Tell the different objects from custom alloc functions with SUPA

[honghai0924]

Hi Yulei,
As we discussed in SVF-tools/SVF#109, I tried SUPA for context-sensitive analysis with code below:

#include <stdlib.h>

void my_malloc(char ** p,unsigned size){
    *p = malloc(size);
}

void use1(char *s1){
    char c1 = s1[0];
}

void use2(char *s2){
    char c2 = s2[1];
}

void f(void){
    char *p1,*p2,*p3,*p4,*p5,*p6;
    p1 = malloc(1);
    p2 = malloc(2);
    my_malloc(&p3,3);
    my_malloc(&p4,4);
    p5 = p3;
    p6 = p4;
    use1(p5);
    use2(p6);
}

I used wpa to get the constraint graph as below.

Then I used

dvf -cxt -query=all -maxcxt=3 -cxtbg=10000 -flowbg=10000 -print-query-pts alloc_test.bc

to get points to result.

......
##<> Source Loc:
Ptr 81 		PointsTo: { 18 }

!!Target NodeID 18	 [<call> Source Loc: ]
##<> Source Loc:
Ptr 83 		PointsTo: { 18 }

!!Target NodeID 18	 [<call> Source Loc: ]
##<> Source Loc:
Ptr 85 		PointsTo: { 18 }

!!Target NodeID 18	 [<call> Source Loc: ]
##<> Source Loc:
Ptr 87 		PointsTo: { 18 }

!!Target NodeID 18	 [<call> Source Loc: ]

From the result above, I saw Ptr 81,83,85,87 all point to PagNode 18, which makes them aliases. But pointer p5 and p6 should not be aliases.

Is that supposed to be right? Or am I doing something wrong here?

[yuleisui]

-print-query-pts will print insensitive results. For context-sensitive analysis please use https://github.com/SVF-tools/SVF/blob/ab806b876e1e6ec1e7fb32eb5052881aa62775d8/include/MemoryModel/PointerAnalysis.h#L374
to obtain points-to targets together with their calling contexts.

For your case, you may wish to refer to alias function to get the non-alias results:

SUPA/lib/DDA/DDAPass.cpp

Line 279 in 3124902

llvm::AliasResult DDAPass::alias(const Value* V1, const Value* V2) {