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References: <CAKRnqNK1D9Wp3uedW62uVk-5FCfzGgDd0xOA2W9qMQeizV1TSw@mail.gmail.com> <553E6D2E.7060403@redhat.com>
From: Bruce Korb <bruce.korb@gmail.com>
Date: Mon, 27 Apr 2015 17:37:00 -0000
Message-ID: <CAKRnqNJtEj_VvXNrF=QXteJAwAYmKZ3K1PAxtb35hY43Nr0ezw@mail.gmail.com>
Subject: Re: pass by value and also snprintf()
To: Richard Henderson <rth@redhat.com>
Cc: libffi-discuss@sourceware.org
Content-Type: text/plain; charset=UTF-8
X-SW-Source: 2015/txt/msg00066.txt.bz2

Like this then:


#include <stdint.h>
#include <stdio.h>
#include <ffi.h>

#define UCONST(_p)  ((void *)(uintptr_t)_p)

int
main(int argc, char ** argv)
{
        char       buffer[0x1000];
        size_t     bufsz  = sizeof(buffer);
        char const fmt[]  = "Allocated sblock_id=%d for band_id=%d\n";
        int32_t    sblock = 1;
        int32_t    band   = 1;
        void *     fn     = sprintf;

        if (sizeof(bufsz) != sizeof(uint64_t))
                return 1;

        ffi_type * typ[5] = {
                [0] = &ffi_type_pointer,
                [1] = &ffi_type_uint64,
                [2] = &ffi_type_pointer,
                [3] = &ffi_type_sint32,
                [4] = &ffi_type_sint32 };

        void * values[5] = {
                [0] = buffer,
                [1] = &bufsz,
                [2] = UCONST(fmt),
                [3] = &sblock,
                [4] = &band };

        ffi_cif cif;

        if (ffi_prep_cif_var(&cif, FFI_DEFAULT_ABI, 3, 5,
&ffi_type_uint32, typ) == FFI_OK) {
uint32_t ret_val;

ffi_call(&cif, fn, &ret_val, values);
                fputs(buffer, stdout);
                return 0;
        }
        return 1;
}

$ cc -o ffi-test ffi-test.c -lffi
$ ./ffi-test
Segmentation fault

On Mon, Apr 27, 2015 at 10:09 AM, Richard Henderson <rth@redhat.com> wrote:
> On 04/27/2015 09:59 AM, Bruce Korb wrote:
>> I hope
>> there is an
>> obvious answer to what I am missing:
>
> Certainly there's no way we can help you further without a complete test case.
>
>
> r~