Re: [PATCH] bug.h: Work around GCC PR82365 in BUG()

From: Vineet Gupta
Date: Tue Dec 19 2017 - 17:38:47 EST

On 12/19/2017 12:13 PM, Arnd Bergmann wrote:

I suppose BUG() implies "dead end" like semantics - which ARC was lacking
before ?
Correct. Using __builtin_trap() here avoids the 'control reaches end of non-void
function' warnings, but then makes us run into the stack size problem that
I work around with the barrier_before_unreachable().

It would be good if you could give this a quick test to see if you get sensible
output from the __builtin_trap();

It does, added a BUG() arbit, hits an abort()

ISA ExtnÂÂÂ : atomic ll64 unalign (not used)
ÂÂÂ ÂÂÂ : mpy[opt 9] div_rem norm barrel-shift swap minmax swape
BPUÂÂÂ ÂÂÂ : partial match, cache:2048, Predict Table:16384
BUG: failure at ../arch/arc/mm/tlb.c:827/arc_mmu_init()!

Tested-by: Vineet Gupta <vgupta@xxxxxxxxxxxx>

FWIW newer ARC gcc actually implements the builtin so we get a trap 5 instruction now, vs., abort() calls before.

BTW I missed reading the hunk of your changelog where this addresses the long standing mystery with ARC builds and numerous -Wreturn-type warnings. I always wondered why they were not fixed upstream already, being too lazy to investigate myself, and turns out this was due to this BUG() thingy. phew !