[foreign-jextract] Function pointer typedef name clashes with existing function name

[Filip Krakowski]

Hi,

thanks for filing the issue! I found that I can use the "--filter" flag 
to exclude ucx's
header containing the function pointer (since it doesn't contain any 
symbols I use at the moment).

I will use this method as a workaround for now.

Filip

On 2/10/21 3:20 PM, Maurizio Cimadamore wrote:
> Hi Filip,
> thanks for the report - I've filed this:
>
> https://bugs.openjdk.java.net/browse/JDK-8261511
>
> I believe jextract adds constants to the constant holder
> sources/classes on a name-based basis. So if you happen to have two
> descriptors that are required for different things (e.g. a function and
> an upcall which happen to have same name), there is a chance that one
> constant will be re-used for the other.
>
> The solution is, of course, to use a more robust keying scheme when
> adding constants, rather than just using the name.
>
> Maurizio
>
> On Wed, 2021-02-10 at 15:05 +0100, Filip Krakowski wrote:
>> Hi,
>>
>> I think I found another bug regarding name clashes with typedefs for
>> function pointers.
>>
>> The library I use declares a function pointer within a struct's
>> field
>> named "read" [1]. I think you see where this is going...
>>
>>      typedef struct ucs_config_parser {
>>           int                      (*read) (const char *buf, void
>> *dest,
>>      const void *arg);
>>           int                      (*write)(char *buf, size_t max,
>>                                             const void *src, const
>> void
>>      *arg);
>>           ucs_status_t             (*clone)(const void *src, void
>> *dest,
>>      const void *arg);
>>           void                     (*release)(void *ptr, const void
>> *arg);
>>           void                     (*help)(char *buf, size_t max,
>> const
>>      void *arg);
>>           const void               *arg;
>>      } ucs_config_parser_t;
>>
>>
>> Since "unistd.h" also declares a "read" function [2], jextract then
>> (correctly) generates a MethodHandle for it
>> but uses the wrong FunctionDescriptor belonging to ucx's "read" in
>> the
>> process.
>>
>>      static final FunctionDescriptor read$FUNC_ =
>>      FunctionDescriptor.of(C_INT,
>>               C_POINTER,
>>               C_POINTER,
>>               C_POINTER
>>      );
>>
>>      static final MethodHandle read$MH_ =
>> RuntimeHelper.downcallHandle(
>>               LIBRARIES, "read",
>>               "(ILjdk/incubator/foreign/MemoryAddress;J)J",
>>               read$FUNC_, false
>>      );
>>
>>
>> As you can see the generated FunctionDescriptor and the descriptor
>> string ("(ILjdk/incubator/foreign/MemoryAddress;J)J")
>> do not match. On startup, I immediately get the following Exception
>> originating from the downcallHandle call.
>>
>>      Caused by: java.lang.IllegalArgumentException: Carrier size
>>      mismatch: int != b64[abi/kind=POINTER]
>>
>> My guess is that the FunctionDescriptor is generated correctly at
>> first,
>> but gets overridden once the parser reaches the
>> function pointer declared within the struct in [1].
>>
>>
>> Best regards
>> Filip
>>
>> [1]
>> https://github.com/openucx/ucx/blob/16ad2cc56b6c63a0fdc39bac3dce03463d6d137f/src/ucs/config/parser.h#L40-L48
>> [2] https://linux.die.net/man/2/read