posix shared memory with wamr

[VaibhavVgithub]

[01:25:19:899 - 7F01820E5580]: warning: failed to link import function (env, shm_open) [01:25:19:909 - 7F01820E5580]: warning: failed to link import function (env, ftruncate) Exception: failed to call unlinked import function (env, shm_open)

---

can someone please explain how to resolve this issue. I want shared memory functionalities in my 'main.c'. And also, Can someone suggest any other procedure than native-lib example to use shared memory applications with wamr?

[lum1n0us]

May I ask:

• which toolchain, (like wasi-sdk, emscripten, or something else), is used to generate the .wasm?
• what kind of compilation option groups is used to generate the .wasm?

[VaibhavVgithub]

I am using wasi-sdk 20.0 to generate .wasm

---

set (CMAKE_SYSTEM_PROCESSOR wasm32)

set (CMAKE_SYSROOT ${WAMR_ROOT_DIR}/wamr-sdk/app/libc-builtin-sysroot)

if (NOT DEFINED WASI_SDK_DIR) set (WASI_SDK_DIR "/opt/wasi-sdk") endif () set (CMAKE_C_FLAGS "-nostdlib -pthread -Qunused-arguments -D_WASI_EMULATED_MMAN") set (CMAKE_C_COMPILER_TARGET "wasm32-wasi") set (CMAKE_C_COMPILER "${WASI_SDK_DIR}/bin/clang")

set (CMAKE_EXE_LINKER_FLAGS "-Wl,--max-memory=131072, -z stack-size=32768 \ -Wl,--shared-memory \ -g \ -lwasi-emulated-mman \ -Wl,--export-all \ -Wl,--no-entry,--strip-all \ -Wl,--export=main_argc_argv \ -Wl,--export=heap_base, -Wl,--export=__data_end \ -Wl,--allow-undefined \ -pthread" ) add_executable(test.wasm main.c) target_link_libraries(test.wasm)

---

this is what I am using to create "test.wasm". flags for linking & compiling for shared memory support

[lum1n0us]

-nostdlib might be the reason. Since shm_open and ftruncate are all provided by WASI-SDK.

[VaibhavVgithub]

Hi, No, That can't be reason atleast, because I earlier didn't use "-nostdlib" but that gave me below error,

---

In file included from /home/vaibhav/Desktop/wasm-micro-runtime-main/samples/shm_open/wasm-app/main.c:8: /opt/wasi-sdk-20.0/bin/../share/wasi-sysroot/include/sys/mman.h:2:2: error: "WASI lacks a true mmap; to enable minimal mmap emulation, compile with -D_WASI_EMULATED_MMAN and link with -lwasi-emulated-mman"

error "WASI lacks a true mmap; to enable minimal mmap emulation, \

^ /home/vaibhav/Desktop/wasm-micro-runtime-main/samples/shm_open/wasm-app/main.c:78:20: error: call to undeclared function 'shm_open'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration] int shmem_fd = shm_open(mem, oflag, mode); ^ 2 errors generated. make[2]: [wasm-app/CMakeFiles/test.wasm.dir/build.make:76: wasm-app/CMakeFiles/test.wasm.dir/main.c.o] Error 1 make[1]: [CMakeFiles/Makefile2:210: wasm-app/CMakeFiles/test.wasm.dir/all] Error 2 make: *** [Makefile:91: all] Error 2

---

and like this

---

[100%] Linking C executable test.wasm wasm-ld: error: --shared-memory is disallowed by dlmalloc.o because it was not compiled with 'atomics' or 'bulk-memory' features. wasm-ld: error: 'atomics' feature must be used in order to use shared memory clang-16: error: linker command failed with exit code 1 (use -v to see invocation) make[2]: [wasm-app/CMakeFiles/test.wasm.dir/build.make:97: wasm-app/test.wasm] Error 1 make[1]: [CMakeFiles/Makefile2:210: wasm-app/CMakeFiles/test.wasm.dir/all] Error 2 make: *** [Makefile:91: all] Error 2

---

so I added those options after taking reference from wamr docs

[lum1n0us]

😵‍💫 My mistake. WASI has limited support on mmap (https://github.com/WebAssembly/wasi-libc/blob/main/libc-bottom-half/mman/mman.c) and is lack of IPC supporting. There is ongoing discussion about IPC module.

On the opposite, EMSDK has shared memory supporting but lack of file APIs unless trying WASMFS