIZE)/1024/1024);
+#else
+    return;
+#endif
+}
+#endif
 
 void
 erts_mseg_init(ErtsMsegInit_t *init)
@@ -1328,6 +1376,10 @@ erts_mseg_init(ErtsMsegInit_t *init)
 	erl_exit(ERTS_ABORT_EXIT, "erts_mseg: unable to open /dev/zero\n");
 #endif
 
+#if HAVE_MMAP && HALFWORD_HEAP
+    halfword_reserve();
+#endif
+
     page_size = GET_PAGE_SIZE;
 
     page_shift = 1;
-- 
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