[build] E: Build libxslt.so and libexslt.so

Produce position-independent libxslt.so / libexslt.so alongside
the existing static libxslt.a / libexslt.a, matching the
shared-library transition already started for libxml2 in
esaurez/libxml2 (`feat/build-shared-library`).

Each shared object is self-contained: libxslt.so embeds the lower
libxml2.a + libz.a via --whole-archive, and libexslt.so embeds
libxslt.a on top of that. No DT_NEEDED entries are emitted, so the
loader does not require sibling .so files to be present in the
search path. libc/libm/libposix symbols remain unresolved and bind
to the host executable's .dynsym at dlopen time, matching the
CPython extension model already in use across the Nanvix port.

Concretely:

* `--enable-static --disable-shared` stays in configure (libtool's
  shared-library detection has no rules for i686-nanvix); `-fPIC`
  is added to CFLAGS so the same .o files are usable for both
  archives.
* Two new `.so` targets link the shared libraries manually with
  `-shared -fPIC -nostdlib`, setting DT_SONAME=libxslt.so /
  DT_SONAME=libexslt.so so downstream consumers (lxml) emit the
  correct DT_NEEDED entry.
* `make test` now sanity-checks each .so: presence, DT_SONAME, and
  that the public entry points (xsltParseStylesheetDoc,
  exsltRegisterAll) appear in .dynsym.
* `.nanvix/z.py` `_BUILD_OUTPUTS` and `release()` ship both the
  static and shared variants.

Runtime dependency: this shared-library build only becomes useful
once esaurez/nanvix#27 ([syscall] E: Run dlopen ctors/dtors and
DT_RUNPATH) ships, because libxml2's internal constructors must
fire for libxslt to function correctly. The unit-test in this PR
exercises only the static archives; the .so end-to-end test will
live in the downstream lxml binding.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Enrique Saurez

.nanvix/Makefile.nanvix

@@ -6,10 +6,17 @@
 #    NANVIX_TOOLCHAIN=<toolchain> [target]
 #
 # Targets:
-#   all              Build libxslt.a, libexslt.a, and the test ELF
+#   all              Build libxslt.{a,so}, libexslt.{a,so}, and the test ELF
 #   test             Verify functional-test prerequisites (build artifacts).
 #                    The runtime execution is driven by z.py on the host.
 #   clean            Remove build artifacts
+#
+# Dependencies:
+#   The shared-library build requires the Nanvix dynamic loader to honour
+#   `.init_array` constructors, shipped in esaurez/nanvix#27. libxml2 is
+#   embedded inside libxslt.so/libexslt.so via --whole-archive, so the
+#   shared objects are self-contained and do not require libxml2.so to
+#   be present at runtime.
 
 # ===========================================================================
 # Global Variables
@@ -28,10 +35,12 @@ EXE = .elf
 
 STATICLIB_XSLT  := libxslt/.libs/libxslt.a
 STATICLIB_EXSLT := libexslt/.libs/libexslt.a
+SHAREDLIB_XSLT  := libxslt/.libs/libxslt.so
+SHAREDLIB_EXSLT := libexslt/.libs/libexslt.so
 TEST_SRC        := .nanvix/test/test_libxslt.c
 TEST_ELF        := test_libxslt$(EXE)
 
-_NANVIX_DOCKER_BUILD_GOALS := all $(STATICLIB_XSLT) $(STATICLIB_EXSLT) $(TEST_ELF)
+_NANVIX_DOCKER_BUILD_GOALS := all $(STATICLIB_XSLT) $(STATICLIB_EXSLT) $(SHAREDLIB_XSLT) $(SHAREDLIB_EXSLT) $(TEST_ELF)
 _NANVIX_GOALS := $(or $(MAKECMDGOALS),$(.DEFAULT_GOAL))
 
 # Ensure required variables are defined.
@@ -66,8 +75,13 @@ endif
 # Build Targets
 # ===========================================================================
 
