[utest]: Allow the linker to remove any part of utest if not used #2559
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| RawSerial greentea_serial(USBTX, USBRX); | ||
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| RawSerial& greentea_serial() { | ||
| static RawSerial serial(USBTX, USBRX); |
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Is this guaranteed by the C++ standard to be initialized on first use or could it also be initialized at boot? Also, I doubt this is thread safe for GCC, although if utest calls this in its initialization sequence then it will be initialized in a single threaded manner. Maybe leave a comment here? Either that or you could ensure that it is thread safe by using the singleton_lock().
Also, @bridadan I know you made this change locally. Do you have any feedback on this? This version might be cleaner that using a singleton class.
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My change was actually just merged in, but yeah this may be another alternative. I suppose one benefit of this is that the RawSerial instance is on the stack, not the heap. But yeah I think it'd be worth verifying your concerns you voiced above @c1728p9.
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Both this instance and the SingletonPtr instance should be allocated globally. According to this post, gcc by default emits thread-safe static constructors, although I'm not sure if we need to tie into hooks for that:
http://stackoverflow.com/questions/1270927/are-function-static-variables-thread-safe-in-gcc
It also raises the question of thread-safety on other toolchains.
If this is garunteed to be thread-safe per the C++03 standard, it may be a better solution over the existing SingletonPtr and we may want consider deprecating the SingletonPtr class in favor of this method. But that is a big if at the moment.
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I will update the PR to take advantages of the changes from @bridadan.
As a side note:
Is this guaranteed by the C++ standard to be initialized on first use or could it also be initialized at boot?
Yes it is guaranteed to be initialized on first use.
lso, I doubt this is thread safe for GCC, although if utest calls this in its initialization sequence then it will be initialized in a single threaded manner.
No its not thread safe in C++03 (it is in C++11) but it can be thread safe for abi conforming to the itanium ABI: https://mentorembedded.github.io/cxx-abi/abi.html#once-ctor
It is possible to overload these definitions:
extern "C" int __cxa_guard_acquire ( __int64_t *guard_object );extern "C" void __cxa_guard_release ( __int64_t *guard_object );extern "C" void __cxa_guard_abort ( __int64_t *guard_object );
because the ARMEABI is based on itanium ABI and therefore it is possible to have thread safe static objects constructions on mbed without any workaround.
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If this is garunteed to be thread-safe per the C++03 standard, it may be a better solution over the existing SingletonPtr and we may want consider deprecating the SingletonPtr class in favor of this method. But that is a big if at the moment.
The singleton pointer class is still good to create PODs without wrapping everything as a static, in a function and it is immune to the static initialization fiasco.
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Since these both solve the same problem of global-initialization, shouldn't we chose one solution and consolidate?
👍
I would be all for getting rid of the SingletonPtr class. It is not very intuitive to declare.
Though this was to be renamed to LazyInitialization
Only downside is it won't have the semantics of pointer access to a global class.
The semantics of returning a reference and not being able to overloading the dot operator is very unintuitive. Pointer access to a global class is a HUGE 👍 for readability and clarity IMO.
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From what I understand, the static-initializer solution has several benefits over LazyInstance:
- Language-based solution, no delicate tip-toeing around the definition of a POD type
- Little concerns for regressions and one less class to support
- Can easily do non-trivial amount of work (and accept arguments)
- Is forward compatible with non-trivial changes to the initialization of the object
(for example global thread instances could still start the thread in the access function)
If the only issue is the semantics of a reference over pointer, these functions could be easily changed to return a pointer.
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Hmm, I'm probably missing it, but I'm not sure I see where SingletonPtr benefits over static initialization other than the syntax difference, but both cases are different from the syntax for global objects.
Ok, let me go back to the start.
When a compilation unit define global (extern or static) variable(s) that are not initialized at compile time, then the compiler generate an initialization function which will initialize these global variables of this compilation unit before the entry in the main function.
Some examples of runtime global:
extern "C" {
int foo();
const int bar = foo();
}
// the definition is omitted but Baz is not a POD
class Baz;
Baz baz;This initialization function will be referenced in special section which contains all the initialization functions of the program. Before the entry in main, the c runtime will execute every functions referenced in this section.
The main issue with that model is that global variables initialized at runtime can't be removed from the output because even if it seems like the variable is not used, it is used by the c runtime.
Then the dependency chain is:
c runtime -> initialization_function_array -> compilation unit initialization -> global variable.
That was the issue with the utest code and what this PR fix. A lot of global variables initialized at runtime were here and these variables, not collectable by the linker GC, pulled code and data from the utest library.
Global runtime (static or extern) variables are never an option for embedded libraries.
Wrapping the variable inside a LazyInstance or a function scope (as static) is the only option here (both have their advantages and inconvenient).
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Thanks @pan- for providing the answers.
