diff --git a/third_party/ashmem/ashmem-dev.c b/third_party/ashmem/ashmem-dev.c
index 52b3f47eeae0..25a33cdcd0c8 100644
--- a/third_party/ashmem/ashmem-dev.c
+++ b/third_party/ashmem/ashmem-dev.c
@@ -14,23 +14,115 @@
* limitations under the License.
*/
-/*
- * Implementation of the user-space ashmem API for devices, which have our
- * ashmem-enabled kernel. See ashmem-sim.c for the "fake" tmp-based version,
- * used by the simulator.
- */
+#include "ashmem.h"
+#include <dlfcn.h>
+#include <errno.h>
#include <unistd.h>
+#include <stdlib.h>
#include <string.h>
+#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
+#include <sys/stat.h> /* for fdstat() */
#include <fcntl.h>
#include <linux/ashmem.h>
-#include "ashmem.h"
+#include <sys/system_properties.h>
-#define ASHMEM_DEVICE "/dev/ashmem"
+#define ASHMEM_DEVICE "/dev/ashmem"
+
+/* Technical note regarding reading system properties.
+ *
+ * Try to use the new __system_property_read_callback API that appeared in
+ * Android O / API level 26 when available. Otherwise use the deprecated
+ * __system_property_get function.
+ *
+ * For more technical details from an NDK maintainer, see:
+ * https://bugs.chromium.org/p/chromium/issues/detail?id=392191#c17
+ */
+
+/* Weak symbol import */
+void __system_property_read_callback(
+ const prop_info* info,
+ void (*callback)(
+ void* cookie, const char* name, const char* value, uint32_t serial),
+ void* cookie) __attribute__((weak));
+
+/* Callback used with __system_property_read_callback. */
+static void prop_read_int(void* cookie,
+ const char* name,
+ const char* value,
+ uint32_t serial) {
+ *(int *)cookie = atoi(value);
+ (void)name;
+ (void)serial;
+}
+
+static int system_property_get_int(const char* name) {
+ int result = 0;
+ if (__system_property_read_callback) {
+ const prop_info* info = __system_property_find(name);
+ if (info)
+ __system_property_read_callback(info, &prop_read_int, &result);
+ } else {
+ char value[PROP_VALUE_MAX] = {};
+ if (__system_property_get(name, value) >= 1)
+ result = atoi(value);
+ }
+ return result;
+}
+
+static int device_api_level() {
+ static int s_api_level = -1;
+ if (s_api_level < 0)
+ s_api_level = system_property_get_int("ro.build.version.sdk");
+ return s_api_level;
+}
+
+typedef enum {
+ ASHMEM_STATUS_INIT,
+ ASHMEM_STATUS_NOT_SUPPORTED,
+ ASHMEM_STATUS_SUPPORTED,
+} AshmemStatus;
+
+static AshmemStatus s_ashmem_status = ASHMEM_STATUS_INIT;
+static dev_t s_ashmem_dev;
+
+/* Return the dev_t of a given file path, or 0 if not available, */
+static dev_t ashmem_find_dev(const char* path) {
+ struct stat st;
+ dev_t result = 0;
+ if (stat(path, &st) == 0 && S_ISCHR(st.st_mode))
+ result = st.st_dev;
+ return result;
+}
+
+static AshmemStatus ashmem_get_status(void) {
+ /* NOTE: No need to make this thread-safe, assuming that
+ * all threads will find the same value. */
+ if (s_ashmem_status != ASHMEM_STATUS_INIT)
+ return s_ashmem_status;
+
+ s_ashmem_dev = ashmem_find_dev(ASHMEM_DEVICE);
+ s_ashmem_status = (s_ashmem_dev == 0) ? ASHMEM_STATUS_NOT_SUPPORTED
+ : ASHMEM_STATUS_SUPPORTED;
+ return s_ashmem_status;
+}
+
+/* Returns true iff the ashmem device ioctl should be used for a given fd.
