c / c ++：如何知道已用闪存的大小？

Question

I recently faced flash overflow problem. After doing some optimization in code, I saved some flash memory and executed software successfully. I want to how much flash memory is saved through my changes. Please let me know how can I check for used flash / available flash memory. Also I want to how much flash is utilized by particular function/file.

Below mentioned are some info about my developing environment. - Avr microcontroller with 64 k ram and 512 K flash. - Using freeRtos. - Using GNU C++ compiler. - Using AVRATJTAGEICE for programming and Debugging.

Please let me know the solution.

Regards, Jagadeep.

Answer 1

Use size command from binutils on the generated elf file. As you seem to use an AVR chip, use avr-size .

To get the size of functions, use nm command from binutils ( avr-nm on AVR chips).

Answer 2

Please let me know the solution.

Sorry, there's no the solution ! You've gotta getting through what's linked to your final ELF, and decide if it was linked by intend, or unwanted default.

Please let me know how can I check for used flash / available flash memory.

That primarily depends on your actual target hardware platform, so you have to manage to get your .text section fitting in there.

Also I want to how much flash is utilized by particular function/file.

The nm tool of the GCC binutils provides detailed information about any (global) symbol found in an ELF file and the space it occupies in it's associated section. You'll just need to grep the results for particular functions/classes/namespaces (best demangled!) to accumulate section type and symbol filtered outputs for analysis.

That's the approach, I've been using for a little tool called nmalyzr . Sorry to say, as it stands on the GIT repo, its not really working as intended (I've got working versions, that aren't pushed back).

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In general, it's a good strategy to chase for code that has #include <iostream> statements (no matter if std::cout or alike are used or not, static instances are provided!), or unwanted newlib/libstdc++ bindings as for eg default exception handling.

Answer 3

GCC's size program is what you're looking for.

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size can be passed the full compiled .elf file. It will, by default, output something like this:

$ size linked-file.elf
   text    data     bss     dec     hex filename
  11228     112    1488   12828    321c linked-file.elf

This is saying:

There are 11228 bytes in the .text "section" of this file. This is generally for functions.
There are 112 bytes of initialized data : global variables in the program with initial values.
There are 1488 bytes of uninitialized data : global variables without initial values.

dec is simply the sum of the previous 3 values: 11228 + 112 + 1488 = 12828 .
hex is simply the hexadecimal representation of the dec value: 0x321c == 12828 .

For embedded systems, generally dec needs to be smaller than the flash size of your target device (or the available space on the device).

It is generally sufficient to simply watch the dec or text outputs of GCC's size command to monitor the size of your compiled code over time. A large jump in size often indicates a poorly implemented new feature or constexpr that are not getting compiled away. (Don't forget function-sections and data-sections ).

Note : For AVR's, you'll want to use avr-size for checking the linked size of AVR .elf files. avr-size takes an extra argument of the target chip and will automatically calculate the percentage of used flash for your chosen chip.

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GCC's size also works directly on intermediate object files.

This is particularly useful if you want to check the compiled size of functions.

You should see something like this excerpt:

$ size -A main.cpp.o
main.cpp.o  :
section                                                                size   addr
.group                                                                    8      0
.group                                                                    8      0
.text                                                                     0      0
.data                                                                     0      0
.bss                                                                      0      0
.text._Z8sendByteh                                                        8      0
.text._ZN3XMC5IOpin7setModeENS0_4ModeE                                   64      0
.text._ZN7NamSpac6OptionIN5Clock4TimeEEmmEi                              76      0
.text.Default_Handler                                                    24      0
.text.HardFault_Handler                                                  16      0
.text.SVC_Handler                                                        16      0
.text.PendSV_Handler                                                     16      0
.text.SysTick_Handler                                                    28      0
.text._Z5errorPKc                                                         8      0
.text._ZN7NamSpac5Motor2goEi                                            368      0
.text._ZN7NamSpac5Motor3getEv                                            12      0
.rodata.cst1                                                              1      0
.text.startup.main                                                      632      0
.text._ZN7NamSpac7Program3runEv                                         380      0
.text._ZN7NamSpac8Position4tickEv                                        24      0
.text.startup._GLOBAL__sub_I__ZN7NamSpac7displayE                       292      0
.init_array                                                               4      0
.bss._ZN5Debug9formatterE                                                 4      0
.rodata._ZL10dispDigits                                                   8      0
.bss.position                                                             4      0
.bss.motorState                                                           4      0
.bss.count                                                                4      0
.rodata._ZL9diameters                                                    20      0
.bss._ZN7NamSpac8diameterE                                               16      0
.bss._ZN5Debug3pinE                                                      12      0
.bss._ZN7NamSpac7displayE                                                24      0
.rodata.str1.4                                                          153      0
.rodata._ZL12dispSegments                                                32      0
.bss._ZL16diametersDisplay                                               10      0
.bss.loadAggregate                                                        4      0
.bss.startCount                                                           4      0
.bss._ZL15runtimesDisplay                                                10      0
.bss._ZN7NamSpac7runtimeE                                                16      0
.bss.startTime                                                            4      0
.rodata._ZL8runtimes                                                     20      0
.comment                                                                111      0
.ARM.attributes                                                          49      0
Total                                                                  2494