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

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strict aliasing violations.

Essentially, the problem is that large parts of the server were
developed in simpler times (last decades, pre C99 standard) when
strict aliasing and compilers supporting such optimizations were
rare to non-existent. Thus, when compiling the server with a modern
compiler that uses strict aliasing rules to perform optimizations,
there are several places in the code that might trigger undefined
behavior.

As evinced by some recent bugs, GCC does a somewhat good of job
misoptimizing such code, but on the other hand also gives warnings
about suspicious code. One problem is that the warnings aren't
always accurate, yet we can't afford to just shut them off as we
might miss real cases. False-positive cases are aggravated mostly
by casts that are likely to trigger undefined behavior.

The solution is to start a cleanup process focused on fixing and
reducing the amount of strict-aliasing related warnings produced
by GCC and others compilers. A good deal of noise reduction can
be achieved by just removing useless casts that are product of
historical cruft and are likely to trigger undefined behavior if
dereferenced.
This commit is contained in:
Davi Arnaut
2010-06-10 17:16:43 -03:00
parent e3b4d33187
commit bb036c93b4
35 changed files with 1248 additions and 1111 deletions
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60
sql/sql_plugin.cc
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@@ -1913,10 +1913,6 @@ typedef DECLARE_MYSQL_THDVAR_SIMPLE(thdvar_uint_t, uint);
typedef DECLARE_MYSQL_THDVAR_SIMPLE(thdvar_ulong_t, ulong);
typedef DECLARE_MYSQL_THDVAR_SIMPLE(thdvar_ulonglong_t, ulonglong);
#define SET_PLUGIN_VAR_RESOLVE(opt)\
*(mysql_sys_var_ptr_p*)&((opt)->resolve)= mysql_sys_var_ptr
typedef uchar *(*mysql_sys_var_ptr_p)(void* a_thd, int offset);
/****************************************************************************
default variable data check and update functions
@@ -2445,11 +2441,49 @@ static uchar *intern_sys_var_ptr(THD* thd, int offset, bool global_lock)
return (uchar*)thd->variables.dynamic_variables_ptr + offset;
}
static uchar *mysql_sys_var_ptr(void* a_thd, int offset)
/**
For correctness and simplicity's sake, a pointer to a function
must be compatible with pointed-to type, that is, the return and
parameters types must be the same. Thus, a callback function is
defined for each scalar type. The functions are assigned in
construct_options to their respective types.
*/
static char *mysql_sys_var_char(THD* thd, int offset)
{
return intern_sys_var_ptr((THD *)a_thd, offset, true);
return (char *) intern_sys_var_ptr(thd, offset, true);
}
static int *mysql_sys_var_int(THD* thd, int offset)
{
return (int *) intern_sys_var_ptr(thd, offset, true);
}
static long *mysql_sys_var_long(THD* thd, int offset)
{
return (long *) intern_sys_var_ptr(thd, offset, true);
}
static unsigned long *mysql_sys_var_ulong(THD* thd, int offset)
{
return (unsigned long *) intern_sys_var_ptr(thd, offset, true);
}
static long long *mysql_sys_var_longlong(THD* thd, int offset)
{
return (long long *) intern_sys_var_ptr(thd, offset, true);
}
static unsigned long long *mysql_sys_var_ulonglong(THD* thd, int offset)
{
return (unsigned long long *) intern_sys_var_ptr(thd, offset, true);
}
static char **mysql_sys_var_str(THD* thd, int offset)
{
return (char **) intern_sys_var_ptr(thd, offset, true);
}
void plugin_thdvar_init(THD *thd)
{
@@ -3020,25 +3054,25 @@ static int construct_options(MEM_ROOT *mem_root, struct st_plugin_int *tmp,
continue;
switch (opt->flags & PLUGIN_VAR_TYPEMASK) {
case PLUGIN_VAR_BOOL:
SET_PLUGIN_VAR_RESOLVE((thdvar_bool_t *) opt);
((thdvar_bool_t *) opt)->resolve= mysql_sys_var_char;
break;
case PLUGIN_VAR_INT:
SET_PLUGIN_VAR_RESOLVE((thdvar_int_t *) opt);
((thdvar_int_t *) opt)->resolve= mysql_sys_var_int;
break;
case PLUGIN_VAR_LONG:
SET_PLUGIN_VAR_RESOLVE((thdvar_long_t *) opt);
((thdvar_long_t *) opt)->resolve= mysql_sys_var_long;
break;
case PLUGIN_VAR_LONGLONG:
SET_PLUGIN_VAR_RESOLVE((thdvar_longlong_t *) opt);
((thdvar_longlong_t *) opt)->resolve= mysql_sys_var_longlong;
break;
case PLUGIN_VAR_STR:
SET_PLUGIN_VAR_RESOLVE((thdvar_str_t *) opt);
((thdvar_str_t *) opt)->resolve= mysql_sys_var_str;
break;
case PLUGIN_VAR_ENUM:
SET_PLUGIN_VAR_RESOLVE((thdvar_enum_t *) opt);
((thdvar_enum_t *) opt)->resolve= mysql_sys_var_ulong;
break;
case PLUGIN_VAR_SET:
SET_PLUGIN_VAR_RESOLVE((thdvar_set_t *) opt);
((thdvar_set_t *) opt)->resolve= mysql_sys_var_ulonglong;
break;
default:
sql_print_error("Unknown variable type code 0x%x in plugin '%s'.",