+ * NOTE: Try not to use fstat() when possible to avoid performance issues. */
+static int ashmem_dev_fd_check(int fd) {
+ if (device_api_level() <= __ANDROID_API_O_MR1__)
+ return 1;
+ if (ashmem_get_status() == ASHMEM_STATUS_SUPPORTED) {
+ struct stat st;
+ return (fstat(fd, &st) == 0 && S_ISCHR(st.st_mode) &&
+ st.st_dev != 0 && st.st_dev == s_ashmem_dev);
+ }
+ return 0;
+}
/*
* ashmem_create_region - creates a new ashmem region and returns the file
@@ -39,67 +131,133 @@
* `name' is an optional label to give the region (visible in /proc/pid/maps)
* `size' is the size of the region, in page-aligned bytes
*/
-int ashmem_create_region(const char *name, size_t size)
-{
- int fd, ret;
+static int ashmem_dev_create_region(const char *name, size_t size) {
+ int fd = open(ASHMEM_DEVICE, O_RDWR);
+ if (fd < 0)
+ return fd;
- fd = open(ASHMEM_DEVICE, O_RDWR);
- if (fd < 0)
- return fd;
+ int ret;
+ if (name) {
+ char buf[ASHMEM_NAME_LEN];
+ strlcpy(buf, name, sizeof(buf));
+ ret = ioctl(fd, ASHMEM_SET_NAME, buf);
+ if (ret < 0)
+ goto error;
+ }
+ ret = ioctl(fd, ASHMEM_SET_SIZE, size);
+ if (ret < 0)
+ goto error;
- if (name) {
- char buf[ASHMEM_NAME_LEN];
+ return fd;
- strlcpy(buf, name, sizeof(buf));
- ret = ioctl(fd, ASHMEM_SET_NAME, buf);
- if (ret < 0)
- goto error;
- }
+error:
+ close(fd);
+ return ret;
+}
- ret = ioctl(fd, ASHMEM_SET_SIZE, size);
- if (ret < 0)
- goto error;
+static int ashmem_dev_set_prot_region(int fd, int prot) {
+ return ioctl(fd, ASHMEM_SET_PROT_MASK, prot);
+}
- return fd;
+static int ashmem_dev_get_prot_region(int fd) {
+ return ioctl(fd, ASHMEM_GET_PROT_MASK);
+}
-error:
- close(fd);
- return ret;
+static int ashmem_dev_pin_region(int fd, size_t offset, size_t len) {
+ struct ashmem_pin pin = { offset, len };
+ return ioctl(fd, ASHMEM_PIN, &pin);
}
-int ashmem_set_prot_region(int fd, int prot)
-{
- return ioctl(fd, ASHMEM_SET_PROT_MASK, prot);
+static int ashmem_dev_unpin_region(int fd, size_t offset, size_t len) {
+ struct ashmem_pin pin = { offset, len };
+ return ioctl(fd, ASHMEM_UNPIN, &pin);
}
-int ashmem_get_prot_region(int fd)
-{
- return ioctl(fd, ASHMEM_GET_PROT_MASK);
+static size_t ashmem_dev_get_size_region(int fd) {
+ return ioctl(fd, ASHMEM_GET_SIZE, NULL);
}
-int ashmem_pin_region(int fd, size_t offset, size_t len)
-{
- struct ashmem_pin pin = { offset, len };
- return ioctl(fd, ASHMEM_PIN, &pin);
+// Starting with API level 26, the following functions from
+// libandroid.so should be used to create shared memory regions.
+typedef int(*ASharedMemory_createFunc)(const char*, size_t);
+typedef size_t(*ASharedMemory_getSizeFunc)(int fd);
+typedef int(*ASharedMemory_setProtFunc)(int fd, int prot);
+
+// Function pointers to shared memory functions.
