feat(preload): experimental LD_PRELOAD env hook

images/dash0-instrumentation/preload/Makefile

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+# SPDX-FileCopyrightText: Copyright 2024 Dash0 Inc.
+# SPDX-License-Identifier: Apache-2.0
+
+ARCH := $(shell uname -m)
+CFLAGS ?= -Wall -Werror -Wextra -O2
+LIB_LINKER_FLAGS ?= -nostdlib -rdynamic -shared -ldl
+
+SRC_DIR := src
+OBJ_DIR := obj
+LIB_DIR := lib
+LIB_NAME := $(LIB_DIR)/libdash0envhook_$(ARCH).so
+TEST_DIR := test
+TESTBIN_DIR := testbin/$(ARCH)
+SRC_EXT := c
+
+OS := $(shell uname -s)
+SHELL := sh
+
+NAMES := $(notdir $(basename $(wildcard $(SRC_DIR)/*.$(SRC_EXT))))
+OBJECTS :=$(patsubst %,$(OBJ_DIR)/%.o,$(NAMES))
+
+TEST_NAMES := $(notdir $(basename $(wildcard $(TEST_DIR)/*.$(SRC_EXT))))
+TEST_OBJECTS :=$(patsubst %,$(TESTBIN_DIR)/%.o,$(TEST_NAMES))
+
+all: $(LIB_NAME)
+
+$(LIB_NAME): $(OBJECTS)
+	$(CC) $(CFLAGS) $(LIB_LINKER_FLAGS) $(OBJECTS) -o $(LIB_NAME)
+
+$(OBJ_DIR)/%.o: $(SRC_DIR)/%.$(SRC_EXT)
+	$(CC) -c -fPIC $^ -o $@ $(DEBUG) $(CFLAGS) $(LIBS)
+
+clean: clean-test
+	@rm -f $(OBJECTS) $(LIB_NAME)
+
+clean-test:
+	@rm -f $(TEST_OBJECTS)
+
+build-test: $(TEST_OBJECTS)
+
+$(TESTBIN_DIR)/%.o: $(TEST_DIR)/%.$(SRC_EXT)
+	$(CC) $(CFLAGS) -o $@ $(DEBUG) $^
+
+.PHONY: all clean install clean-test build-test

images/dash0-instrumentation/preload/README.md

@@ -0,0 +1,5 @@
+Dash0 LD_PRELOAD Env Hook
+=========================
+
+Overrides [getenv](https://man7.org/linux/man-pages/man3/getenv.3.html) to dynamically add environment variables to
+executables after the fact.

images/dash0-instrumentation/preload/docker/Dockerfile-build

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+# SPDX-FileCopyrightText: Copyright 2024 Dash0 Inc.
+# SPDX-License-Identifier: Apache-2.0
+
+FROM ubuntu:24.10
+
+RUN apt update && \
+  apt-get install -y \
+    build-essential
+
+WORKDIR /usr/src/dash0/preload/
+
+CMD ["scripts/make-clean.sh"]

images/dash0-instrumentation/preload/docker/Dockerfile-test-glibc

@@ -0,0 +1,12 @@
+# SPDX-FileCopyrightText: Copyright 2024 Dash0 Inc.
+# SPDX-License-Identifier: Apache-2.0
+
+FROM ubuntu:24.10
+
+RUN apt update && \
+  apt-get install -y \
+    build-essential
+
+WORKDIR /usr/src/dash0/preload/
+
+CMD ["test/run-tests.sh"]

images/dash0-instrumentation/preload/docker/Dockerfile-test-musl

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+# SPDX-FileCopyrightText: Copyright 2024 Dash0 Inc.
+# SPDX-License-Identifier: Apache-2.0
+
+FROM alpine:3.20.1
+
+RUN apk add --no-cache build-base
+
+WORKDIR /usr/src/dash0/preload/
+
+CMD ["test/run-tests.sh"]

