[dlfcn] E: Add dlfcn-weak-c tests for STB_WEAK loader semantics

.nanvix/z.py

@@ -65,6 +65,7 @@
     "dlfcn-global-c",
     "dlfcn-needed-c",
     "dlfcn-pie-c",
+    "dlfcn-weak-c",
     "echo-c",
     "echo-cpp",
     "file-c",
@@ -98,6 +99,7 @@
 STANDALONE_ONLY_SUITES = [
     "dlfcn-c",
     "dlfcn-pie-c",
+    "dlfcn-weak-c",
 ]
 
 # Suites that require host networking (passed as -allow-host-networking to nanvixd).
@@ -110,6 +112,15 @@
 SUITE_RAMFS_LIBS: dict[str, list[tuple[str, str]]] = {
     "dlfcn-c": [("libmul.so", "lib/libmul.so")],
     "dlfcn-pie-c": [("libmul-pie.so", "lib/libmul-pie.so")],
+    "dlfcn-weak-c": [
+        ("libweak-func-resolved.so", "lib/libweak-func-resolved.so"),
+        ("libweak-func-missing.so", "lib/libweak-func-missing.so"),
+        ("libweak-data-resolved.so", "lib/libweak-data-resolved.so"),
+        ("libweak-data-missing.so", "lib/libweak-data-missing.so"),
+        ("libweak-plt-resolved.so", "lib/libweak-plt-resolved.so"),
+        ("libweak-plt-missing.so", "lib/libweak-plt-missing.so"),
+        ("libstrong-missing.so", "lib/libstrong-missing.so"),
+    ],
 }
 
 # Docker image for cross-compilation.

src/Makefile

@@ -65,7 +65,7 @@ export LIBRARIES_DIR ?= $(BINARIES_DIR)
 # Test Suites
 #===============================================================================
 
-SUITES := c-bindings dlfcn-c dlfcn-global-c dlfcn-needed-c dlfcn-pie-c echo-c echo-cpp file-c hello-c hello-cpp memory-c misc-c network-c noop-c noop-cpp thread-c
+SUITES := c-bindings dlfcn-c dlfcn-global-c dlfcn-needed-c dlfcn-pie-c dlfcn-weak-c echo-c echo-cpp file-c hello-c hello-cpp memory-c misc-c network-c noop-c noop-cpp thread-c
 
 #===============================================================================
 # Build Rules
@@ -91,7 +91,7 @@ $(BINARIES_DIR):
 #===============================================================================
 
 # Test suites that can run via plain nanvixd invocation.
-# dlfcn-c and dlfcn-pie-c need shared libraries inside the VM filesystem.
+# dlfcn-c, dlfcn-pie-c, and dlfcn-weak-c need shared libraries inside the VM filesystem.
 # file-c needs VFS access (tests open/read/write on files).
 # network-c needs network infrastructure (sockets).
 # misc-c needs environment variable setup (NANVIX_TEST).

