x86 asm: move RDTSC from x86-assembly-cheat, create RDTSCP

Author: cirosantilli

README.adoc

@@ -12489,47 +12489,35 @@ Generated some polemic when kernel devs wanted to use it as part of `/dev/random
 
 RDRAND sets the carry flag when data is ready so we must loop if the carry flag isn't set.
 
-=== x86 SIMD
+=== x86 system instructions
 
-History:
+<<intel-manual-1>> 5.20 "SYSTEM INSTRUCTIONS"
 
-* link:https://en.wikipedia.org/wiki/MMX_(instruction_set)[MMX]: MultiMedia eXtension (unofficial name). 1997. MM0-MM7 64-bit registers.
-* link:https://en.wikipedia.org/wiki/Streaming_SIMD_Extensions[SSE]: Streaming SIMD Extensions. 1999. XMM0-XMM7 128-bit registers, XMM0-XMM15 for AMD in 64-bit mode.
-* link:https://en.wikipedia.org/wiki/SSE2[SSE2]: 2004
-* link:https://en.wikipedia.org/wiki/SSE3[SSE3]: 2006
-* link:https://en.wikipedia.org/wiki/SSE4[SSE4]: 2006
-* link:https://en.wikipedia.org/wiki/Advanced_Vector_Extensions[AVX]: Advanced Vector Extensions. 2011. YMM0–YMM15 256-bit registers in 64-bit mode. Extension of XMM.
-* AVX2:2013
-* AVX-512: 2016. 512-bit ZMM registers. Extension of YMM.
-
-==== x86 SSE2
-
-===== x86 ADDPD instruction
-
-link:userland/arch/x86_64/addpd.S[]: ADDPS, ADDPD
+==== x86 RDTSC instruction
 
-Good first instruction to learn SIMD: <<simd-assembly>>
+Sources:
 
-===== x86 PADDQ instruction
+* link:userland/arch/x86_64/rdtsc.S[]
+* link:userland/arch/x86_64/intrinsics/rdtsc.c[]
 
-link:userland/arch/x86_64/paddq.S[]: PADDQ, PADDL, PADDW, PADDB
+Try running the programs multiple times, and watch the value increase, and then try to correlate it with `/proc/cpuinfo` frequency!
 
-Good first instruction to learn SIMD: <<simd-assembly>>
+....
+while true; do sleep 1 && ./userland/arch/x86_64/rdtsc.out; done
+....
 
-=== x86 RDTSC instruction
+RDTSC stores its output to EDX:EAX, even in 64-bit mode, top bits are zeroed out.
 
 TODO: review this section, make a more controlled userland experiment with <<m5ops>> instrumentation.
 
 Let's have some fun and try to correlate the gem5 <<stats-txt>> `system.cpu.numCycles` cycle count with the link:https://en.wikipedia.org/wiki/Time_Stamp_Counter[x86 RDTSC instruction] that is supposed to do the same thing:
 
 ....
-./build-userland --static userland/arch/x86_64/inline_asm/rdtsc.c
-./run --eval './arch/x86_64/c/rdtsc.out;m5 exit;' --emulator gem5
+./build-userland --static userland/arch/x86_64/inline_asm/rdtsc.S
+./run --eval './arch/x86_64/rdtsc.out;m5 exit;' --emulator gem5
 ./gem5-stat
 ....
 
-Source: link:userland/arch/x86_64/rdtsc.c[]
-
 RDTSC outputs a cycle count which we compare with gem5's `gem5-stat`:
 
 * `3828578153`: RDTSC
@@ -12544,14 +12532,69 @@ Bibliography:
 * https://en.wikipedia.org/wiki/Time_Stamp_Counter
 * https://stackoverflow.com/questions/9887839/clock-cycle-count-wth-gcc/9887979
 
-==== ARM PMCCNTR register
+===== x86 RDTSCP instruction
+
+RDTSCP is like RDTSP, but it also stores the CPU ID into ECX: this is convenient because the value of RDTSC depends on which core we are currently on, so you often also want the core ID when you want the RDTSC.
+
+Sources:
+
+* link:userland/arch/x86_64/rdtscp.S[]
+* link:userland/arch/x86_64/intrinsics/rdtscp.c[]
+
+We can observe its operation with the good and old `taskset`, for example:
+
+....
+taskset -c 0 ./userland/arch/x86_64/rdtscp.out | tail -n 1
+taskset -c 1 ./userland/arch/x86_64/rdtscp.out | tail -n 1
+....
+
+produces:
+
+....
+0x00000000
+0x00000001
+....
+
+
+There is also the RDPID instruction that reads just the processor ID, but it appears to be very new for QEMU 4.0.0 or <<p51>>, as it fails with SIGILL on both.
+
+Bibliography: https://stackoverflow.com/questions/22310028/is-there-an-x86-instruction-to-tell-which-core-the-instruction-is-being-run-on/56622112#56622112
+
+===== ARM PMCCNTR register
 