Since these both solve the same problem of global-initialization, shouldn't we chose one solution and consolidate?
In this manner, yes they are the same, but from the perspective of singleton, they are not, thus depends on the usage. Therefore I proposed a name change for SingletonPtr, not to confuse that this class is not a singleton. As @pan- wrote:
Wrapping the variable inside a LazyInstance or a function scope (as static) is the only option here (both have their advantages and inconvenient).
As there's PR for providing locks for local static variables, any other concerns?
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@pan- You are a wizard :) Nice work on this, I took a crack at this once and I admit I fell short due to my lack of C++ foo. But all the changes you've made seem quite sane to me. The only immediate issue I see with this PR is my PR changing greentea-client to use a SingletonPtr for the |
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This should provide the same code size reduction. The next step for unity and greentea-client is to use the retargeted stdio once updated to use RTOS or Events |
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@sg- This PR actually goes a further step by preventing parts of utest that were coming in in addition to the RawSerial instance, so this actually reduces the code size by quite a bit more! My PR only removed a few 100 bytes I think. |
| handlers.test_setup = defaults.get_handler(specification.setup_handler); | ||
| handlers.test_teardown = defaults.get_handler(specification.teardown_handler); | ||
| handlers.test_failure = defaults.get_handler(specification.failure_handler); | ||
| defaults() = specification.defaults; |
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sigh, C++, the only language this line could make sense in...
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Excellent PR @pan-. Looking at the before and after map files it looks like this PR strips out ALL mbed global constructors. Looks like these were removed: |
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/morph test |
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@mbed-bot: TEST HOST_OSES=ALL |
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[Build 852] |
Result: FAILUREYour command has finished executing! Here's what you wrote!
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@c1728p9 This has merge conflicts that need to be fixed before running CI again |
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@pan- +1 for this patch. Please rebase if this is completed Note: As you mentioned earlier in the discussion, this type of optimizations might be worth capturing in the guidelines (I imagine we would provide C++ API guideline) where we could describe what we follow to make the footprint minimal (Lazy instance, POD vs nonPOD in the global scope, ODR, etc). That would explain nicely this patch and others that landed recently. Let's write it ? |
That way it is not a global object anymore and is not attached to the .init section and init array. If the function which contain the object is not called then the serial object will not be present in the final binary.
The change of scope allow the linker to remove the variable if not used.
It save space and fix the ODR violation.
Replace const control_t instances by this POD. This save memory and prevent inclusion of the constants in the binary if they are not used.
* Add conversion operator in control_t to convert instances to base_control_t
This change allow a lot of code from utest to be removed from the final binary if not used.
* provide missing member functions from control_t in base_control_t * construction of control_t from reference of base_control_t instead of value. * overload operator+ for all permutations between control_t and base_control_t.
Both branches of a ternary operator should yield the same type; compatibility is not enough in that case.
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@0xc0170 It has been rebased, please test :) |
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/morph test |
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@pan- I think another change to utest needs to be made before this is ready: https://github.com/pan-/mbed/blob/a9d9987d7c375ed3915654adede8981a74ffa7e1/features/frameworks/utest/utest/utest_serial.h#L24 My previous PR allowed greentea and utest to share the same |
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Awesome, thanks @pan- /morph test |
Result: FAILUREYour command has finished executing! Here's what you wrote!
Outputmbed Build Number: 759 Test Prep failed! |
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/morph test |
Result: FAILUREYour command has finished executing! Here's what you wrote!
Outputmbed Build Number: 767 Test failed! |
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/morph test |
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@bridadan utest with this PR on ARMCC and IAR, I'm investigating why. |
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@pan- Thanks, we are observing strange behavior where some USB devices are being reset mid test by the Windows OS causing some failures to occur, we are looking into this as well. |
| @@ -66,7 +66,10 @@ static volatile utest_v1_harness_callback_t minimal_callback; | |||
| static volatile utest_v1_harness_callback_t ticker_callback; | |||
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| // Timeout object used to control the scheduling of test case callbacks | |||
| Timeout utest_timeout_object; | |||
| static Timeout& utest_timeout_object() { | |||
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Can we use SingletonPtr same as RawSerial?
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Yes, this bit cause a failure on some tests with ARMCC, it will be replaced.
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@pan- can you provide info on the ARMCC tests that were failing? This could be indicative of a more serious problem. I would like to investigate this regardless of if function local static initialization is used by this patch.
Result: FAILUREYour command has finished executing! Here's what you wrote!
Outputmbed Build Number: 771 Test failed! |
Makes sure to initialize it, otherwize, it might be initialized in interrupt context.
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@bridadan I've updated the PR, it should be good now. |
| @@ -47,8 +47,15 @@ namespace | |||
| size_t case_failed = 0; | |||
| size_t case_failed_before = 0; | |||
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| handlers_t defaults = default_handlers; | |||
| handlers_t handlers = defaults; | |||
| handlers_t& defaults() { | |||
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Can handlers_t not be a class to and use the SingletonPtr paradigm for consistency?
