{"id":7407,"date":"2022-09-08T14:49:11","date_gmt":"2022-09-08T09:19:11","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-indexing-args-as-an-array-in-the-windows-x86-64-abi-closed\/"},"modified":"2022-09-08T14:49:11","modified_gmt":"2022-09-08T09:19:11","slug":"solved-indexing-args-as-an-array-in-the-windows-x86-64-abi-closed","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-indexing-args-as-an-array-in-the-windows-x86-64-abi-closed\/","title":{"rendered":"[Solved] Indexing args as an array in the Windows x86-64 ABI [closed]"},"content":{"rendered":"

[ad_1]
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Jester’s suggestion to write it in C is probably a good one, esp. if it can be inlined into calls where some of the args are compile-time constants. Your example use-case passes mostly compile-time-constant args, including the function pointer. Any decent optimizing compiler will inline this and optimize away the indirection into just a normal function call with the right args.<\/strong> Make sure you put the definition somewhere it can be inlined.<\/p>\n

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However, if you can’t get the compiler to make nice code:<\/p>\n

Indexing arguments as an array is the only piece of functionality that’s non-obvious how to implement in the 64bit ABI where some args are in regs. <\/p>\n

The Windows 64bit calling convention provides space for storing the 4 register args right below the stack args (the shadow space), so you actually can<\/em> create an array of args you can index with only at most 4 instructions (store the args into those slots). You don’t need to special-case the first 4 args.<\/p>\n

Don’t forget to put the outgoing args into regs instead of the stack, too, and leave shadow-space for the function you call.<\/p>\n

As Ross Ridge points out, make sure you include directives to create SEH unwind info in the stand-alone asm. This is another good reason to favour a pure C++ solution, esp. if the number of args is limited to a small number.<\/p>\n

See the x86 tag wiki for links to calling conventions and so on.<\/p>\n

I’m not a fan of the Windows calling convention in general, but it does make implementing var-args functions simple. I’m pretty sure that’s why the “shadow space” exists in the ABI.<\/p>\n<\/p><\/div>\n

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8<\/span> <\/p><\/div>\n<\/div>\n

[ad_2]<\/p>\n

solved Indexing args as an array in the Windows x86-64 ABI [closed] <\/p>\n","protected":false},"excerpt":{"rendered":"

[ad_1] Jester’s suggestion to write it in C is probably a good one, esp. if it can be inlined into calls where some of the args are compile-time constants. Your example use-case passes mostly compile-time-constant args, including the function pointer. Any decent optimizing compiler will inline this and optimize away the indirection into just a … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[465,2059,992,523],"class_list":["post-7407","post","type-post","status-publish","format-standard","hentry","category-solved","tag-assembly","tag-calling-convention","tag-visual-c","tag-x86"],"yoast_head":"\n[Solved] Indexing args as an array in the Windows x86-64 ABI [closed] - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-indexing-args-as-an-array-in-the-windows-x86-64-abi-closed\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] Indexing args as an array in the Windows x86-64 ABI [closed] - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] Jester’s suggestion to write it in C is probably a good one, esp. if it can be inlined into calls where some of the args are compile-time constants. 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