From 4f53612725ad1fe4b4d125fe53c85dedc05e1482 Mon Sep 17 00:00:00 2001
From: Robert O'Callahan <rocallahan@google.com>
Date: Wed, 21 Jan 2026 03:18:12 +0000
Subject: [PATCH] Add `linux_perf` command to turn Linux perf recording on and
 off.

This is extremely useful for profiling specific passes.
---
 passes/cmds/Makefile.inc  |  1 +
 passes/cmds/linux_perf.cc | 96 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 97 insertions(+)
 create mode 100644 passes/cmds/linux_perf.cc

diff --git a/passes/cmds/Makefile.inc b/passes/cmds/Makefile.inc
index dc12c92c2..5e2994a53 100644
--- a/passes/cmds/Makefile.inc
+++ b/passes/cmds/Makefile.inc
@@ -37,6 +37,7 @@ OBJS += passes/cmds/chformal.o
 OBJS += passes/cmds/chtype.o
 OBJS += passes/cmds/blackbox.o
 OBJS += passes/cmds/ltp.o
+OBJS += passes/cmds/linux_perf.o
 ifeq ($(DISABLE_SPAWN),0)
 OBJS += passes/cmds/bugpoint.o
 endif
diff --git a/passes/cmds/linux_perf.cc b/passes/cmds/linux_perf.cc
new file mode 100644
index 000000000..f57a887fb
--- /dev/null
+++ b/passes/cmds/linux_perf.cc
@@ -0,0 +1,96 @@
+/*
+ *  yosys -- Yosys Open SYnthesis Suite
+ *
+ *  Copyright (C) 2014  Claire Xenia Wolf <claire@yosyshq.com>
+ *  Copyright (C) 2014  Johann Glaser <Johann.Glaser@gmx.at>
+ *
+ *  Permission to use, copy, modify, and/or distribute this software for any
+ *  purpose with or without fee is hereby granted, provided that the above
+ *  copyright notice and this permission notice appear in all copies.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ */
+
+#include "kernel/yosys.h"
+#include "kernel/log_help.h"
+
+#include <fcntl.h>
+#include <stdlib.h>
+
+USING_YOSYS_NAMESPACE
+PRIVATE_NAMESPACE_BEGIN
+
+#ifdef __linux__
+struct LinuxPerf : public Pass {
+	LinuxPerf() : Pass("linux_perf", "turn linux perf recording off or on") { }
+	void help() override
+	{
+		log("This pass turns Linux 'perf' profiling on or off, when it has been configured to use control FIFOs.\n");
+		log("\n");
+		log("Example shell command line:\n");
+		log("mkfifo /tmp/perf.fifo /tmp/perf-ack.fifo\n");
+		log("YOSYS_PERF_CTL=/tmp/perf.fifo YOSYS_PERF_ACK=/tmp/perf-ack.fifo \\\n");
+		log("  perf record --latency --delay=-1 \\\n");
+		log("  --control=fifo:/tmp/perf.fifo,/tmp/perf-ack.fifo --call-graph=dwarf ./yosys -dt -p \\\n");
+		log("  \"read_rtlil design.rtlil; linux_perf on; opt_clean; linux_perf off\"\n");
+		log("\n");
+		log("    linux_perf on\n");
+		log("\n");
+		log("Start perf recording. YOSYS_PERF_CTL and YOSYS_PERF_ACK must point to Linux perf control FIFOs.\n");
+		log("\n");
+		log("    linux_perf off\n");
+		log("\n");
+		log("Stop perf recording.\n");
+		log("\n");
+	}
+	void execute(std::vector<std::string> args, RTLIL::Design *) override
+	{
+		if (args.size() > 2)
+			cmd_error(args, 2, "Unexpected argument.");
+
+		std::string_view ctl_msg;
+		if (args.size() == 2) {
+			if (args[1] == "on")
+				ctl_msg = "enable\n";
+			else if (args[1] == "off")
+				ctl_msg = "disable\n";
+			else
+				cmd_error(args, 1, "Unexpected argument.");
+		}
+
+		const char *ctl_fifo = std::getenv("YOSYS_PERF_CTL");
+		if (!ctl_fifo)
+			log_error("YOSYS_PERF_CTL environment variable not set.");
+		const char *ack_fifo = std::getenv("YOSYS_PERF_ACK");
+		if (!ack_fifo)
+			log_error("YOSYS_PERF_ACK environment variable not set.");
+
+		int ctl_fd = open(ctl_fifo, O_WRONLY);
+		if (ctl_fd < 0)
+			log_error("Failed to open YOSYS_PERF_CTL.");
+		int ack_fd = open(ack_fifo, O_RDONLY);
+		if (ack_fd < 0)
+			log_error("Failed to open YOSYS_PERF_ACK.");
+		int result = write(ctl_fd, ctl_msg.data(), ctl_msg.size());
+		if (result != static_cast<int>(ctl_msg.size()))
+			log_error("Failed to write to YOSYS_PERF_CTL.");
+		char buffer[64];
+		result = read(ack_fd, buffer, sizeof(buffer));
+		close(ctl_fd);
+		close(ack_fd);
+		if (result <= 0)
+			log_error("Failed to read from YOSYS_PERF_ACK.");
+		if (strcmp(buffer, "ack\n") != 0)
+			log_error("YOSYS_PERF_ACK did not return 'ack'.");
+	}
+} LinuxPerf;
+#endif
+
+PRIVATE_NAMESPACE_END