Having a weird issue here: if I dlsym() something in a constructor, but don't use the result; the shared library segfaults at load.

README.md

gcc -shared -O2 -fPIC bug-shared.c -ldl -o shared.so
gcc -O2 -fPIC bug-main.c -ldl
./a.out

Now comment out the printf of the pointer in bug-shared.c

Backtrace:

#0  0x00007ffff7de4b77 in _dl_lookup_symbol_x () from /lib64/ld-linux-x86-64.so.2
#1  0x00007ffff7951b91 in do_sym () from /usr/lib/libc.so.6
#2  0x00007ffff7bd80f4 in ?? () from /usr/lib/libdl.so.2
#3  0x00007ffff7de9f94 in _dl_catch_error () from /lib64/ld-linux-x86-64.so.2
#4  0x00007ffff7bd85e1 in ?? () from /usr/lib/libdl.so.2
#5  0x00007ffff7bd8148 in dlsym () from /usr/lib/libdl.so.2
#6  0x00007ffff7dea0ea in call_init.part () from /lib64/ld-linux-x86-64.so.2
#7  0x00007ffff7dea1fb in _dl_init () from /lib64/ld-linux-x86-64.so.2
#8  0x00007ffff7dee627 in dl_open_worker () from /lib64/ld-linux-x86-64.so.2
#9  0x00007ffff7de9f94 in _dl_catch_error () from /lib64/ld-linux-x86-64.so.2
#10 0x00007ffff7dede01 in _dl_open () from /lib64/ld-linux-x86-64.so.2
#11 0x00007ffff7bd7fc9 in ?? () from /usr/lib/libdl.so.2
#12 0x00007ffff7de9f94 in _dl_catch_error () from /lib64/ld-linux-x86-64.so.2
#13 0x00007ffff7bd85e1 in ?? () from /usr/lib/libdl.so.2
#14 0x00007ffff7bd8061 in dlopen () from /usr/lib/libdl.so.2
#15 0x0000000000400622 in main ()

I've attached the compiled assembly of bus-shared.c

bug-main.c

#define _GNU_SOURCE
#include <dlfcn.h>

int main() {
	void *foo = dlopen("./shared.so", RTLD_NOW);
	void (*some_exported_function)() = dlsym(foo, "some_exported_function");
	some_exported_function();
	return 0;
}

bug-shared.c

#define _GNU_SOURCE
#include <dlfcn.h>
#include <stdio.h>

static int (*pointer) ();
static int stub () { return 0; }
__attribute__((constructor)) static void some_init() {
	if ((pointer = dlsym(RTLD_DEFAULT, "anything")) == NULL) {
		pointer = stub;
	}
}

void some_exported_function() {
	printf("in some_exported_function\n");
	printf("%p\n", pointer);
}

bus-shared.s

	.file	"bug-shared.c"
	.section	.text.unlikely,"ax",@progbits
.LCOLDB0:
	.text
.LHOTB0:
	.p2align 4,,15
	.type	stub, @function
stub:
.LFB12:
	.cfi_startproc
	xorl	%eax, %eax
	ret
	.cfi_endproc
.LFE12:
	.size	stub, .-stub
	.section	.text.unlikely
.LCOLDE0:
	.text
.LHOTE0:
	.section	.rodata.str1.1,"aMS",@progbits,1
.LC1:
	.string	"anything"
	.section	.text.unlikely
.LCOLDB2:
	.section	.text.startup,"ax",@progbits
.LHOTB2:
	.p2align 4,,15
	.type	some_init, @function
some_init:
.LFB13:
	.cfi_startproc
	leaq	.LC1(%rip), %rsi
	xorl	%edi, %edi
	jmp	dlsym@PLT
	.cfi_endproc
.LFE13:
	.size	some_init, .-some_init
	.section	.text.unlikely
.LCOLDE2:
	.section	.text.startup
.LHOTE2:
	.section	.init_array,"aw"
	.align 8
	.quad	some_init
	.section	.rodata.str1.1
.LC3:
	.string	"in some_exported_function"
	.section	.text.unlikely
.LCOLDB4:
	.text
.LHOTB4:
	.p2align 4,,15
	.globl	some_exported_function
	.type	some_exported_function, @function
some_exported_function:
.LFB14:
	.cfi_startproc
	leaq	.LC3(%rip), %rdi
	jmp	puts@PLT
	.cfi_endproc
.LFE14:
	.size	some_exported_function, .-some_exported_function
	.section	.text.unlikely
.LCOLDE4:
	.text
.LHOTE4:
	.ident	"GCC: (GNU) 5.1.0"
	.section	.note.GNU-stack,"",@progbits