Bare metal ARM Cross compiler for arm-none-eabi target without libunwind?

Bare metal ARM Cross compiler for arm-none-eabi target without libunwind?

[Fredrik Hederstierna]

Hi

We've been using a bare-metal 'arm-elf' cross-compiler toolchain over the years since GCC 2.95.x/GCC3/GCC4, and it has worked fine.
Now it seems though like the 'arm-elf' target seems obsolete, and we are trying to switch to 'arm-none-eabi'.

We use no standard-libs at all, we are really hard bare-metal with our own memcpy() etc.

Now when we try to build GCC 4.7.0 we get errors that LibGCC has dependencies on UnWind stuff we cannot get rid of.
We want to skip unwind support.

We try building toolchain with

--disable-shared --disable-libunwind-exceptions --with-newlib

(--disable-libunwind-exceptions seems obsoleted though)
(We only use newlib for headers only though, we dont use any code from it.)

We compile with flags on all files:

-fno-unwind-tables -fno-excpetions

Still we are getting link errors that LibGCC want to link with unwind-libs, and they are not present in libgcc libfile.

We also tried --with-system-libunwind, but same thing.

So, how can we get rid of all unwind-stuff for a real bare-metal arm-none-eabi cross compiler?
Someone suggested to put

char __aeabi_unwind_cpp_pr0[0];

in a C-file, but then it seems like division-stuff still thinks unwinding is supported and may fail?

(Similar thread at, but does not work for us.
http://gcc.gnu.org/ml/gcc-help/2009-10/msg00302.html)

Thanks and Best Regards,
Fredrik Hederstierna

Re: Bare metal ARM Cross compiler for arm-none-eabi target without libunwind?

[Ian Lance Taylor]

Fredrik Hederstierna <fredrik.hederstierna@securitas-direct.com> writes:

> Now when we try to build GCC 4.7.0 we get errors that LibGCC has dependencies on UnWind stuff we cannot get rid of.

Please always tell us the exact error messages.  When we have to guess
what is going wrong, we often guess wrong.

In fact in this case I can't even guess.  It's true that libgcc includes
code for stack unwinding, but I can't think of any reason why that
should matter when you are building gcc.

Ian

Re: Bare metal ARM Cross compiler for arm-none-eabi target without libunwind?

[Fredrik Hederstierna]

Hi

Sorry I maybe did not describe my problem clear enough.
It is not primary the gcc-toolchain that doesn't build.
It is the built bare metal arm libgcc that does not contain all symbols, and does not link with out compiled binary.

