first write of mmap

uboot-compiler/shmbuffer/main.c

+#include<stdio.h>
+#include<stddef.h>
+#include<sys/mman.h>
+#include<fcntl.h>
+
+#define SHMADDR 0x3F000000
+
+int main(int argc, char *argv[])
+{
+    int fd;
+    int * memaddr;
+
+    fd = open("/dev/mem", O_RDWR);
+
+    if (fd == -1)
+    {
+        printf("can not access /dev/mem\n" );
+        return -1;
+    }
+
+    memaddr =
+    (int*)mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_SHARED, fd, SHMADDR);
+    if (memaddr == MAP_FAILED)
+    {
+        printf("mmap failed\n" );
+        return -1;
+    }
+    printf("value=%d\n", *memaddr);
+    
+
+}
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