Miosix code size optimization - Revision history

Fede.tft at 13:49, 2 October 2026

2026-10-02T13:49:48Z

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 </source>
-With the default settings and, at the time of writing, Miosix version 3.01, the kernel size is a little over 40KB: 41304 bytes. With this guide it is possible to reduce code size down to 13KB with configuration options alone, and down to 8KB by slimming also the board support package.
+With the default settings and, at the time of writing, Miosix version 3.01, the kernel size is a little over 40KB: 41288 bytes. With this guide it is possible to reduce code size down to 13KB with configuration options alone, and down to 8KB by slimming also the board support package.
 Note that optimizations can be applied in any order, there are no dependencies between the steps presented in this page, so you can mix and match to configure a kernel that suits the needs of your application.
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 With this optimization, the code size is reduced to 13084 bytes.
 == One more thing, disable the serial port ==
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 </source>
-By applying also this last tip code size can be reduced to 8436 bytes.
+By applying also this last tip code size can be reduced to 8400 bytes.
 [[Category:Installation and Configuration]]
 [[Category:Optimization]]

Fede.tft at 21:10, 10 May 2026

2026-05-10T21:10:47Z

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	The code size will usually decrease as a percentage of the total code size, as this option affects how the compiler generates code. 5 to 10% decrease is a common figure. Although I haven't found benchmarks showing how much this affects execution speed, usually the impact isn't that high, and code runs definitely much faster with respect to disabling optimizations altogether (with ''-O0''), so if you are tight on code size this is an easy option that does not require to sacrifice any feature of the kernel.		The code size will usually decrease as a percentage of the total code size, as this option affects how the compiler generates code. 5 to 10% decrease is a common figure. Although I haven't found benchmarks showing how much this affects execution speed, usually the impact isn't that high, and code runs definitely much faster with respect to disabling optimizations altogether (with ''-O0''), so if you are tight on code size this is an easy option that does not require to sacrifice any feature of the kernel.

	With the empty ''main()'', Miosix v3.10 and the stm32f411ce_blackpill, the code size was reduced to 39368 bytes.		With the empty ''main()'', Miosix v3.01 and the stm32f411ce_blackpill, the code size was reduced to 39368 bytes.

	== Disable DevFs ==		== Disable DevFs ==

Fede.tft at 21:07, 10 May 2026

2026-05-10T21:07:54Z

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	However, the kernel is very modular, so you don't have to pay the code size cost of unused features in your application.		However, the kernel is very modular, so you don't have to pay the code size cost of unused features in your application.

	This guide lists a number of tips to adapt the Miosix kernel to the needs of code-size constrained embedded applications. The exact figures presented here may change as the kernel is developed further, but the tips are expected to remain valid. In this page we'll use as example the [[stm32f411ce_blackpill]] ~~boardbut~~ the tips presented here are generally applicable. For the application, we'll use an empty ''main()'' to focus on the size of the components of the kernel that are included by default as part of the boot phase:		This guide lists a number of tips to adapt the Miosix kernel to the needs of code-size constrained embedded applications. The exact figures presented here may change as the kernel is developed further, but the tips are expected to remain valid. In this page we'll use as example the [[stm32f411ce_blackpill]] board but the tips presented here are generally applicable. For the application, we'll use an empty ''main()'' to focus on the size of the components of the kernel that are included by default as part of the boot phase:

	<source lang="CPP">		<source lang="CPP">

Fede.tft at 14:15, 10 May 2026

2026-05-10T14:15:33Z

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Andreabont: Adding Categories

2015-01-22T20:04:57Z

Adding Categories

← Older revision		Revision as of 20:04, 22 January 2015
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	By applying also this last tip code size can be reduced to around 6KB.		By applying also this last tip code size can be reduced to around 6KB.

			[[Category:Installation and Configuration]]
			[[Category:Optimization]]

Fede.tft at 11:31, 4 May 2014

2014-05-04T11:31:32Z

← Older revision		Revision as of 11:31, 4 May 2014
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	</source>		</source>

	~~TODO: how much size is saved?~~		This saves aroud 5KB.

	== Disable the filesystem entirely ==		== Disable the filesystem entirely ==

Fede.tft at 11:01, 4 May 2014

2014-05-04T11:01:02Z

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	</source>		</source>

	This saves nearly 20KB but comes with quite an important side effect, though: if the heap is full, the kernel will reboot the machine. To explain why it is so, consider that the normal behaviour in Miosix to handle a full heap is that the C ''malloc()'' returns ''NULL'', while the C++ ''operator new'' throws an exception of type ''bad_alloc''. Now, when exceptions are disabled, 'new'' can no longer throw, but C++ code doesn't check for ''NULL'', as it expects an exception, and that would result in undefined behaviour. The only way to prevent undefined behaviour, is to reboot the machine, and that is what happens.		This saves nearly 20KB but comes with quite an important side effect, though: if the heap is full, the kernel will reboot the machine. To explain why it is so, consider that the normal behaviour in Miosix to handle a full heap is that the C ''malloc()'' returns ''NULL'', while the C++ ''operator new'' throws an exception of type ''bad_alloc''. Now, when exceptions are disabled, ''new'' can no longer throw, but C++ code doesn't check for ''NULL'', as it expects an exception, and that would result in undefined behaviour. The only way to prevent undefined behaviour, is to reboot the machine, and that is what happens.

