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Bug#42733: Type-punning warnings when compiling MySQL --

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strict aliasing violations.

Another rather noisy violation of strict aliasing rules
is the spatial code which makes use of stack-based memory
(of type Geometry_buffer) to provide placement for Geometry
objects. Although a placement new is allowed to dynamically
change the type of a object, the object returned by the
new placement was being ignored and the original stack-based
object was being casted to the new type, thus violating strict
aliasing rules.

The solution is to reorganize the code so that the object
returned by the new placement is used instead of casting the
original object. Also, to ensure that the stack-based object
is properly aligned with respect to the objects it provides
placement for, a set of compiler-dependent macros and types
are introduced so that the alignment of objects can be inquired
and specified.
This commit is contained in:
Davi Arnaut 2010-07-14 09:27:13 -03:00
commit 21f63caf8e
6 changed files with 166 additions and 41 deletions
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4
sql/sql_show.cc
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@ -2202,8 +2202,8 @@ static bool show_status_array(THD *thd, const char *wild,
bool ucase_names,
COND *cond)
{
MY_ALIGNED_BYTE_ARRAY(buff_data, SHOW_VAR_FUNC_BUFF_SIZE, long);
char * const buff= (char *) &buff_data;
my_aligned_storage<SHOW_VAR_FUNC_BUFF_SIZE, MY_ALIGNOF(long)> buffer;
char * const buff= buffer.data;
char *prefix_end;
/* the variable name should not be longer than 64 characters */
char name_buffer[64];