Fix for 689-zygote-jit-deopt on kernels before 3.11rc2
No JIT for zygote if cache flushes can signal faults. JIT for zygote
needs dual code mappings by design and the old kernel behaviour is
incompatible with this. The new test 689-zygote-jit-deopt was running
up against this issue on Nexus 6P test devices.
Test: art/test/testrunner/testrunner.py --target --64 -t 689
Bug: 136584457
Change-Id: Ibdafca270962d9e4a22ce1d9ba04f15771144899
diff --git a/runtime/jit/jit_memory_region.cc b/runtime/jit/jit_memory_region.cc
index dba2768..b3c2d7e 100644
--- a/runtime/jit/jit_memory_region.cc
+++ b/runtime/jit/jit_memory_region.cc
@@ -17,6 +17,7 @@
#include "jit_memory_region.h"
#include <fcntl.h>
+#include <sys/utsname.h>
#include <unistd.h>
#include <android-base/unique_fd.h>
@@ -487,7 +488,36 @@
#if defined(__BIONIC__) && defined(ART_TARGET)
// The code below only works on bionic on target.
+bool CacheOperationsMaySegFault() {
+#if defined(__linux__) && defined(__aarch64__)
+ // Avoid issue on older ARM64 kernels where data cache operations could be classified as writes
+ // and cause segmentation faults. This was fixed in Linux 3.11rc2:
+ //
+ // https://github.com/torvalds/linux/commit/db6f41063cbdb58b14846e600e6bc3f4e4c2e888
+ //
+ // This behaviour means we should avoid the dual view JIT on the device. This is just
+ // an issue when running tests on devices that have an old kernel.
+ static constexpr int kRequiredMajor = 3;
+ static constexpr int kRequiredMinor = 12;
+ struct utsname uts;
+ int major, minor;
+ if (uname(&uts) != 0 ||
+ strcmp(uts.sysname, "Linux") != 0 ||
+ sscanf(uts.release, "%d.%d", &major, &minor) != 2 ||
+ (major < kRequiredMajor || (major == kRequiredMajor && minor < kRequiredMinor))) {
+ return true;
+ }
+#endif
+ return false;
+}
+
int JitMemoryRegion::CreateZygoteMemory(size_t capacity, std::string* error_msg) {
+ if (CacheOperationsMaySegFault()) {
+ // Zygote JIT requires dual code mappings by design. We can only do this if the cache flush
+ // and invalidate instructions work without raising faults.
+ *error_msg = "Zygote memory only works with dual mappings";
+ return -1;
+ }
/* Check if kernel support exists, otherwise fall back to ashmem */
static const char* kRegionName = "/jit-zygote-cache";
if (art::IsSealFutureWriteSupported()) {
diff --git a/test/knownfailures.json b/test/knownfailures.json
index 71ecfd7..ad0cbe8 100644
--- a/test/knownfailures.json
+++ b/test/knownfailures.json
@@ -1227,11 +1227,5 @@
"575-checker-string-init-alias"],
"variant": "baseline",
"description": [ "Working as intended tests that don't pass with baseline." ]
- },
- {
- "tests": ["689-zygote-jit-deopt"],
- "bug": "b/136584457",
- "variant": "target & 64",
- "description": [ "Fails on old kernels." ]
}
]