Re: [Tarantool-patches] [PATCH luajit 1/4] FFI: Fix ffi.alignof() for reference types.

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

[-- Attachment #1: Type: text/plain, Size: 3882 bytes --]

Hi, Sergey


thanks for the patch! LGTM


On 03.06.2024 17:33, Sergey Kaplun wrote:
> From: Mike Pall <mike>
>
> Reported by Eric Gouyer.
>
> (cherry picked from commit 36b2962d400db3981a7d7322f85c469240eb6f3b)
>
> According to C++ Standard (5.3.6.3) [1], the `alignof()` 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
> `ffi.alignof()`.
>
> 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
> ---
>   src/lib_ffi.c                                 |  2 +-
>   src/lj_ctype.c                                |  8 ++++++
>   src/lj_ctype.h                                |  1 +
>   .../lj-861-ctype-attributes.test.lua          | 26 +++++++++++++++++++
>   4 files changed, 36 insertions(+), 1 deletion(-)
>   create mode 100644 test/tarantool-tests/lj-861-ctype-attributes.test.lua
>
> diff --git a/src/lib_ffi.c b/src/lib_ffi.c
> index e60e7b19..2bfca25a 100644
> --- a/src/lib_ffi.c
> +++ b/src/lib_ffi.c
> @@ -639,7 +639,7 @@ LJLIB_CF(ffi_alignof)	LJLIB_REC(ffi_xof FF_ffi_alignof)
>     CTState *cts = ctype_cts(L);
>     CTypeID id = ffi_checkctype(L, cts, NULL);
>     CTSize sz = 0;
> -  CTInfo info = lj_ctype_info(cts, id, &sz);
> +  CTInfo info = lj_ctype_info_raw(cts, id, &sz);
>     setintV(L->top-1, 1 << ctype_align(info));
>     return 1;
>   }
> diff --git a/src/lj_ctype.c b/src/lj_ctype.c
> index 0874fa61..83042118 100644
> --- a/src/lj_ctype.c
> +++ b/src/lj_ctype.c
> @@ -345,6 +345,14 @@ CTInfo lj_ctype_info(CTState *cts, CTypeID id, CTSize *szp)
>     return qual;
>   }
>   
> +/* Ditto, but follow a reference. */
> +CTInfo lj_ctype_info_raw(CTState *cts, CTypeID id, CTSize *szp)
> +{
> +  CType *ct = ctype_get(cts, id);
> +  if (ctype_isref(ct->info)) id = ctype_cid(ct->info);
> +  return lj_ctype_info(cts, id, szp);
> +}
> +
>   /* Get ctype metamethod. */
>   cTValue *lj_ctype_meta(CTState *cts, CTypeID id, MMS mm)
>   {
> diff --git a/src/lj_ctype.h b/src/lj_ctype.h
> index fce29409..8edbd561 100644
> --- a/src/lj_ctype.h
> +++ b/src/lj_ctype.h
> @@ -467,6 +467,7 @@ LJ_FUNC CType *lj_ctype_rawref(CTState *cts, CTypeID id);
>   LJ_FUNC CTSize lj_ctype_size(CTState *cts, CTypeID id);
>   LJ_FUNC CTSize lj_ctype_vlsize(CTState *cts, CType *ct, CTSize nelem);
>   LJ_FUNC CTInfo lj_ctype_info(CTState *cts, CTypeID id, CTSize *szp);
> +LJ_FUNC CTInfo lj_ctype_info_raw(CTState *cts, CTypeID id, CTSize *szp);
>   LJ_FUNC cTValue *lj_ctype_meta(CTState *cts, CTypeID id, MMS mm);
>   LJ_FUNC GCstr *lj_ctype_repr(lua_State *L, CTypeID id, GCstr *name);
>   LJ_FUNC GCstr *lj_ctype_repr_int64(lua_State *L, uint64_t n, int isunsigned);
> diff --git a/test/tarantool-tests/lj-861-ctype-attributes.test.lua b/test/tarantool-tests/lj-861-ctype-attributes.test.lua
> new file mode 100644
> index 00000000..d88045a5
> --- /dev/null
> +++ b/test/tarantool-tests/lj-861-ctype-attributes.test.lua
> @@ -0,0 +1,26 @@
> +local tap = require('tap')
> +
> +-- Test file to demonstrate LuaJIT incorrect behaviour during
> +-- parsing and working with ctypes with attributes.
> +-- See also:https://github.com/LuaJIT/LuaJIT/issues/861.
> +
> +local test = tap.test('lj-861-ctype-attributes')
> +local ffi = require('ffi')
> +
> +test:plan(2)
> +
> +local EXPECTED_ALIGN = 4
> +
> +ffi.cdef([[
> +struct __attribute__((aligned($))) s_aligned {
> +  uint8_t a;
> +};
> +]], EXPECTED_ALIGN)
> +
> +local ref_align = ffi.alignof(ffi.typeof('struct s_aligned &'))
> +
> +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:done(true)

[-- Attachment #2: Type: text/html, Size: 4440 bytes --]