Why does this example C code run and yet SHOULD either not compile or give a segmentation fault?


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Originally Posted by Corona688
It's necessary sometimes, if you're building an operating system for example, to insert special instructions here and there without the compiler's interference. That's the kind of thing asm() is for. gcc will insert raw assembly if you ask, but you really have to know what you're doing since it can't protect you( though some more advanced syntax lets you warn gcc about side-effects instead). Plain, non-ASM goto (yes, it exists, very rarely used) wouldn't let you jump out of bounds.
As I have said in the distant past that I have coded assembly in 16 and 32 bit intel architecture but no experience in 64 bit, although I suspect there is not much difference.
And, I would only use it for mission critical stuff of which these days there is no need as HW interface APIs are usually far more than good enough for this purpose especially as the UNIX ethos is that everything is a file.

One thing for sure I am getting to know how gcc __thinks__ and compared to say Dice-C or VBCC for the AMIGA it is mega-powerful.
And finally I know that 'goto' is local to the function that uses it, and a good thing it is too.
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OUTB(2) 						     Linux Programmer's Manual							   OUTB(2)

NAME
outb, outw, outl, outsb, outsw, outsl, inb, inw, inl, insb, insw, insl, outb_p, outw_p, outl_p, inb_p, inw_p, inl_p - port I/O DESCRIPTION
This family of functions is used to do low-level port input and output. The out* functions do port output, the in* functions do port input; the b-suffix functions are byte-width and the w-suffix functions word-width; the _p-suffix functions pause until the I/O completes. They are primarily designed for internal kernel use, but can be used from user space. You compile with -O or -O2 or similar. The functions are defined as inline macros, and will not be substituted in without optimization enabled, causing unresolved references at link time. You use ioperm(2) or alternatively iopl(2) to tell the kernel to allow the user space application to access the I/O ports in question. Failure to do this will cause the application to receive a segmentation fault. CONFORMING TO
outb() and friends are hardware-specific. The value argument is passed first and the port argument is passed second, which is the opposite order from most DOS implementations. SEE ALSO
ioperm(2), iopl(2) COLOPHON
This page is part of release 3.27 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. Linux 1995-11-29 OUTB(2)

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