This is what the linker output

Linking sniffer2.elf ..
/usr/local/gcc/arm-elf-tools-4.7.0/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o): In function `get_eit_entry':
/home/fredrikh/arm_toolchain/toolchain-4.7.0/build/gcc/arm-none-eabi/thumb/libgcc/../../../../../gcc-4.7.0/libgcc/unwind-arm-common.inc:275: undefined reference to `__exidx_start'
/home/fredrikh/arm_toolchain/toolchain-4.7.0/build/gcc/arm-none-eabi/thumb/libgcc/../../../../../gcc-4.7.0/libgcc/unwind-arm-common.inc:275: undefined reference to `__exidx_end'
/usr/local/gcc/arm-elf-tools-4.7.0/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o): In function `unwind_phase2_forced':
/home/fredrikh/arm_toolchain/toolchain-4.7.0/build/gcc/arm-none-eabi/thumb/libgcc/../../../../../gcc-4.7.0/libgcc/unwind-arm-common.inc:319: undefined reference to `memcpy'
/home/fredrikh/arm_toolchain/toolchain-4.7.0/build/gcc/arm-none-eabi/thumb/libgcc/../../../../../gcc-4.7.0/libgcc/unwind-arm-common.inc:346: undefined reference to `memcpy'
/home/fredrikh/arm_toolchain/toolchain-4.7.0/build/gcc/arm-none-eabi/thumb/libgcc/../../../../../gcc-4.7.0/libgcc/unwind-arm-common.inc:376: undefined reference to `memcpy'
/usr/local/gcc/arm-elf-tools-4.7.0/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o): In function `unwind_phase2':
/home/fredrikh/arm_toolchain/toolchain-4.7.0/build/gcc/arm-none-eabi/thumb/libgcc/../../../../../gcc-4.7.0/libgcc/unwind-arm-common.inc:289: undefined reference to `abort'
/usr/local/gcc/arm-elf-tools-4.7.0/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o): In function `__gnu_Unwind_RaiseException':
/home/fredrikh/arm_toolchain/toolchain-4.7.0/build/gcc/arm-none-eabi/thumb/libgcc/../../../../../gcc-4.7.0/libgcc/unwind-arm-common.inc:420: undefined reference to `memcpy'
/usr/local/gcc/arm-elf-tools-4.7.0/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o): In function `__gnu_Unwind_Resume':
/home/fredrikh/arm_toolchain/toolchain-4.7.0/build/gcc/arm-none-eabi/thumb/libgcc/../../../../../gcc-4.7.0/libgcc/unwind-arm-common.inc:505: undefined reference to `abort'
/usr/local/gcc/arm-elf-tools-4.7.0/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o): In function `__gnu_Unwind_Backtrace':
/home/fredrikh/arm_toolchain/toolchain-4.7.0/build/gcc/arm-none-eabi/thumb/libgcc/../../../../../gcc-4.7.0/libgcc/unwind-arm-common.inc:560: undefined reference to `memcpy'
/usr/local/gcc/arm-elf-tools-4.7.0/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(pr-support.o): In function `_Unwind_GetDataRelBase':
/home/fredrikh/arm_toolchain/toolchain-4.7.0/build/gcc/arm-none-eabi/thumb/libgcc/../../../../../gcc-4.7.0/libgcc/config/arm/pr-support.c:394: undefined reference to `abort'
/usr/local/gcc/arm-elf-tools-4.7.0/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(pr-support.o): In function `_Unwind_GetTextRelBase':
/home/fredrikh/arm_toolchain/toolchain-4.7.0/build/gcc/arm-none-eabi/thumb/libgcc/../../../../../gcc-4.7.0/libgcc/config/arm/pr-support.c:400: undefined reference to `abort'
make[1]: *** [../../../build/sniffer2/sniffer2.elf] Error 1
make[1]: Leaving directory `/home/fredrikh/workspace/product/app/sniffer2'
make: *** [all] Error 2

The first problem with __exidx_start we could try workaround by adding a few lines to linker-script.

__exidx_start = .;
.ARM.exidx   : { *(.ARM.exidx* .gnu.linkonce.armexidx.*) }
__exidx_end = .;

But since we have an extreme bare metal system with custom memcpy(), no abort() etc,
the libgcc does not link.

We've tried to compile all files without unwind info nor exceptions.

If we build toolchain with 'arm-elf' taget instead, it works fine.

I submit script to build non-working toolchain.
If we just change to "TARGET=arm-none-elf" instead and add "--enable-obsolete" to configure, then it works fine.
It seems to TARGET=arm-none-eabi" introduces dependencies of libc functions like memcpy() and abort() that did not excist in previous versions.
Also I don't understand how I could work-around these dependencies or get rid of them.

------------- SCRIPT START BUILD TOOLCHAIN ARM EABI -------------
#!/bin/sh

set -e -x 

TARGET=arm-none-eabi

BINUTILS_VERSION=2.22
GCC_VERSION=4.7.0
NEWLIB_VERSION=1.20.0

DEST="/usr/local/gcc/arm-elf-tools-$GCC_VERSION"

BINUTILS_DIR="binutils-$BINUTILS_VERSION" 
GCC_DIR="gcc-$GCC_VERSION" 
NEWLIB_DIR="newlib-$NEWLIB_VERSION" 

# set rwx access

umask 022 

# unpack tar-balls

rm -fr "$BINUTILS_DIR" "$GCC_DIR" "$NEWLIB_DIR"
tar xvjf "binutils-$BINUTILS_VERSION.tar.bz2" 
tar xvjf "gcc-$GCC_VERSION.tar.bz2" 
tar xvzf "newlib-$NEWLIB_VERSION.tar.gz" 

cd "$GCC_DIR"
ln -s "../$NEWLIB_DIR/newlib" newlib 
ln -s "../$NEWLIB_DIR/libgloss" libgloss 
cd ..

rm -fr build 
mkdir -p build/binutils build/gcc build/newlib

# Build binutils

cd build/binutils 
"../../$BINUTILS_DIR/configure" --target="$TARGET" --prefix="$DEST" --disable-nls
make LDFLAGS=-s all install 

