| QueryService (2)<\/td>\n<\/tr>\n<\/table>\n \nIn the diagram, p is the pointer returned when the IPersist interface\nis needed, and q is the pointer for the IQueryService interface.\n<\/p>\n \nNow, there is only one QueryInterface method, but there are two entries,\none for each vtable. Remember that each function in a vtable receives\nthe corresponding interface pointer as its “this” parameter. That’s\njust fine for QueryInterface (1); its interface pointer is the\nsame as the object’s interface pointer. But that’s bad news for\nQueryInterface (2), since its interface pointer is q, not p.\n<\/p>\n \nThis is where the adjustor thunks come in.\n<\/p>\n \nThe entry for QueryInterface (2) is a stub function that\nchanges q to p, and then lets QueryInterface (1) do the\nrest of the work. This stub function is the adjustor thunk.\n<\/p>\n \n[thunk]:CSample::QueryInterface`adjustor{4}':\n sub DWORD PTR [esp+4], 4 ; this -= sizeof(lpVtbl)\n jmp CSample::QueryInterface\n<\/pre>\n\nThe adjustor thunk takes the “this” pointer and subtracts 4,\nconverting q into p, then it jumps to the QueryInterface (1)\nfunction to do the real work.\n<\/p>\n Whenever you have multiple inheritance and a virtual function is\nimplemented on multiple base classes, you will get an\nadjustor thunk for the second and subsequent base\nclass methods in order to convert the “this” pointer into a common\nformat.<\/p>\n","protected":false},"excerpt":{"rendered":" Yesterday we learned about the layout of COM objects and I hinted at “adjustor thunks”. If you find yourself debugging in disassembly, you’ll sometimes find strange little functions called “adjustor thunks”. Let’s take another look at the object we laid out last time: class CSample : public IPersist, public IServiceProvider { public: \/\/ *** IUnknown […]<\/p>\n","protected":false},"author":1069,"featured_media":111744,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[2],"class_list":["post-40723","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-history"],"acf":[],"blog_post_summary":" Yesterday we learned about the layout of COM objects and I hinted at “adjustor thunks”. If you find yourself debugging in disassembly, you’ll sometimes find strange little functions called “adjustor thunks”. Let’s take another look at the object we laid out last time: class CSample : public IPersist, public IServiceProvider { public: \/\/ *** IUnknown […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/40723","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/users\/1069"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/comments?post=40723"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/40723\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media\/111744"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media?parent=40723"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=40723"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=40723"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}} |