block_to_imp.c

// On some platforms, we need _GNU_SOURCE to expose asprintf()
#ifndef _GNU_SOURCE
#define _GNU_SOURCE 1
#endif
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <ctype.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/mman.h>
#include "objc/runtime.h"
#include "objc/blocks_runtime.h"
#include "blocks_runtime.h"
#include "lock.h"
#include "visibility.h"

#ifndef __has_builtin
#define __has_builtin(x) 0
#endif
#if __has_builtin(__builtin___clear_cache)
#	define clear_cache __builtin___clear_cache
#else
void __clear_cache(void* start, void* end);
#	define clear_cache __clear_cache
#endif


/* QNX needs a special header for asprintf() */
#ifdef __QNXNTO__
#include <nbutil.h>
#endif

#define PAGE_SIZE 4096

static void *executeBuffer;
static void *writeBuffer;
static ptrdiff_t offset;
static mutex_t trampoline_lock;
#ifndef SHM_ANON
static char *tmpPattern;
static void initTmpFile(void)
{
	char *tmp = getenv("TMPDIR");
	if (NULL == tmp)
	{
		tmp = "/tmp/";
	}
	if (0 > asprintf(&tmpPattern, "%s/objc_trampolinesXXXXXXXXXXX", tmp))
	{
		abort();
	}
}
static int getAnonMemFd(void)
{
	const char *pattern = strdup(tmpPattern);
	int fd = mkstemp(pattern);
	unlink(pattern);
	free(pattern);
	return fd;
}
#else
static void initTmpFile(void) {}
static int getAnonMemFd(void)
{
	return shm_open(SHM_ANON, O_CREAT | O_RDWR, 0);
}
#endif

struct wx_buffer
{
	void *w;
	void *x;
};

PRIVATE void init_trampolines(void)
{
	INIT_LOCK(trampoline_lock);
	initTmpFile();
}

static struct wx_buffer alloc_buffer(size_t size)
{
	LOCK_FOR_SCOPE(&trampoline_lock);
	if ((0 == offset) || (offset + size >= PAGE_SIZE))
	{
		int fd = getAnonMemFd();
		ftruncate(fd, PAGE_SIZE);
		void *w = mmap(NULL, PAGE_SIZE, PROT_WRITE, MAP_SHARED, fd, 0);
		executeBuffer = mmap(NULL, PAGE_SIZE, PROT_READ|PROT_EXEC, MAP_SHARED, fd, 0);
		*((void**)w) = writeBuffer;
		writeBuffer = w;
		offset = sizeof(void*);
	}
	struct wx_buffer b = { writeBuffer + offset, executeBuffer + offset };
	offset += size;
	return b;
}

extern void __objc_block_trampoline;
extern void __objc_block_trampoline_end;
extern void __objc_block_trampoline_sret;
extern void __objc_block_trampoline_end_sret;

IMP imp_implementationWithBlock(void *block)
{
	struct Block_layout *b = block;
	void *start;
	void *end;

	if ((b->flags & BLOCK_USE_SRET) == BLOCK_USE_SRET)
	{
		start = &__objc_block_trampoline_sret;
		end = &__objc_block_trampoline_end_sret;
	}
	else
	{
		start = &__objc_block_trampoline;
		end = &__objc_block_trampoline_end;
	}

	size_t trampolineSize = end - start;
	// If we don't have a trampoline intrinsic for this architecture, return a
	// null IMP.
	if (0 >= trampolineSize) { return 0; }

	struct wx_buffer buf = alloc_buffer(trampolineSize + 2*sizeof(void*));
	void **out = buf.w;
	out[0] = (void*)b->invoke;
	out[1] = Block_copy(b);
	memcpy(&out[2], start, trampolineSize);
	out = buf.x;
	char *newIMP = (char*)&out[2];
	clear_cache(newIMP, newIMP+trampolineSize);
	return (IMP)newIMP;
}

static void* isBlockIMP(void *anIMP)
{
	LOCK(&trampoline_lock);
	void *e = executeBuffer;
	void *w = writeBuffer;
	UNLOCK(&trampoline_lock);
	while (e)
	{
		if ((anIMP > e) && (anIMP < e + PAGE_SIZE))
		{
			return ((char*)w) + ((char*)anIMP - (char*)e);
		}
		e = *(void**)e;
		w = *(void**)w;
	}
	return 0;
}

void *imp_getBlock(IMP anImp)
{
	if (0 == isBlockIMP((void*)anImp)) { return 0; }
	return *(((void**)anImp) - 1);
}
BOOL imp_removeBlock(IMP anImp)
{
	void *w = isBlockIMP((void*)anImp);
	if (0 == w) { return NO; }
	Block_release(((void**)anImp) - 1);
	return YES;
}

PRIVATE size_t lengthOfTypeEncoding(const char *types);

char *block_copyIMPTypeEncoding_np(void*block)
{
	char *buffer = strdup(block_getType_np(block));
	if (NULL == buffer) { return NULL; }
	char *replace = buffer;
	// Skip the return type
	replace += lengthOfTypeEncoding(replace);
	while (isdigit(*replace)) { replace++; }
	// The first argument type should be @? (block), and we need to transform
	// it to @, so we have to delete the ?.  Assert here because this isn't a
	// block encoding at all if the first argument is not a block, and since we
	// got it from block_getType_np(), this means something is badly wrong.
	assert('@' == *replace);
	replace++;
	assert('?' == *replace);
	// Use strlen(replace) not replace+1, because we want to copy the NULL
	// terminator as well.
	memmove(replace, replace+1, strlen(replace));
	// The next argument should be an object, and we want to replace it with a
	// selector
	while (isdigit(*replace)) { replace++; }
	if ('@' != *replace)
	{
		free(buffer);
		return NULL;
	}
	*replace = ':';
	return buffer;
}