ubsan sample

ub.c

double func(double a) {}
  
int main() {
  func(1.0);
}

Test on Mac OS X (mojave 10.14.1)

$ g++ ub.c 
ub.c: In function 'double func(double)':
ub.c:1:24: warning: no return statement in function returning non-void [-Wreturn-type]
 double func(double a) {}
                        ^

$ ./a.out; echo $?
0

$ g++ -O1 ub.c 
ub.c: In function 'double func(double)':
ub.c:1:24: warning: no return statement in function returning non-void [-Wreturn-type]
 double func(double a) {}
                        ^

$ ./a.out; echo $?
zsh: illegal hardware instruction  ./a.out
132

$ g++ -Q --help=common |grep sanitize
  -fsanitize-address-use-after-scope 	[disabled]
  -fsanitize-coverage=        		
  -fsanitize-recover          		
  -fsanitize-recover=         		
  -fsanitize-sections=<sec1,sec2,...> 	
  -fsanitize-undefined-trap-on-error 	[disabled]
  -fsanitize=

$ g++ -O1 -Q --help=common |grep sanitize  
  -fsanitize-address-use-after-scope 	[disabled]
  -fsanitize-coverage=        		
  -fsanitize-recover          		
  -fsanitize-recover=         		
  -fsanitize-sections=<sec1,sec2,...> 	
  -fsanitize-undefined-trap-on-error 	[disabled]
  -fsanitize=