# Build GCC

cd ../gcc 
PATH="$DEST/bin:$PATH" 
"../../$GCC_DIR/configure" --enable-languages=c --target="$TARGET" --prefix="$DEST" --with-gnu-as --with-gnu-ld --disable-nls --disable-shared --with-newlib --disable-libunwind-exceptions --enable-target-optspace
make LDFLAGS=-s all all-gcc install install-gcc

# Remove uncompressed sources

cd ../.. 
rm -fr "$BINUTILS_DIR" "$GCC_DIR" "$NEWLIB_DIR" build

------------- SCRIPT END -------------

Thanks and Best Regards/Fredrik




-----Ian Lance Taylor <iant@google.com> wrote: -----

>To: Fredrik Hederstierna <fredrik.hederstierna@securitas-direct.com>
>From: Ian Lance Taylor <iant@google.com>
>Date: 03/26/2012 10:53PM
>Cc: gcc-help@gcc.gnu.org
>Subject: Re: Bare metal ARM Cross compiler for arm-none-eabi target
>without libunwind?
>
>Fredrik Hederstierna <fredrik.hederstierna@securitas-direct.com>
>writes:  > Now when we try to build GCC 4.7.0 we get errors that
>LibGCC has dependencies on UnWind stuff we cannot get rid of.  Please
>always tell us the exact error messages.  When we have to guess what
>is going wrong, we often guess wrong.  In fact in this case I can't
>even guess.  It's true that libgcc includes code for stack unwinding,
>but I can't think of any reason why that should matter when you are
>building gcc.  Ian 

Re: Bare metal ARM Cross compiler for arm-none-eabi target without libunwind?

[Ian Lance Taylor]

Fredrik Hederstierna <fredrik.hederstierna@securitas-direct.com> writes:

> /usr/local/gcc/arm-elf-tools-4.7.0/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o): In function `get_eit_entry':

You need to find out why unwind-arm.o is being included in your link.
You could easily remove it from libgcc.a, but that would just leave you
with some other undefined symbol.  unwind-arm.o is only being pulled in
because it defines some symbol that your program refers to.  What
symbol?

If you are using the GNU linker you can find out easily enough by adding
-Wl,-M to your link command.  That will produce a map file.  The first
part of the file will be a list starting with "Archive member included
because of file (symbol)".  Look for the symbol that causes unwind-arm.o
to be included.

Ian

Re: Bare metal ARM Cross compiler for arm-none-eabi target without libunwind?

[Fredrik Hederstierna]

Hi

We generate the map-file, the content tells that (if I understand correctly)

"_divdi3.o"  use "__aeabi_unwind_cpp_pr0" which resides in "unwind-arm.o".

Is it really correct that we need unwind-support if just using division?
Could it be that _divdi3 can 'throw' division-by-zero 'exception' ?
(We have overloaded div0: "void __div0(void) { assert(0); }" so we dont want unwinding here anyway...)

If I declare this symbol myself in a file as

char __aeabi_unwind_cpp_pr0[0];
 
the binary links successfully, but I'm not sure its 100% working and correct.
(I have some problems with crashes on the new built eabi target, but could also be other reasons.)


----------------MAP FILE----------------

Archive member included because of file (symbol)
 
/usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_thumb1_case_uqi.o)
                              ../../../build/sniffer2/datetime_utils.o (__gnu_thumb1_case_uqi)
/usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_thumb1_case_uhi.o)
                              ../../../build/sniffer2/radio_cc110x.o (__gnu_thumb1_case_uhi)
/usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_udivsi3.o)
                              ../../../build/sniffer2/printf.o (__aeabi_uidiv)
/usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_divsi3.o)
                              ../../../build/sniffer2/app_start.o (__aeabi_idiv)
/usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_dvmd_tls.o)
                              /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_udivsi3.o) (__aeabi_idiv0)
/usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_aeabi_ldivmod.o)
                              ../../../build/sniffer2/91x_uart.o (__aeabi_ldivmod)
/usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_aeabi_uldivmod.o)
                              ../../../build/sniffer2/sleep.o (__aeabi_uldivmod)
/usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_muldi3.o)
                              ../../../build/sniffer2/sleep.o (__aeabi_lmul)
/usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(bpabi.o)
                              /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_aeabi_ldivmod.o) (__gnu_ldivmod_helper)
/usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_divdi3.o)
                              /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(bpabi.o) (__divdi3)
/usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_udivdi3.o)
                              /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(bpabi.o) (__udivdi3)
/usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
                              /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_divdi3.o) (__aeabi_unwind_cpp_pr0)
/usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
                              /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o) (restore_core_regs)
/usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(pr-support.o)
                              /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o) (__gnu_unwind_execute)
/usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_clzsi2.o)
                              /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_divdi3.o) (__clzsi2)
 
