unknown import, could not find host function for import number: 0 named env.__assert_fail

[biggujo]

Description

When I try to instantiate gifsicle.wasm (built from https://github.com/kohler/gifsicle), an exception is thrown.

The built binary gifsicle works in the CLI. But gifsicle.wasm does not work with Endive.

Steps to reproduce

1. Clone https://github.com/biggujo/endive-gifsicle-problem.
2. Run Main.java.

How to Build WASM

If you need to create a WASM by yourself, do the following.

1. Clone and open https://github.com/biggujo/endive-autotools.
2. Build Dockerfile: docker build -t emscripten-autotools:6.0.1 ..
3. Clone and open https://github.com/kohler/gifsicle.
4. Build:

docker run \
  --rm \
  -v $(pwd):/src \
  -u $(id -u):$(id -g) \
  emscripten-autotools:6.0.1 \
  autoreconf -i

docker run \
  --rm \
  -v $(pwd):/src \
  -u $(id -u):$(id -g) \
  emscripten-autotools:6.0.1 \
  emconfigure ./configure

docker run \
  --rm \
  -v $(pwd):/src \
  -u $(id -u):$(id -g) \
  emscripten-autotools:6.0.1 \
  emmake make

5. Copy src/gifsicle.wasm to endive-gifsicle-problem repository folder: endive-gifsicle-problem/src/main/resources/gifsicle.wasm.

Expected Behavior

1. gifsicle works in CLI (if you run src/gifsicle after build).
2. gifsicle works in Endive.

Actual Behavior

1. gifsicle works in CLI (if you run src/gifsicle after build).
2. gifsicle does not work in Endive.

Attachments

Java source code:

package com.example;

import run.endive.wasm.Parser;
import run.endive.runtime.Instance;
import java.io.File;
import java.net.URISyntaxException;

public class Main {
  static void main() throws URISyntaxException {
    var file = new File(Main.class.getResource("/gifsicle.wasm").toURI());
    var module = Parser.parse(file);
    var instance = Instance.builder(module).build(); // throws here
  }
}

Exception output:

Exception in thread "main" run.endive.wasm.UnlinkableException: unknown import, could not find host function for import number: 0 named env.__assert_fail
	at run.endive.runtime.Instance$Builder.mapHostImports(Instance.java:1013)
	at run.endive.runtime.Instance$Builder.build(Instance.java:1075)
	at ua.karazin.Main.main(Main.java:12)

pom.xml:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>endive-gifsicle-problem</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>25</maven.compiler.source>
        <maven.compiler.target>25</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>
        <dependency>
            <groupId>run.endive</groupId>
            <artifactId>runtime</artifactId>
            <version>1.0.0</version>
            <scope>compile</scope>
        </dependency>
    </dependencies>
</project>

Screenshot of the built working gifsicle in CLI:

Occurrence Frequency

3/3. I tried building WASM multiple times.

Environment

• macOS 15.5 (24F74).
• Docker version 28.1.1, build 4eba377.

Java:

openjdk version "25" 2025-09-16
OpenJDK Runtime Environment (build 25+36-3489)
OpenJDK 64-Bit Server VM (build 25+36-3489, mixed mode, sharing)

[andreaTP]

Hi @biggujo and thanks for your interest in this project!

The gifsicle.wasm was compiled with Emscripten, which requires 9 extra env.* host functions.
These are not provided by any standard WASI runtime, including Endive.

You can provide custom host functions using the Host Functions API.
Here's approximately what it would look like for your case:

package com.example;

import run.endive.runtime.HostFunction;
import run.endive.runtime.ImportValues;
import run.endive.runtime.Instance;
import run.endive.wasi.WasiOptions;
import run.endive.wasi.WasiPreview1;
import run.endive.wasm.Parser;
import run.endive.wasm.types.FunctionType;
import run.endive.wasm.types.ValType;

import java.io.File;
import java.net.URISyntaxException;
import java.util.List;

public class Main {
    static final long ENOSYS = -38;

    public static void main(String[] args) throws URISyntaxException {
        var file = new File(Main.class.getResource("/gifsicle.wasm").toURI());
        var module = Parser.parse(file);

        var wasi = WasiPreview1.builder()
                .withOptions(WasiOptions.builder().inheritSystem().build())
                .build();

