Example: provenance_equality_global_fn_yx.c

#include <stdio.h>
#include <string.h>
int y=2, x=1;
void f(int* p, int* q) {
_Bool b = (p==q);
// can this be false even with identical addresses?
printf("(p==q) = %s\n", b?"true":"false");
return;
}
int main() {
int *p = &x + 1;
int *q = &y;
printf("Addresses: p=%p q=%p\n",(void*)p,(void*)q);
f(p,q);
return 0;
}
[link to test in Cerberus and Compiler Explorer]

Experimental data (what does this mean?)

gcc-8.1-O0 Addresses: p=0x600a10 q=0x600a08
(p==q) = false
gcc-8.1-O2 Addresses: p=0x6009cc q=0x6009cc
(p==q) = false
gcc-8.1-O3 Addresses: p=0x6009cc q=0x6009cc
(p==q) = false
gcc-8.1-O2-no-strict-aliasing Addresses: p=0x6009cc q=0x6009cc
(p==q) = false
gcc-8.1-O3-no-strict-aliasing Addresses: p=0x6009cc q=0x6009cc
(p==q) = false
clang-6.0-O0 Addresses: p=0x601040 q=0x601038
(p==q) = false
clang-6.0-O2 Addresses: p=0x601040 q=0x601038
(p==q) = false
clang-6.0-O3 Addresses: p=0x601040 q=0x601038
(p==q) = false
clang-6.0-O2-no-strict-aliasing Addresses: p=0x601040 q=0x601038
(p==q) = false
clang-6.0-O3-no-strict-aliasing Addresses: p=0x601040 q=0x601038
(p==q) = false
clang-6.0-UBSAN Addresses: p=0x631b58 q=0x631b50
(p==q) = false
clang-6.0-ASAN Addresses: p=0x716ba4 q=0x716b60
(p==q) = false
clang-6.0-MSAN Addresses: p=0x6b7af8 q=0x6b7af0
(p==q) = false
icc-19-O0 Addresses: p=0x600b38 q=0x600b30
(p==q) = false
icc-19-O2 Addresses: p=0x6046c8 q=0x6046c0
(p==q) = false
icc-19-O3 Addresses: p=0x6046c8 q=0x6046c0
(p==q) = false
icc-19-O2-no-strict-aliasing Addresses: p=0x6046c8 q=0x6046c0
(p==q) = false
icc-19-O3-no-strict-aliasing Addresses: p=0x6046c8 q=0x6046c0
(p==q) = false
cerberus-concrete BEGIN EXEC[0]
Defined {value: "Specified(0)", stdout: "Addresses: p=<8>:80 q=<7>:72\n(p==q) = false\n", blocked: "false"}
END EXEC[0]
BEGIN EXEC[1]
Defined {value: "Specified(0)", stdout: "Addresses: p=<8>:80 q=<7>:72\n(p==q) = false\n", blocked: "false"}
END EXEC[1]
Time spent: 0.054948 seconds
cerberus-symbolic BEGIN EXEC[0]
Undefined [other_location(Core parser)]{id: [DUMMY(rev_listFromStr_aux)]}
END EXEC[0]
Time spent: 0.083687 seconds
gcc-4.9-shadowprov Addresses: p=0x41413c q=0x41413c
(p==q) = true
CHERI:MIPS-O0 Addresses: p=0x30028 q=0x30020
(p==q) = false
CHERI:MIPS-O2 Addresses: p=0x30028 q=0x30020
(p==q) = false
CHERI:MIPS-O2-no-strict-aliasing Addresses: p=0x30028 q=0x30020
(p==q) = false
CHERI:CHERI-O0-uintcap-addr-exact-equals Addresses: p=0x120020018 q=0x120020010
(p==q) = false
CHERI:CHERI-O2-uintcap-addr-exact-equals Addresses: p=0x120020018 q=0x120020010
(p==q) = false
CHERI:CHERI-O2-no-strict-aliasing-uintcap-addr-exact-equals Addresses: p=0x120020018 q=0x120020010
(p==q) = false
CHERI:CHERI-O0-uintcap-offset-exact-equals Addresses: p=0x120020018 q=0x120020010
(p==q) = false
CHERI:CHERI-O2-uintcap-offset-exact-equals Addresses: p=0x120020018 q=0x120020010
(p==q) = false
CHERI:CHERI-O2-no-strict-aliasing-uintcap-offset-exact-equals Addresses: p=0x120020018 q=0x120020010
(p==q) = false
CHERI:CHERI-O0-uintcap-addr Addresses: p=0x120020018 q=0x120020010
(p==q) = false
CHERI:CHERI-O2-uintcap-addr Addresses: p=0x120020018 q=0x120020010
(p==q) = false
CHERI:CHERI-O2-no-strict-aliasing-uintcap-addr Addresses: p=0x120020018 q=0x120020010
(p==q) = false
CHERI:CHERI-O0-uintcap-offset Addresses: p=0x120020018 q=0x120020010
(p==q) = false
CHERI:CHERI-O2-uintcap-offset Addresses: p=0x120020018 q=0x120020010
(p==q) = false
CHERI:CHERI-O2-no-strict-aliasing-uintcap-offset Addresses: p=0x120020018 q=0x120020010
(p==q) = false
RV-Match Addresses: p=(nil) q=(nil)
(p==q) = true
Comparison of unspecified value:
> in f at provenance_equality_global_fn_yx.c:7:3
in main at provenance_equality_global_fn_yx.c:14:3