-------------//...//-------------
 
.ARM.extab     0x00000000        0x0 /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_divdi3.o)
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.ARM.extab     0x00000000        0x0 /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_udivdi3.o)
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-------------//...//-------------
 
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                0x00009260                __gnu_Unwind_Restore_WMMXD
                0x000092a4                __gnu_Unwind_Save_WMMXD
                0x000092e8                __gnu_Unwind_Restore_WMMXC
                0x000092fc                __gnu_Unwind_Save_WMMXC
                0x00009310                ___Unwind_RaiseException
                0x00009310                _Unwind_RaiseException
                0x0000933c                ___Unwind_Resume
                0x0000933c                _Unwind_Resume
                0x00009368                _Unwind_Resume_or_Rethrow
                0x00009368                ___Unwind_Resume_or_Rethrow
                0x00009394                ___Unwind_ForcedUnwind
                0x00009394                _Unwind_ForcedUnwind
                0x000093c0                _Unwind_Backtrace
                0x000093c0                ___Unwind_Backtrace
.text          0x000093ec      0x35c /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(pr-support.o)
                0x00009442                __gnu_unwind_execute
                0x000096ec                __gnu_unwind_frame
                0x00009716                _Unwind_GetRegionStart
                0x00009724                _Unwind_GetLanguageSpecificData
                0x0000973c                _Unwind_GetDataRelBase
                0x00009742                _Unwind_GetTextRelBase
 
-------------//...//-------------
 
 
.ARM.exidx      0x040004c0       0xf0 load address 0x0000a6f4
.ARM.exidx     0x040004c0        0x8 /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_divdi3.o)
.ARM.exidx     0x040004c8        0x8 /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_udivdi3.o)
.ARM.exidx     0x040004d0       0xa8 /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
                                 0xd8 (size before relaxing)
.ARM.exidx     0x04000578       0x38 /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(pr-support.o)
                                 0x48 (size before relaxing)
 
.ARM.extab      0x040005b0       0x78 load address 0x0000a7e4
.ARM.extab     0x040005b0       0x54 /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
.ARM.extab     0x04000604       0x24 /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(pr-support.o)
 
-------------//...//-------------
 
_Unwind_Backtrace                                 /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
_Unwind_Complete                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
_Unwind_DeleteException                           /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
_Unwind_ForcedUnwind                              /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
_Unwind_GetCFA                                    /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
_Unwind_GetDataRelBase                            /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(pr-support.o)
_Unwind_GetLanguageSpecificData                   /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(pr-support.o)
_Unwind_GetRegionStart                            /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(pr-support.o)
_Unwind_GetTextRelBase                            /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(pr-support.o)
_Unwind_RaiseException                            /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
_Unwind_Resume                                    /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
_Unwind_Resume_or_Rethrow                         /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
_Unwind_VRS_Get                                   /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(pr-support.o)
_Unwind_VRS_Pop                                   /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(pr-support.o)
_Unwind_VRS_Set                                   /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(pr-support.o)
__FMI_EraseSector                                 ../../../build/sniffer2/crashdump.o
__FMI_WaitForLastOperation                        ../../../build/sniffer2/crashdump.o
__FMI_WriteHalfWord                               ../../../build/sniffer2/crashdump.o
__FMI_WriteProtectionCmd                          ../../../build/sniffer2/crashdump.o
___Unwind_Backtrace                               /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
___Unwind_ForcedUnwind                            /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
___Unwind_RaiseException                          /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
___Unwind_Resume                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
___Unwind_Resume_or_Rethrow                       /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
 
-------------//...//-------------
 
__aeabi_unwind_cpp_pr0                            /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(pr-support.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_udivdi3.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_divdi3.o)
__aeabi_unwind_cpp_pr1                            /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(pr-support.o)
__aeabi_unwind_cpp_pr2                            /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
 
