https://sourceware.org/bugzilla/show_bug.cgi?id=17704
Bug ID: 17704
Summary: icf doesn't respect section alignment
Product: binutils
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: gold
Assignee: ccoutant at google dot com
Reporter: rafael.espindola at gmail dot com
CC: ian at airs dot com
Created attachment 8008
--> https://sourceware.org/bugzilla/attachment.cgi?id=8008&action=edit
testcase
With the attached testcase, running
gcc -c t1.s
ld -o foo t1.o
./foo
echo $?
ld -o foo t1.o --icf=safe
./foo
echo $?
Will print
0
1
The problem is that icf is merging foo and bar but not enforcing the stricter
alignment requirements of bar.
While this reduced testcase is assembly, the original was c++.
The check of the least significant bit of a function pointer comes from how
member functions are implemented:
* For non virtual functions, a plain pointer is passed.
* For virtual functions it is 1 + the vtable offset
To ensure that this works, the compiler has to align member functions, but has
no such requirement for regular functions. For example, given
struct S {
void f() { }
};
inline void g() {}
void f(S *x) {
g();
x->f();
}
gcc will align f but not g.
It is possible for a member function to codegen to the same bits as a
non-member function, which is how this bug was found.
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