one-shot-token.so LD_PRELOAD fails on musl/Alpine hosts (ARC self-hosted runners)

[lpcox]

Context

Reported upstream in github/agentic-workflows#535. Enterprise customers using ARC self-hosted runners with Alpine-based DinD images (docker:dind) cannot run AWF because the one-shot-token.so library fails to load.

Problem

The one-shot-token.so LD_PRELOAD library is compiled from C against glibc (libc6-dev) in the agent container Dockerfile (containers/agent/Dockerfile). When entrypoint.sh copies it to /host/tmp/awf-lib/one-shot-token.so and sets LD_PRELOAD, the host process (running on Alpine/musl) fails with:

Error relocating /tmp/awf-lib/one-shot-token.so: __fprintf_chk: symbol not found

__fprintf_chk is a glibc-specific fortified I/O function with no musl equivalent. Alpine's gcompat / libc6-compat packages do not cover it.

Affected code path

1. containers/agent/Dockerfile — compiles one-shot-token.c with gcc -shared against glibc
2. containers/agent/entrypoint.sh — copies .so to /host/tmp/awf-lib/ and sets LD_PRELOAD
3. Host process loads the .so via LD_PRELOAD — fails on musl-based hosts

Potential Solutions

Option A: Statically link one-shot-token.so (Recommended)

Compile with -static or use musl-compatible build flags. Since the library only uses basic libc functions (getenv, setenv, unsetenv, dlsym), it can avoid glibc-specific fortified functions:

# Compile without fortification to avoid __fprintf_chk
gcc -shared -fPIC -fvisibility=hidden -O2 -Wall -s \
    -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=0 \
    -o /usr/local/lib/one-shot-token.so /tmp/one-shot-token.c -ldl -lpthread

This removes the dependency on __fprintf_chk while keeping the library dynamically loadable. The one-shot-token code is security-sensitive but simple — it only intercepts getenv() to provide one-shot access to API tokens.

Option B: Build a musl-compatible variant

Add a multi-stage build step that compiles a second .so using musl-gcc or an Alpine build stage. At runtime, detect the libc and load the appropriate variant.

Option C: Graceful degradation

If the .so fails to load, fall back to the non-LD_PRELOAD behavior (tokens remain in env). This is already partially implemented — entrypoint.sh checks if [ -f /usr/local/lib/one-shot-token.so ] — but the failure occurs at load time, not at the file check.

Add a runtime probe before committing to LD_PRELOAD:

if LD_PRELOAD=/host/tmp/awf-lib/one-shot-token.so /bin/true 2>/dev/null; then
    ONE_SHOT_TOKEN_LIB="/tmp/awf-lib/one-shot-token.so"
else
    echo "[WARN] one-shot-token.so incompatible with host libc, tokens will remain in env"
fi

Impact

Blocking enterprise ARC deployments on Alpine-based DinD runners. Option A is likely the simplest fix — just disable _FORTIFY_SOURCE in the gcc flags.