diff --git a/frontends/verilog/verilog_lexer.l b/frontends/verilog/verilog_lexer.l
index e2d7a2cd9..de74f595f 100644
--- a/frontends/verilog/verilog_lexer.l
+++ b/frontends/verilog/verilog_lexer.l
@@ -124,7 +124,7 @@ static bool is_hex_dig(char c, int *val)
 		*val = c - 'A' + 0xA;
 		return true;
 	} else if (c == 'x' || c == 'X' || c == 'z' || c == 'Z' || c == '?') {
-		log_file_warning(AST::current_filename.c_str(), frontend_verilog_yyget_lineno(), "'%c' not a valid digit in hex escape sequence.\n", c);
+		log_file_warning(AST::current_filename, frontend_verilog_yyget_lineno(), "'%c' not a valid digit in hex escape sequence.\n", c);
 		*val = 0; // not semantically valid in hex escape...
 		return true; // ...but still processed as part of hex token
 	}
@@ -138,7 +138,7 @@ static bool is_oct_dig(char c, int *val)
 		*val = c - '0';
 		return true;
 	} else if (c == 'x' || c == 'X' || c == 'z' || c == 'Z' || c == '?') {
-		log_file_warning(AST::current_filename.c_str(), frontend_verilog_yyget_lineno(), "'%c' not a valid digit in octal escape sequence.\n", c);
+		log_file_warning(AST::current_filename, frontend_verilog_yyget_lineno(), "'%c' not a valid digit in octal escape sequence.\n", c);
 		*val = 0; // not semantically valid in octal escape...
 		return true; // ...but still processed as part of octal token
 	}
@@ -158,7 +158,7 @@ static std::string *process_str(char *str, int len, bool triple)
 			if (in + 1 < str + len && (in[1] ^ *in) == ('\n' ^ '\r'))
 				in++;
 			if (!triple)
-				log_file_warning(AST::current_filename.c_str(), frontend_verilog_yyget_lineno(), "Multi-line string literals should be triple-quoted or escaped.\n");
+				log_file_warning(AST::current_filename, frontend_verilog_yyget_lineno(), "Multi-line string literals should be triple-quoted or escaped.\n");
 			*out++ = '\n';
 			break;
 		case '\\':
@@ -195,7 +195,7 @@ static std::string *process_str(char *str, int len, bool triple)
 					}
 					out++;
 				} else
-					log_file_warning(AST::current_filename.c_str(), frontend_verilog_yyget_lineno(), "ignoring invalid hex escape.\n");
+					log_file_warning(AST::current_filename, frontend_verilog_yyget_lineno(), "ignoring invalid hex escape.\n");
 				break;
 			case '\\':
 				*out++ = '\\';
@@ -218,7 +218,7 @@ static std::string *process_str(char *str, int len, bool triple)
 						in++;
 						if (in + 1 < str + len && is_oct_dig(in[1], &val)) {
 							if (*out >= 040)
-								log_file_warning(AST::current_filename.c_str(), frontend_verilog_yyget_lineno(), "octal escape exceeds \\377\n");
+								log_file_warning(AST::current_filename, frontend_verilog_yyget_lineno(), "octal escape exceeds \\377\n");
 							*out = *out * 010 + val;
 							in++;
 						}
diff --git a/kernel/io.h b/kernel/io.h
index ea2499e43..a05ed731e 100644
--- a/kernel/io.h
+++ b/kernel/io.h
@@ -423,6 +423,7 @@ public:
 	{
 		return format_emit_toplevel(fmt, has_escapes, specs, args...);
 	}
+	std::string_view format_string() const { return fmt; }
 private:
 	std::string_view fmt;
 	bool has_escapes = false;
diff --git a/kernel/log.cc b/kernel/log.cc
index 679a55562..8ba20d64d 100644
--- a/kernel/log.cc
+++ b/kernel/log.cc
@@ -101,17 +101,16 @@ int gettimeofday(struct timeval *tv, struct timezone *tz)
 }
 #endif
 