images/dash0-instrumentation/preload/lib/.gitignore

@@ -0,0 +1 @@
+*.so

images/dash0-instrumentation/preload/obj/.gitignore

@@ -0,0 +1 @@
+*.o

images/dash0-instrumentation/preload/scripts/build-in-container.sh

@@ -0,0 +1,56 @@
+#!/usr/bin/env sh
+
+# SPDX-FileCopyrightText: Copyright 2024 Dash0 Inc.
+# SPDX-License-Identifier: Apache-2.0
+
+set -eu
+
+cd "$(dirname "$0")"/..
+
+# TODO build multi platform image
+
+if [ -z "${ARCH:-}" ]; then
+  ARCH=arm64
+fi
+if [ "$ARCH" = arm64 ]; then
+  docker_platform=linux/arm64
+elif [ "$ARCH" = x86_64 ]; then
+  docker_platform=linux/amd64
+else
+  echo "The architecture $ARCH is not supported."
+  exit 1
+fi
+
+dockerfile_name=docker/Dockerfile-build
+image_name=dash0-env-hook-builder-$ARCH
+container_name=$image_name
+
+docker_run_extra_arguments=""
+if [ "${INTERACTIVE:-}" = "true" ]; then
+  docker_run_extra_arguments=/bin/bash
+fi
+
+echo
+echo
+echo ">>> Building the library on $ARCH <<<"
+
+docker rm -f "$container_name" 2> /dev/null
+
+# Note: This is not the multi-platform image that we will need eventually. The combination of docker build and docker
+# run here basically only builds the library binary for the given CPU architecture and places it in the lib folder. And
+# since the lib folder is mounted, the binary is then available in the host file system for further testing (for
+# example, via other container images using a specific CPU architecture).
+docker build \
+  --platform "$docker_platform" \
+  . \
+  -f "$dockerfile_name" \
+  -t "$image_name"
+
+docker run \
+  --platform "$docker_platform" \
+  --name "$container_name" \
+  -it \
+  --volume "$(pwd):/usr/src/dash0/preload/" \
+  "$image_name" \
+  $docker_run_extra_arguments
+

images/dash0-instrumentation/preload/scripts/make-clean.sh

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+#!/usr/bin/env sh
+
+# SPDX-FileCopyrightText: Copyright 2024 Dash0 Inc.
+# SPDX-License-Identifier: Apache-2.0
+
+set -eu
+
+cd "$(dirname "$0")"/..
+
+make clean
+make
+

images/dash0-instrumentation/preload/scripts/run-tests-in-container.sh

@@ -0,0 +1,69 @@
+#!/usr/bin/env sh
+
+# SPDX-FileCopyrightText: Copyright 2024 Dash0 Inc.
+# SPDX-License-Identifier: Apache-2.0
+
+set -eu
+
+cd "$(dirname "$0")"/..
+
+if [ -z "${ARCH:-}" ]; then
+  ARCH=arm64
+fi
+if [ "$ARCH" = arm64 ]; then
+  docker_platform=linux/arm64
+  expected_cpu_architecture=aarch64
+elif [ "$ARCH" = x86_64 ]; then
+  docker_platform=linux/amd64
+  expected_cpu_architecture=x86_64
+else
+  echo "The architecture $ARCH is not supported."
+  exit 1
+fi
+
+if [ -z "${LIBC:-}" ]; then
+  LIBC=glibc
+fi
+
+dockerfile_name="docker/Dockerfile-test-$LIBC"
+if [ ! -f "$dockerfile_name" ]; then
+  echo "The file \"$dockerfile_name\" does not exist, the libc flavor $LIBC is not supported."
+  exit 1
+fi
+
+image_name=dash0-env-hook-test-$ARCH-$LIBC
+container_name=$image_name
+
+docker_run_extra_arguments=""
+if [ "${INTERACTIVE:-}" = "true" ]; then
+  if [ "$LIBC" = glibc ]; then
+    docker_run_extra_arguments=/bin/bash
+  elif [ "$LIBC" = musl ]; then
+    docker_run_extra_arguments=/bin/sh
+  else
+    echo "The libc flavor $LIBC is not supported."
+    exit 1
+  fi
+fi
+
+echo
+echo ---------------------------------------
+echo "testing the library on $ARCH and $LIBC"
+echo ---------------------------------------
+
+docker rm -f "$container_name"
+docker build \
+  --platform "$docker_platform" \
+  . \
+  -f "$dockerfile_name" \
+  -t "$image_name"
+
+docker run \
+  --platform "$docker_platform" \
+  --env EXPECTED_CPU_ARCHITECTURE="$expected_cpu_architecture" \
+  --name "$container_name" \
+  -it \
+  --volume "$(pwd):/usr/src/dash0/preload/" \
+  "$image_name" \
+  $docker_run_extra_arguments
+

