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-rw-r--r--nanosec.c109
1 files changed, 109 insertions, 0 deletions
diff --git a/nanosec.c b/nanosec.c
new file mode 100644
index 0000000..f82d47a
--- /dev/null
+++ b/nanosec.c
@@ -0,0 +1,109 @@
+#include <u.h>
+#include <libc.h>
+#include <tos.h>
+
+/*
+ * This code is a mixture of cpuid(1) and the nanosec() found in vmx,
+ * in order to force the use of nsec(2) in case we are running in a
+ * virtualized environment where the clock is mis-bhyve-ing.
+ */
+
+typedef struct Res {
+ ulong ax, bx, cx, dx;
+} Res;
+
+static uchar _cpuid[] = {
+ 0x5E, /* POP SI (PC) */
+ 0x5D, /* POP BP (Res&) */
+ 0x58, /* POP AX */
+ 0x59, /* POP CX */
+
+ 0x51, /* PUSH CX */
+ 0x50, /* PUSH AX */
+ 0x55, /* PUSH BP */
+ 0x56, /* PUSH SI */
+
+ 0x31, 0xDB, /* XOR BX, BX */
+ 0x31, 0xD2, /* XOR DX, DX */
+
+ 0x0F, 0xA2, /* CPUID */
+
+ 0x89, 0x45, 0x00, /* MOV AX, 0(BP) */
+ 0x89, 0x5d, 0x04, /* MOV BX, 4(BP) */
+ 0x89, 0x4d, 0x08, /* MOV CX, 8(BP) */
+ 0x89, 0x55, 0x0C, /* MOV DX, 12(BP) */
+ 0xC3, /* RET */
+};
+
+static Res (*cpuid)(ulong ax, ulong cx) = (Res(*)(ulong, ulong)) _cpuid;
+
+/*
+ * nsec() is wallclock and can be adjusted by timesync
+ * so need to use cycles() instead, but fall back to
+ * nsec() in case we can't
+ */
+uvlong
+nanosec(void)
+{
+ static uvlong fasthz, xstart;
+ char buf[13], path[128];
+ ulong w;
+ uvlong x, div;
+ int fd;
+ Res r;
+
+ if(fasthz == ~0ULL)
+ return nsec() - xstart;
+
+ if(fasthz == 0){
+ /* first long in a.out header */
+ snprint(path, sizeof path, "/proc/%d/text", getpid());
+ fd = open(path, OREAD);
+ if(fd < 0)
+ goto Wallclock;
+ if(read(fd, buf, 4) != 4){
+ close(fd);
+ goto Wallclock;
+ }
+ close(fd);
+
+ w = ((ulong *) buf)[0];
+
+ switch(w){
+ default:
+ goto Wallclock;
+ case 0x978a0000: /* amd64 */
+ /* patch out POP BP -> POP AX */
+ _cpuid[1] = 0x58;
+ case 0xeb010000: /* 386 */
+ break;
+ }
+ segflush(_cpuid, sizeof(_cpuid));
+
+ r = cpuid(0x40000000, 0);
+ ((ulong *) buf)[0] = r.bx;
+ ((ulong *) buf)[1] = r.cx;
+ ((ulong *) buf)[2] = r.dx;
+ buf[12] = 0;
+
+ if(strstr(buf, "bhyve") != nil)
+ goto Wallclock;
+
+ if(_tos->cyclefreq){
+ fasthz = _tos->cyclefreq;
+ cycles(&xstart);
+ } else {
+Wallclock:
+ fasthz = ~0ULL;
+ xstart = nsec();
+ }
+ return 0;
+ }
+ cycles(&x);
+ x -= xstart;
+
+ /* this is ugly */
+ for(div = 1000000000ULL; x < 0x1999999999999999ULL && div > 1 ; div /= 10ULL, x *= 10ULL);
+
+ return x / (fasthz / div);
+}