Unspecified value or behavior (USP-CERL7):
see C11 section 6.5.9 http://rvdoc.org/C11/6.5.9
see MISRA-C section 8.1:3 http://rvdoc.org/MISRA-C/8.1

ch2o Fatal error: exception Main.Unknown_specifier(_)
Raised at file "map.ml", line 117, characters 16-25
Called from file "str.ml", line 253, characters 6-29
compcert-3.2 Addresses: p=0x601040 q=0x601038
(p==q) = false
compcert-3.2-O Addresses: p=0x601040 q=0x601038
(p==q) = false
compcert-3.2-interp Time 0: calling main()
--[step_internal_function]-->
Time 1: in function main, statement
p = &x + 1;
q = &y;
printf(__stringlit_4, (void *) p, (void *) q);
f(p, q);
return 0;
return 0;
--[step_seq]-->
Time 2: in function main, statement
p = &x + 1;
q = &y;
printf(__stringlit_4, (void *) p, (void *) q);
f(p, q);
return 0;
--[step_seq]-->
Time 3: in function main, statement p = &x + 1;
--[step_do_1]-->
Time 4: in function main, expression p = &x + 1
--[red_var_local]-->
Time 5: in function main, expression <loc p> = &x + 1
--[red_var_global]-->
Time 6: in function main, expression <loc p> = &<loc x> + 1
--[red_addrof]-->
Time 7: in function main, expression <loc p> = <ptr x> + 1
--[red_binop]-->
Time 8: in function main, expression <loc p> = <ptr x+4>
--[red_assign]-->
Time 9: in function main, expression <ptr x+4>
--[step_do_2]-->
Time 10: in function main, statement /*skip*/;
--[step_skip_seq]-->
Time 11: in function main, statement
q = &y; printf(__stringlit_4, (void *) p, (void *) q); f(p, q); return 0;
--[step_seq]-->
Time 12: in function main, statement q = &y;
--[step_do_1]-->
Time 13: in function main, expression q = &y
--[red_var_local]-->
Time 14: in function main, expression <loc q> = &y
--[red_var_global]-->
Time 15: in function main, expression <loc q> = &<loc y>
--[red_addrof]-->
Time 16: in function main, expression <loc q> = <ptr y>
--[red_assign]-->
Time 17: in function main, expression <ptr y>
--[step_do_2]-->
Time 18: in function main, statement /*skip*/;
--[step_skip_seq]-->
Time 19: in function main, statement
printf(__stringlit_4, (void *) p, (void *) q); f(p, q); return 0;
--[step_seq]-->
Time 20: in function main, statement
printf(__stringlit_4, (void *) p, (void *) q);
--[step_do_1]-->
Time 21: in function main, expression
printf(__stringlit_4, (void *) p, (void *) q)
--[red_var_global]-->
Time 22: in function main, expression
printf(<loc __stringlit_4>, (void *) p, (void *) q)
--[red_rvalof]-->
Time 23: in function main, expression
printf(<ptr __stringlit_4>, (void *) p, (void *) q)
--[red_var_local]-->
Time 24: in function main, expression
printf(<ptr __stringlit_4>, (void *) <loc p>, (void *) q)
