Changeset 231118 in webkit for trunk/Source/JavaScriptCore/assembler/MacroAssemblerARM64.cpp

Timestamp:

Apr 27, 2018, 5:01:14 PM (7 years ago)

Author:

Yusuke Suzuki

Message:

[JSC][ARM64][Linux] Add collectCPUFeatures using auxiliary vector
​https://bugs.webkit.org/show_bug.cgi?id=185055

Reviewed by JF Bastien.

This patch is paving the way to emitting jscvt instruction if possible.
To do that, we need to determine jscvt instruction is supported in the
given CPU.

We add a function collectCPUFeatures, which is responsible to collect
CPU features if necessary. In Linux, we can use auxiliary vector to get
the information without parsing /proc/cpuinfo.

Currently, nobody calls this function. It is later called when we emit
jscvt instruction. To make it possible, we also need to add disassembler
support too.

• assembler/AbstractMacroAssembler.h:
• assembler/MacroAssemblerARM64.cpp:

(JSC::MacroAssemblerARM64::collectCPUFeatures):

• assembler/MacroAssemblerARM64.h:
• assembler/MacroAssemblerX86Common.h:

File:

• trunk/Source/JavaScriptCore/assembler/MacroAssemblerARM64.cpp (modified) (2 diffs)

trunk/Source/JavaScriptCore/assembler/MacroAssemblerARM64.cpp

@@ -31 +31 @@
 #include "ProbeContext.h"
 #include <wtf/InlineASM.h>
+
+#if OS(LINUX)
+#include <asm/hwcap.h>
+#include <sys/auxv.h>
+#endif
 
 namespace JSC {
@@ -527 +532 @@
 #endif // ENABLE(MASM_PROBE)
 
+void MacroAssemblerARM64::collectCPUFeatures()
+{
+    static std::once_flag onceKey;
+    std::call_once(onceKey, [] {
+#if OS(LINUX)
+        // A register for describing ARM64 CPU features are only accessible in kernel mode.
+        // Thus, some kernel support is necessary to collect CPU features. In Linux, the
+        // kernel passes CPU feature flags in AT_HWCAP auxiliary vector which is passed
+        // when the process starts. While this may pose a bit conservative information
+        // (for example, the Linux kernel may add a flag for a feature after the feature
+        // is shipped and implemented in some CPUs. In that case, even if the CPU has
+        // that feature, the kernel does not tell it to users.), it is a stable approach.
+        // https://www.kernel.org/doc/Documentation/arm64/elf_hwcaps.txt
+        unsigned long hwcaps = getauxval(AT_HWCAP);
+
+#if !defined(HWCAP_JSCVT)
+#define HWCAP_JSCVT (1 << 13)
+#endif
+
+        s_jscvtCheckState = (hwcaps & HWCAP_JSCVT) ? CPUIDCheckState::Set : CPUIDCheckState::Clear;
+#else
+        s_jscvtCheckState = CPUIDCheckState::Clear;
+#endif
+    });
+}
+
+MacroAssemblerARM64::CPUIDCheckState MacroAssemblerARM64::s_jscvtCheckState = CPUIDCheckState::NotChecked;
+
 } // namespace JSC