SK-AM64: Bare metal C++ on A53 core of AM64xx is not calling global objects' constructors

Dario Pennisi

Part Number: SK-AM64

I am also having trouble running bare metal C++ on the A53 core of AM64xx. i'm on mcu_plus_sdk_am64x_08_05_00_24 and using gcc-arm-aarch64-none-eabi_9_2_1. the issue is that current SDK doesn't seem to handle init_array, fini_array and so on and as a consequence constructors for global objects are not called whereas those for every other object are.

i have worked this around by doing the following:

- make sure linker script includes the proper sections and that these are output on the elf file. this works but only if i inject the following in a section like ro_data:

PROVIDE_HIDDEN (__preinit_array_start = .);
KEEP (*(.preinit_array))
PROVIDE_HIDDEN (__preinit_array_end = .);
PROVIDE_HIDDEN (__init_array_start = .);
KEEP (*(SORT_BY_INIT_PRIORITY(.init_array.*) SORT_BY_INIT_PRIORITY(.ctors.*)))
KEEP (*(.init_array EXCLUDE_FILE (*crtbegin.o *crtbegin?.o *crtend.o *crtend?.o ) .ctors))
PROVIDE_HIDDEN (__init_array_end = .);
PROVIDE_HIDDEN (__fini_array_start = .);
KEEP (*(SORT_BY_INIT_PRIORITY(.fini_array.*) SORT_BY_INIT_PRIORITY(.dtors.*)))
KEEP (*(.fini_array EXCLUDE_FILE (*crtbegin.o *crtbegin?.o *crtend.o *crtend?.o ) .dtors))
PROVIDE_HIDDEN (__fini_array_end = .);

whereas if i create separate sections called .preinit_array, .init_array and .fini_array these are stripped by elf2rprc.js

- add the following code in my main:

extern void (*__preinit_array_start []) (void) __attribute__((weak));
extern void (*__preinit_array_end []) (void) __attribute__((weak));
extern void (*__init_array_start []) (void) __attribute__((weak));
extern void (*__init_array_end []) (void) __attribute__((weak));
extern void (*__fini_array_start []) (void) __attribute__((weak));
extern void (*__fini_array_end []) (void) __attribute__((weak));

void __libc_init_array (void)
{
size_t count;
size_t i;

count = __preinit_array_end - __preinit_array_start;
for (i = 0; i < count; i++)
__preinit_array_start[i] ();

count = __fini_array_end - __fini_array_start;
for (i = 0; i < count; i++)
__fini_array_start[i] ();

count = __init_array_end - __init_array_start;
for (i = 0; i < count; i++)
__init_array_start[i] ();
}

so... with the above everything works BUT:

1) it's ugly to have to inject those sections somewhere else... why is elf2rprc.js stripping them if they're in the properly named sections?

2) would be nice to have the above code merged in \mcu_plus_sdk_am64x_08_05_00_24\source\kernel\nortos\dpl\a53\boot_armv8.c in __system_start() in a future revision of the sdk. so that other people could have that working out of the box

over 1 year ago

0 Dario Pennisi over 1 year ago

Prodigy 95 points

of course i forgot to say that the added function shall be called as first thing in main()...

0 Ashwani Goel over 1 year ago

TI__Mastermind 22460 points

Hi,

Thanks for query.

Dario Pennisi said:
the issue is that current SDK doesn't seem to handle init_array

Can you please try with latest MCUSDK (www.ti.com/.../08.06.00.43) and update the results ?

Best Regards

Ashwani

0 Abhimanyu Singh over 1 year ago

Prodigy 223 points

I had the same problem a few months ago: https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1171562/sk-am64-a53-gcc-global-variable-constructor-not-called

I manually call the constructors at start of main as a workaround uptil now

0 Dario Pennisi over 1 year ago in reply to Abhimanyu Singh

Prodigy 95 points

Manually calling your constructors isn't enough as there are also some constructors to be called in libc.. if you inspect init_array structure you'll see.there's more than your objects

0 Dario Pennisi over 1 year ago in reply to Ashwani Goel

Prodigy 95 points

No it doesn't fix anything. You can tell by just looking at github.com/.../boot_armv8.c which doesn't contain any reference to init_array. As I mentioned in my post you should just insert the code I suggested in there AND fix the js script that strips the section...

0 Abhimanyu Singh over 1 year ago in reply to Dario Pennisi

Prodigy 223 points

Dario Pennisi said:
Manually calling your constructors isn't enough as there are also some constructors to be called in libc.. if you inspect init_array structure you'll see.there's more than your objects

I see, Yes that is a problem. Like Pekka Varis in the other thread said TI has no support for C++ yet, so I don't know if we can do anything about it. Maybe some of the TI guys can give us a timeline on when we will get support for C++.

I see you have already found a workaround. I don't anyways use the precompiled libraries for debugging purposes and also because I have already injected my own modifed interruprt API in the DLP source code for more tighter latencies. So ill copy your code in my boot_armv8.c next time when I will overhaul my code and hope if everyhting works. Thanks.

0 Tushar Thakur over 1 year ago

TI__Mastermind 29353 points

Hi Dario,

Dario Pennisi said:
i have worked this around by doing the following:

- make sure linker script includes the proper sections and that these are output on the elf file. this works but only if i inject the following in a section like ro_data:

Thanks for the detailed explanation.

As in the given e2e thread SK-AM64: A53 gc global variable constructor not called, it is already mentioned that currently we don't have examples and support for C++ bare metal on the A53 cores in the Sitara family.

Regards,

Tushar

Processors

Processors forum

SK-AM64: Bare metal C++ on A53 core of AM64xx is not calling global objects' constructors