Using base pointer register in C++ inline asm

I want to be able to use the base pointer register (%rbp) within inline asm. A toy example of this is like so:

void Foo(int &x)
{
    asm volatile ("pushq %%rbp;"         // 'prologue'"movq %%rsp, %%rbp;"   // 'prologue'"subq $12, %%rsp;"     // make room

                  "movl $5, -12(%%rbp);" // some asm instruction

                  "movq %%rbp, %%rsp;"  // 'epilogue'"popq %%rbp;"         // 'epilogue'
                  : : : );
    x = 5;
}

int main() 
{
    int x;
    Foo(x);
    return 0;
}

I hoped that, since I am using the usual prologue/epilogue function-calling method of pushing and popping the old %rbp, this would be ok. However, it seg faults when I try to access x after the inline asm.

The GCC-generated assembly code (slightly stripped-down) is:

_Foo:
    pushq   %rbp
    movq    %rsp, %rbp
    movq    %rdi, -8(%rbp)

    # INLINEASM
    pushq %rbp;          // prologue
    movq %rsp, %rbp;     // prologue
    subq $12, %rsp;      // make room
    movl $5, -12(%rbp);  // some asm instruction
    movq %rbp, %rsp;     // epilogue
    popq %rbp;           // epilogue
    # /INLINEASM

    movq    -8(%rbp), %rax
    movl    $5, (%rax)      // x=5;
    popq    %rbp
    ret

main:
    pushq   %rbp
    movq    %rsp, %rbp
    subq    $16, %rsp
    leaq    -4(%rbp), %rax
    movq    %rax, %rdi
    call    _Foo
    movl    $0, %eax
    leave
    ret

Can anyone tell me why this seg faults? It seems that I somehow corrupt %rbp but I don't see how. Thanks in advance.

I'm running GCC 4.8.4 on 64-bit Ubuntu 14.04.