net/frr[89] revealed an interesting edge-case on arm when dynamically
linking a shared library that declares more than one static TLS variable
with at least one using the "initial-exec" TLS model. In the case
of frr[89], this library was libfrr.so which essentially does the
following:
#include <stdio.h>
#include "lib.h"
static __thread int *a
__attribute__((tls_model("initial-exec")));
void lib_test()
{
static __thread int b = -1;
printf("&a = %p\n", &a);
printf(" a = %p\n", a);
printf("\n");
printf("&b = %p\n", &b);
printf(" b = %d\n", b);
}
Allocates a file scoped `static __thread` pointer with
tls_model("initial-exec") and later a block scoped TLS int. Notice in
the above minimal reproducer, `b == -1`. The relocation process does
the wrong thing and ends up pointing both `a` and `b` at the same place
in memory.