/* Copyright 2013 Google Inc. All Rights Reserved. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ /* * This "tool" can be used to brute force the XOR bitmask that a memory * controller uses to interleave addresses onto its two channels. To use it, * you need to have a bunch of addresses that are known to go to only one * of the memory channels... easiest way to get these is to run stressapptest on * a machine while holding a soldering iron close to the chips of one channel. * Generate about a thousand failures and extract their physical addresses * from the output. Write them to findmask.inc in a way that forms a valid * definition for the addrs array. Make and run on a big machine. * * The program iterates over all possible bitmasks within the first NUM_BITS, * parallelizing execution over NUM_THREADS. Every integer is masked * onto all supplied addresses, counting the amount of times this results in * an odd or even amount of bits. If all but NOISE addresses fall on one side, * it will print that mask to stdout. Note that the script will always "find" * the mask 0x0, and may also report masks such as 0x100000000 depending on * your test machines memory size... you will need to use your own judgement to * interpret the results. * * As the program might run for a long time, you can send SIGUSR1 to it to * output the last mask that was processed and get a rough idea of the * current progress. */ #include <inttypes.h> #include <pthread.h> #include <signal.h> #include <stdint.h> #include <stdlib.h> #include <stdio.h> #define NOISE 20 #define NUM_BITS 32 #define NUM_THREADS 128 // keep this a power of two static uint64_t addrs[] = { #include "findmask.inc" }; static uint64_t lastmask; __attribute__((optimize(3, "unroll-loops"))) void* thread_func(void* arg) { register uint64_t mask; register uintptr_t num = (uintptr_t)arg; for (mask = num; mask < (1ULL << (NUM_BITS + 1)); mask += NUM_THREADS) { register const uint64_t* cur; register int a = 0; register int b = 0; for (cur = addrs; (char*)cur < (char*)addrs + sizeof(addrs); cur++) { #ifdef __x86_64__ register uint64_t addr asm("rdx") = *cur & mask; register uint32_t tmp asm("ebx"); // Behold: the dark bit counting magic! asm ( // Fold high and low 32 bits onto each other "MOVl %%edx, %%ebx\n\t" "SHRq $32, %%rdx\n\t" "XORl %%ebx, %%edx\n\t" // Fold high and low 16 bits onto each other "MOVl %%edx, %%ebx\n\t" "SHRl $16, %%edx\n\t" "XORw %%bx, %%dx\n\t" // Fold high and low 8 bits onto each other "XORb %%dh, %%dl\n\t" // Invoke ancient 8086 parity flag (only counts lowest byte) "SETnp %%bl\n\t" "SETp %%dl\n\t" // Stupid SET instruction can only affect the lowest byte... "ANDl $1, %%ebx\n\t" "ANDl $1, %%edx\n\t" // Increment either 'a' or 'b' without needing another branch "ADDl %%ebx, %2\n\t" "ADDl %%edx, %1\n\t" : "=b" (tmp), "+r"(a), "+r"(b) : "d"(addr) : "cc"); #else // generic processor register uint64_t addr = *cur & mask; register uint32_t low = (uint32_t)addr; register uint32_t high = (uint32_t)(addr >> 32); // Takes about twice as long as the version above... take that GCC! __builtin_parity(low) ^ __builtin_parity(high) ? a++ : b++; #endif // Early abort: probably still the most valuable optimization in here if (a >= NOISE && b >= NOISE) break; } if (a < NOISE) b = a; if (b < NOISE) { printf("Found mask with just %d deviations: 0x%" PRIx64 "\n", b, mask); fflush(stdout); } // I'm a little paranoid about performance: don't write to memory too often if (!(mask & 0x7ff)) lastmask = mask; } return 0; } void signal_handler(int signum) { printf("Received signal... currently evaluating mask 0x%" PRIx64 "!\n", lastmask); fflush(stdout); } int main(int argc, char** argv) { uintptr_t i; pthread_t threads[NUM_THREADS]; signal(SIGUSR1, signal_handler); for (i = 0; i < NUM_THREADS; i++) pthread_create(&threads[i], 0, thread_func, (void*)i); for (i = 0; i < NUM_THREADS; i++) pthread_join(threads[i], 0); return 0; }