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roberto-ieruroberto-ieru
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Avoid casts to 'union GCUnion*'
The union may have alignment requirements stricter than some of its members. Some checking tools (e.g., gcc with options -fsanitize) can then complain that the result of a cast from pointer to member to pointer to the union is misaligned.
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Lines changed: 20 additions & 20 deletions

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‎lstate.h‎

Lines changed: 20 additions & 20 deletions
Original file line numberDiff line numberDiff line change
@@ -383,7 +383,7 @@ typedef struct global_State {
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/*
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** Union of all collectable objects (only for conversions)
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** Union of all collectable objects
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** ISO C99, 6.5.2.3 p.5:
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** "if a union contains several structures that share a common initial
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** sequence [...], and if the union object currently contains one
@@ -403,32 +403,32 @@ union GCUnion {
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};
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/*
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** ISO C99, 6.7.2.1 p.14:
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** "A pointer to a union object, suitably converted, points to each of
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** its members [...], and vice versa."
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/* macros to convert a GCObject into a specific value
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** ISO C99, 6.3.2.2 p.7:
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** "A pointer to an object or incomplete type may be converted to a
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** pointer to a different object or incomplete type. If the resulting
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** pointer is not correctly aligned for the pointed-to type, the
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** behavior is undefined. Otherwise, when converted back again, the
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** result shall compare equal to the original pointer."
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*/
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#define cast_u(o) cast(union GCUnion *, (o))
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/* macros to convert a GCObject into a specific value */
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#define gco2ts(o) \
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check_exp(novariant((o)->tt) == LUA_TSTRING, &((cast_u(o))->ts))
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#define gco2u(o) check_exp((o)->tt == LUA_VUSERDATA, &((cast_u(o))->u))
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#define gco2lcl(o) check_exp((o)->tt == LUA_VLCL, &((cast_u(o))->cl.l))
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#define gco2ccl(o) check_exp((o)->tt == LUA_VCCL, &((cast_u(o))->cl.c))
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#define gco2cl(o) \
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check_exp(novariant((o)->tt) == LUA_TFUNCTION, &((cast_u(o))->cl))
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#define gco2t(o) check_exp((o)->tt == LUA_VTABLE, &((cast_u(o))->h))
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#define gco2p(o) check_exp((o)->tt == LUA_VPROTO, &((cast_u(o))->p))
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#define gco2th(o) check_exp((o)->tt == LUA_VTHREAD, &((cast_u(o))->th))
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#define gco2upv(o) check_exp((o)->tt == LUA_VUPVAL, &((cast_u(o))->upv))
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#define gco2(v,T,o) check_exp((o)->tt == v, cast(T*, o))
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#define gco2nv(t,T,o) check_exp(novariant((o)->tt) == t, cast(T*, o))
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#define gco2ts(o) gco2nv(LUA_TSTRING, TString, o)
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#define gco2u(o) gco2(LUA_VUSERDATA, Udata, o)
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#define gco2lcl(o) (&gco2(LUA_VLCL, Closure, o)->l)
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#define gco2ccl(o) (&gco2(LUA_VCCL, Closure, o)->c)
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#define gco2cl(o) gco2nv(LUA_TFUNCTION, Closure, o)
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#define gco2t(o) gco2(LUA_VTABLE, Table, o)
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#define gco2p(o) gco2(LUA_VPROTO, Proto, o)
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#define gco2th(o) gco2(LUA_VTHREAD, lua_State, o)
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#define gco2upv(o) gco2(LUA_VUPVAL, UpVal, o)
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/*
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** macro to convert a Lua object into a GCObject
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*/
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#define obj2gco(v) \
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check_exp(novariant((v)->tt) >= LUA_TSTRING, &(cast_u(v)->gc))
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check_exp(novariant((v)->tt) >= LUA_TSTRING, cast(GCObject*, v))
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/* actual number of total memory allocated */

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