src/dlfcn-weak-c/Makefile

@@ -0,0 +1,109 @@
+# Copyright(c) The Maintainers of Nanvix.
+# Licensed under the MIT License.
+
+PROGRAM_NAME := dlfcn-weak-c
+
+BINARIES_DIR ?= $(CURDIR)/../../build
+LIBRARIES_DIR ?= $(BINARIES_DIR)
+READELF ?= readelf
+
+ifeq ($(OS),Windows_NT)
+define REMOVE
+if exist "$(1)" del /F /Q "$(1)"
+endef
+else
+define REMOVE
+rm -f $(1)
+endef
+endif
+
+SOURCES := $(wildcard *.c)
+OBJECTS := $(SOURCES:.c=.o)
+BINARY  := $(PROGRAM_NAME).elf
+
+# Relocation+symbol assertions for the produced .so files.
+#
+# We assert both the relocation type and the symbol name (and where
+# meaningful, that the symbol binding is WEAK / UND) so that fixtures cannot
+# silently drift to exercising the wrong symbol.
+#
+# Weak function refs guarded by `if (&fn) fn();` compile to a GOT load +
+# indirect call, so only R_386_GLOB_DAT is emitted.  Weak data refs go through
+# the GOT for the same reason.  Strong undefined function calls go through
+# the PLT and produce R_386_JUMP_SLOT.  Weak undefined function calls without
+# a NULL check (the weak-PLT fixtures below) also produce R_386_JUMP_SLOT,
+# allowing us to exercise the loader's handling of weak `JUMP_SLOT`.
+
+# Macro: assert that `$(1)` contains a `R_386_<type>` relocation against
+# the symbol named `$(2)`.  Uses `readelf -rW` so symbol names are not
+# truncated, and `grep -E` so the pattern stays robust against extra columns.
+define ASSERT_RELOC
+@if ! $(READELF) -rW $(1) | grep -E -q '$(2)[[:space:]].*[[:space:]]$(3)$$'; then \
+	echo "Error: expected $(2) relocation against $(3) in $(1)"; \
+	$(READELF) -rW $(1); \
+	exit 1; \
+fi
+endef
+
+# Macro: assert that `$(1)` declares `$(2)` as an undefined dynamic symbol
+# with binding `$(3)` (WEAK or GLOBAL).  We deliberately do not check the
+# symbol type: the linker may emit `NOTYPE` for undefined function refs that
+# carry no in-module definition, while OBJECT/FUNC are reserved for symbols
+# with a known kind.  The intended *use* is verified by the relocation-type
+# assertion below; here we only prove the symbol is undefined and weak/global.
+define ASSERT_DYNSYM
+@if ! $(READELF) -WsD $(1) | grep -E -q '$(3)[[:space:]]+(DEFAULT|HIDDEN|PROTECTED|INTERNAL)[[:space:]]+UND[[:space:]]+$(2)$$'; then \
+	echo "Error: expected $(3) UND dynamic symbol $(2) in $(1)"; \
+	$(READELF) -WsD $(1); \
+	exit 1; \
+fi
+endef
+
+all: $(OBJECTS) libs-all
+	$(CC) $(LDFLAGS) -pie -rdynamic -Wl,--no-dynamic-linker $(OBJECTS) $(LIBRARIES) -o $(BINARIES_DIR)/$(BINARY)
+
+clean: libs-clean
+	$(call REMOVE,$(OBJECTS))
+	$(call REMOVE,$(BINARIES_DIR)/$(BINARY))
+
+libs-all:
+	# Weak function ref with NULL-guard (R_386_GLOB_DAT) — resolved variant.
+	$(CC) $(CFLAGS) libs/weak_func.c -shared -fPIC -DCALLBACK_NAME=main_callback -o $(LIBRARIES_DIR)/libweak-func-resolved.so
+	$(call ASSERT_DYNSYM,$(LIBRARIES_DIR)/libweak-func-resolved.so,main_callback,WEAK)
+	$(call ASSERT_RELOC,$(LIBRARIES_DIR)/libweak-func-resolved.so,R_386_GLOB_DAT,main_callback)
+	# Weak function ref with NULL-guard (R_386_GLOB_DAT) — missing variant.
+	$(CC) $(CFLAGS) libs/weak_func.c -shared -fPIC -DCALLBACK_NAME=missing_callback -o $(LIBRARIES_DIR)/libweak-func-missing.so
+	$(call ASSERT_DYNSYM,$(LIBRARIES_DIR)/libweak-func-missing.so,missing_callback,WEAK)
+	$(call ASSERT_RELOC,$(LIBRARIES_DIR)/libweak-func-missing.so,R_386_GLOB_DAT,missing_callback)
+	# Weak data ref (R_386_GLOB_DAT) — resolved variant.
+	$(CC) $(CFLAGS) libs/weak_data.c -shared -fPIC -DWEAK_DATA_NAME=weak_data -o $(LIBRARIES_DIR)/libweak-data-resolved.so
+	$(call ASSERT_DYNSYM,$(LIBRARIES_DIR)/libweak-data-resolved.so,weak_data,WEAK)
+	$(call ASSERT_RELOC,$(LIBRARIES_DIR)/libweak-data-resolved.so,R_386_GLOB_DAT,weak_data)
+	# Weak data ref (R_386_GLOB_DAT) — missing variant.
+	$(CC) $(CFLAGS) libs/weak_data.c -shared -fPIC -DWEAK_DATA_NAME=missing_weak_data -o $(LIBRARIES_DIR)/libweak-data-missing.so
+	$(call ASSERT_DYNSYM,$(LIBRARIES_DIR)/libweak-data-missing.so,missing_weak_data,WEAK)
+	$(call ASSERT_RELOC,$(LIBRARIES_DIR)/libweak-data-missing.so,R_386_GLOB_DAT,missing_weak_data)
+	# Weak function ref WITHOUT NULL-guard (R_386_JUMP_SLOT) — resolved variant.
+	$(CC) $(CFLAGS) libs/weak_func_plt.c -shared -fPIC -DCALLBACK_NAME=main_callback -o $(LIBRARIES_DIR)/libweak-plt-resolved.so
+	$(call ASSERT_DYNSYM,$(LIBRARIES_DIR)/libweak-plt-resolved.so,main_callback,WEAK)
+	$(call ASSERT_RELOC,$(LIBRARIES_DIR)/libweak-plt-resolved.so,R_386_JUMP_SLOT,main_callback)
+	# Weak function ref WITHOUT NULL-guard (R_386_JUMP_SLOT) — missing variant.
+	$(CC) $(CFLAGS) libs/weak_func_plt.c -shared -fPIC -DCALLBACK_NAME=missing_plt_callback -o $(LIBRARIES_DIR)/libweak-plt-missing.so
+	$(call ASSERT_DYNSYM,$(LIBRARIES_DIR)/libweak-plt-missing.so,missing_plt_callback,WEAK)
+	$(call ASSERT_RELOC,$(LIBRARIES_DIR)/libweak-plt-missing.so,R_386_JUMP_SLOT,missing_plt_callback)
+	# Strong undefined function call (R_386_JUMP_SLOT) — regression guard.
+	$(CC) $(CFLAGS) libs/strong_missing.c -shared -fPIC -o $(LIBRARIES_DIR)/libstrong-missing.so
+	$(call ASSERT_DYNSYM,$(LIBRARIES_DIR)/libstrong-missing.so,strong_missing,GLOBAL)
+	$(call ASSERT_RELOC,$(LIBRARIES_DIR)/libstrong-missing.so,R_386_JUMP_SLOT,strong_missing)
+
+libs-clean:
+	$(call REMOVE,$(LIBRARIES_DIR)/libweak-func-resolved.so)
+	$(call REMOVE,$(LIBRARIES_DIR)/libweak-func-missing.so)
+	$(call REMOVE,$(LIBRARIES_DIR)/libweak-data-resolved.so)
+	$(call REMOVE,$(LIBRARIES_DIR)/libweak-data-missing.so)
+	$(call REMOVE,$(LIBRARIES_DIR)/libweak-plt-resolved.so)
+	$(call REMOVE,$(LIBRARIES_DIR)/libweak-plt-missing.so)
+	$(call REMOVE,$(LIBRARIES_DIR)/libstrong-missing.so)
+
+%.o: %.c
+	$(CC) $(CFLAGS) -fPIE $< -c -o $@

