https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79828
Bug ID: 79828
Summary: missing div-by-zero warning
Product: gcc
Version: 7.0.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: arnd at linaro dot org
Target Milestone: ---
Building the kernel with gcc-7.0.1 (r245831 at the time of testing), we ran
into a warning from objtool about a function ending in an undefined
instruction:
drivers/pwm/pwm-hibvt.o: warning: objtool: hibvt_pwm_get_state() falls through
to next function hibvt_pwm_apply()
I reduced the test case to a trivial division by zero:
static inline int return0(void) { return 0; }
int provoke_div0_warning(void) { return 1 / return0(); }
which gets turned into a single trapping instruction
(aarch64)
0000000000000018 <provoke_div0_warning>:
18: d4207d00 brk #0x3e8
(x86-64)
0000000000000010 <provoke_div0_warning>:
10: 0f 0b ud2
This seems to be a result of r242636, and in the discussion
on that patch, I found a remark from Jeff Law that there
should be a warning for it:
https://gcc.gnu.org/ml/gcc-patches/2016-11/msg00508.html
I think that having this gcc warning would have been
rather useful in debugging the kernel build warning.
Any chance this could be added?
