strace output problems solve

Question

I tried to run strace in linux for my Program.

Here is the example Output :

brk(0) = 0x804b000 brk(0x806c000) = 0x806c000 open("test.txt", O_RDONLY) = 3 fstat64(3, {st_mode=S_IFREG|0600, st_size=216, ...}) = 0 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7728000 read(3, "10\n10\n2\t3\t3\t5\t4\t7\t7\t2\t2\t7\t\n8\t3\t1"..., 4096) = 216 read(3, "", 4096) = 0 read(3, "", 4096) = 0 close(3) = 0 munmap(0xb7728000, 4096) = 0 **open(NULL, O_RDONLY) = -1 EFAULT (Bad address)** dup(2) = 3 fcntl64(3, F_GETFL) = 0x2 (flags O_RDWR) fstat64(3, {st_mode=S_IFCHR|0600, st_rdev=makedev(136, 0), ...}) = 0 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7728000 **_llseek(3, 0, 0xbfc97a44, SEEK_CUR) = -1 ESPIPE (Illegal seek)** write(3, "Can't open file!: Bad address\n", 30Can't open file!: Bad address

Why i get some errors in that two line. what **open(NULL, O_RDONLY)** does it means?

You are opening a file whose name is NULL. At least the filename containing variable is NULL — Shiplu Mokaddim
– Shiplu Mokaddim, Commented Oct 30, 2013 at 19:13

Olsonist · Accepted Answer · 2019-03-28 07:38:20Z

**open(NULL, O_RDONLY)

You're passing a NULL string as file name. According to the documentation, EFAULT is generated when the pathname points outside your accessible address space.

_llseek(3, 0, 0xbfc97a44, SEEK_CUR)

You are trying to set the offset of a file descriptor which does not support this function.

In fact, you are trying to move the offset of the STANDARD ERROR (3 is the result of dup(2)), which does not make sense as it is not a real file. According to the documentation, ESPIPE is generated when a file descriptor is associated with a pipe, socket, or FIFO.

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