-void logv(const char *format, va_list ap)
-{
-	while (format[0] == '\n' && format[1] != 0) {
-		log("\n");
-		format++;
+static void logv_string(std::string_view format, std::string str) {
+	size_t remove_leading = 0;
+	while (format.size() > 1 && format[0] == '\n') {
+		logv_string("\n", "\n");
+		format = format.substr(1);
+		++remove_leading;
+	}
+	if (remove_leading > 0) {
+		str = str.substr(remove_leading);
 	}
-
-	if (log_make_debug && !ys_debug(1))
-		return;
-
-	std::string str = vstringf(format, ap);
 
 	if (str.empty())
 		return;
@@ -144,13 +143,13 @@ void logv(const char *format, va_list ap)
 			time_str += stringf("[%05d.%06d] ", int(tv.tv_sec), int(tv.tv_usec));
 		}
 
-		if (format[0] && format[strlen(format)-1] == '\n')
+		if (!format.empty() && format[format.size() - 1] == '\n')
 			next_print_log = true;
 
 		// Special case to detect newlines in Python log output, since
 		// the binding always calls `log("%s", payload)` and the newline
 		// is then in the first formatted argument
-		if (!strcmp(format, "%s") && str.back() == '\n')
+		if (format == "%s" && str.back() == '\n')
 			next_print_log = true;
 
 		for (auto f : log_files)
@@ -203,7 +202,14 @@ void logv(const char *format, va_list ap)
 	}
 }
 
-void logv_header(RTLIL::Design *design, const char *format, va_list ap)
+void log_formatted_string(std::string_view format, std::string str)
+{
+	if (log_make_debug && !ys_debug(1))
+		return;
+	logv_string(format, std::move(str));
+}
+
+void log_formatted_header(RTLIL::Design *design, std::string_view format, std::string str)
 {
 	bool pop_errfile = false;
 
@@ -222,7 +228,7 @@ void logv_header(RTLIL::Design *design, const char *format, va_list ap)
 		header_id += stringf("%s%d", header_id.empty() ? "" : ".", c);
 
 	log("%s. ", header_id.c_str());
-	logv(format, ap);
+	log_formatted_string(format, std::move(str));
 	log_flush();
 
 	if (log_hdump_all)
@@ -242,10 +248,8 @@ void logv_header(RTLIL::Design *design, const char *format, va_list ap)
 		log_files.pop_back();
 }
 
-static void logv_warning_with_prefix(const char *prefix,
-                                     const char *format, va_list ap)
+void log_formatted_warning(std::string_view prefix, std::string message)
 {
-	std::string message = vstringf(format, ap);
 	bool suppressed = false;
 
 	for (auto &re : log_nowarn_regexes)
@@ -254,7 +258,7 @@ static void logv_warning_with_prefix(const char *prefix,
 
 	if (suppressed)
 	{
-		log("Suppressed %s%s", prefix, message.c_str());
+		log("Suppressed %s%s", prefix, message);
 	}
 	else
 	{
@@ -263,7 +267,7 @@ static void logv_warning_with_prefix(const char *prefix,
 
 		for (auto &re : log_werror_regexes)
 			if (std::regex_search(message, re))
-				log_error("%s",  message.c_str());
+				log_error("%s", message);
 
 		bool warning_match = false;
 		for (auto &item : log_expect_warning)
@@ -274,7 +278,7 @@ static void logv_warning_with_prefix(const char *prefix,
 
 		if (log_warnings.count(message))
 		{
-			log("%s%s", prefix, message.c_str());
+			log("%s%s", prefix, message);
 			log_flush();
 		}
 		else
@@ -282,7 +286,7 @@ static void logv_warning_with_prefix(const char *prefix,
 			if (log_errfile != NULL && !log_quiet_warnings)
 				log_files.push_back(log_errfile);
 
-			log("%s%s", prefix, message.c_str());
+			log("%s%s", prefix, message);
 			log_flush();
 
 			if (log_errfile != NULL && !log_quiet_warnings)
@@ -298,41 +302,19 @@ static void logv_warning_with_prefix(const char *prefix,
 	}
 }
 
