Linux 3.15 Can Almost Be Compiled Under LLVM's Clang

http://www.phoronix.com/scan.php?page=news_item&px=MTY2MjY

by 01walid • 12 years ago

7 5 12 years ago

acqq3• 12 years ago

I like the flexibility of Gcc even if it's maybe slower than clang. And I really don't support the attitude reflected in this clang error message:

"error: fields must have a constant size: 'variable length array in structure' extension will never be supported"

Even if something isn't in the standard, if it allows less code to be written, it is a good thing. My question is then:

Why?

msbarnett2• 12 years ago

Clang's user manual has this to say: "clang does not support the gcc extension that allows variable-length arrays in structures. This is for a few reasons: one, it is tricky to implement, two, the extension is completely undocumented, and three, the extension appears to be rarely used. Note that clang does support flexible array members (arrays with a zero or unspecified size at the end of a structure)."

acqq3• 12 years ago

Arrays with zero size at the end have completely another semantics. This one that clang swears to "never implement" allows avoiding explicit alloca calls, instead the programmer can simply pass the expected size.

It's obviously used in kernel, that's how I discovered about that clang curiously worded error message: by reading the LLVMLinux site:

http://llvm.linuxfoundation.org/index.php/Broken_kernel_opti...

Linux 3.15 Can Almost Be Compiled Under LLVM's Clang

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