Re: [Tarantool-patches] [PATCH luajit 2/4] FFI: Fix sizeof expression in C parser for reference types.

[Sergey Bronnikov via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

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Hi, Sergey

thanks for the patch! LGTM

On 03.06.2024 17:34, Sergey Kaplun wrote:
> From: Mike Pall <mike>
>
> (cherry picked from commit 899093a9e0fa5b16f27016381ef4b15529dadff2)
>
> According to C++ Standard, the `alignof()` (5.3.6.3) [1] and `sizeof()`
> (5.3.3.2) [2] for the reference should be the same as for the referenced
> type. This patch fixes the behaviour by following the reference to get a
> child id for `alignof()` and `sizeof()` while parsing C definitions via
> `ffi.cdef()`.
>
> Sergey Kaplun:
> * added the description and the test for the problem
>
> Part of tarantool/tarantool#9924
>
> [1]:https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4594.pdf#subsection.5.3.6
> [2]:https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4594.pdf#subsection.5.3.3
> ---
>   src/lj_cparse.c                                  |  2 +-
>   .../lj-861-ctype-attributes.test.lua             | 16 +++++++++++++++-
>   2 files changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/src/lj_cparse.c b/src/lj_cparse.c
> index 01deb3bf..8506d719 100644
> --- a/src/lj_cparse.c
> +++ b/src/lj_cparse.c
> @@ -468,7 +468,7 @@ static void cp_expr_sizeof(CPState *cp, CPValue *k, int wantsz)
>     } else {
>       cp_expr_unary(cp, k);
>     }
> -  info = lj_ctype_info(cp->cts, k->id, &sz);
> +  info = lj_ctype_info_raw(cp->cts, k->id, &sz);
>     if (wantsz) {
>       if (sz != CTSIZE_INVALID)
>         k->u32 = sz;
> diff --git a/test/tarantool-tests/lj-861-ctype-attributes.test.lua b/test/tarantool-tests/lj-861-ctype-attributes.test.lua
> index d88045a5..e8b29d67 100644
> --- a/test/tarantool-tests/lj-861-ctype-attributes.test.lua
> +++ b/test/tarantool-tests/lj-861-ctype-attributes.test.lua
> @@ -7,7 +7,7 @@ local tap = require('tap')
>   local test = tap.test('lj-861-ctype-attributes')
>   local ffi = require('ffi')
>   
> -test:plan(2)
> +test:plan(4)
>   
>   local EXPECTED_ALIGN = 4
>   
> @@ -15,6 +15,15 @@ ffi.cdef([[
>   struct __attribute__((aligned($))) s_aligned {
>     uint8_t a;
>   };
> +
> +struct test_parsing_sizeof {
> +  char a[sizeof(struct s_aligned &)];
> +};
> +
> +struct test_parsing_alignof {
> +  char a[__alignof__(struct s_aligned &)];
> +};
> +
>   ]], EXPECTED_ALIGN)
>   
>   local ref_align = ffi.alignof(ffi.typeof('struct s_aligned &'))
> @@ -23,4 +32,9 @@ test:is(ref_align, EXPECTED_ALIGN, 'the reference alignment is correct')
>   test:is(ref_align, ffi.alignof(ffi.typeof('struct s_aligned')),
>           'the alignment of a reference is the same as for the referenced type')
>   
> +test:is(ffi.sizeof('struct test_parsing_sizeof'), EXPECTED_ALIGN,
> +        'correct sizeof during C parsing')
> +test:is(ffi.sizeof('struct test_parsing_alignof'), EXPECTED_ALIGN,
> +        'correct alignof during C parsing')
> +
>   test:done(true)

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