On Sun, Mar 05, 2017 at 06:37:37AM -0600, Segher Boessenkool wrote: > On Sun, Mar 05, 2017 at 09:26:47PM +1100, Michael Ellerman wrote: > > > I see a panic in early boot when building with a recent gcc toolchain. > > > The issue is a divide by zero, which is undefined. Older toolchains > > > let us get away with it: > > > > > > int foo(int a) { return a / 0; } > > > > > > foo: > > > li 9,0 > > > divw 3,3,9 > > > extsw 3,3 > > > blr > > > > > > But newer ones catch it: > > > > > > foo: > > > trap > > > > > > Add a check to avoid the divide by zero. > > > > Erk sorry. One of the static checkers spotted it, but I hadn't got > > around to fixing it because it seemed to not actually blow up, guess > > not. > > The PowerPC divw etc. instructions do not trap by themselves, but recent > GCC inserts trap instructions on code paths that are always undefined > behaviour (like, dividing by zero).
Is it systematic or does it depend from, e.g., optimization levels? Is there anything in the standards about this feature? Gabriel