feat(esp_trace): add compiler-instrumented function tracing support

examples/system/function_tracing/components/ft_demo/CMakeLists.txt

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+idf_component_register(SRCS "ft_demo.c" "ft_demo_hot.c" "ft_demo_quiet.c"
+                       INCLUDE_DIRS "include")
+
+# Opt the whole component into compiler-instrumented function tracing by adding
+# -finstrument-functions to its build. The guard keeps the flag out when the
+# feature is off, otherwise the __cyg_profile_* hooks would be undefined at link.
+# The exclude-list flags skip specific files / functions:
+#  - ft_demo_hot.c and ft_demo_quiet.c are excluded by file (comma-separated)
+#  - ft_demo_secret is excluded by function name
+if(CONFIG_ESP_TRACE_FUNCTION_TRACE)
+    target_compile_options(${COMPONENT_LIB} PRIVATE
+        -finstrument-functions
+        -finstrument-functions-exclude-file-list=ft_demo_hot,ft_demo_quiet
+        -finstrument-functions-exclude-function-list=ft_demo_secret)
+endif()

examples/system/function_tracing/components/ft_demo/ft_demo.c

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+/*
+ * SPDX-FileCopyrightText: 2026 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Function Tracing Example - demo library
+*/
+
+#include "ft_demo.h"
+
+/* noinline keeps each function as a distinct call so the compiler inserts
+ * enter/exit hooks instead of inlining them away. */
+static uint32_t __attribute__((noinline)) ft_demo_level2(uint32_t v)
+{
+    return v * 3u + 1u;
+}
+
+static uint32_t __attribute__((noinline)) ft_demo_level1(uint32_t v)
+{
+    return ft_demo_level2(v) + ft_demo_level2(v + 1u);
+}
+
+void ft_demo_run(uint32_t iteration)
+{
+    volatile uint32_t r = ft_demo_level1(iteration);
+    (void)r;
+}
+
+void __attribute__((noinline)) ft_demo_secret(void)
+{
+    /* Excluded from instrumentation by name, so no enter/exit is recorded even
+     * though this file is compiled with -finstrument-functions. */
+    __asm__ volatile("");
+}

examples/system/function_tracing/components/ft_demo/ft_demo_hot.c

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+/*
+ * SPDX-FileCopyrightText: 2026 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Function Tracing Example - demo library (excluded file)
+*/
+
+#include "ft_demo.h"
+
+/* This whole file is listed in the component's -finstrument-functions-exclude-file-list
+ * flag, so none of its functions are instrumented even though the component opts
+ * in. Use this for hot paths you do not want to trace. */
+uint32_t ft_demo_hot_loop(uint32_t n)
+{
+    uint32_t acc = 0;
+    for (uint32_t i = 0; i < n; i++) {
+        acc += i * i;
+    }
+    return acc;
+}

examples/system/function_tracing/components/ft_demo/ft_demo_quiet.c

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+/*
+ * SPDX-FileCopyrightText: 2026 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Function Tracing Example - demo library (second excluded file)
+*/
+
+#include "ft_demo.h"
+
+/* A second file added to the component's -finstrument-functions-exclude-file-list
+ * as a separate, comma-separated entry. It shows the exclude list accepts more
+ * than one substring. Like ft_demo_hot.c, none of its functions are instrumented. */
+uint32_t ft_demo_quiet_path(uint32_t n)
+{
+    uint32_t acc = 1;
+    for (uint32_t i = 1; i <= n; i++) {
+        acc = (acc * i) % 1000u;
+    }
+    return acc;
+}

examples/system/function_tracing/components/ft_demo/include/ft_demo.h

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+/*
+ * SPDX-FileCopyrightText: 2026 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Function Tracing Example - demo library
+*/
+#pragma once
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Runs a small nested call graph (ft_demo_run -> level1 -> level2). These
+ * functions are instrumented and appear as function_enter/function_exit. */
+void ft_demo_run(uint32_t iteration);
+
+/* Instrumented file, but excluded by name through the component's
+ * -finstrument-functions-exclude-function-list flag: it produces no events. */
+void ft_demo_secret(void);
+
+/* Lives in ft_demo_hot.c, which is excluded as a whole through the component's
+ * -finstrument-functions-exclude-file-list flag: it produces no events. */
+uint32_t ft_demo_hot_loop(uint32_t n);
+
+/* Lives in ft_demo_quiet.c, a second comma-separated entry in the component's
+ * -finstrument-functions-exclude-file-list flag: it also produces no events. */
+uint32_t ft_demo_quiet_path(uint32_t n);
+
+#ifdef __cplusplus
+}
+#endif