+typedef struct {
+ ASharedMemory_createFunc create;
+ ASharedMemory_getSizeFunc getSize;
+ ASharedMemory_setProtFunc setProt;
+} ASharedMemoryFuncs;
+
+const ASharedMemoryFuncs* ashmem_get_funcs() {
+ static ASharedMemoryFuncs s_ashmem_funcs = {};
+ ASharedMemoryFuncs* funcs = &s_ashmem_funcs;
+ if (funcs->create == NULL) {
+ if (device_api_level() >= __ANDROID_API_O__) {
+ /* Leaked intentionally! */
+ void* lib = dlopen("libandroid.so", RTLD_NOW);
+ funcs->create = (ASharedMemory_createFunc)
+ dlsym(lib, "ASharedMemory_create");
+ funcs->getSize = (ASharedMemory_getSizeFunc)
+ dlsym(lib, "ASharedMemory_getSize");
+ funcs->setProt = (ASharedMemory_setProtFunc)
+ dlsym(lib, "ASharedMemory_setProt");
+ } else {
+ funcs->create = &ashmem_dev_create_region;
+ funcs->getSize = &ashmem_dev_get_size_region;
+ funcs->setProt = &ashmem_dev_set_prot_region;
+ }
+ }
+ return funcs;
}
-int ashmem_unpin_region(int fd, size_t offset, size_t len)
-{
- struct ashmem_pin pin = { offset, len };
- return ioctl(fd, ASHMEM_UNPIN, &pin);
+int ashmem_create_region(const char* name, size_t size) {
+ return ashmem_get_funcs()->create(name, size);
}
-int ashmem_get_size_region(int fd)
-{
- return ioctl(fd, ASHMEM_GET_SIZE, NULL);
+int ashmem_set_prot_region(int fd, int prot) {
+ return ashmem_get_funcs()->setProt(fd, prot);
}
-int ashmem_purge_all(void)
-{
- const int fd = open(ASHMEM_DEVICE, O_RDWR);
- if (fd < 0)
- return fd;
- const int ret = ioctl(fd, ASHMEM_PURGE_ALL_CACHES, 0);
- close(fd);
- return ret;
+int ashmem_get_prot_region(int fd) {
+ if (ashmem_dev_fd_check(fd))
+ return ashmem_dev_get_prot_region(fd);
+ /* There are only two practical values to return here: either
+ * PROT_READ|PROT_WRITE or just PROT_READ, so try to determine
+ * the flags by trying to mmap() the region read-write first.
+ */
+ int result = PROT_READ;
+ const size_t page_size = (size_t)sysconf(_SC_PAGESIZE);
+ void* m = mmap(NULL, page_size, PROT_READ|PROT_WRITE,
+ MAP_PRIVATE, fd, 0);
+ if (m != MAP_FAILED) {
+ munmap(m, page_size);
+ result = PROT_READ|PROT_WRITE;
+ }
+ return result;
+}
+
+int ashmem_pin_region(int fd, size_t offset, size_t len) {
+ if (ashmem_dev_fd_check(fd))
+ return ashmem_dev_pin_region(fd, offset, len);
+ return ASHMEM_NOT_PURGED;
+}
+
+int ashmem_unpin_region(int fd, size_t offset, size_t len) {
+ if (ashmem_dev_fd_check(fd))
+ return ashmem_dev_unpin_region(fd, offset, len);
+ /* NOTE: It is not possible to use madvise() here because it requires a
+ * memory address. This could be done in the caller though, instead of
+ * this function. */
+ return 0;
+}
+
+int ashmem_get_size_region(int fd) {
+ /* NOTE: Original API returns an int. Avoid breaking it. */
+ return (int)ashmem_get_funcs()->getSize(fd);
+}
+
+int ashmem_device_is_supported(void) {
+ return ashmem_get_status() == ASHMEM_STATUS_SUPPORTED;
}
diff --git a/third_party/ashmem/ashmem.h b/third_party/ashmem/ashmem.h
index d8afccbd2a6e..f3675c98b19a 100644
--- a/third_party/ashmem/ashmem.h
+++ b/third_party/ashmem/ashmem.h
@@ -16,13 +16,20 @@
extern "C" {
#endif
+/* Returns true if the ashmem device is supported on this device.
+ * Not that even if the device is not supported,
+ * ashmem_{create,set_prot,get_prot,get_size}_region() will still work
+ * because they will use the ASharedMemory functions from libandroid.so
+ * instead. But ashmem_{pin,unpin}_region() will be no-ops.
+ */
+int ashmem_device_is_supported(void);
+
int ashmem_create_region(const char *name, size_t size);
int ashmem_set_prot_region(int fd, int prot);
int ashmem_get_prot_region(int fd);
int ashmem_pin_region(int fd, size_t offset, size_t len);
int ashmem_unpin_region(int fd, size_t offset, size_t len);
int ashmem_get_size_region(int fd);
-int ashmem_purge_all(void);
#ifdef __cplusplus
}
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