[clang] "modular_format" attribute for functions using format strings #147431
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This provides a C language version of the new IR modular-format attribute. This, in concert with the format attribute, allows a library function to declare that a modular version of its implementation is available. See issue #146159 for context.
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| The second argument is a implementation name, and the remaining arguments are | ||
| aspects of the format string for the compiler to report. If the compiler does | ||
| not understand a aspect, it must summarily report that the format string has |
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| not understand a aspect, it must summarily report that the format string has | |
| not understand an aspect, it must summarily report that the format string has |
| not understand a aspect, it must summarily report that the format string has | ||
| that aspect. | ||
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| The compiler reports an aspect by issing a relocation for the symbol |
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| The compiler reports an aspect by issing a relocation for the symbol | |
| The compiler reports an aspect by issuing a relocation for the symbol |
| @@ -2569,6 +2569,18 @@ void CodeGenModule::ConstructAttributeList(StringRef Name, | |||
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| if (TargetDecl->hasAttr<ArmLocallyStreamingAttr>()) | |||
| FuncAttrs.addAttribute("aarch64_pstate_sm_body"); | |||
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| if (auto *ModularFormat = TargetDecl->getAttr<ModularFormatAttr>()) { | |||
| // TODO: Error checking | |||
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This is a heck of a TODO :) Though, I'd expect us to do diagnostics during our normal checking of the format string, so we shouldn't really require anything here.
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Hah, fair; this is very much a Draft PR. My intent was to get this in front of a bunch of eyes sooner rather than later, as this PR set touches everything every layer from the compiler through to libc (skipping the linker).
Very fair; I was relying a lot on the tracking issue and RFC discussion for context. I've added some meat to the PR description, and I've added a brief example to the attribute docs. I'll add a test once I get the chance. |
This provides a C language
modular_formatattribute. This combines with information from the existingformatto set the new IRmodular-formatattribute.The purpose of these attributes is to enable "modular printf". A statically linked libc can provide a modular variant of printf that only weakly references implementation routines. Regular printf would strongly reference those routines, and the compiler would transform calls with constant format strings to calls to the modular printf, along with strong references to aspect symbols that bring in those aspects.
See issue #146159 for context.