diff --git a/.github/workflows/extra-builds.yml b/.github/workflows/extra-builds.yml
index 503145e97..b22a399db 100644
--- a/.github/workflows/extra-builds.yml
+++ b/.github/workflows/extra-builds.yml
@@ -73,8 +73,8 @@ jobs:
           persist-credentials: false
       - name: Build
         run: |
-          WASI_SDK=wasi-sdk-19.0
-          WASI_SDK_URL=https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-19/wasi-sdk-19.0-linux.tar.gz
+          WASI_SDK=wasi-sdk-27.0-x86_64-linux
+          WASI_SDK_URL=https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-27/wasi-sdk-27.0-x86_64-linux.tar.gz
           if ! [ -d ${WASI_SDK} ]; then curl -L ${WASI_SDK_URL} | tar xzf -; fi
 
           FLEX_VER=2.6.4
diff --git a/Makefile b/Makefile
index da6aa71fa..cc3828d8e 100644
--- a/Makefile
+++ b/Makefile
@@ -286,12 +286,11 @@ ifeq ($(WASI_SDK),)
 CXX = clang++
 AR = llvm-ar
 RANLIB = llvm-ranlib
-WASIFLAGS := -target wasm32-wasi --sysroot $(WASI_SYSROOT) $(WASIFLAGS)
+WASIFLAGS := -target wasm32-wasi $(WASIFLAGS)
 else
 CXX = $(WASI_SDK)/bin/clang++
 AR = $(WASI_SDK)/bin/ar
 RANLIB = $(WASI_SDK)/bin/ranlib
-WASIFLAGS := --sysroot $(WASI_SDK)/share/wasi-sysroot $(WASIFLAGS)
 endif
 CXXFLAGS := $(WASIFLAGS) -std=$(CXXSTD) $(OPT_LEVEL) -D_WASI_EMULATED_PROCESS_CLOCKS $(filter-out -fPIC,$(CXXFLAGS))
 LINKFLAGS := $(WASIFLAGS) -Wl,-z,stack-size=1048576 $(filter-out -rdynamic,$(LINKFLAGS))
diff --git a/backends/cxxrtl/cxxrtl_backend.cc b/backends/cxxrtl/cxxrtl_backend.cc
index 48710aff8..d575b5879 100644
--- a/backends/cxxrtl/cxxrtl_backend.cc
+++ b/backends/cxxrtl/cxxrtl_backend.cc
@@ -637,20 +637,6 @@ std::string escape_cxx_string(const std::string &input)
 	return output;
 }
 
-std::string basename(const std::string &filepath)
-{
-#ifdef _WIN32
-	const std::string dir_seps = "\\/";
-#else
-	const std::string dir_seps = "/";
-#endif
-	size_t sep_pos = filepath.find_last_of(dir_seps);
-	if (sep_pos != std::string::npos)
-		return filepath.substr(sep_pos + 1);
-	else
-		return filepath;
-}
-
 template<class T>
 std::string get_hdl_name(T *object)
 {
@@ -2858,7 +2844,7 @@ struct CxxrtlWorker {
 		}
 
 		if (split_intf)
-			f << "#include \"" << basename(intf_filename) << "\"\n";
+			f << "#include \"" << name_from_file_path(intf_filename) << "\"\n";
 		else
 			f << "#include <cxxrtl/cxxrtl.h>\n";
 		f << "\n";
diff --git a/frontends/ast/simplify.cc b/frontends/ast/simplify.cc
index 81018e137..97abf7452 100644
--- a/frontends/ast/simplify.cc
+++ b/frontends/ast/simplify.cc
@@ -30,6 +30,7 @@
 #include "libs/sha1/sha1.h"
 #include "frontends/verilog/verilog_frontend.h"
 #include "ast.h"
+#include "kernel/io.h"
 
 #include <sstream>
 #include <stdarg.h>
@@ -4474,12 +4475,7 @@ std::unique_ptr<AstNode> AstNode::readmem(bool is_readmemh, std::string mem_file
 	std::ifstream f;
 	f.open(mem_filename.c_str());
 	if (f.fail()) {
-#ifdef _WIN32
-		char slash = '\\';
-#else
-		char slash = '/';
-#endif
-		std::string path = location.begin.filename->substr(0, location.begin.filename->find_last_of(slash)+1);
+		std::string path = parent_from_file_path(*location.begin.filename);
 		f.open(path + mem_filename.c_str());
 		yosys_input_files.insert(path + mem_filename);
 	} else {
diff --git a/frontends/verilog/preproc.cc b/frontends/verilog/preproc.cc
index 1858edc97..7675bab62 100644
--- a/frontends/verilog/preproc.cc
+++ b/frontends/verilog/preproc.cc
@@ -895,11 +895,7 @@ frontend_verilog_preproc(std::istream                 &f,
 				// if the include file was not found, it is not given with an absolute path, and the
 				// currently read file is given with a path, then try again relative to its directory
 				ff.clear();
-#ifdef _WIN32
-				fixed_fn = filename.substr(0, filename.find_last_of("/\\")+1) + fn;
-#else
-				fixed_fn = filename.substr(0, filename.rfind('/')+1) + fn;
-#endif
+				fixed_fn = parent_from_file_path(filename) + fn;
 				ff.open(fixed_fn);
 			}
 			if (ff.fail() && fn.size() > 0 && fn_relative) {
diff --git a/kernel/io.cc b/kernel/io.cc
index 4c593501c..094a7fbf8 100644
--- a/kernel/io.cc
+++ b/kernel/io.cc
@@ -2,6 +2,7 @@
 #include "kernel/log.h"
 #include <iostream>
 #include <string>
+#include <filesystem>
 
 #if !defined(WIN32)
 #include <dirent.h>
@@ -384,6 +385,24 @@ std::string escape_filename_spaces(const std::string& filename)
 	return out;
 }
 
+std::string name_from_file_path(std::string path) {
+	return std::filesystem::path(path).filename().string();
+}
+
+// Includes OS_PATH_SEP at the end if present
+std::string parent_from_file_path(std::string path) {
+	auto parent = std::filesystem::path(path).parent_path();
+	if (parent.empty()) {
+		return "";
+	}
+	// Add trailing separator to match original behavior
+	std::string result = parent.string();
+	if (!result.empty() && result.back() != std::filesystem::path::preferred_separator) {
+		result += std::filesystem::path::preferred_separator;
+	}
+	return result;
+}
+
 void format_emit_unescaped(std::string &result, std::string_view fmt)
 {
 	result.reserve(result.size() + fmt.size());
diff --git a/kernel/io.h b/kernel/io.h
index 2ad0a6466..fc893ed37 100644
--- a/kernel/io.h
+++ b/kernel/io.h
@@ -469,6 +469,8 @@ bool is_absolute_path(std::string filename);
 void remove_directory(std::string dirname);
 bool create_directory(const std::string& dirname);
 std::string escape_filename_spaces(const std::string& filename);
+std::string name_from_file_path(std::string path);
+std::string parent_from_file_path(std::string path);
 
 YOSYS_NAMESPACE_END