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Check if it works -- add tests
Example illustrating how IntToPtr can be used to create a pointer to an escaping object, translated into English:
C Code:
int *leak_example(int x) {
int *p = (int *)(x + 10); // Create a pointer to an address calculated from x
return p; // Return the pointer
}LLVM IR:
define dso_local i32* @leak_example(i32 %x) #0 {
entry:
%add = add nsw i32 %x, 10 // Calculate the address
%0 = inttoptr i32 %add to i32* // Convert the integer to a pointer
ret i32* %0 // Return the pointer
}In this example:
- The function
leak_exampletakes an integer argumentx. - Inside the function, an address is calculated by adding
xto 10. - The
inttoptrinstruction converts the resulting integer to a pointer of typei32*. - The function returns the created pointer.
Problem:
- We don't know what the created pointer refers to.
- It might refer to a valid object in memory, but it could also point to unallocated memory or memory that has already been freed.
- Consequently, dereferencing this pointer could lead to undefined behavior.
Leakage:
- In this example, the pointer
pescapes from the functionleak_example. - If the caller uses this pointer without checking its validity, it might result in an error.
Escape Analysis:
- Escape analysis must consider
IntToPtrinstructions since they can create pointers to escaping objects. - In this example, escape analysis should mark the pointer returned from
leak_exampleas escaping.
Conclusion:
IntToPtris a powerful instruction that allows you to work with memory at a low level.- However, its use requires caution as it can lead to undefined behavior and memory leaks.
- Escape analysis must consider
IntToPtrfor accurate leak analysis.
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