-------------//...//-------------
 
__cxa_begin_cleanup                               /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
__cxa_call_unexpected                             /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
__cxa_type_match                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
 
-------------//...//-------------
 
__exidx_end                                       /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
__exidx_start                                     /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
 
-------------//...//-------------

__gnu_Unwind_Backtrace                            /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
__gnu_Unwind_Find_exidx                           /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
__gnu_Unwind_ForcedUnwind                         /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
__gnu_Unwind_RaiseException                       /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
__gnu_Unwind_Restore_VFP                          /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
__gnu_Unwind_Restore_VFP_D                        /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
__gnu_Unwind_Restore_VFP_D_16_to_31               /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
__gnu_Unwind_Restore_WMMXC                        /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
__gnu_Unwind_Restore_WMMXD                        /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
__gnu_Unwind_Resume                               /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
__gnu_Unwind_Resume_or_Rethrow                    /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
__gnu_Unwind_Save_VFP                             /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
__gnu_Unwind_Save_VFP_D                           /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
__gnu_Unwind_Save_VFP_D_16_to_31                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
__gnu_Unwind_Save_WMMXC                           /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
__gnu_Unwind_Save_WMMXD                           /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
__gnu_ldivmod_helper                              /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(bpabi.o)
 
-------------//...//-------------
 
__gnu_thumb1_case_uqi                             /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(_thumb1_case_uqi.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
 
__gnu_unwind_execute                              /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(pr-support.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
__gnu_unwind_frame                                /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(pr-support.o)
 
__restore_core_regs                               /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
 
abort                                             /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(pr-support.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
 
memcpy                                            /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
 
restore_core_regs                                 /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(libunwind.o)
                                                  /usr/local/gcc/arm-elf-tools-4.7.0-eabi/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o)
 
-------------MAP FILE END-------------

Do you have any idea how to proceed?
Thanks!/Fredrik


-----Ian Lance Taylor <iant@google.com> wrote: -----
To: Fredrik Hederstierna <fredrik.hederstierna@securitas-direct.com>
From: Ian Lance Taylor <iant@google.com>
Date: 03/27/2012 03:30PM
Cc: gcc-help@gcc.gnu.org
Subject: Re: Bare metal ARM Cross compiler for arm-none-eabi target without libunwind?

Fredrik Hederstierna <fredrik.hederstierna@securitas-direct.com> writes:

> /usr/local/gcc/arm-elf-tools-4.7.0/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o): In function `get_eit_entry':

You need to find out why unwind-arm.o is being included in your link.
You could easily remove it from libgcc.a, but that would just leave you
with some other undefined symbol.  unwind-arm.o is only being pulled in
because it defines some symbol that your program refers to.  What
symbol?

If you are using the GNU linker you can find out easily enough by adding
-Wl,-M to your link command.  That will produce a map file.  The first
part of the file will be a list starting with "Archive member included
because of file (symbol)".  Look for the symbol that causes unwind-arm.o
to be included.

Ian

Re: Bare metal ARM Cross compiler for arm-none-eabi target without libunwind?

[Thomas Martitz]

Am 28.03.2012 09:09, schrieb Fredrik Hederstierna:
> Hi
>
> We generate the map-file, the content tells that (if I understand correctly)
>
> "_divdi3.o"  use "__aeabi_unwind_cpp_pr0" which resides in "unwind-arm.o".
>
> Is it really correct that we need unwind-support if just using division?
> Could it be that _divdi3 can 'throw' division-by-zero 'exception' ?
> (We have overloaded div0: "void __div0(void) { assert(0); }" so we dont want unwinding here anyway...)
>
> If I declare this symbol myself in a file as
>
> char __aeabi_unwind_cpp_pr0[0];
>
> the binary links successfully, but I'm not sure its 100% working and correct.
> (I have some problems with crashes on the new built eabi target, but could also be other reasons.)
>
>

We (Rockbox) also faced this problem and patch gcc to leave exceptions 
out[1].

Best regards.

[1]: 
http://git.rockbox.org/?p=www.git;a=blob;f=gcc/rockbox-multilibs-noexceptions-arm-elf-eabi-gcc-4.4.2_1.diff;h=3397153495dbc4486f9a32c024a3264bf66708d3;hb=HEAD

Re: Bare metal ARM Cross compiler for arm-none-eabi target without libunwind?