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handlers_t is not a class, it is a POD.
The cause of the trouble is related to the initialization of these handlers: the initialization is made by copy of default_handlers.
This is not something done at compile time, the initialization happen at runtime.
That mean that the variables defaults and handlers will be kept even if there is no code using them after the initialization.
That also means that the variable default_handlers will be kept and the various function pointers which initialize it will be kept.
It is not possible to use directly a SingletonPtr here because there is no way to specify the initialization sequence.
On the other hand, it can be worked around by creating a new class derived from handlers_t which default initialize to default_handlers . Do you prefer this solution ?
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On the other hand, it can be worked around by creating a new class derived from handlers_t which default initialize to default_handlers . Do you prefer this solution ?
That would be great!
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@sg- I've updated the PR. Now, then handlers in utest_harness use a SingletonPtr. |
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/morph test |
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@mbed-bot: TEST HOST_OSES=ALL |
Result: SUCCESSYour command has finished executing! Here's what you wrote!
Outputmbed Build Number: 795 All builds and test passed! |
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[Build 884] |
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/morph test |
Result: SUCCESSYour command has finished executing! Here's what you wrote!
Outputmbed Build Number: 803 All builds and test passed! |
Release mbed-os-5.1.4 Changes: New Targets: 2504: [Disco_F769NI] adding new target [#2504] 2654: DELTA_DFBM_NQ620 platform porting [#2654] 2615: [MTM_MTCONNECT04S] Added support for MTM_MTCONNECT04S [#2615] 2548: Nucleof303ze [#2548] Fixes: 2678: Fixing NCS36510 compile on Linux #2678 2657: [MAX326xx] Removed echoing of characters and carriage return. #2657 2651: Use lp_timer to count time in the deepsleep tests #2651 2645: NUCLEO_F446ZE - Enable mbed5 release version #2645 2643: Fix thread self termination #2643 2634: Updated USBHost for library changes #2634 2633: Updated USBDevice to use Callback #2633 2630: Test names not dependent on disk location of root #2630 2624: CFSTORE Bugfix for realloc() moving KV area and cfstore_file_t data structures not being updated correctly #2624 2623: DISCO_L476VG - Add Serial Flow Control pins + add SERIAL_FC macro #2623 2617: STM32F2xx - Enable Serial Flow Control #2617 2613: Correctly providing directories to build_apis #2613 2607: Fix uvisor memory tracing #2607 2604: Tools - Fix fill section size variation #2604 2601: Adding ON Semiconductor copyright notice to source and header files. #2601 2597: [HAL] Fixed "intrinsic is deprecated" warnings #2597 2596: [HAL] Improve memory tracer #2596 2594: Fix TCPServer constructor #2594 2593: Add app config command line switch for test and make #2593 2589: [NUC472] Fix heap configuration error with armcc #2589 2588: Timing tests drift refactor #2588 2587: add PTEx pins as option for SPI on Hexiwear - for SD Card Interface #2587 2584: Set size of callback irq array to IrqCnt #2584 2583: github issue and PR templates #2583 2582: [GCC_CR] fix runtime hang for baremetal build #2582 2580: lwip - Add check for previously-bound socket #2580 2579: lwip - Fix handling of max sockets in socket_accept #2579 2578: Fix double free in NanostackInterface #2578 2576: Add smoke test that builds example programs with mbed-cli #2576 2575: tools-config! - Allow an empty or mal-formed config to be passed to the config system #2575 2562: Fix GCC lazy init race condition and add test #2562 2559: [utest]: Allow the linker to remove any part of utest if not used #2559 2545: Added define guards for SEQUENTIAL_FLASH_JOURNAL_MAX_LOGGED_BLOBS so #2545 2538: STM32F4xx - Add support of ADC internal channels (Temp, VRef, VBat) #2538 2521: [NUCLEO_F207ZG] Add MBED5 capability #2521 2514: Updated FlexCan and SAI SDK drivers #2514 2487: Runtime dynamic memory tracing #2487 2442: Malloc heap info #2442 2419: [STM32F1] Add asynchronous serial #2419 2393: [tools] Prevent trace-backs from incomplete args #2393 2245: Refactor export subsystem #2245 2130: stm32 : reduce number of device.h files #2130
This PR allow application to not embed any parts of utest if they don't use it.
Different changes where operated:
For more information see each commit.
This PR introduce the POD type
base_control_twhich is the base of the non PODcontrol_t.Every constant of the framework now use ``base_control_t
instead ofcontrol_t`The maximum has been made to makes these two type compatible and this change has transparent as possible.
In only one case the compatibility is not preserved: ternary operator.