bug: MemoryInstance::getPointer function changed. The example get-string is outdated and needs to fix

[sarrah-basta]

Summary

I have encountered a bug in one of WasmEdge's example plugins, specifically in the "get-string" (WasmEdge/examples/plugin/get-string/) example. While trying to test my new plugin for WasmEdge (Wasi-OCR) (#2356 (comment)), (which was completely developed and seamlessly working 3 months ago) I found that the "get-string" example, provided by WasmEdge, is not working as expected. The problem seems to be related to the MemInst->getPointer function, which is causing a compilation error. This specific example was referred by me earlier as well and was working then, and it is the only reference I have found so far that illustrates memory transfer of strings via the WasmEdge C++ Plugin API.

Current State

I have encountered a bug in one of WasmEdge's example plugins, specifically in the "get-string" example. The issue appears to be related to changes in memory access functions, leading to the following compilation error:

/home/sarrah/1_data/wasmedge_intern/WasmEdge/examples/plugin/get-string/getstring.cpp: In member function 'WasmEdge::Expect<void> {anonymous}::GetString::body(const WasmEdge::Runtime::CallingFrame&, uint32_t, uint32_t, uint32_t)':
/home/sarrah/1_data/wasmedge_intern/WasmEdge/examples/plugin/get-string/getstring.cpp:39:50: error: no matching function for call to 'WasmEdge::Runtime::Instance::MemoryInstance::getPointer<char*>(uint32_t&, uint32_t&)'
   39 |     char *const Buf = MemInst->getPointer<char *>(BufPtr, BufLen);
      |                       ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~

Expected State

The expected behavior is that the "get-string" example provided by WasmEdge should build successfully without any compilation errors, as it did previously.

Additional Information :

• I have developed a new plugin (Wasi-OCR) for WasmEdge, which also relies on memory access functions. I suspect that the issue may be related to recent changes in these memory access functions.
• Link to the Wasi-OCR plugin details: Wasi-OCR Plugin
• Additionally, I've created a Rust library crate that utilizes the Wasi-OCR plugin for image processing. Here's the link to the Rust library: Wasi-OCR Rust Library

I kindly request assistance in resolving this issue or guidance on how to adapt the "get-string" example and consequentially my developed plugin to work seamlessly with the latest changes in memory access functions in WasmEdge.

Reproduction steps

1. Build WasmEdge with options '-DWASMEDGE_BUILD_EXAMPLE=ON'

cd WasmEdge
mkdir build && cd build
cmake -DCMAKE_BUILD_TYPE=Release -DWASMEDGE_BUILD_EXAMPLE=ON ..

2. Execute the build command:
   make

### Screenshots

_No response_

### Any logs you want to share for showing the specific issue

```bash
[ 98%] Building CXX object examples/plugin/get-string/CMakeFiles/GetString.dir/getstring.cpp.o
/home/sarrah/1_data/wasmedge_intern/WasmEdge/examples/plugin/get-string/getstring.cpp: In member function ‘WasmEdge::Expect<void> {anonymous}::GetString::body(const WasmEdge::Runtime::CallingFrame&, uint32_t, uint32_t, uint32_t)’:
/home/sarrah/1_data/wasmedge_intern/WasmEdge/examples/plugin/get-string/getstring.cpp:39:50: error: no matching function for call to ‘WasmEdge::Runtime::Instance::MemoryInstance::getPointer<char*>(uint32_t&, uint32_t&)’
   39 |     char *const Buf = MemInst->getPointer<char *>(BufPtr, BufLen);
      |                       ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~
In file included from /home/sarrah/1_data/wasmedge_intern/WasmEdge/include/runtime/instance/module.h:23,
                 from /home/sarrah/1_data/wasmedge_intern/WasmEdge/include/plugin/plugin.h:21,
                 from /home/sarrah/1_data/wasmedge_intern/WasmEdge/examples/plugin/get-string/getstring.cpp:4:
/home/sarrah/1_data/wasmedge_intern/WasmEdge/include/runtime/instance/memory.h:227:3: note: candidate: ‘std::enable_if_t<is_pointer_v<T>, T> WasmEdge::Runtime::Instance::MemoryInstance::getPointer(uint32_t) const [with T = char*; std::enable_if_t<is_pointer_v<T>, T> = char*; uint32_t = unsigned int]’
  227 |   getPointer(uint32_t Offset) const noexcept {
      |   ^~~~~~~~~~
/home/sarrah/1_data/wasmedge_intern/WasmEdge/include/runtime/instance/memory.h:227:3: note:   candidate expects 1 argument, 2 provided
make[2]: *** [examples/plugin/get-string/CMakeFiles/GetString.dir/build.make:76: examples/plugin/get-string/CMakeFiles/GetString.dir/getstring.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:1088: examples/plugin/get-string/CMakeFiles/GetString.dir/all] Error 2
make: *** [Makefile:156: all] Error 2

Components

C SDK, Rust SDK

WasmEdge Version or Commit you used

01829c

Operating system information

Ubuntu 22.04

Hardware Architecture

x86_64

Compiler flags and options

• C++ Compiler Version :
  GNU Make 4.3
  Built for x86_64-pc-linux-gnu
• CMake Version :
  cmake version 3.22.1
• Compiler Flags :
  -DCMAKE_BUILD_TYPE=Release -DWASMEDGE_BUILD_EXAMPLE=ON

[hydai]

Hi @sarrah-basta
I believe the example needs to be updated.

The API is changed to ensure memory safety.
https://github.com/WasmEdge/WasmEdge/blob/master/include/runtime/instance/memory.h#L224-L234

All the plugins bundled in the WasmEdge repo are modified to the new APIs.

WasmEdge/plugins/wasi_nn/wasinnfunc.cpp

Line 45 in 4808085

uint32_t *GraphId = MemInst->getPointer<uint32_t *>(GraphIdPtr);

[hydai]

Hi @sarrah-basta
I updated the example so you can follow the same way to update your own plugin. Thanks for this issue :-).

[sarrah-basta]

Hello @hydai , thank you so much for the help!