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| // Compile with: | |
| // g++ -c -fpic -o hack.o hack.cpp && g++ -shared -o libhack.so hack.o | |
| // Then load with the Python | |
| // import ctypes; ctypes.CDLL('libhack.so') | |
| #include <stdio.h> | |
| #include <dlfcn.h> | |
| #include <stddef.h> | |
| #include <stdint.h> | |
| #include <sys/mman.h> | |
| #include <sys/user.h> | |
| static int cudaGetDeviceFake(int* device) { | |
| *device = 0; | |
| return 0; | |
| } | |
| static int cudaSetDeviceFake(int device) { | |
| return 0; | |
| } | |
| // Taken from http://jmkeyes.github.io/post/hot-patching-unconditional-jumps-x86-x86-64/ | |
| static void write_redirection_medium(unsigned char *source, unsigned char *destination) { | |
| ptrdiff_t delta = (destination - (source + 5)); | |
| if (delta < -2147483648 || delta > 2147483647) { | |
| perror("unable to redirect function: jmp to large"); | |
| return; | |
| } | |
| /* 0xe9 is the unconditional jump opcode. */ | |
| source[0] = 0xe9; | |
| /* Write each of the octets of the delta. */ | |
| source[1] = (delta >> 0) & 0xff; | |
| source[2] = (delta >> 8) & 0xff; | |
| source[3] = (delta >> 16) & 0xff; | |
| source[4] = (delta >> 24) & 0xff; | |
| return; | |
| } | |
| static void alter_page_attributes(const unsigned char *address, unsigned long length, int mask) { | |
| /* mprotect() needs an address that is page-aligned. */ | |
| unsigned char *addr = (unsigned char *) ((unsigned long) address & PAGE_MASK); | |
| length += (address - addr); | |
| if (mprotect(addr, length, mask) == -1) { | |
| perror("mprotect"); | |
| } | |
| return; | |
| } | |
| static void redirect(const char* sym, void* dst) { | |
| unsigned char* src = (unsigned char*)dlsym(NULL, sym); | |
| if (!src) { | |
| perror("src symbol not found"); | |
| return; | |
| } | |
| alter_page_attributes(src, 5, PROT_READ|PROT_WRITE); | |
| write_redirection_medium(src, (unsigned char*)dst); | |
| alter_page_attributes(src, 5, PROT_READ|PROT_EXEC); | |
| printf("patched %s\n", sym); | |
| } | |
| __attribute__((constructor)) static void init() { | |
| redirect("cudaGetDevice", (void*)&cudaGetDeviceFake); | |
| redirect("cudaSetDevice", (void*)&cudaSetDeviceFake); | |
| } |
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awesome hack, thanks.