-void logv_warning(const char *format, va_list ap)
+void log_formatted_file_warning(std::string_view filename, int lineno, std::string str)
 {
-	logv_warning_with_prefix("Warning: ", format, ap);
+	std::string prefix = stringf("%s:%d: Warning: ", filename, lineno);
+	log_formatted_warning(prefix, std::move(str));
 }
 
-void logv_warning_noprefix(const char *format, va_list ap)
+void log_formatted_file_info(std::string_view filename, int lineno, std::string str)
 {
-	logv_warning_with_prefix("", format, ap);
-}
-
-void log_file_warning(const std::string &filename, int lineno,
-                      const char *format, ...)
-{
-	va_list ap;
-	va_start(ap, format);
-	std::string prefix = stringf("%s:%d: Warning: ",
-			filename.c_str(), lineno);
-	logv_warning_with_prefix(prefix.c_str(), format, ap);
-	va_end(ap);
-}
-
-void log_file_info(const std::string &filename, int lineno,
-                      const char *format, ...)
-{
-	va_list ap;
-	va_start(ap, format);
-	std::string fmt = stringf("%s:%d: Info: %s",
-			filename.c_str(), lineno, format);
-	logv(fmt.c_str(), ap);
-	va_end(ap);
+	log("%s:%d: Info: %s", filename, lineno, str);
 }
 
 [[noreturn]]
-static void logv_error_with_prefix(const char *prefix,
-                                   const char *format, va_list ap)
+static void log_error_with_prefix(std::string_view prefix, std::string str)
 {
 #ifdef EMSCRIPTEN
 	auto backup_log_files = log_files;
@@ -349,8 +331,8 @@ static void logv_error_with_prefix(const char *prefix,
 			if (f == stdout)
 				f = stderr;
 
-	log_last_error = vstringf(format, ap);
-	log("%s%s", prefix, log_last_error.c_str());
+	log_last_error = std::move(str);
+	log("%s%s", prefix, log_last_error);
 	log_flush();
 
 	log_make_debug = bak_log_make_debug;
@@ -379,86 +361,35 @@ static void logv_error_with_prefix(const char *prefix,
 #endif
 }
 
-void logv_error(const char *format, va_list ap)
+void log_formatted_file_error(std::string_view filename, int lineno, std::string str)
 {
-	logv_error_with_prefix("ERROR: ", format, ap);
+	std::string prefix = stringf("%s:%d: ERROR: ", filename, lineno);
+	log_error_with_prefix(prefix, str);
 }
 
 void logv_file_error(const string &filename, int lineno,
                      const char *format, va_list ap)
 {
-	std::string prefix = stringf("%s:%d: ERROR: ",
-				     filename.c_str(), lineno);
-	logv_error_with_prefix(prefix.c_str(), format, ap);
+	log_formatted_file_error(filename, lineno, vstringf(format, ap));
 }
 
-void log_file_error(const string &filename, int lineno,
-                    const char *format, ...)
+void log_experimental(const std::string &str)
 {
-	va_list ap;
-	va_start(ap, format);
-	logv_file_error(filename, lineno, format, ap);
-}
-
-void log(const char *format, ...)
-{
-	va_list ap;
-	va_start(ap, format);
-	logv(format, ap);
-	va_end(ap);
-}
-
-void log_header(RTLIL::Design *design, const char *format, ...)
-{
-	va_list ap;
-	va_start(ap, format);
-	logv_header(design, format, ap);
-	va_end(ap);
-}
-
-void log_warning(const char *format, ...)
-{
-	va_list ap;
-	va_start(ap, format);
-	logv_warning(format, ap);
-	va_end(ap);
-}
-
-void log_experimental(const char *format, ...)
-{
-	va_list ap;
-	va_start(ap, format);
-	string s = vstringf(format, ap);
-	va_end(ap);
-
-	if (log_experimentals_ignored.count(s) == 0 && log_experimentals.count(s) == 0) {
-		log_warning("Feature '%s' is experimental.\n", s.c_str());
-		log_experimentals.insert(s);
+	if (log_experimentals_ignored.count(str) == 0 && log_experimentals.count(str) == 0) {
+		log_warning("Feature '%s' is experimental.\n", str);
+		log_experimentals.insert(str);
 	}
 }
 
