Compiler output -v:

Using built-in specs.
COLLECT_GCC=aarch64-elf-gcc.exe
COLLECT_LTO_WRAPPER=c:/git/s74100gcc11/s74100cpu/s7p.tools/aarch64_gcc_elf_11.2.0/bin/../libexec/gcc/aarch64-elf/11.2.0/lto-wrapper.exe
Target: aarch64-elf
Configured with: ../../gcc-11.2.0//configure --host=x86_64-w64-mingw32 --build=x86_64-w64-mingw32 --prefix=/build/aarch64-elf_11.2.0-1/cross-gcc/aarch64-elf --target=aarch64-elf --disable-nls --enable-multilib --with-multilib-list=lp64,ilp32 --enable-languages=c,c++ --disable-decimal-float --with-sysroot=/build/aarch64-elf_11.2.0-1/cross-gcc/aarch64-elf --without-headers --disable-shared --disable-threads --disable-lto --disable-libmudflap --disable-libssp --disable-libgomp --disable-libffi --disable-libstdcxx-pch --disable-win32-registry --with-host-libstdcxx='-static-libgcc -Wl,-Bstatic,-lstdc++,-Bdynamic -lm' --with-newlib --with-gcc --with-gnu-as --with-gnu-ld --with-gmp=/build/aarch64-elf_11.2.0-1/host --with-mpfr=/build/aarch64-elf_11.2.0-1/host --with-mpc=/build/aarch64-elf_11.2.0-1/host --with-isl=/build/aarch64-elf_11.2.0-1/host --with-zstd=/build/aarch64-elf_11.2.0-1/host : (reconfigured) ../../gcc-11.2.0//configure --host=x86_64-w64-mingw32 --build=x86_64-w64-mingw32 --enable-languages=c,c++ --enable-multilib --with-multilib-list=lp64,ilp32 --disable-lto --disable-libmudflap --disable-libssp --disable-libgomp --disable-libffi --with-newlib --with-gcc --with-gnu-ld --with-gnu-as --with-stabs --disable-shared --disable-threads --disable-win32-registry --disable-nls --disable-libstdcxx-pch --with-host-libstdcxx='-static-libgcc -Wl,-Bstatic,-lstdc++,-Bdynamic -lm' --target=aarch64-elf --prefix=/build/aarch64-elf_11.2.0-1/cross-gcc/aarch64-elf --with-gmp=/build/aarch64-elf_11.2.0-1/host --with-mpfr=/build/aarch64-elf_11.2.0-1/host --with-mpc=/build/aarch64-elf_11.2.0-1/host --with-isl=/build/aarch64-elf_11.2.0-1/host --with-zstd=/build/aarch64-elf_11.2.0-1/host --with-sysroot=/build/aarch64-elf_11.2.0-1/cross-gcc/aarch64-elf
Thread model: single
Supported LTO compression algorithms: zlib zstd
gcc version 11.2.0 (GCC)


The problem occurs on our Windows to Arm Cortex A53 Cross compile.
No errors or warnings during compilation. We have enabled alignment check for some purposes and we cannot disable it. This problem occurs also in C++, not only in C (iam sorry if i put the bug wrong).

(for readability i removed all defines and link inputs)
Command Line: 
../../../../aarch64_gcc_elf_11.2.0/bin/aarch64-elf-gcc           -fno-builtin    -c    -std=gnu11    -Wno-pointer-to-int-cast    -Wno-int-to-pointer-cast    -Wno-maybe-uninitialized       -Werror                
-mabi=ilp32 -march=armv8-a+crypto+crc -mtune=cortex-a53 -mstrict-align -mno-outline-atomics      -Werror=return-type   -Werror=format   -Werror=address   -Werror=array-bounds   -Werror=format-extra-args   -Werror=init-self   -Wno-error=array-bounds        -Wno-error=stringop-overflow     -Wno-error=free-nonheap-object       -mlittle-endian   -fno-common   -fno-merge-constants   -ffunction-sections   -fdata-sections   -fno-toplevel-reorder   -O0      -Werror      -nostdinc   -ggdb

For some reason the GCC 11.2 is using floating point register instructions to optimize initialization of structs if a lot of members are initialized with the same constant successively. 
The problem is that the GCC generates the following instructions:
stp   q0, q0, [x0]  //128 bit alignment required problem -> usually we use 64 bit 
                    //alignment
str   q0, [x0, #32] // 64 bit alignment -> ok
stur  q0, [x0, #44] // offset with 32 bit alignment but intruction with 64 bit 
                    //required alignment -> hard problem

My assumption is the compiler somehow thinks the FP registers are 4 byte or the instructions require 4 byte alignment. I expected the compiler to ensure the alignment if he is optimizing, which i can clearly see he is ignoring or doing it wrong. If more informations are needed please contact me.

With kind regards
Keven Kloeckner