From 6276a4f6a5dbba84e87eaccc21495ffee5f64b51 Mon Sep 17 00:00:00 2001
From: Peter Johanson <peter@peterjohanson.com>
Date: Thu, 26 Sep 2024 00:05:40 -0600
Subject: [PATCH] Various stack size reduction tweaks

* Add option for skipping size checks when encoding submessages
* Tweak inline/noinline for functions to reduce stack size.
---
 pb.h        | 16 ++++++++++++++++
 pb_encode.c | 22 ++++++++++++----------
 2 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/pb.h b/pb.h
index 8745ecc6a..e9fe8dba0 100644
--- a/pb.h
+++ b/pb.h
@@ -28,6 +28,9 @@
 /* Disable support for error messages in order to save some code space. */
 /* #define PB_NO_ERRMSG 1 */
 
+/* Disable checks to ensure sub-message encoded size is consistent when re-run. */
+/* #define PB_NO_ENCODE_SIZE_CHECK 1 */
+
 /* Disable support for custom streams (support only memory buffers). */
 /* #define PB_BUFFER_ONLY 1 */
 
@@ -126,6 +129,19 @@ extern "C" {
 #   define pb_packed
 #endif
 
+// Define for explicitly not inlining a given function
+#if defined(__GNUC__) || defined(__clang__)
+    /* For GCC and clang */
+#   define pb_noinline __attribute__((noinline))
+#elif defined(__ICCARM__) || defined(__CC_ARM)
+    /* For IAR ARM and Keil MDK-ARM compilers */
+#   define pb_noinline
+#elif defined(_MSC_VER) && (_MSC_VER >= 1500)
+#   define pb_noinline __declspec(noinline)
+#else
+#   define pb_noinline
+#endif
+
 /* Detect endianness */
 #ifndef PB_LITTLE_ENDIAN_8BIT
 #if ((defined(__BYTE_ORDER) && __BYTE_ORDER == __LITTLE_ENDIAN) || \
diff --git a/pb_encode.c b/pb_encode.c
index 7f5620125..635807244 100644
--- a/pb_encode.c
+++ b/pb_encode.c
@@ -26,7 +26,7 @@ static bool checkreturn pb_check_proto3_default_value(const pb_field_iter_t *fie
 static bool checkreturn encode_basic_field(pb_ostream_t *stream, const pb_field_iter_t *field);
 static bool checkreturn encode_callback_field(pb_ostream_t *stream, const pb_field_iter_t *field);
 static bool checkreturn encode_field(pb_ostream_t *stream, pb_field_iter_t *field);
-static bool checkreturn encode_extension_field(pb_ostream_t *stream, const pb_field_iter_t *field);
+static pb_noinline bool checkreturn encode_extension_field(pb_ostream_t *stream, const pb_field_iter_t *field);
 static bool checkreturn default_extension_encoder(pb_ostream_t *stream, const pb_extension_t *extension);
 static bool checkreturn pb_encode_varint_32(pb_ostream_t *stream, uint32_t low, uint32_t high);
 static bool checkreturn pb_enc_bool(pb_ostream_t *stream, const pb_field_iter_t *field);
@@ -483,7 +483,7 @@ static bool checkreturn default_extension_encoder(pb_ostream_t *stream, const pb
 
 /* Walk through all the registered extensions and give them a chance
  * to encode themselves. */
-static bool checkreturn encode_extension_field(pb_ostream_t *stream, const pb_field_iter_t *field)
+static pb_noinline bool checkreturn encode_extension_field(pb_ostream_t *stream, const pb_field_iter_t *field)
 {
     const pb_extension_t *extension = *(const pb_extension_t* const *)field->pData;
 
@@ -724,8 +724,6 @@ bool checkreturn pb_encode_submessage(pb_ostream_t *stream, const pb_msgdesc_t *
 {
     /* First calculate the message size using a non-writing substream. */
     pb_ostream_t substream = PB_OSTREAM_SIZING;
-    size_t size;
-    bool status;
     
     if (!pb_encode(&substream, fields, src_struct))
     {
@@ -735,17 +733,20 @@ bool checkreturn pb_encode_submessage(pb_ostream_t *stream, const pb_msgdesc_t *
         return false;
     }
     
-    size = substream.bytes_written;
-    
-    if (!pb_encode_varint(stream, (pb_uint64_t)size))
+    if (!pb_encode_varint(stream, (pb_uint64_t)substream.bytes_written))
         return false;
     
     if (stream->callback == NULL)
-        return pb_write(stream, NULL, size); /* Just sizing */
+        return pb_write(stream, NULL, substream.bytes_written); /* Just sizing */
     
-    if (stream->bytes_written + size > stream->max_size)
+    if (stream->bytes_written + substream.bytes_written > stream->max_size)
         PB_RETURN_ERROR(stream, "stream full");
         
+#if PB_NO_ENCODE_SIZE_CHECK
+    return pb_encode(stream, fields, src_struct);
+#else
+    bool status;
+    size_t size = substream.bytes_written;
     /* Use a substream to verify that a callback doesn't write more than
      * what it did the first time. */
     substream.callback = stream->callback;
@@ -766,8 +767,9 @@ bool checkreturn pb_encode_submessage(pb_ostream_t *stream, const pb_msgdesc_t *
     
     if (substream.bytes_written != size)
         PB_RETURN_ERROR(stream, "submsg size changed");
-    
+
     return status;
+#endif
 }
 
 /* Field encoders */