-void log_warning_noprefix(const char *format, ...)
+void log_formatted_error(std::string str)
 {
-	va_list ap;
-	va_start(ap, format);
-	logv_warning_noprefix(format, ap);
-	va_end(ap);
+	log_error_with_prefix("ERROR: ", std::move(str));
 }
 
-void log_error(const char *format, ...)
+void log_formatted_cmd_error(std::string str)
 {
-	va_list ap;
-	va_start(ap, format);
-	logv_error(format, ap);
-}
-
-void log_cmd_error(const char *format, ...)
-{
-	va_list ap;
-	va_start(ap, format);
-
 	if (log_cmd_error_throw) {
-		log_last_error = vstringf(format, ap);
+		log_last_error = str;
 
 		// Make sure the error message gets through any selective silencing
 		// of log output
@@ -468,7 +399,7 @@ void log_cmd_error(const char *format, ...)
 			pop_errfile = true;
 		}
 
-		log("ERROR: %s", log_last_error.c_str());
+		log("ERROR: %s", log_last_error);
 		log_flush();
 
 		if (pop_errfile)
@@ -477,7 +408,7 @@ void log_cmd_error(const char *format, ...)
 		throw log_cmd_error_exception();
 	}
 
-	logv_error(format, ap);
+	log_formatted_error(str);
 }
 
 void log_spacer()
diff --git a/kernel/log.h b/kernel/log.h
index e26ef072c..6bfc0b421 100644
--- a/kernel/log.h
+++ b/kernel/log.h
@@ -119,30 +119,11 @@ extern int log_make_debug;
 extern int log_force_debug;
 extern int log_debug_suppressed;
 
-void logv(const char *format, va_list ap);
-void logv_header(RTLIL::Design *design, const char *format, va_list ap);
-void logv_warning(const char *format, va_list ap);
-void logv_warning_noprefix(const char *format, va_list ap);
-[[noreturn]] void logv_error(const char *format, va_list ap);
 [[noreturn]] void logv_file_error(const string &filename, int lineno, const char *format, va_list ap);
 
-void log(const char *format, ...)  YS_ATTRIBUTE(format(printf, 1, 2));
-void log_header(RTLIL::Design *design, const char *format, ...) YS_ATTRIBUTE(format(printf, 2, 3));
-void log_warning(const char *format, ...) YS_ATTRIBUTE(format(printf, 1, 2));
-void log_experimental(const char *format, ...) YS_ATTRIBUTE(format(printf, 1, 2));
-
 void set_verific_logging(void (*cb)(int msg_type, const char *message_id, const char* file_path, unsigned int left_line, unsigned int left_col, unsigned int right_line, unsigned int right_col, const char *msg));
 extern void (*log_verific_callback)(int msg_type, const char *message_id, const char* file_path, unsigned int left_line, unsigned int left_col, unsigned int right_line, unsigned int right_col, const char *msg);
 
-// Log with filename to report a problem in a source file.
-void log_file_warning(const std::string &filename, int lineno, const char *format, ...) YS_ATTRIBUTE(format(printf, 3, 4));
-void log_file_info(const std::string &filename, int lineno, const char *format, ...) YS_ATTRIBUTE(format(printf, 3, 4));
-
-void log_warning_noprefix(const char *format, ...) YS_ATTRIBUTE(format(printf, 1, 2));
-[[noreturn]] void log_error(const char *format, ...) YS_ATTRIBUTE(format(printf, 1, 2));
-[[noreturn]] void log_file_error(const string &filename, int lineno, const char *format, ...) YS_ATTRIBUTE(format(printf, 3, 4));
-[[noreturn]] void log_cmd_error(const char *format, ...) YS_ATTRIBUTE(format(printf, 1, 2));
-
 #ifndef NDEBUG
 static inline bool ys_debug(int n = 0) { if (log_force_debug) return true; log_debug_suppressed += n; return false; }
 #else
@@ -150,6 +131,74 @@ static inline bool ys_debug(int = 0) { return false; }
 #endif
 #  define log_debug(...) do { if (ys_debug(1)) log(__VA_ARGS__); } while (0)
 