-all: $(STATICLIB_XSLT) $(STATICLIB_EXSLT) $(TEST_ELF)
+all: $(STATICLIB_XSLT) $(STATICLIB_EXSLT) $(SHAREDLIB_XSLT) $(SHAREDLIB_EXSLT) $(TEST_ELF)
 
+# Build the static archives with -fPIC so the same objects can be
+# linked into position-independent .so files below. autotools'
+# libtool shared-library detection does not know about i686-nanvix,
+# so we keep --disable-shared and link the .so files ourselves from
+# the .a archives.
 $(STATICLIB_XSLT) $(STATICLIB_EXSLT):
 	sh -c '\
 	  export PATH="$(NANVIX_TOOLCHAIN)/bin:$$PATH" && \
@@ -77,15 +91,49 @@ $(STATICLIB_XSLT) $(STATICLIB_EXSLT):
 	    --enable-static --disable-shared --disable-maintainer-mode \
 	    --without-python --without-crypto \
 	    --without-debugger --without-plugins \
+	    --with-pic \
 	    --with-libxml-prefix="$(BUILDROOT_PATH)" \
 	    --with-libxml-include-prefix="$(BUILDROOT_PATH)/include/libxml2" \
 	    --with-libxml-libs-prefix="$(BUILDROOT_PATH)/lib" \
-	    CFLAGS="-I$(BUILDROOT_PATH)/include -I$(BUILDROOT_PATH)/include/libxml2" \
+	    CFLAGS="-I$(BUILDROOT_PATH)/include -I$(BUILDROOT_PATH)/include/libxml2 -fPIC" \
 	    LDFLAGS="-L$(BUILDROOT_PATH)/lib" \
 	    LIBS="-lxml2 -lz" && \
 	  make -C libxslt -j$(NPROC) && \
 	  make -C libexslt -j$(NPROC)'
 