        var imports = ImportValues.builder()
                .addFunction(wasi.toHostFunctions())
                .addFunction(
                        new HostFunction("env", "__assert_fail",
                                FunctionType.of(
                                        List.of(ValType.I32, ValType.I32, ValType.I32, ValType.I32),
                                        List.of()),
                                (inst, a) -> {
                                    var assertion = inst.memory().readCString((int) a[0]);
                                    var f = inst.memory().readCString((int) a[1]);
                                    throw new RuntimeException(
                                            "assert failed: " + assertion + " at " + f + ":" + a[2]);
                                }),
                        new HostFunction("env", "exit",
                                FunctionType.of(List.of(ValType.I32), List.of()),
                                (inst, a) -> {
                                    throw new RuntimeException("exit(" + a[0] + ")");
                                }),
                        new HostFunction("env", "emscripten_resize_heap",
                                FunctionType.of(List.of(ValType.I32), List.of(ValType.I32)),
                                (inst, a) -> {
                                    var mem = inst.memory();
                                    int current = mem.pages() * 65536;
                                    if ((int) a[0] <= current) return new long[]{1};
                                    int needed = ((int) a[0] - current + 65535) / 65536;
                                    return new long[]{mem.grow(needed) >= 0 ? 1 : 0};
                                }),
                        new HostFunction("env", "__syscall_openat",
                                FunctionType.of(List.of(ValType.I32, ValType.I32, ValType.I32, ValType.I32), List.of(ValType.I32)),
                                (inst, a) -> new long[]{ENOSYS}),
                        new HostFunction("env", "__syscall_fcntl64",
                                FunctionType.of(List.of(ValType.I32, ValType.I32, ValType.I32), List.of(ValType.I32)),
                                (inst, a) -> new long[]{ENOSYS}),
                        new HostFunction("env", "__syscall_ioctl",
                                FunctionType.of(List.of(ValType.I32, ValType.I32, ValType.I32), List.of(ValType.I32)),
                                (inst, a) -> new long[]{ENOSYS}),
                        new HostFunction("env", "__syscall_unlinkat",
                                FunctionType.of(List.of(ValType.I32, ValType.I32, ValType.I32), List.of(ValType.I32)),
                                (inst, a) -> new long[]{ENOSYS}),
                        new HostFunction("env", "__syscall_rmdir",
                                FunctionType.of(List.of(ValType.I32), List.of(ValType.I32)),
                                (inst, a) -> new long[]{0}),
                        new HostFunction("env", "__syscall_umask",
                                FunctionType.of(List.of(ValType.I32), List.of(ValType.I32)),
                                (inst, a) -> new long[]{0}))
                .build();

        var instance = Instance.builder(module).withImportValues(imports).build();
        System.out.println("Instance created successfully!");
    }
}

Please note that the syscall stubs above return -ENOSYS, so the module will instantiate but file I/O will fail at runtime (gifsicle won't be able to read/write GIF files).

I'd recommend recompiling gifsicle with wasi-sdk instead of Emscripten, that produces a pure WASI module that works out of the box with WasiPreview1, no custom stubs needed.

[biggujo]

@andreaTP , thanks. I am looking into wasi-sdk now.

I ran the following:

docker run -v `pwd`:/src -w /src ghcr.io/webassembly/wasi-sdk autoreconf -i

docker run -v `pwd`:/src -w /src ghcr.io/webassembly/wasi-sdk sh -c './configure --host=wasm32-wasi'

docker run -v `pwd`:/src -w /src ghcr.io/webassembly/wasi-sdk make

It fails with a couple of errors.

I assume it is a limitation of WASI. Is a rewrite for gifsicle needed to make it able to be compiled with wasi-sdk?

xform.c:154:20: warning: 'tmpnam' is deprecated: tmpnam is not defined on WASI [-Wdeprecated-declarations]
  154 |   char *tmp_file = tmpnam(0);
      |                    ^
/opt/wasi-sdk/bin/../share/wasi-sysroot/include/wasm32-wasip1/stdio.h:152:37: note: 'tmpnam' has been explicitly marked deprecated here
  152 | char *tmpnam(char *) __attribute__((__deprecated__("tmpnam is not defined on WASI")));
      |                                     ^
xform.c:174:7: error: call to undeclared function 'popen'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
  174 |   f = popen(new_command, "w");
      |       ^
xform.c:174:7: note: did you mean 'fopen'?
/opt/wasi-sdk/bin/../share/wasi-sysroot/include/wasm32-wasip1/stdio.h:83:7: note: 'fopen' declared here
   83 | FILE *fopen(const char *__restrict, const char *__restrict);
      |       ^
xform.c:174:5: error: incompatible integer to pointer conversion assigning to 'FILE *' (aka 'struct _IO_FILE *') from 'int' [-Wint-conversion]
  174 |   f = popen(new_command, "w");
      |     ^ ~~~~~~~~~~~~~~~~~~~~~~~
xform.c:183:12: error: call to undeclared function 'pclose'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
  183 |   status = pclose(f);
      |            ^
1 warning and 3 errors generated.
make[2]: Leaving directory '/src/src'
make[2]: *** [Makefile:426: xform.o] Error 1
make[1]: *** [Makefile:455: all-recursive] Error 1
make[1]: Leaving directory '/src'
make: *** [Makefile:353: all] Error 2