+void log_formatted_string(std::string_view format, std::string str);
+template <typename... Args>
+inline void log(FmtString<TypeIdentity<Args>...> fmt, Args... args)
+{
+	if (log_make_debug && !ys_debug(1))
+		return;
+	log_formatted_string(fmt.format_string(), fmt.format(args...));
+}
+
+void log_formatted_header(RTLIL::Design *design, std::string_view format, std::string str);
+template <typename... Args>
+inline void log_header(RTLIL::Design *design, FmtString<TypeIdentity<Args>...> fmt, Args... args)
+{
+	log_formatted_header(design, fmt.format_string(), fmt.format(args...));
+}
+
+void log_formatted_warning(std::string_view prefix, std::string str);
+template <typename... Args>
+inline void log_warning(FmtString<TypeIdentity<Args>...> fmt, Args... args)
+{
+	log_formatted_warning("Warning: ", fmt.format(args...));
+}
+template <typename... Args>
+inline void log_warning_noprefix(FmtString<TypeIdentity<Args>...> fmt, Args... args)
+{
+	log_formatted_warning("", fmt.format(args...));
+}
+
+void log_experimental(const std::string &str);
+
+// Log with filename to report a problem in a source file.
+void log_formatted_file_warning(std::string_view filename, int lineno, std::string str);
+template <typename... Args>
+void log_file_warning(std::string_view filename, int lineno, FmtString<TypeIdentity<Args>...> fmt, Args... args)
+{
+	log_formatted_file_warning(filename, lineno, fmt.format(args...));
+}
+
+void log_formatted_file_info(std::string_view filename, int lineno, std::string str);
+template <typename... Args>
+void log_file_info(std::string_view filename, int lineno, FmtString<TypeIdentity<Args>...> fmt, Args... args)
+{
+	if (log_make_debug && !ys_debug(1))
+		return;
+	log_formatted_file_info(filename, lineno, fmt.format(args...));
+}
+
+[[noreturn]] void log_formatted_error(std::string str);
+template <typename... Args>
+[[noreturn]] void log_error(FmtString<TypeIdentity<Args>...> fmt, Args... args)
+{
+	log_formatted_error(fmt.format(args...));
+}
+
+[[noreturn]] void log_formatted_file_error(std::string_view filename, int lineno, std::string str);
+template <typename... Args>
+[[noreturn]] void log_file_error(std::string_view filename, int lineno, FmtString<TypeIdentity<Args>...> fmt, Args... args)
+{
+	log_formatted_file_error(filename, lineno, fmt.format(args...));
+}
+
+[[noreturn]] void log_formatted_cmd_error(std::string str);
+template <typename... Args>
+[[noreturn]] void log_cmd_error(FmtString<TypeIdentity<Args>...> fmt, Args... args)
+{
+	log_formatted_cmd_error(fmt.format(args...));
+}
+
 static inline void log_suppressed() {
 	if (log_debug_suppressed && !log_make_debug) {
 		log("<suppressed ~%d debug messages>\n", log_debug_suppressed);
@@ -350,8 +399,22 @@ static inline void log_dump_val_worker(unsigned long int v) { log("%lu", v); }
 static inline void log_dump_val_worker(long long int v) { log("%lld", v); }
 static inline void log_dump_val_worker(unsigned long long int v) { log("%lld", v); }
 #endif
-static inline void log_dump_val_worker(char c) { log(c >= 32 && c < 127 ? "'%c'" : "'\\x%02x'", c); }
-static inline void log_dump_val_worker(unsigned char c) { log(c >= 32 && c < 127 ? "'%c'" : "'\\x%02x'", c); }
+static inline void log_dump_val_worker(char c)
+{
+	if (c >= 32 && c < 127) {
+		log("'%c'", c);
+	} else {
+		log("'\\x%02x'", c);
+	}
+}
+static inline void log_dump_val_worker(unsigned char c)
+{
+	if (c >= 32 && c < 127) {
+		log("'%c'", c);
+	} else {
+		log("'\\x%02x'", c);
+	}
+}
 static inline void log_dump_val_worker(bool v) { log("%s", v ? "true" : "false"); }
 static inline void log_dump_val_worker(double v) { log("%f", v); }
 static inline void log_dump_val_worker(char *v) { log("%s", v); }
@@ -373,7 +436,7 @@ static inline void log_dump_val_worker(dict<K, T> &v) {
 	log("{");
 	bool first = true;
 	for (auto &it : v) {
-		log(first ? " " : ", ");
+		log("%s ", first ? "" : ",");
 		log_dump_val_worker(it.first);
 		log(": ");
 		log_dump_val_worker(it.second);
@@ -387,7 +450,7 @@ static inline void log_dump_val_worker(pool<K> &v) {
 	log("{");
 	bool first = true;
 	for (auto &it : v) {
-		log(first ? " " : ", ");
+		log("%s ", first ? "" : ",");
 		log_dump_val_worker(it);
 		first = false;
 	}
@@ -399,7 +462,7 @@ static inline void log_dump_val_worker(std::vector<K> &v) {
 	log("{");
 	bool first = true;
 	for (auto &it : v) {
-		log(first ? " " : ", ");
+		log("%s ", first ? "" : ",");
 		log_dump_val_worker(it);
 		first = false;
 	}
diff --git a/kernel/register.cc b/kernel/register.cc
index af1823b5b..38b8c8dc8 100644
--- a/kernel/register.cc
+++ b/kernel/register.cc
@@ -253,7 +253,7 @@ void Pass::call(RTLIL::Design *design, std::vector<std::string> args)
 		log_cmd_error("No such command: %s (type 'help' for a command overview)\n", args[0].c_str());
 
