Bizarre use of conditional operator in Linux

Question

In the 3.0.4 Linux kernel, mm/filemap.c has this line of code:

retval = retval ?: desc.error;

I\'ve tried compiling a similar minimal test

Answer 1

It's a gcc extension. x ?: y is equivalent to x ? x : y --- see http://gcc.gnu.org/onlinedocs/gcc/Conditionals.html#Conditionals.

Yes, I think it's evil too.