[Andrew Haley]

On 03/28/2012 08:09 AM, Fredrik Hederstierna wrote:

> We generate the map-file, the content tells that (if I understand correctly)
> 
> "_divdi3.o"  use "__aeabi_unwind_cpp_pr0" which resides in "unwind-arm.o".
> 
> Is it really correct that we need unwind-support if just using division?
> Could it be that _divdi3 can 'throw' division-by-zero 'exception' ?
> (We have overloaded div0: "void __div0(void) { assert(0); }" so we dont want unwinding here anyway...)

I suspect (but you'll have to check) that this is because _divdi3 is
compiled with exceptions, and this is indeed because division by zero
might throw.  The simplest fix is to compile it without exceptions.
The correct fix is to make unwinding work on your platform.

Andrew.

Re: Bare metal ARM Cross compiler for arm-none-eabi target without libunwind?

[Fredrik Hederstierna]

>> We generate the map-file, the content tells that (if I understand correctly)
>> 
>> "_divdi3.o"  use "__aeabi_unwind_cpp_pr0" which resides in "unwind-arm.o".
>> 
>> Is it really correct that we need unwind-support if just using division?
>> Could it be that _divdi3 can 'throw' division-by-zero 'exception' ?
>> (We have overloaded div0: "void __div0(void) { assert(0); }" so we dont want unwinding here anyway...)
>

>I suspect (but you'll have to check) that this is because _divdi3 is
>compiled with exceptions, and this is indeed because division by zero
>might throw.  The simplest fix is to compile it without exceptions.
>The correct fix is to make unwinding work on your platform.

Sorry I don't fully agree, we don't want the unwinding stuff.
We are very short on flash memory, and we do not want to waste bytes on unnecessary code.

Also, why does it work with 'arm-none-elf', shouldn't it be the same regarding __div0?
The correct solution would be to exclude dependency to unwind from _divdi3 when building a bare metal toolchain.

Thanks to Thomas Martitz for the proposed patch.
This patch makes libgcc to be compiled with "-fno-exception" instead of "-fexception".

I propose an even better patch maybe to re-introduce a configure option alike "--disable-libunwind-exceptions" or similar.
This configuration option could control this "-f(no)-exception" flag when compiling GCC toolchain.
Then it could be optional for the developer to be able to exclude the exceptions on a extreme bare metal toolchain.

If you think such a patch would be accepted by the community, I could think of spending some time to fix it myself.

Thanks for you feedback and help, its most appreciated!
/Fredrik Hederstierna

Re: Bare metal ARM Cross compiler for arm-none-eabi target without libunwind?

[Sebastian Huber]

On 03/28/2012 11:33 AM, Fredrik Hederstierna wrote:
>
>>> We generate the map-file, the content tells that (if I understand correctly)
>>>
>>> "_divdi3.o"  use "__aeabi_unwind_cpp_pr0" which resides in "unwind-arm.o".
>>>
>>> Is it really correct that we need unwind-support if just using division?
>>> Could it be that _divdi3 can 'throw' division-by-zero 'exception' ?
>>> (We have overloaded div0: "void __div0(void) { assert(0); }" so we dont want unwinding here anyway...)
>>
>
>> I suspect (but you'll have to check) that this is because _divdi3 is
>> compiled with exceptions, and this is indeed because division by zero
>> might throw.  The simplest fix is to compile it without exceptions.
>> The correct fix is to make unwinding work on your platform.
>
> Sorry I don't fully agree, we don't want the unwinding stuff.
> We are very short on flash memory, and we do not want to waste bytes on unnecessary code.
>
> Also, why does it work with 'arm-none-elf', shouldn't it be the same regarding __div0?
> The correct solution would be to exclude dependency to unwind from _divdi3 when building a bare metal toolchain.

For me it is also unclear why we need this division by zero exception in the 
bare metal tool chain.  See also:

http://gcc.gnu.org/ml/gcc-help/2011-03/msg00149.html

-- 
Sebastian Huber, embedded brains GmbH

Address : Obere Lagerstr. 30, D-82178 Puchheim, Germany
Phone   : +49 89 18 90 80 79-6
Fax     : +49 89 18 90 80 79-9
E-Mail  : sebastian.huber@embedded-brains.de
PGP     : Public key available on request.

Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.

Re: Bare metal ARM Cross compiler for arm-none-eabi target without libunwind?