 	if (pass_register[args[0]]->experimental_flag)
-		log_experimental("%s", args[0].c_str());
+		log_experimental(args[0]);
 
 	size_t orig_sel_stack_pos = design->selection_stack.size();
 	auto state = pass_register[args[0]]->pre_execute();
diff --git a/passes/cmds/logcmd.cc b/passes/cmds/logcmd.cc
index 3b82ac48c..9f57eb455 100644
--- a/passes/cmds/logcmd.cc
+++ b/passes/cmds/logcmd.cc
@@ -97,13 +97,13 @@ struct LogPass : public Pass {
 			text += args[argidx] + ' ';
 		if (!text.empty()) text.resize(text.size()-1);
 
-		const char *fmtline = newline ? "%s\n" : "%s";
+		const char *line_end = newline ? "\n" : "";
 
-		if (to_stdout) fprintf(stdout, fmtline, text.c_str());
-		if (to_stderr) fprintf(stderr, fmtline, text.c_str());
+		if (to_stdout) fprintf(stdout, "%s%s", text.c_str(), line_end);
+		if (to_stderr) fprintf(stderr, "%s%s", text.c_str(), line_end);
 		if (to_log) {
-			if (!header) log(fmtline, text.c_str());
-			else log_header(design, fmtline, text.c_str());
+			if (!header) log("%s%s", text.c_str(), line_end);
+			else log_header(design, "%s%s", text.c_str(), line_end);
 		}
 	}
 } LogPass;
diff --git a/passes/cmds/stat.cc b/passes/cmds/stat.cc
index 6b93621f1..bb12b237b 100644
--- a/passes/cmds/stat.cc
+++ b/passes/cmds/stat.cc
@@ -474,7 +474,7 @@ struct StatPass : public Pass {
 
 		if (json_mode) {
 			log("\n");
-			log(top_mod == nullptr ? "   }\n" : "   },\n");
+			log("%s", top_mod == nullptr ? "   }\n" : "   },\n");
 		}
 
