EmbDev.net

Forum: ARM programming with GCC/GNU tools Changing C++ exception handling default catch functions


Author: Dan Quinz (danq)
Posted on:

Rate this post
0 useful
not useful
Hello all,

I have determined that the default exception handlers for uncaught
exceptions, memory allocation failures, etc. that come pre-compiled in
the libstdc++ library perform a write to 'stderr' when executed.  This
causes the linker to include 'open/read/write/close' along with a whole
bunch of string functions and greatly adds to the code and data size.
While there are run-time functions for redirecting these default
handlers to point to user code, the pre-compiled routines still get
linked in.

Is there a way to extract the default handlers from the libstdc++
library and replace them with my own versions so that no stream IO is
performed?

If anyone knows how to do this or knows where to get docs discussing
this in more detail, I'd appreciate it.

Cheers!

Daniel Quinz, P. Eng.

Acacetus Inc.

Author: Jim Kaz (ancaritha)
Posted on:

Rate this post
0 useful
not useful
Dan Quinz wrote:
> Is there a way to extract the default handlers from the libstdc++
> library and replace them with my own versions so that no stream IO is
> performed?


I've been wondering this as well!  I'd love to get rid of the exception
handling stuff to free up some flash and ram space.  I've been looking
into it but haven't made any progress.  Let me know if you find anything
interest please.

Thanks

Author: Jim Kaz (ancaritha)
Posted on:

Rate this post
0 useful
not useful
Actually, now that I think about it, I want to removed exception
handling entirely.  For instance:

0x124
c:/winarm/bin/../lib/gcc/arm-elf/4.1.2/../../../../arm-elf/lib/thumb/int 
erwork\libstdc++.a(eh_alloc.o)
                0x000196bc                __cxa_free_exception
                0x000196f8                __cxa_allocate_exception
 .text          0x000197e0       0x34
c:/winarm/bin/../lib/gcc/arm-elf/4.1.2/../../../../arm-elf/lib/thumb/int 
erwork\libstdc++.a(eh_call.o)
                0x000197e0                __cxa_call_terminate
 .text          0x00019814      0x154
c:/winarm/bin/../lib/gcc/arm-elf/4.1.2/../../../../arm-elf/lib/thumb/int 
erwork\libstdc++.a(eh_catch.o)
                0x0001981c                std::uncaught_exception()
                0x00019814                __cxa_get_exception_ptr
                0x00019830                __cxa_end_catch
                0x00019898                __cxa_begin_catch
 .text          0x00019968       0x7c
c:/winarm/bin/../lib/gcc/arm-elf/4.1.2/../../../../arm-elf/lib/thumb/int 
erwork\libstdc++.a(eh_exception.o)
                0x00019994                std::exception::~exception()
                0x00019968                std::exception::what() const
                0x000199d0
std::bad_exception::~bad_exception()
                0x000199bc
std::bad_exception::~bad_exception()
                0x000199a0
std::bad_exception::~bad_exception()
                0x00019988                std::exception::~exception()
                0x00019974                std::exception::~exception()
 .text          0x000199e4       0x10
c:/winarm/bin/../lib/gcc/arm-elf/4.1.2/../../../../arm-elf/lib/thumb/int 
erwork\libstdc++.a(eh_globals.o)
                0x000199e4                __cxa_get_globals_fast
                0x000199ec                __cxa_get_globals
 .text          0x000199f4       0x14
c:/winarm/bin/../lib/gcc/arm-elf/4.1.2/../../../../arm-elf/lib/thumb/int 
erwork\libstdc++.a(eh_type.o)
                0x000199f4                __cxa_current_exception_type


I do not need or want those.  However, I have added -fno-exceptions and
-fno-enforce-eh-specs to my makefile, and they still get included.  Any
one have any ideas?

Author: Dan Quinz (danq)
Posted on:

Rate this post
0 useful
not useful
Hi Jim,

I have found a compile and link setup that seems to eliminate all teh
exception handling code (as long as you don't use exceptions).

Here it is:


Compile:

arm-elf-g++ -c -ffunction-sections -fdata-sections -fno-builtin
-gdwarf-2 -O3 -Wall -Wcast-align -Wcast-qual -Wimplicit -Wpointer-arith
-Wswitch -Wredundant-decls -Wreturn-type -Wunused -mno-sched-prolog
-fno-rtti -fno-exceptions -mcpu=arm7tdmi -DXTAL_OSC=20000000
-DOS_USE_HOOK_CONTEXT=0 -DDBG_IMAGE=0 -DEXTERN_C_ENTER="extern \"C\" {"
-DEXTERN_C_LEAVE="} ;" -I. -Iinc.device -Iinc.hw_lpc -Iinc.task
-Iinc.void -Ilib.can -Ilib.clk_info -Ilib.dbg -Ilib.hw_can -Ilib.hw_uart
-Ilib.iap -Ilib.info -Ilib.os -Ilib.os_lpc -Ilib.reset -Ilib.sio
-Ilib.sio_uart -Ilib.sys -Ilib.task_main -Ilib.ui -Ilib.vic -Ilib.wdog
-Ibin.main -Wa,-adhlns=lib.wdog/lib.lpc/wdog_reset.lst -MD -MP
wdog_reset.cpp -o lib.lpc/wdog_reset.o

Link:

arm-elf-gcc -gdwarf-2 -O3 -MD -MP -nostartfiles -Wl,--gc-sections
-mcpu=arm7tdmi -I. -Wa,-adhlns=main.lst crt0.o main.o --output main.elf
-Wl,-Map=main.map,--cref -lstdc++ -lgcc -lc -lm -lnewlib-lpc
-Tlpc2129.ld
arm-elf-objcopy -O ihex main.elf main.hex
arm-elf-objdump -h -S -C main.elf > main.lss
arm-elf-nm -n main.elf > main.sym

When I compile and link with these options, the executable for my little
test program is only 2k with minimal RAM.  This is small when compared
to the original 40k+ FLASH and 2k+ RAM when exception handling is used.

