From 623f7249b81a93eed745118f76333762256f3e3c Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Fri, 13 Mar 2026 18:05:07 -1000
Subject: [PATCH] [esp32] Add ISR safety check for constrained env logging

constrained_env combines three conditions: scheduler not running,
in ISR, or cache disabled. Only the first is safe for flash access.

Check xPortInIsrContext() (IRAM-resident) explicitly:
- In ISR: output tag only via esp_rom_printf (ROM). Flash may be
  inaccessible. This matches V1 behavior where ISR logging was
  best-effort.
- Not in ISR (scheduler not running, PHY init): call flash-resident
  esp_log_format_early_ which formats the full message.

This ensures the override is safe for all constrained env cases
without pulling in esp_rom_vprintf (1.2KB IRAM).
---
 esphome/core/log.cpp | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/esphome/core/log.cpp b/esphome/core/log.cpp
index c155fb20bbe..21fc9936a1d 100644
--- a/esphome/core/log.cpp
+++ b/esphome/core/log.cpp
@@ -140,12 +140,25 @@ extern "C" {
 void IRAM_ATTR esp_log_format(esp_log_msg_t *message) {
   extern vprintf_like_t esp_log_vprint_func;
   extern int vprintf(const char *, __gnuc_va_list);  // NOLINT
-  if (esp_log_vprint_func == &vprintf || message->config.opts.constrained_env) [[unlikely]] {
-    // Early boot or constrained env (PHY init, ISR): can't use the ESPHome
-    // hook (fwrite locks crash during PHY init on USB JTAG devices).
-    // Format to stack buffer with vsnprintf + esp_rom_printf (both safe
-    // without stdio locks). vsnprintf writes to a buffer (no stdio init
-    // needed), esp_rom_printf is ROM-resident.
+  if (message->config.opts.constrained_env) [[unlikely]] {
+    // Constrained env: constrained_env combines three conditions —
+    // scheduler not running, in ISR, or cache disabled. Only the first
+    // is safe for flash access. Check ISR context explicitly to decide.
+    if (xPortInIsrContext()) {
+      // In ISR: flash may be inaccessible. Output tag only via ROM printf.
+      // This matches V1 behavior where ISR logging was best-effort.
+      static DRAM_ATTR const char isr_fmt[] = "[%s] (ISR log)\n";
+      esp_rom_printf(isr_fmt, message->tag ? message->tag : "idf");
+    } else {
+      // Scheduler not running or PHY init: flash is accessible.
+      // Use stack buffer formatting (can't use ESPHome hook — fwrite
+      // locks crash during PHY init on USB JTAG devices).
+      esp_log_format_early_(message);
+    }
+    return;
+  }
+  if (esp_log_vprint_func == &vprintf) [[unlikely]] {
+    // Early boot: hook not installed yet. Format with ESPHome style.
     esp_log_format_early_(message);
     return;
   }