https://pagedout.institute/webview.php?issue=9&page=37&artic...
1 long typedef[[]]*($)(void*($),...);
2 int main() {
3 char* str = "Hello, world.";
4 $ $ asm("puts");
5 $:&&$&&$(str);
6 }
it's obfuscated as follows:
- typedef is a specifier and can go on either side of the type, same as int const/const int
- [[ ]] is an empty list of attributes
- "void*($)" is an argument named '$' of type void*, but parameter names are ignored in declarations.
- you can put parens in declarations since sometimes you need to group prefixes and postfixes in a different order
- dollar signs in names are allowed in many c compilers (and some other c-like languages)
- "..." are variadic arguments. puts doesn't have those, but the first argument uses the same register either way so it happens to work out in this case
(4) declares a function named '$' of type '$', shadowing the type, and links it to the assembly label "puts". calling $ calls puts.
normally it looks like `int call_foo(void) asm("foo");`
(5) is parsed as: "label $: address-of-label $ and function $ called on str. the address of a label is truthy, so the function also gets called.
unary && looks for the argument in the label namespace, but other operators don't, so the two dollars refer to different things.
that's about it. if you're familiar with the c standard and some common gnu extentions, you can deconstruct the examples into their basic elements easily enough
The C Programming Language K&R