{"id":1066,"date":"2011-07-27T11:22:38","date_gmt":"2011-07-27T09:22:38","guid":{"rendered":"http:\/\/mariusbancila.ro\/blog\/?p=1066"},"modified":"2011-07-27T11:24:08","modified_gmt":"2011-07-27T09:24:08","slug":"typical-error-porting-application-from-32-to-64-bit","status":"publish","type":"post","link":"https:\/\/mariusbancila.ro\/blog\/2011\/07\/27\/typical-error-porting-application-from-32-to-64-bit\/","title":{"rendered":"Typical error porting application from 32- to 64-bit"},"content":{"rendered":"

I recently ran across a bug with an application ported to the x64 platform. After debugging the application the error turned to be due to integrals layout and casting. I think this is a typical example worth mentioning.<\/p>\n

It starts with this definition:<\/p>\n

\r\n#define COMBO_VALUE -99\r\n<\/pre>\n
which is used for a combo box with SetItemData:<\/p>\n
\r\npCombo->SetItemData(index, (DWORD)COMBO_VALUE);\r\n<\/pre>\n
Notice the cast to DWORD, which is an integral type represented on 32-bits both on x86 and x64. At a later point this value was retrieved and tested against COMBO_VALUE:<\/p>\n
\r\nif (pCombo->GetItemData(pCombo->GetCurSel()) == COMBO_VALUE)\r\n<\/pre>\n
They key here is how the value of -99 is represented:<\/p>\n\n\n\n\n\n\n
 <\/th>\n32-bit platform<\/th>\n64-bit platform<\/th>\n<\/tr>\n
-99<\/td>\nFFFFFF9D<\/tt><\/td>\nFFFFFFFFFFFFFF9D<\/tt><\/td>\n<\/tr>\n
(DWORD)-99<\/td>\nFFFFFF9D<\/tt><\/td>\nFFFFFF9D<\/tt><\/td>\n<\/tr>\n
(DWORD_PTR)-99<\/td>\nFFFFFF9D<\/tt><\/td>\nFFFFFFFFFFFFFF9D<\/tt><\/td>\n<\/tr>\n
(DWORD_PTR)(DWORD)-99<\/td>\nFFFFFF9D<\/tt><\/td>\n00000000FFFFFF9D<\/tt><\/td>\n<\/tr>\n<\/table>\n
GetItemData returns a DWORD_PTR, so FFFFFF9D becomes 00000000FFFFFF9D on x64. Then -99 is also interpreted as a DWORD. Thus the condition in the above if statement resolves to 00000000FFFFFF9D == FFFFFFFFFFFFFF9D on x64, which of course is false.<\/p>\n
To fix the problem, the if statement should be re-written like this:<\/p>\n
\r\nif ((DWORD)pCombo->GetItemData(pCombo->GetCurSel()) == COMBO_VALUE)\r\n<\/pre>\n
A very simply fix, but not so simple to spot the root of the problem when just reading the code.<\/p>\n","protected":false},"excerpt":{"rendered":"
I recently ran across a bug with an application ported to the x64 platform. After debugging the application the error turned to be due to integrals layout and casting. I think this is a typical example worth mentioning. It starts with this definition: #define COMBO_VALUE -99 which is used for a combo box with SetItemData: … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_uag_custom_page_level_css":"","advgb_blocks_editor_width":"","advgb_blocks_columns_visual_guide":"","_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[237,7],"tags":[283,236,239,238],"class_list":["post-1066","post","type-post","status-publish","format-standard","hentry","category-64bit","category-c","tag-cast","tag-error","tag-porting","tag-x64"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t