Exploring GNU extensions in the Linux kernel(maskray.me)

71 pointsby ingve2 lata temu8 comments

Exploring GNU extensions in the Linux kernel

https://maskray.me/blog/2024-05-12-exploring-gnu-extensions-in-linux-kernel

8 comments

I am fantastic on Linux kernel and on Clang compiler. This article teaches me what GNU extension characteristic will be when Linux kernel is accepting more modern C11 standard.

For example, Linux kernel use local labels, inline assembly and builtin functions heavily.

This article inspires me to persist studying in Linux kernel and Clang compiler.

jcalvinowens2 lata temu

Clang supports the extensions, you can build the Linux kernel with clang today:

  make -s LLVM=1

e63f67dd-065b2 lata temu

As sibling mentioned, you can build the kernel with clang today. `make CC=clang`, and for whatever reason I've found that it produces code that's significantly more pleasant to step through under a debugger than gcc.

If anybody has an explanation for this I'd love to hear it.

MaskRay2 lata temu

Interesting. Traditionally, Clang's -O1 and higher optimizations have been considered less debuggable than GCC's.

Sony developers have proposed changes to improve the debugging experience and some work has been done, e.g. https://discourse.llvm.org/t/rfc-redefine-og-o1-and-add-a-ne...

* change representation to help make -g not change codegen : https://discourse.llvm.org/t/rfc-debuginfo-proposed-changes-...

o11c2 lata temu

I don't kernel, but:

Empty structures are useful, but behave weirdly. Structures containing a zero-size `char` array are much more portable.

Although `__builtin_choose_expr` isn't available in C++, it's trivial to implement using templates. Actually a lot of these are a reminder that GNU C exists for people who refuse to use C++ for political reasons.

`__builtin_types_compatible_p` is mostly not needed now that C11 `_Generic` exists.

omoikane2 lata temu

I wonder what it would take to have the Elvis operator to be standardized in C and C++, since GCC and Clang have supported this extension for years.

https://en.wikipedia.org/wiki/Elvis_operator

pjmlp2 lata temu

Write a language improvement paper and fight for it at WG14 meetings, so that when voting comes to be, it is voted in.

AstroJetson2 lata temu

I've done a few bytecode interpreters but have mostly used the case of Operator type of driving loop. I was impressed by this

static void tbl[] = {&&do_ret, &&do_inc, &&do_dec};

#define NEXT goto tbl[*pc++]

NEXT;

for(;;) {

do_ret: return val;

do_inc: val++; NEXT;

do_dec: val--; NEXT;

}