From bb036c93b44b8342c3bea1b07e5b7644189d36c0 Mon Sep 17 00:00:00 2001 From: Davi Arnaut Date: Thu, 10 Jun 2010 17:16:43 -0300 Subject: Bug#42733: Type-punning warnings when compiling MySQL -- 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. --- sql/sql_plugin.cc | 60 +++++++++++++++++++++++++++++++++++++++++++------------ 1 file changed, 47 insertions(+), 13 deletions(-) (limited to 'sql/sql_plugin.cc') diff --git a/sql/sql_plugin.cc b/sql/sql_plugin.cc index 94a2b506207..7383d59a1d9 100644 --- a/sql/sql_plugin.cc +++ b/sql/sql_plugin.cc @@ -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 (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 intern_sys_var_ptr((THD *)a_thd, offset, true); + 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'.", -- cgit v1.2.1