From panama-dev:
https://mail.openjdk.java.net/pipermail/panama-dev/2019-December/006812.html

Consider the following functions:

int (*reserved00)(void *, void *, void *, void *, void *, void *, void *, void *);
int (*reserved01)(void *, void *, void *, void *, void *, void *, void *, void *);
int (*reserved02)(void *, void *, void *, void *, void *, void *, void *, void *);

jextract correctly creates annotations from this, e.g.:
u64(reserved00):(u64:vu64:vu64:vu64:vu64:vu64:vu64:vu64:v)i32

The layout names are incorrectly parsed as: reserved0, reserved1 and reserved2, respectively. And at binding-time, this cause an exception (as the symbols could not be resolved):

Exception in thread "main" java.lang.IllegalStateException: java.lang.RuntimeException: Failed to generate implementation for class interface com.example.fuse.fuse_h$fuse_operations
at java.base/java.foreign.memory.Pointer.lambda$get$3(Pointer.java:170)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:312)
at java.base/java.foreign.memory.Pointer.get(Pointer.java:166)
at java.base/jdk.internal.foreign.ScopeImpl.allocateStruct(ScopeImpl.java:160)
at com.example.fusepanama.Main.main(Main.java:28)
Caused by: java.lang.RuntimeException: Failed to generate implementation for class interface com.example.fuse.fuse_h$fuse_operations
at java.base/jdk.internal.foreign.LibrariesHelper.generateImpl(LibrariesHelper.java:67)
at java.base/jdk.internal.foreign.LibrariesHelper$1.computeValue(LibrariesHelper.java:76)
at java.base/jdk.internal.foreign.LibrariesHelper$1.computeValue(LibrariesHelper.java:72)
at java.base/java.lang.ClassValue.getFromHashMap(ClassValue.java:226)
at java.base/java.lang.ClassValue.getFromBackup(ClassValue.java:208)
at java.base/java.lang.ClassValue.get(ClassValue.java:114)
at java.base/jdk.internal.foreign.LibrariesHelper.getStructImplClass(LibrariesHelper.java:92)
at java.base/jdk.internal.foreign.memory.References$OfStruct.makeSpecializedGetter(References.java:542)
at java.base/jdk.internal.foreign.memory.References$OfStruct.getter(References.java:527)
at java.base/jdk.internal.foreign.memory.LayoutTypeImpl.getter(LayoutTypeImpl.java:87)
at java.base/java.foreign.memory.Pointer.lambda$get$3(Pointer.java:168)
... 4 more
Caused by: java.lang.RuntimeException: Failed to generate method public abstract java.foreign.memory.Callback com.example.fuse.fuse_h$fuse_operations.reserved00$get()
at java.base/jdk.internal.foreign.BinderClassGenerator.generateMembers(BinderClassGenerator.java:159)
at java.base/jdk.internal.foreign.StructImplGenerator.generateMembers(StructImplGenerator.java:59)
at java.base/jdk.internal.foreign.BinderClassGenerator.generate(BinderClassGenerator.java:110)
at java.base/jdk.internal.foreign.LibrariesHelper.lambda$generateImpl$0(LibrariesHelper.java:64)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:312)
at java.base/jdk.internal.foreign.LibrariesHelper.generateImpl(LibrariesHelper.java:63)
... 14 more
Caused by: java.lang.NullPointerException
at java.base/jdk.internal.foreign.StructImplGenerator.generateFieldAccessor(StructImplGenerator.java:113)
at java.base/jdk.internal.foreign.StructImplGenerator.generateMethodImplementation(StructImplGenerator.java:105)
at java.base/jdk.internal.foreign.BinderClassGenerator.generateMembers(BinderClassGenerator.java:156)
... 19 more