[Fredrik Hederstierna]

-----Fredrik Hederstierna/INT/SE/DIR/SECURITAS wrote: -----
To: aph@redhat.com
From: Fredrik Hederstierna/INT/SE/DIR/SECURITAS
Date: 03/28/2012 11:33AM
Cc: gcc-help@gcc.gnu.org
Subject: Re: Bare metal ARM Cross compiler for arm-none-eabi target without libunwind?

>> We generate the map-file, the content tells that (if I understand correctly)
>> 
>> "_divdi3.o"  use "__aeabi_unwind_cpp_pr0" which resides in "unwind-arm.o".
>> 
>> Is it really correct that we need unwind-support if just using division?
>> Could it be that _divdi3 can 'throw' division-by-zero 'exception' ?
>> (We have overloaded div0: "void __div0(void) { assert(0); }" so we dont want unwinding here anyway...)
>

>I suspect (but you'll have to check) that this is because _divdi3 is
>compiled with exceptions, and this is indeed because division by zero
>might throw.  The simplest fix is to compile it without exceptions.
>The correct fix is to make unwinding work on your platform.

I've been investigating the libgcc sources, what do you think of something alike this solution

Today in "gcc/libgcc/Makefile.in" its filtered on which functions that should be compiled with unwind-info:

  # These might cause a divide overflow trap and so are compiled with
  # unwinder info.
  LIB2_DIVMOD_FUNCS = _divdi3 _moddi3 _udivdi3 _umoddi3 _udiv_w_sdiv _udivmoddi4

What if this could be overridden by configuration option?

Eg.

+# Check if we want to exclude unwind support.
+ifeq ($(enable_libunwind_exceptions),yes)
   # These might cause a divide overflow trap and so are compiled with
   # unwinder info.
   LIB2_DIVMOD_FUNCS = _divdi3 _moddi3 _udivdi3 _umoddi3 _udiv_w_sdiv _udivmoddi4
+endif

In this case all libgcc will be build 'normally' without extra unwind build stuff?
The 'enable_libunwind_exceptions' have to be set somehow when running 'configure'.

Thanks/Fredrik

Re: Bare metal ARM Cross compiler for arm-none-eabi target without libunwind?

[Sebastian Huber]

On 03/28/2012 12:26 PM, Fredrik Hederstierna wrote:
> I've been investigating the libgcc sources, what do you think of something alike this solution
>
> Today in "gcc/libgcc/Makefile.in" its filtered on which functions that should be compiled with unwind-info:
>
>    # These might cause a divide overflow trap and so are compiled with
>    # unwinder info.
>    LIB2_DIVMOD_FUNCS = _divdi3 _moddi3 _udivdi3 _umoddi3 _udiv_w_sdiv _udivmoddi4
>
> What if this could be overridden by configuration option?

In addition to that it would be nice if the target configuration can override 
this also.

-- 
Sebastian Huber, embedded brains GmbH

Address : Obere Lagerstr. 30, D-82178 Puchheim, Germany
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Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.

Re: Bare metal ARM Cross compiler for arm-none-eabi target without libunwind?

[Fredrik Hederstierna]

>I suspect (but you'll have to check) that this is because _divdi3 is
>compiled with exceptions, and this is indeed because division by zero
>might throw.  The simplest fix is to compile it without exceptions.
>The correct fix is to make unwinding work on your platform.

I found this on gcc-patches from 2011-11, maybe it does solve something also for ARM?

"[patch, ia64, libgcc] Patch to fix libunwind build on IA64"
http://gcc.gnu.org/ml/gcc-patches/2011-11/msg01926.html

The patch is basically modding Makefile.in as:

 # Build LIBUNWIND.
 
-c_flags := -fexceptions
+c_flags := -fno-exceptions

I though think my patch proposal could be interesting though to be able to control it from configure.

Thanks &Best Regards/Fredrik

Re: Bare metal ARM Cross compiler for arm-none-eabi target without libunwind?