--[red_rvalof]-->
Time 25: in function main, expression
printf(<ptr __stringlit_4>, (void *) <ptr x+4>, (void *) q)
--[red_cast]-->
Time 26: in function main, expression
printf(<ptr __stringlit_4>, <ptr x+4>, (void *) q)
--[red_var_local]-->
Time 27: in function main, expression
printf(<ptr __stringlit_4>, <ptr x+4>, (void *) <loc q>)
--[red_rvalof]-->
Time 28: in function main, expression
printf(<ptr __stringlit_4>, <ptr x+4>, (void *) <ptr y>)
--[red_cast]-->
Time 29: in function main, expression
printf(<ptr __stringlit_4>, <ptr x+4>, <ptr y>)
Addresses: p=<58+4> q=<57+0>
Time 29: observable event:
extcall printf(& __stringlit_4, & x+4,
& y) -> 29
--[red_builtin]-->
Time 30: in function main, expression 29
--[step_do_2]-->
Time 31: in function main, statement /*skip*/;
--[step_skip_seq]-->
Time 32: in function main, statement f(p, q); return 0;
--[step_seq]-->
Time 33: in function main, statement f(p, q);
--[step_do_1]-->
Time 34: in function main, expression f(p, q)
--[red_var_global]-->
Time 35: in function main, expression <loc f>(p, q)
--[red_rvalof]-->
Time 36: in function main, expression <ptr f>(p, q)
--[red_var_local]-->
Time 37: in function main, expression <ptr f>(<loc p>, q)
--[red_rvalof]-->
Time 38: in function main, expression <ptr f>(<ptr x+4>, q)
--[red_var_local]-->
Time 39: in function main, expression <ptr f>(<ptr x+4>, <loc q>)
--[red_rvalof]-->
Time 40: in function main, expression <ptr f>(<ptr x+4>, <ptr y>)
--[red_call]-->
Time 41: calling f(<ptr x+4>, <ptr y>)
--[step_internal_function]-->
Time 42: in function f, statement
b = p == q;
printf(__stringlit_3, b ? __stringlit_2 : __stringlit_1);
return;
--[step_seq]-->
Time 43: in function f, statement b = p == q;
--[step_do_1]-->
Time 44: in function f, expression b = p == q
--[red_var_local]-->
Time 45: in function f, expression <loc b> = p == q
--[red_var_local]-->
Time 46: in function f, expression <loc b> = <loc p> == q
--[red_rvalof]-->
Time 47: in function f, expression <loc b> = <ptr x+4> == q
--[red_var_local]-->
Time 48: in function f, expression <loc b> = <ptr x+4> == <loc q>
--[red_rvalof]-->
Time 49: in function f, expression <loc b> = <ptr x+4> == <ptr y>
Stuck state: in function f, expression <loc b> = <ptr x+4> == <ptr y>
Stuck subexpression: <ptr x+4> == <ptr y>
ERROR: Undefined behavior
In file included from provenance_equality_global_fn_yx.c:1:
In file included from /usr/include/stdio.h:64:
In file included from /usr/include/_stdio.h:68:
/usr/include/sys/cdefs.h:81:2: warning: "Unsupported compiler detected" [-W#warnings]
#warning "Unsupported compiler detected"
^
1 warning generated.