1. 24 1月, 2011 1 次提交
    • R
      BUILD_BUG_ON: make it handle more cases · 7ef88ad5
      Rusty Russell 提交于
      BUILD_BUG_ON used to use the optimizer to do code elimination or fail
      at link time; it was changed to first the size of a negative array (a
      nicer compile time error), then (in
      8c87df45) to a bitfield.
      
      This forced us to change some non-constant cases to MAYBE_BUILD_BUG_ON();
      as Jan points out in that commit, it didn't work as intended anyway.
      
      bitfields: needs a literal constant at parse time, and can't be put under
      	"if (__builtin_constant_p(x))" for example.
      negative array: can handle anything, but if the compiler can't tell it's
      	a constant, silently has no effect.
      link time: breaks link if the compiler can't determine the value, but the
      	linker output is not usually as informative as a compiler error.
      
      If we use the negative-array-size method *and* the link time trick,
      we get the ability to use BUILD_BUG_ON() under __builtin_constant_p()
      branches, and maximal ability for the compiler to detect errors at
      build time.
      
      We also document it thoroughly.
      Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>
      Cc: Jan Beulich <JBeulich@novell.com>
      Acked-by: NHollis Blanchard <hollisb@us.ibm.com>
      7ef88ad5
  2. 22 1月, 2011 16 次提交
  3. 21 1月, 2011 23 次提交