	== Putting it all together ==		== Putting it all together ==

Fede.tft at 11:00, 4 May 2014

2014-05-04T11:00:18Z

← Older revision		Revision as of 11:00, 4 May 2014
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	== Disable the C++ exception runtime ==		== Disable the C++ exception runtime ==

	The Miosix kernel is by default compiled with support for C++ exceptions, and unless you're also enabling [[Miosix processes\|processes]] that depend on C++ exceptions, it is possible to disable their support. To di so, open [Makefile.inc\|miosix/config/Makefile.inc]] and uncomment the following line:		The Miosix kernel is by default compiled with support for C++ exceptions, and unless you're also enabling [[Miosix processes\|processes]] that depend on C++ exceptions, it is possible to disable their support. To di so, open [[Makefile.inc\|miosix/config/Makefile.inc]] and uncomment the following line:

	<source lang="bash">		<source lang="bash">

Fede.tft at 10:59, 4 May 2014

2014-05-04T10:59:15Z

← Older revision		Revision as of 10:59, 4 May 2014
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	Maybe you're not using ''printf()'' at all in your application, however in this case you're still paying for the code size of ''iprintf()'' as the kernel uses it to print boot logs and error logs. To disable them, you can open [[miosix_settings.h\|miosix/config/miosix_settings.h]] and uncomment ''WITH_BOOTLOG'' and ''WITH_ERRLOG''. This allows to save an additional 17KB of code size, but this is only true if there's no ''printf()'' call in your code, otherewise the code size saving will be minimal.		Maybe you're not using ''printf()'' at all in your application, however in this case you're still paying for the code size of ''iprintf()'' as the kernel uses it to print boot logs and error logs. To disable them, you can open [[miosix_settings.h\|miosix/config/miosix_settings.h]] and uncomment ''WITH_BOOTLOG'' and ''WITH_ERRLOG''. This allows to save an additional 17KB of code size, but this is only true if there's no ''printf()'' call in your code, otherewise the code size saving will be minimal.

	Also, keep in mind that error logs are a powerful tool to debug crashes of your application or the kernel during code development, so you may want to disable them only in release builds, and keep them enabled during ~~developemnt~~.		Also, keep in mind that error logs are a powerful tool to debug crashes of your application or the kernel during code development, so you may want to disable them only in release builds, and keep them enabled during development.

	Finally, note that you can still access the serial port without using ''printf()'', by means of the POSIX calls ''write()'' and ''read()'', using ''STDOUT_FILENO'' and ''STDIN_FILENO'' as the ''fd'' argument.		Finally, note that you can still access the serial port without using ''printf()'', by means of the POSIX calls ''write()'' and ''read()'', using ''STDOUT_FILENO'' and ''STDIN_FILENO'' as the ''fd'' argument.

Fede.tft at 10:58, 4 May 2014

2014-05-04T10:58:18Z

← Older revision		Revision as of 10:58, 4 May 2014
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	== Disable boot logs ==		== Disable boot logs ==

	Maybe you're no using ''printf()'' at all in your application, however in this case you're still paying for the code size of ''iprintf()'' as the kernel uses it to print boot logs and error logs. To disable them, you can open [[miosix_settings.h\|miosix/config/miosix_settings.h]] and uncomment ''WITH_BOOTLOG'' and ''WITH_ERRLOG''. This allows to save an additional 17KB of code size, but this is only true if there's no ''printf()'' call in your code, otherewise the code size saving will be minimal.		Maybe you're not using ''printf()'' at all in your application, however in this case you're still paying for the code size of ''iprintf()'' as the kernel uses it to print boot logs and error logs. To disable them, you can open [[miosix_settings.h\|miosix/config/miosix_settings.h]] and uncomment ''WITH_BOOTLOG'' and ''WITH_ERRLOG''. This allows to save an additional 17KB of code size, but this is only true if there's no ''printf()'' call in your code, otherewise the code size saving will be minimal.

	Also, keep in mind that error logs are a powerful tool to debug crashes of your application or the kernel during code development, so you may want to disable them only in release builds, and keep them enabled during developemnt.		Also, keep in mind that error logs are a powerful tool to debug crashes of your application or the kernel during code development, so you may want to disable them only in release builds, and keep them enabled during developemnt.