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From: DJ Delorie <dj@redhat.com>
To: Anthony Green <green@redhat.com>
Cc: libffi-discuss@sourceware.org, fweimer@redhat.com
Subject: Re: segfault in ffi_data_to_code_pointer
In-Reply-To: <875zoirazv.fsf@laptop.atgreen.org> (message from Anthony Green on Wed, 03 Jul 2019 18:47:48 -0400)
Date: Wed, 03 Jul 2019 22:54:00 -0000
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Anthony Green <green@redhat.com> writes:
> No, they should be using ffi_closure_alloc().
>
> Can you point me at the ruby code that does this?

ruby 2.6.3
ext/fiddle/closure.c

In the failing case, USE_FFI_CLOSURE_ALLOC is not set

static VALUE
allocate(VALUE klass)
{
    fiddle_closure * closure;

    VALUE i = TypedData_Make_Struct(klass, fiddle_closure,
            &closure_data_type, closure);

fprintf (stderr, "DJ: allocate\n");
#if USE_FFI_CLOSURE_ALLOC
    closure->pcl = ffi_closure_alloc(sizeof(ffi_closure), &closure->code);
#else
    closure->pcl = mmap(NULL, sizeof(ffi_closure), PROT_READ | PROT_WRITE,
        MAP_ANON | MAP_PRIVATE, -1, 0);
#endif

    return i;
}

initialize()
{
 . . .
#if USE_FFI_CLOSURE_ALLOC
    result = ffi_prep_closure_loc(pcl, cif, callback,
                (void *)self, cl->code);
#else
    result = ffi_prep_closure(pcl, cif, callback, (void *)self);
    cl->code = (void *)pcl;
    i = mprotect(pcl, sizeof(*pcl), PROT_READ | PROT_EXEC);
    if (i) {
        rb_sys_fail("mprotect");
    }
#endif
 . . .
}