images/dash0-instrumentation/preload/scripts/test-all.sh

@@ -0,0 +1,48 @@
+#!/usr/bin/env sh
+
+# SPDX-FileCopyrightText: Copyright 2024 Dash0 Inc.
+# SPDX-License-Identifier: Apache-2.0
+
+set -eu
+
+RED='\033[0;31m'
+GREEN='\033[0;32m'
+NC='\033[0m'
+
+cd "$(dirname "$0")"/..
+
+ARCH=arm64 scripts/build-in-container.sh
+ARCH=x86_64 scripts/build-in-container.sh
+
+exit_code=0
+summary=""
+
+run_tests_for_architecture_and_libc_flavor() {
+  arch=$1
+  libc=$2
+  set +e
+  ARCH=$arch LIBC=$libc scripts/run-tests-in-container.sh
+  test_exit_code=$?
+  set -e
+  echo
+  echo ---------------------------------------
+  if [ $test_exit_code != 0 ]; then
+    printf "${RED}tests for %s/%s failed (see above for details)${NC}\n" "$arch" "$libc"
+    exit_code=1
+    summary="$summary\n$arch/$libc:\tfailed"
+  else
+    printf "${GREEN}tests for %s/%s were successful${NC}\n" "$arch" "$libc"
+    summary="$summary\n$arch/$libc:\tok"
+  fi
+  echo ---------------------------------------
+  echo
+}
+
+run_tests_for_architecture_and_libc_flavor arm64 glibc
+run_tests_for_architecture_and_libc_flavor x86_64 glibc
+run_tests_for_architecture_and_libc_flavor arm64 musl
+run_tests_for_architecture_and_libc_flavor x86_64 musl
+
+echo "$summary"
+exit $exit_code
+

images/dash0-instrumentation/preload/src/libdash0envhook.c

@@ -0,0 +1,70 @@
+// SPDX-FileCopyrightText: Copyright 2024 Dash0 Inc.
+// SPDX-License-Identifier: Apache-2.0
+
+#include <dlfcn.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+
+#include "map.h"
+
+typedef char* (*getenv_fun_ptr)(const char* name);
+
+typedef char* (*secure_getenv_fun_ptr)(const char* name);
+
+getenv_fun_ptr original_getenv;
+secure_getenv_fun_ptr original_secure_getenv;
+
+int num_map_entries = 1;
+Entry map[1];
+
+char* default_node_options_value = "--require /opt/dash0/instrumentation/node.js/node_modules/@dash0/opentelemetry/src/index.js";
+
+__attribute__((constructor)) static void setup(void) {
+  Entry node_options_entry = { .key = "NODE_OPTIONS", .value = NULL };
+  map[0] = node_options_entry;
+}
+
+char* _getenv(char* (*original_function)(const char* name), const char* name)
+{
+  if (strcmp(name, "NODE_OPTIONS") != 0) {
+ 	  return original_function(name);
+  }
+
+  char* cached = get_map_entry(map, num_map_entries, name);
+  if (cached != NULL) {
+    return cached;
+  }
+
+ 	char* original_value = original_function(name);
+  if (original_value == NULL) {
+    return default_node_options_value;
+  }
+
+  char* modified_value = malloc(strlen(default_node_options_value) + 1 + strlen(original_value) + 1);
+  strcpy(modified_value, default_node_options_value);
+  strcat(modified_value, " ");
+  strcat(modified_value, original_value);
+
+  // Note: it is probably okay to not free the modified_value, as long as we only malloc a very limited number of char*
+  // instances, i.e. only one for every environment variable name we want to override.
+  put_map_entry(map, num_map_entries, name, modified_value);
+  return modified_value;
+}
+
+char* getenv(const char* name) {
+  if (!original_getenv) {
+    original_getenv = (getenv_fun_ptr)dlsym(RTLD_NEXT, "getenv");
+  }
+  return _getenv(original_getenv, name);
+}
+
+char* secure_getenv(const char* name) {
+  if (!original_secure_getenv) {
+    original_secure_getenv = (secure_getenv_fun_ptr)dlsym(RTLD_NEXT, "secure_getenv");
+  }
+  return _getenv(original_secure_getenv, name);
+}
+

images/dash0-instrumentation/preload/src/map.c

@@ -0,0 +1,33 @@
+// SPDX-FileCopyrightText: Copyright 2024 Dash0 Inc.
+// SPDX-License-Identifier: Apache-2.0
+
+#include <string.h>
+
+#include "map.h"
+
+Entry* find(Entry map[], int len, const char* key) {
+  for (int i = 0; i < len; i++) {
+    Entry* e = &map[i];
+    if (strcmp(e->key, key) == 0) {
+      return e;
+    }
+  }
+  return NULL;
+}
+
+char* get_map_entry(Entry map[], int len, const char* key) {
+  Entry* e = find(map, len, key);
+  if (e == NULL) {
+    return NULL;
+  }
+  return e->value;
+}
+
+void put_map_entry(Entry* map, int len, const char* key, char* value) {
+  Entry* e = find(map, len, key);
+  if (e == NULL) {
+    return;
+  }
+  e->value = value;
+}
+

images/dash0-instrumentation/preload/src/map.h

@@ -0,0 +1,12 @@
+// SPDX-FileCopyrightText: Copyright 2024 Dash0 Inc.
+// SPDX-License-Identifier: Apache-2.0
+
+typedef struct Entry {
+  const char* key;
+  char* value;
+} Entry;
+
+char* get_map_entry(Entry map[], int len, const char* key);
+
+void put_map_entry(Entry* map, int len, const char* key, char* value);
+