114 lines
3.0 KiB
C
114 lines
3.0 KiB
C
/* go-trampoline.c -- allocate a trampoline for a nested function.
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Copyright 2009 The Go Authors. All rights reserved.
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Use of this source code is governed by a BSD-style
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license that can be found in the LICENSE file. */
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#include "config.h"
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#include <stddef.h>
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#include <stdint.h>
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#include <unistd.h>
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#ifdef HAVE_SYS_MMAN_H
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#include <sys/mman.h>
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#endif
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#include "runtime.h"
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#include "arch.h"
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#include "malloc.h"
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#include "go-assert.h"
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/* Trampolines need to run in memory that is both writable and
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executable. In order to implement them, we grab a page of memory
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and mprotect it. We fill in the page with trampolines as they are
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required. When we run out of space, we drop the pointer to the
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page and allocate a new one. The page will be freed by the garbage
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collector when there are no more variables of type func pointing to
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it. */
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/* A lock to control access to the page of closures. */
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static Lock trampoline_lock;
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/* The page of closures. */
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static unsigned char *trampoline_page;
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/* The size of trampoline_page. */
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static uintptr_t trampoline_page_size;
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/* The number of bytes we have used on trampoline_page. */
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static uintptr_t trampoline_page_used;
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/* Allocate a trampoline of SIZE bytes that will use the closure in
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CLOSURE. */
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void *
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__go_allocate_trampoline (uintptr_t size, void *closure)
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{
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uintptr_t ptr_size;
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uintptr_t full_size;
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unsigned char *ret;
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/* Because the garbage collector only looks at aligned addresses, we
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need to store the closure at an aligned address to ensure that it
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sees it. */
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ptr_size = sizeof (void *);
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full_size = (((size + ptr_size - 1) / ptr_size) * ptr_size);
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full_size += ptr_size;
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runtime_lock (&trampoline_lock);
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if (full_size < trampoline_page_size - trampoline_page_used)
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trampoline_page = NULL;
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if (trampoline_page == NULL)
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{
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uintptr_t page_size;
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unsigned char *page;
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page_size = getpagesize ();
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__go_assert (page_size >= full_size);
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page = (unsigned char *) runtime_mallocgc (2 * page_size - 1, 0, 0, 0);
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page = (unsigned char *) (((uintptr_t) page + page_size - 1)
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& ~ (page_size - 1));
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#ifdef HAVE_SYS_MMAN_H
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{
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int i;
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i = mprotect (page, page_size, PROT_READ | PROT_WRITE | PROT_EXEC);
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__go_assert (i == 0);
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}
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#endif
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trampoline_page = page;
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trampoline_page_size = page_size;
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trampoline_page_used = 0;
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}
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ret = trampoline_page + trampoline_page_used;
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trampoline_page_used += full_size;
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runtime_unlock (&trampoline_lock);
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__builtin_memcpy (ret + full_size - ptr_size, &closure, ptr_size);
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return (void *) ret;
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}
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/* Scan the trampoline page when running the garbage collector. This
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just makes sure that the garbage collector sees the pointer in
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trampoline_page, so that the page itself is not freed if there are
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no other references to it. */
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void
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runtime_trampoline_scan (void (*addroot) (Obj))
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{
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if (trampoline_page != NULL)
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addroot ((Obj){(byte *) &trampoline_page, sizeof trampoline_page, 0});
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}
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