fix(esp_libc): picolibc: add workaround for setvbuf on _IONBF

components/esp_libc/CMakeLists.txt

@@ -77,7 +77,9 @@ else()
          "src/picolibc/picolibc_init.c"
          "src/picolibc/rand.c"
          "src/picolibc/open_memstream.c"
-         "src/picolibc/errno.c")
+         "src/picolibc/errno.c"
+         "src/picolibc/bufio_setvbuf.c") # TODO IDF-15494: remove this and the following lines
+         list(APPEND EXTRA_LINK_FLAGS "-Wl,--wrap=__bufio_setvbuf")
     if(CONFIG_LIBC_PICOLIBC_NEWLIB_COMPATIBILITY)
         list(APPEND srcs "src/picolibc/getreent.c")
         list(APPEND srcs "src/picolibc/fopencookie.c")

components/esp_libc/src/picolibc/bufio_setvbuf.c

@@ -0,0 +1,39 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#include <stdio-bufio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+int __real___bufio_setvbuf(FILE *f, char *buf, int mode, size_t size);
+int __wrap___bufio_setvbuf(FILE *f, char *buf, int mode, size_t size)
+{
+    // File lock is already acquired by the caller
+    int ret = -1;
+    bool workaround = false;
+    if (mode == _IONBF) {
+        workaround = true;
+        mode = _IOFBF;
+        size = 1;
+        buf = malloc(size);
+        if (buf == NULL) {
+            goto exit;
+        }
+    }
+    ret = __real___bufio_setvbuf(f, buf, mode, size);
+    if (workaround) {
+        struct __file_bufio *bf = (struct __file_bufio *)f;
+
+        // Free buf if not applied
+        if (ret != 0 || bf->buf != buf) {
+            free(buf);
+            goto exit;
+        }
+        bf->bflags |= __BALL;
+    }
+
+exit:
+    return ret;
+}