libroot/x86_64: rewrite system_time[_nsecs]() to C++

No functional change intended, just code deobfuscation.

Signed-off-by: Paweł Dziepak <[email protected]>

src/system/kernel/lib/arch/x86_64/Jamfile

@@ -14,8 +14,7 @@ SEARCH_SOURCE += [ FDirName $(librootSources) os arch generic ] ;
 
 KernelMergeObject kernel_os_arch_$(TARGET_ARCH).o :
 	byteorder.S
-	system_time_asm.S
+	system_time.cpp
-	system_time.c
 
 	generic_atomic.cpp
 	: $(TARGET_KERNEL_PIC_CCFLAGS)

src/system/libroot/os/arch/x86_64/Jamfile

@@ -18,7 +18,7 @@ for architectureObject in [ MultiArchSubDirSetup x86_64 ] {
 			byteorder.S
 			get_stack_frame.S
 			system_info.cpp
-			system_time_asm.S
+			system_time.cpp
 			thread.cpp
 			time.cpp
 			tls.cpp

src/system/libroot/os/arch/x86_64/system_time.c

@@ -1,4 +0,0 @@
-/*
-	Just a dummy to avoid a special case in the build system. system_time()
-	is implemented in system_time_asm.S.
-*/

src/system/libroot/os/arch/x86_64/system_time.cpp

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2014, Paweł Dziepak, [email protected].
+ * Distributed under the terms of the MIT License.
+ */
+
+
+#include <stdint.h>
+
+
+static uint64_t cv_factor;
+static uint64_t cv_factor_nsec;
+
+
+extern "C" void
+__x86_setup_system_time(uint64_t cv, uint64_t cv_nsec)
+{
+    cv_factor = cv;
+    cv_factor_nsec = cv_nsec;
+}
+
+
+static inline uint64_t
+rdtsc()
+{
+    uint64_t lo, hi;
+    __asm__("rdtsc" : "=a" (lo), "=d" (hi));
+    return lo | (hi << 32);
+}
+
+
+extern "C" [[gnu::optimize("omit-frame-pointer")]] int64_t
+system_time()
+{
+    __uint128_t time = static_cast<__uint128_t>(rdtsc()) * cv_factor;
+    return time >> 64;
+}
+
+
+extern "C" [[gnu::optimize("omit-frame-pointer")]] int64_t
+system_time_nsecs()
+{
+    __uint128_t t = static_cast<__uint128_t>(rdtsc()) * cv_factor_nsec;
+    return t >> 32;
+}
+

src/system/libroot/os/arch/x86_64/system_time_asm.S

@@ -1,76 +0,0 @@
-/*
- * Copyright 2009, Ingo Weinhold, ingo_weinhold@gmx.de.
- * Copyright 2012, Alex Smith, alex@alex-smith.me.uk.
- * Distributed under the terms of the MIT License.
- *
- * Copyright 2001, Travis Geiselbrecht. All rights reserved.
- * Distributed under the terms of the NewOS License.
- */
-
-
-#include <asm_defs.h>
-
-
-/* saves the conversion factor needed for system_time */
-.lcomm cv_factor				8
-.lcomm cv_factor_nsecs			8
-
-
-.text
-
-
-FUNCTION(__x86_setup_system_time):
-	movq	%rdi, cv_factor(%rip)
-	movq	%rsi, cv_factor_nsecs(%rip)
-	ret
-FUNCTION_END(__x86_setup_system_time)
-
-
-/* int64 system_time(); */
-FUNCTION(system_time):
-	// (rdtsc * cv_factor) >> 32.
-	// Factor is pre-shifted left by 32 bits.
-
-	movq	cv_factor(%rip), %rcx
-
-	// Load 64-bit TSC into %eax (low), %edx (high).
-	rdtsc
-
-	// Convert into a single 64-bit value.
-	shl		$32, %rdx
-	orq		%rdx, %rax
-
-	// Multiply by conversion factor, result in %rax (low), %rdx (high).
-	mulq	%rcx
-
-	// Due to pre-shifting of the factor the whole result in high.
-	movq	%rdx, %rax
-	ret
-FUNCTION_END(system_time)
-
-
-/* int64 system_time_nsecs(); */
-FUNCTION(system_time_nsecs):
-	// Same algorithm as system_time(), but with a different factor.
-	// (rdtsc * cv_factor_nsecs) >> 32.
-	// Factor has not been pre-shifted here, otherwise we may lose the upper
-	// 32 bits.
-
-	movq	cv_factor_nsecs(%rip), %rcx
-
-	// Load 64-bit TSC into %eax (low), %edx (high).
-	rdtsc
-
-	// Convert into a single 64-bit value.
-	shl		$32, %rdx
-	orq		%rdx, %rax
-
-	// Multiply by conversion factor, result in %rax (low), %rdx (high).
-	mulq	%rcx
-
-	// Shift the result right by 32 bits.
-	shr		$32, %rax
-	shl		$32, %rdx
-	orq		%rdx, %rax
-	ret
-FUNCTION_END(system_time_nsecs)