+# libxslt.so: self-contained; embeds libxml2.a and libz.a so the
+# shared object can be loaded standalone without requiring a separate
+# libxml2.so / libz.so in the loader search path. libc/libm/libposix
+# symbols are left unresolved and bound at dlopen time against the
+# host executable's .dynsym.
+$(SHAREDLIB_XSLT): $(STATICLIB_XSLT)
+	sh -c '\
+	  export PATH="$(NANVIX_TOOLCHAIN)/bin:$$PATH" && \
+	  i686-nanvix-gcc -shared -fPIC -nostdlib \
+	    -Wl,-soname,libxslt.so -Wl,-z,noexecstack \
+	    -Wl,--whole-archive \
+	      $(STATICLIB_XSLT) \
+	      $(BUILDROOT_PATH)/lib/libxml2.a \
+	      $(BUILDROOT_PATH)/lib/libz.a \
+	    -Wl,--no-whole-archive \
+	    -o $(SHAREDLIB_XSLT)'
+
+# libexslt.so: same shape — bundles libexslt.a + libxslt.a +
+# libxml2.a + libz.a. No DT_NEEDED entries; cpython-style loaders
+# resolve everything against the host executable.
+$(SHAREDLIB_EXSLT): $(STATICLIB_EXSLT) $(STATICLIB_XSLT)
+	sh -c '\
+	  export PATH="$(NANVIX_TOOLCHAIN)/bin:$$PATH" && \
+	  i686-nanvix-gcc -shared -fPIC -nostdlib \
+	    -Wl,-soname,libexslt.so -Wl,-z,noexecstack \
+	    -Wl,--whole-archive \
+	      $(STATICLIB_EXSLT) \
+	      $(STATICLIB_XSLT) \
+	      $(BUILDROOT_PATH)/lib/libxml2.a \
+	      $(BUILDROOT_PATH)/lib/libz.a \
+	    -Wl,--no-whole-archive \
+	    -o $(SHAREDLIB_EXSLT)'
+
 $(TEST_ELF): $(TEST_SRC)
 	@test -f $(STATICLIB_XSLT) || { echo "  FAIL: $(STATICLIB_XSLT) not found; run 'build' first"; exit 1; }
 	@test -f $(STATICLIB_EXSLT) || { echo "  FAIL: $(STATICLIB_EXSLT) not found; run 'build' first"; exit 1; }
@@ -113,7 +161,17 @@ test:
 	@echo "=== libxslt functional tests ==="
 	@test -f $(STATICLIB_XSLT)  || { echo "  FAIL: $(STATICLIB_XSLT) not found";  exit 1; }
 	@test -f $(STATICLIB_EXSLT) || { echo "  FAIL: $(STATICLIB_EXSLT) not found"; exit 1; }
+	@test -f $(SHAREDLIB_XSLT)  || { echo "  FAIL: $(SHAREDLIB_XSLT) not found";  exit 1; }
+	@test -f $(SHAREDLIB_EXSLT) || { echo "  FAIL: $(SHAREDLIB_EXSLT) not found"; exit 1; }
 	@test -s $(TEST_ELF)        || { echo "  FAIL: $(TEST_ELF) missing or empty"; exit 1; }
+	@$(NANVIX_TOOLCHAIN)/bin/i686-nanvix-readelf -d $(SHAREDLIB_XSLT) | grep -q 'SONAME.*libxslt.so' \
+	  || { echo "  FAIL: SONAME=libxslt.so not set on $(SHAREDLIB_XSLT)"; exit 1; }
+	@$(NANVIX_TOOLCHAIN)/bin/i686-nanvix-readelf -d $(SHAREDLIB_EXSLT) | grep -q 'SONAME.*libexslt.so' \
+	  || { echo "  FAIL: SONAME=libexslt.so not set on $(SHAREDLIB_EXSLT)"; exit 1; }
+	@$(NANVIX_TOOLCHAIN)/bin/i686-nanvix-nm -D $(SHAREDLIB_XSLT) | grep -q 'T xsltParseStylesheetDoc' \
+	  || { echo "  FAIL: xsltParseStylesheetDoc missing from $(SHAREDLIB_XSLT) .dynsym"; exit 1; }
+	@$(NANVIX_TOOLCHAIN)/bin/i686-nanvix-nm -D $(SHAREDLIB_EXSLT) | grep -q 'T exsltRegisterAll' \
+	  || { echo "  FAIL: exsltRegisterAll missing from $(SHAREDLIB_EXSLT) .dynsym"; exit 1; }
 	@echo "  OK: build artifacts present (runtime execution is driven by z.py on the host)"
 	@echo "=== libxslt functional test prerequisites PASSED ==="
 

.nanvix/z.py

@@ -34,7 +34,9 @@
 _BUILD_OUTPUTS = [
     "test_libxslt.elf",
     "libxslt/.libs/libxslt.a",
+    "libxslt/.libs/libxslt.so",
     "libexslt/.libs/libexslt.a",
+    "libexslt/.libs/libexslt.so",
 ]
 
 IS_WINDOWS = sys.platform == "win32"
@@ -306,10 +308,12 @@ def release(self) -> None:
         xslt_inc.mkdir(parents=True)
         exslt_inc.mkdir(parents=True)
 
-        # Copy static libraries.
+        # Copy static and shared libraries.
         for name, src_dir in [
             ("libxslt.a", repo / "libxslt" / ".libs"),
+            ("libxslt.so", repo / "libxslt" / ".libs"),
             ("libexslt.a", repo / "libexslt" / ".libs"),
+            ("libexslt.so", repo / "libexslt" / ".libs"),
         ]:
             src = src_dir / name
             if not src.is_file():
@@ -341,7 +345,12 @@ def release(self) -> None:
         with tarfile.open(str(tarball), "r:gz") as tf:
             members = tf.getnames()
 
-        for expected in ("sysroot/lib/libxslt.a", "sysroot/lib/libexslt.a"):
+        for expected in (
+            "sysroot/lib/libxslt.a",
+            "sysroot/lib/libxslt.so",
+            "sysroot/lib/libexslt.a",
+            "sysroot/lib/libexslt.so",
+        ):
             if expected not in members:
                 raise ValueError(f"Package missing {expected}")