[andreaTP]

@biggujo I close this issue as it doesn't track an Endive bug, can I invite you to the Zulip channel to get support?

Meanwhile I asked LLM to take a stab at gifsicle using this skill and this is the result, please note that there are additional suggestions to apply if you want to run this in "prod" (first using the build time compiler):

---

Your gifsicle.wasm was compiled with Emscripten, which requires 9 extra env.* host functions on top of WASI. These are not provided by any standard WASI runtime, including Endive.

You can provide custom host functions using the Host Functions API, but the better fix is to recompile with wasi-sdk — the result is a pure WASI module that works out of the box.

Building gifsicle.wasm with wasi-sdk

The only issue is that pipe_color_transformer in xform.c uses popen/pclose/tmpnam/mkstemp/umask, none of which exist in WASI. This function is only used by the --color-transform CLI flag, so we can stub it out with a small patch:

wasi.patch:

--- a/src/xform.c
+++ b/src/xform.c
@@ -139,6 +139,12 @@
 void
 pipe_color_transformer(Gif_Colormap *gfcm, void *thunk)
 {
+#ifdef __wasi__
+  (void)gfcm;
+  (void)thunk;
+  fatal_error("--color-transform is not supported on WASI");
+  return;
+#else
   int i, status;
   FILE *f;
   Gif_Color *col = gfcm->col;
@@ -213,6 +219,7 @@
  done:
   remove(tmp_file);
   Gif_DeleteColormap(new_cm);
+#endif
 }

Dockerfile:

ARG WASI_SDK_VERSION=32
FROM ghcr.io/webassembly/wasi-sdk:wasi-sdk-${WASI_SDK_VERSION}

ENV WASI_SDK_PATH=/opt/wasi-sdk

RUN apt-get update && apt-get install -y automake libtool curl binaryen make xz-utils patch

# gifsicle requires autoconf >= 2.72
RUN curl -sL https://ftp.gnu.org/gnu/autoconf/autoconf-2.72.tar.xz | tar xJ && \
    cd autoconf-2.72 && ./configure && make && make install && cd .. && rm -rf autoconf-2.72

WORKDIR /workspace

ARG GIFSICLE_VERSION=1.95
RUN curl -sL "https://github.com/kohler/gifsicle/archive/refs/tags/v${GIFSICLE_VERSION}.tar.gz" \
    | tar xz --strip-components=1 -C /workspace

COPY wasi.patch /workspace/wasi.patch
RUN patch -p1 < wasi.patch

RUN autoreconf -i

RUN CC="${WASI_SDK_PATH}/bin/clang" \
    CFLAGS="--target=wasm32-wasip1 --sysroot=${WASI_SDK_PATH}/share/wasi-sysroot -O2 -fno-stack-protector" \
    ./configure --host=wasm32-wasi

RUN make

RUN wasm-opt -O3 --strip-debug --low-memory-unused --enable-bulk-memory \
    src/gifsicle -o gifsicle.wasm

Build and extract:

docker build --platform linux/amd64 -t gifsicle-wasi .
docker create --name tmp gifsicle-wasi
docker cp tmp:/workspace/gifsicle.wasm .
docker rm -f tmp

Using it with Endive

The wasi-sdk build produces a pure WASI module (226K vs 1.1MB) with zero env.* imports — just standard WasiPreview1:

var file = new File(Main.class.getResource("/gifsicle.wasm").toURI());
var module = Parser.parse(file);

var wasi = WasiPreview1.builder()
        .withOptions(WasiOptions.builder().inheritSystem().build())
        .build();

var instance = Instance.builder(module)
        .withImportValues(
                ImportValues.builder()
                        .addFunction(wasi.toHostFunctions())
                        .build())
        .build();

Tested — prints LCDF Gifsicle 1.95 with --version.