Re: [PATCH] fread.3: Add example

[Arkadiusz Drabczyk <arkadiusz@drabczyk.org>]

On Thu, Jun 18, 2020 at 08:49:53AM +0000, Walter Harms wrote:
> +    size_t ret = fread(buffer, 4, 1, fp);
> this is the core of the example and should be a bit more verbose:
> maybe this is a bit to cryptic
>    ret = fread(buffer,sizeof (buffer)/sizeof (*buffer), sizeof (*buffer), fp);

ok, I'll use this version in v2.

> +    printf("ELF magic: %#x%x%x%x\en", buffer[0], buffer[1], buffer[2],
> +           buffer[3]);
> +
> this works for /bin/sh but if the user plays round this may show confusing results
> so you could simply do:
>     printf("ELF magic: %#02x%02x%02x%02x\en",
> so you are consistent in all cased. 

ok, I'll do it in v2.

> (until some will test this on a big endian, no idea
> what will happen then).

Nothing, in ELF spec it says that "the initial bytes of the file
specify how to interpret the file, independent of the processor on
which the inquiry is made and independent of the file's remaining
contents.". And of course I tested this example on my router which has
MIPS CPU which is big-endian and runs big-edian ELFs:

$ file sh
sh: ELF 32-bit MSB executable, MIPS, MIPS32 rel2 version 1, dynamically linked, interpreter /lib/ld-uClibc.so.0, corrupted section header size

and output of the example program is the same as on x86.

> 
> +    ret = fread(buffer, 1, 1, fp);
> +    if (ret != 1) {
> +        fprintf(stderr, "fread() failed: %zu\en", ret);
> +        exit(EXIT_FAILURE);
> +    }
> +
> please drop a line what case you want to explain here, looks like the same as above.

As said a few lines above, this retrieves ELF class. I wanted to show
that file pointer moves automatically after fread() finishes.

-- 
Arkadiusz Drabczyk <arkadiusz@drabczyk.org>