Hope this helps you.

Cheers!

Dan





Jim Kaz wrote:
> Actually, now that I think about it, I want to removed exception
> handling entirely.  For instance:



>
> 0x124
> c:/winarm/bin/../lib/gcc/arm-elf/4.1.2/../../../../arm-elf/lib/thumb/int 
erwork\libstdc++.a(eh_alloc.o)
>                 0x000196bc                __cxa_free_exception
>                 0x000196f8                __cxa_allocate_exception
>  .text          0x000197e0       0x34
> c:/winarm/bin/../lib/gcc/arm-elf/4.1.2/../../../../arm-elf/lib/thumb/int 
erwork\libstdc++.a(eh_call.o)
>                 0x000197e0                __cxa_call_terminate
>  .text          0x00019814      0x154
> c:/winarm/bin/../lib/gcc/arm-elf/4.1.2/../../../../arm-elf/lib/thumb/int 
erwork\libstdc++.a(eh_catch.o)
>                 0x0001981c                std::uncaught_exception()
>                 0x00019814                __cxa_get_exception_ptr
>                 0x00019830                __cxa_end_catch
>                 0x00019898                __cxa_begin_catch
>  .text          0x00019968       0x7c
> c:/winarm/bin/../lib/gcc/arm-elf/4.1.2/../../../../arm-elf/lib/thumb/int 
erwork\libstdc++.a(eh_exception.o)
>                 0x00019994                std::exception::~exception()
>                 0x00019968                std::exception::what() const
>                 0x000199d0
> std::bad_exception::~bad_exception()
>                 0x000199bc
> std::bad_exception::~bad_exception()
>                 0x000199a0
> std::bad_exception::~bad_exception()
>                 0x00019988                std::exception::~exception()
>                 0x00019974                std::exception::~exception()
>  .text          0x000199e4       0x10
> c:/winarm/bin/../lib/gcc/arm-elf/4.1.2/../../../../arm-elf/lib/thumb/int 
erwork\libstdc++.a(eh_globals.o)
>                 0x000199e4                __cxa_get_globals_fast
>                 0x000199ec                __cxa_get_globals
>  .text          0x000199f4       0x14
> c:/winarm/bin/../lib/gcc/arm-elf/4.1.2/../../../../arm-elf/lib/thumb/int 
erwork\libstdc++.a(eh_type.o)
>                 0x000199f4                __cxa_current_exception_type
>
>
> I do not need or want those.  However, I have added -fno-exceptions and
> -fno-enforce-eh-specs to my makefile, and they still get included.  Any
> one have any ideas?

Author: Jim Kaz (ancaritha)
Posted on:

Rate this post
0 useful
not useful
Dan Quinz wrote:
> When I compile and link with these options, the executable for my little
> test program is only 2k with minimal RAM.  This is small when compared
> to the original 40k+ FLASH and 2k+ RAM when exception handling is used.
>
> Hope this helps you.
>
> Cheers!
>
> Dan

Sweet!  Thanks Dan!  I'll try this out as soon as I get the chance, but
sadly optimizing code space is the least of my concerns right now.  So
much to do and so little time... I hate deadlines :(

Author: Dan Quinz (danq)
Posted on:

Rate this post
0 useful
not useful
Jim, I also discovered that when you create an class object instance as
a static variable within a function, the compiler will use dynamic
memory allocation.  This in turn can throw an exception, which links in
all the additional stuff.  If you declare the object as global or
file-static, it does not.  Keep that in mind!

Ex:

Object obj ;             // Global, ok.

static Object obj;       // File static, ok.

void some_func (void)
{
  static Object obj;     // Will call dynamic allocation -> bigger
code!!

  Object obj;            // No dynamic call, so ok.
}

Perhaps this is what is causing the stuff to be linked in your case?

Cheers!

Dan



Jim Kaz wrote:
> Dan Quinz wrote:
>> When I compile and link with these options, the executable for my little
>> test program is only 2k with minimal RAM.  This is small when compared
>> to the original 40k+ FLASH and 2k+ RAM when exception handling is used.
>>
>> Hope this helps you.
>>
>> Cheers!
>>
>> Dan
>
> Sweet!  Thanks Dan!  I'll try this out as soon as I get the chance, but
> sadly optimizing code space is the least of my concerns right now.  So
> much to do and so little time... I hate deadlines :(

Reply

Entering an e-mail address is optional. If you want to receive reply notifications by e-mail, please log in.

Rules — please read before posting

  • Post long source code as attachment, not in the text
  • Posting advertisements is forbidden.

Formatting options

  • [c]C code[/c]
  • [avrasm]AVR assembler code[/avrasm]
  • [code]code in other languages, ASCII drawings[/code]
  • [math]formula (LaTeX syntax)[/math]




Bild automatisch verkleinern, falls nötig
Note: the original post is older than 6 months. Please don't ask any new questions in this thread, but start a new one.