src/dlfcn-weak-c/libs/strong_missing.c

@@ -0,0 +1,11 @@
+/*
+ * Copyright(c) The Maintainers of Nanvix.
+ * Licensed under the MIT License.
+ */
+
+extern int strong_missing(void);
+
+int call_strong(void)
+{
+    return (strong_missing());
+}

src/dlfcn-weak-c/libs/weak_data.c

@@ -0,0 +1,21 @@
+/*
+ * Copyright(c) The Maintainers of Nanvix.
+ * Licensed under the MIT License.
+ */
+
+#include <stddef.h>
+
+#ifndef WEAK_DATA_NAME
+#define WEAK_DATA_NAME weak_data
+#endif
+
+extern int WEAK_DATA_NAME __attribute__((weak));
+
+int read_weak_data(void)
+{
+    if (&WEAK_DATA_NAME != NULL) {
+        return (WEAK_DATA_NAME);
+    }
+
+    return (-1);
+}

src/dlfcn-weak-c/libs/weak_func.c

@@ -0,0 +1,21 @@
+/*
+ * Copyright(c) The Maintainers of Nanvix.
+ * Licensed under the MIT License.
+ */
+
+#include <stddef.h>
+
+#ifndef CALLBACK_NAME
+#define CALLBACK_NAME main_callback
+#endif
+
+extern int CALLBACK_NAME(int) __attribute__((weak));
+
+int try_callback(void)
+{
+    if (&CALLBACK_NAME != NULL) {
+        return (CALLBACK_NAME(7));
+    }
+
+    return (-1);
+}

src/dlfcn-weak-c/libs/weak_func_plt.c

@@ -0,0 +1,33 @@
+/*
+ * Copyright(c) The Maintainers of Nanvix.
+ * Licensed under the MIT License.
+ */
+
+/*
+ * Companion to libs/weak_func.c that exercises the *PLT* path for weak
+ * undefined function references.
+ *
+ * Calling the weak symbol without a preceding `&fn != NULL` check lets the
+ * compiler route the call through the PLT, producing a `R_386_JUMP_SLOT`
+ * relocation rather than the GOT-indirect `R_386_GLOB_DAT` emitted by
+ * libs/weak_func.c.  Together the two helpers cover both relocation classes
+ * the dynamic loader must handle for weak undefined symbols.
+ *
+ * Safety note: the `missing` variant of this helper produces a `.so` whose
+ * weak symbol resolves to address zero at runtime.  The main test driver
+ * MUST NOT invoke `call_weak_unchecked` against that variant — doing so
+ * would jump to NULL.  Resolving `dlsym(handle, "call_weak_unchecked")` is
+ * safe; the goal of the missing variant is only to prove that the loader
+ * accepts the `.so` under RTLD_NOW despite the weak undefined PLT entry.
+ */
+
+#ifndef CALLBACK_NAME
+#define CALLBACK_NAME main_callback
+#endif
+
+extern int CALLBACK_NAME(int) __attribute__((weak));
+
+int call_weak_unchecked(int x)
+{
+    return (CALLBACK_NAME(x));
+}