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August 28, 2025 07:43
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allocate memory with mmap
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| #include <stdio.h> | |
| #include <stdlib.h> | |
| #include <string.h> | |
| #include <sys/mman.h> | |
| #include <unistd.h> | |
| #include <errno.h> | |
| #include <stdint.h> | |
| // Size of allocation (1MB by default) | |
| #define ALLOC_SIZE (1024 * 1024) | |
| int main() { | |
| // Target address: 256MB (0x10000000) | |
| void* target_addr = (void*)0x10000000; | |
| // Get system page size | |
| long page_size = sysconf(_SC_PAGESIZE); | |
| printf("System page size: %ld bytes\n", page_size); | |
| printf("Attempting to allocate %d bytes at address %p (256MB)\n", | |
| ALLOC_SIZE, target_addr); | |
| // Try to map memory at the specified address | |
| void* result = mmap( | |
| target_addr, // Requested address | |
| ALLOC_SIZE, // Size of mapping | |
| PROT_READ | PROT_WRITE, // Memory protection | |
| MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, // Flags | |
| -1, // File descriptor (not used for anonymous) | |
| 0 // Offset (not used for anonymous) | |
| ); | |
| if (result == MAP_FAILED) { | |
| printf("Failed to allocate at 256MB: %s\n", strerror(errno)); | |
| return 1; | |
| } | |
| printf("Successfully allocated memory at %p\n", result); | |
| // Write to the memory to ensure it's accessible | |
| memset(result, 0xAB, ALLOC_SIZE); | |
| // Read back first byte to verify | |
| unsigned char* check = (unsigned char*)result; | |
| printf("Memory check: First byte = 0x%02X (expected 0xAB)\n", *check); | |
| // Keep the mapping active until user input | |
| printf("\nPress Enter to unmap and exit...\n"); | |
| getchar(); | |
| // Unmap the memory | |
| munmap(result, ALLOC_SIZE); | |
| printf("Unmapped memory at 256MB\n"); | |
| return 0; | |
| } |
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