 TODO We didn't manage to find a working ARM analogue to <<x86-rdtsc-instruction>>: link:kernel_modules/pmccntr.c[] is oopsing, and even it if weren't, it likely won't give the cycle count since boot since it needs to be activate before it starts counting anything:
 
 * https://stackoverflow.com/questions/40454157/is-there-an-equivalent-instruction-to-rdtsc-in-arm
 * https://stackoverflow.com/questions/31620375/arm-cortex-a7-returning-pmccntr-0-in-kernel-mode-and-illegal-instruction-in-u/31649809#31649809
 * https://blog.regehr.org/archives/794
 
+=== x86 SIMD
+
+History:
+
+* link:https://en.wikipedia.org/wiki/MMX_(instruction_set)[MMX]: MultiMedia eXtension (unofficial name). 1997. MM0-MM7 64-bit registers.
+* link:https://en.wikipedia.org/wiki/Streaming_SIMD_Extensions[SSE]: Streaming SIMD Extensions. 1999. XMM0-XMM7 128-bit registers, XMM0-XMM15 for AMD in 64-bit mode.
+* link:https://en.wikipedia.org/wiki/SSE2[SSE2]: 2004
+* link:https://en.wikipedia.org/wiki/SSE3[SSE3]: 2006
+* link:https://en.wikipedia.org/wiki/SSE4[SSE4]: 2006
+* link:https://en.wikipedia.org/wiki/Advanced_Vector_Extensions[AVX]: Advanced Vector Extensions. 2011. YMM0–YMM15 256-bit registers in 64-bit mode. Extension of XMM.
+* AVX2:2013
+* AVX-512: 2016. 512-bit ZMM registers. Extension of YMM.
+
+==== x86 SSE2
+
+===== x86 ADDPD instruction
+
+link:userland/arch/x86_64/addpd.S[]: ADDPS, ADDPD
+
+Good first instruction to learn SIMD: <<simd-assembly>>
+
+===== x86 PADDQ instruction
+
+link:userland/arch/x86_64/paddq.S[]: PADDQ, PADDL, PADDW, PADDB
+
+Good first instruction to learn SIMD: <<simd-assembly>>
+
 === x86 assembly bibliography
 
 ==== x86 official bibliography

lkmc.c

@@ -56,8 +56,12 @@ void lkmc_assert_memcmp(
     }
 }
 
+void lkmc_print_hex_32(uint32_t x) {
+    printf("0x%08" PRIX32, x);
+}
+
 void lkmc_print_hex_64(uint64_t x) {
-    printf("0x%016" PRIx64, x);
+    printf("0x%016" PRIX64, x);
 }
 
 void lkmc_print_newline() {

userland/arch/x86_64/rdtsc.c renamed to userland/arch/x86_64/intrinsics/rdtsc.c

@@ -1,14 +1,13 @@
 /* https://github.com/cirosantilli/linux-kernel-module-cheat#x86-rdtsc-instruction */
 
+#include <inttypes.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 
 #include <x86intrin.h>
 
 int main(void) {
-    uintmax_t val;
-    val = __rdtsc();
-    printf("%ju\n", val);
+    printf("0x%016" PRIX64 "\n", (uint64_t)__rdtsc());
     return EXIT_SUCCESS;
 }

userland/arch/x86_64/intrinsics/rdtscp.c

@@ -0,0 +1,15 @@
+/* https://github.com/cirosantilli/linux-kernel-module-cheat#x86-rdtscp-instruction */
+
+#include <inttypes.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <x86intrin.h>
+
+int main(void) {
+    uint32_t pid;
+    printf("0x%016" PRIX64 "\n", (uint64_t)__rdtscp(&pid));
+    printf("0x%08" PRIX32 "\n", pid);
+    return EXIT_SUCCESS;
+}

userland/arch/x86_64/rdtsc.S

@@ -0,0 +1,12 @@
+/* https://github.com/cirosantilli/linux-kernel-module-cheat#x86-rdtsc-instruction */
+
+#include <lkmc.h>
+
+LKMC_PROLOGUE
+    rdtsc
+    mov %edx, %edi
+    shl $32, %rdi
+    add %rax, %rdi
+    call lkmc_print_hex_64
+    call lkmc_print_newline
+LKMC_EPILOGUE

userland/arch/x86_64/rdtscp.S

@@ -0,0 +1,20 @@
+/* https://github.com/cirosantilli/linux-kernel-module-cheat#x86-rdtscp-instruction */
+
+#include <lkmc.h>
+
+LKMC_PROLOGUE
+    rdtscp
+    mov %edx, %edi
+    shl $32, %rdi
+    add %rax, %rdi
+    mov %ecx, %r12d
+
+    /* Print RDTSC. */
+    call lkmc_print_hex_64
+    call lkmc_print_newline
+
+    /* Print PID. */
+    mov %r12d, %edi
+    call lkmc_print_hex_32
+    call lkmc_print_newline
+LKMC_EPILOGUE