[Fredrik Hederstierna]

> /usr/local/gcc/arm-elf-tools-4.7.0/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o): In function `get_eit_entry':

I did a patch in libgcc "Makefile.in" that is very similar to Martin's:

This works:

# Build LIB2_DIVMOD_FUNCS.
+ ifeq ($(enable_libgcc_libunwind_exceptions),yes)
+ LIB2_DIVMOD_CFLAGS := -fexceptions -fnon-call-exceptions
+ else
+ LIB2_DIVMOD_CFLAGS := -fno-exceptions -fno-non-call-exceptions
+ endif
lib2-divmod-o = $(patsubst %,%$(objext),$(LIB2_DIVMOD_FUNCS))
$(lib2-divmod-o): %$(objext): $(srcdir)/libgcc2.c
	$(gcc_compile) -DL$* -c $< \
-	  -fexceptions -fnon-call-exceptions $(vis_hide)
+	  $(LIB2_DIVMOD_CFLAGS) $(vis_hide)
libgcc-objects += $(lib2-divmod-o)

ifeq ($(enable_shared),yes)
lib2-divmod-s-o = $(patsubst %,%_s$(objext),$(LIB2_DIVMOD_FUNCS))
$(lib2-divmod-s-o): %_s$(objext): $(srcdir)/libgcc2.c
	$(gcc_s_compile) -DL$* -c $< \
-	  -fexceptions -fnon-call-exceptions
+	   $(LIB2_DIVMOD_CFLAGS)
libgcc-s-objects += $(lib2-divmod-s-o)
endif


It seems to work fine, now I guess some work has to be done to add argument to configure-command line to be truly accepted.
I invented the new argument option 'enable_libgcc_libunwind_exceptions' to not mix-up with the old 'without-libunwind-exceptions'.
(Though I have some problems trying to add new arguments to configure, it does not seem to work fully yet...)

Thanks and Best Regards/Fredrik

Re: Bare metal ARM Cross compiler for arm-none-eabi target without libunwind?

[Ian Lance Taylor]

Fredrik Hederstierna <fredrik.hederstierna@securitas-direct.com> writes:

> We generate the map-file, the content tells that (if I understand correctly)
>
> "_divdi3.o"  use "__aeabi_unwind_cpp_pr0" which resides in "unwind-arm.o".

I took a look at an ARM build I happened to have, and it looks like
there is a relocation for that symbol in the ARM.exidx section.  Looking
into the compiler and assembler, it looks like that relocation is
generated for every object file compiled with the options -fexceptions
or -funwind-tables.  The division routines in libgcc are always compiled
with -fexceptions -fnon-call-exceptions.  So that is where this is
coming from.

> If I declare this symbol myself in a file as
> 
> char __aeabi_unwind_cpp_pr0[0];
>  
> the binary links successfully, but I'm not sure its 100% working and correct.

As far as I can see that should not cause any problems.  The only time
it would cause trouble would be if you had a signal handler that was
invoked due to a division by zero, and that signal handler threw an
exception.

The only other approach I see here would be to edit the libgcc Makefile
to remove -fexceptions -fnon-call-exceptions, or otherwise adjust the
source code to change the way these files are compiled.

Ian

Re: Bare metal ARM Cross compiler for arm-none-eabi target without libunwind?

[Fredrik Hederstierna]

Regarding bare-metal ARM cross-compiler toolchain without libunwind.
Patch now proposed to gcc-patches:

http://gcc.gnu.org/ml/gcc-patches/2012-04/msg00720.html

Thanks & Best Regards Fredrik

-----Ian Lance Taylor <iant@google.com> wrote: -----
To: Fredrik Hederstierna <fredrik.hederstierna@securitas-direct.com>
From: Ian Lance Taylor <iant@google.com>
Date: 03/27/2012 03:30PM
Cc: gcc-help@gcc.gnu.org
Subject: Re: Bare metal ARM Cross compiler for arm-none-eabi target without libunwind?

Fredrik Hederstierna <fredrik.hederstierna@securitas-direct.com> writes:

> /usr/local/gcc/arm-elf-tools-4.7.0/lib/gcc/arm-none-eabi/4.7.0/thumb//libgcc.a(unwind-arm.o): In function `get_eit_entry':

You need to find out why unwind-arm.o is being included in your link.
You could easily remove it from libgcc.a, but that would just leave you
with some other undefined symbol.  unwind-arm.o is only being pulled in
because it defines some symbol that your program refers to.  What
symbol?

If you are using the GNU linker you can find out easily enough by adding
-Wl,-M to your link command.  That will produce a map file.  The first
part of the file will be a list starting with "Archive member included
because of file (symbol)".  Look for the symbol that causes unwind-arm.o
to be included.

Ian