 		if (top_mod != nullptr)
diff --git a/passes/equiv/equiv_simple.cc b/passes/equiv/equiv_simple.cc
index 59974a1e6..ff5f04fed 100644
--- a/passes/equiv/equiv_simple.cc
+++ b/passes/equiv/equiv_simple.cc
@@ -202,7 +202,7 @@ struct EquivSimpleWorker
 				log("    Problem size at t=%d: %d literals, %d clauses\n", step, ez->numCnfVariables(), ez->numCnfClauses());
 
 			if (!ez->solve(ez_context)) {
-				log(verbose ? "    Proved equivalence! Marking $equiv cell as proven.\n" : " success!\n");
+				log("%s", verbose ? "    Proved equivalence! Marking $equiv cell as proven.\n" : " success!\n");
 				equiv_cell->setPort(ID::B, equiv_cell->getPort(ID::A));
 				ez->assume(ez->NOT(ez_context));
 				return true;
diff --git a/passes/opt/opt.cc b/passes/opt/opt.cc
index 146c21cce..ec5760cd9 100644
--- a/passes/opt/opt.cc
+++ b/passes/opt/opt.cc
@@ -196,7 +196,7 @@ struct OptPass : public Pass {
 		design->sort();
 		design->check();
 
-		log_header(design, fast_mode ? "Finished fast OPT passes.\n" : "Finished OPT passes. (There is nothing left to do.)\n");
+		log_header(design, "Finished fast OPT passes.%s\n", fast_mode ? "" : " (There is nothing left to do.)");
 		log_pop();
 	}
 } OptPass;
diff --git a/passes/sat/sat.cc b/passes/sat/sat.cc
index 0c2143fc9..215aac21b 100644
--- a/passes/sat/sat.cc
+++ b/passes/sat/sat.cc
@@ -639,10 +639,10 @@ struct SatHelper
 						    "---------------------------------------------------------------------------------------------------"
 						    "---------------------------------------------------------------------------------------------------";
 				if (last_timestep == -2) {
-					log(max_timestep > 0 ? "  Time " : "  ");
+					log("%s", max_timestep > 0 ? "  Time " : "  ");
 					log("%-*s %11s %9s %*s\n", maxModelName+5, "Signal Name", "Dec", "Hex", maxModelWidth+3, "Bin");
 				}
-				log(max_timestep > 0 ? "  ---- " : "  ");
+				log("%s", max_timestep > 0 ? "  ---- " : "  ");
 				log("%*.*s %11.11s %9.9s %*.*s\n", maxModelName+5, maxModelName+5,
 						hline, hline, hline, maxModelWidth+3, maxModelWidth+3, hline);
 				last_timestep = info.timestep;
diff --git a/passes/techmap/dfflibmap.cc b/passes/techmap/dfflibmap.cc
index 409ac7865..e68620260 100644
--- a/passes/techmap/dfflibmap.cc
+++ b/passes/techmap/dfflibmap.cc
@@ -553,11 +553,11 @@ static void dfflibmap(RTLIL::Design *design, RTLIL::Module *module)
 			new_cell->setPort("\\" + port.first, sig);
 		}
 
-		stats[stringf("  mapped %%d %s cells to %s cells.\n", cell_type.c_str(), new_cell->type.c_str())]++;
+		stats[stringf("%s cells to %s cells", cell_type.c_str(), new_cell->type.c_str())]++;
 	}
 
 	for (auto &stat: stats)
-		log(stat.first.c_str(), stat.second);
+		log("  mapped %d %s.\n", stat.second, stat.first);
 }
 
 struct DfflibmapPass : public Pass {
diff --git a/passes/tests/test_cell.cc b/passes/tests/test_cell.cc
index a34eafc2f..ded0398c7 100644
--- a/passes/tests/test_cell.cc
+++ b/passes/tests/test_cell.cc
@@ -522,7 +522,7 @@ static void run_eval_test(RTLIL::Design *design, bool verbose, bool nosat, std::
 
 	for (int i = 0; i < 64; i++)
 	{
-		log(verbose ? "\n" : ".");
+		log("%s", verbose ? "\n" : ".");
 		gold_ce.clear();
 		gate_ce.clear();