Shouldn't we need to load `swift55_hooks`?

omochimetaru · September 25, 2021, 10:10am

Hello.

I am interested in compatibility of Swift Standard Library.

I noticed that runtime of swift 5.5 has loading override section name which is __swift54_hooks.

apple/swift/blob/swift-5.5-RELEASE/stdlib/public/CompatibilityOverride/CompatibilityOverride.h#L92


      
                                         typedArgs, namedArgs)                           \
            attrs ccAttrs ret namespace swift_##name COMPATIBILITY_PAREN(typedArgs) {    \
              return swift_##name##Impl COMPATIBILITY_PAREN(namedArgs);                  \
            }
          
          
#else // #ifdef SWIFT_RUNTIME_NO_COMPATIBILITY_OVERRIDES
          
          
// Override section name computation. `COMPATIBILITY_OVERRIDE_SECTION_NAME` will
          // resolve to string literal containing the appropriate section name for the
          // current library.
          #define COMPATIBILITY_OVERRIDE_SECTION_NAME_swiftRuntime "__swift54_hooks"
          #define COMPATIBILITY_OVERRIDE_SECTION_NAME_swift_Concurrency "__s_async_hook"
          
          
#define COMPATIBILITY_OVERRIDE_SECTION_NAME                                    \
            COMPATIBILITY_CONCAT(COMPATIBILITY_OVERRIDE_SECTION_NAME_,                   \
                                 SWIFT_TARGET_LIBRARY_NAME)
          
          
// Create typedefs for function pointers to call the original implementation.
          #define OVERRIDE(name, ret, attrs, ccAttrs, namespace, typedArgs, namedArgs)   \
            ccAttrs typedef ret(*Original_##name) COMPATIBILITY_PAREN(typedArgs);
          #include COMPATIBILITY_OVERRIDE_INCLUDE_PATH

Shouldn't this be __swift55_hooks ?

This means that when swift 5.6 is released in the future,
we will not be able to specify different hooks for 5.4 and 5.5 runtimes when we modify the behavior of past runtime functions.

I checked differences in CompatibilityOverrideRuntime.def and found there is no changes from 5.4 to 5.5,
so it seems that same hooks can be specified for 5.5 as for 5.4.
Is that why we didn't rename the section?

However, further examination of changes for CompatibilityOverride.def (file renamed in 5.4) showed that there was also no changes from 5.1 to 5.2 and from 5.2 to 5.3.
Since the section names have changed between 5.2 and 5.3, has the policy changed?