When I tried to access the address mmap returned, a Bus error is occured.
My code is below:
ftruncate(fd, shared_size); addr = mmap(shared_start, shared_size, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_FIXED, fd, 0);
shared_size == 256*1024*1024
shared_start == 401000000000 (I used flag MAP_FIXED)
ftruncate the file to 256M.
-rw-r--r-- 1 root 0 256.0M Mar 4 03:47 mem.alloc
There is nothing wrong when calling mmap, and not all of address range is not allowed to access. From the gdb information below, we can see, the address 0x40100f11ff00 is not allowed, but address 0x40100fe00000 is allowed:
(gdb) p *((char *)addr+0xf11ff00) Cannot access memory at address 0x40100f11ff00 (gdb) p *((char *)addr+0xfe1ff00) Cannot access memory at address 0x40100fe1ff00 (gdb) p *((char *)addr+0xfe00000) $17 = 0 '\000'
From maps information below, we can see the addresses I accessed above are all within the range of mmap address:
0x401000000000 0x401010000000 0x10000000 0x0 /dev/mem.alloc
However, when writing these inaccessible addresses, a bus error occurs: Program received signal SIGBUS, Bus error.
PS.When reducing shared_size from 256M to 128M, there is no issue.
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