Build error: cannot cast char to uint16_t

1

I cannot build px4 even though I cloned fresh copy of both librobotcontrol and Firmware and followed instructions (https://docs.px4.io/en/flight_controller/beaglebone_blue.html) one by one.

env setup

export TOOLCHAIN_ROOT=$HOME/toolchain/gcc-linaro-7.4.1-2019.02-x86_64_arm-linux-gnueabihf
export CROSS_COMPILE=arm-linux-gnueabihf
export ARCH=arm 
export CC=arm-linux-gnueabihf-gcc
export CXX=arm-linux-gnueabihf-g++

NEWP=$(echo $PATH | tr ':' '\n' | grep -v "^$HOME" | tr '\n' ':') 
NEWP=${NEWP%:} 
export PATH=$TOOLCHAIN_ROOT/bin/:$NEWP

robotcontrol

git clone git://github.com/StrawsonDesign/librobotcontrol
cd librobotcontrol
sed 's/gcc/arm-linux-gnueabihf-gcc/' -i `grep gcc * -Rl`
export DESTDIR=~/arm
make install
ls ~/arm

Firmware

export LIBROBOTCONTROL_INSTALL_DIR=~/arm/usr
make beaglebone_blue_cross

[23/698] Building CXX object src/lib/DriverFramework/framework/src/CMakeFiles/df_driver_framework.dir/I2CDevObj.cpp.o
…
/home/mpletty/arm/usr/include/rc/mavlink/common/../protocol.h: In function ‘uint16_t _MAV_RETURN_uint16_t(const mavlink_message_t*, uint8_t)’:
/home/mpletty/arm/usr/include/rc/mavlink/common/../protocol.h:279:49: error: cast from ‘const char*’ to ‘const uint16_t* {aka const short unsigned int*}’ increases required alignment of target type [-Werror=cast-align]
{ return *(const TYPE *)(&_MAV_PAYLOAD(msg)[ofs]);}
^
/home/mpletty/arm/usr/include/rc/mavlink/common/../protocol.h:281:1: note: in expansion of macro ‘_MAV_MSG_RETURN_TYPE’
_MAV_MSG_RETURN_TYPE(uint16_t)

Can anyone else replicate?

2

Looks like a warning leads to an error. Try building without -Werror here:

3

It should work. I found another workaround

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0bfcee70d8..fbe65b2e6a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -370,6 +370,7 @@ px4_generate_airframes_xml(BOARD ${PX4_BOARD})
 #=============================================================================
 # DriverFramework
 #
+add_compile_options(-Wno-cast-align)
 px4_add_git_submodule(TARGET git_driverframework PATH "src/lib/DriverFramework")
 set(OS ${PX4_PLATFORM})
 add_subdirectory(src/lib/DriverFramework/framework)

However, both seems awful. As far as I understand this issue comes from unused but existing function _MAV_RETURN_uint16_t which does that illegal cast from const char* to const uint16_t*. Function defined by macro _MAV_MSG_RETURN_TYPE in a conditional controlled by MAVLINK_ALIGNED_FIELDS and MAVLINK_NEED_BYTE_SWAP in librobotcontrol/include/rc/mavlink/protocol.h. Header included - never used.

Have not flight yet. Hope it works.

4

You’re right, it would be good to fix that in the mavlink header files if it isn’t already.

5

Any news to this? I’m still getting the same error.

I mean if we don’t want to work-around. :slight_smile:

6

Which target are you compiling against? What toolchain is that using? I need to reproduce this again to check. Thanks.

7

Has this issue been resolved? I’m on ‘18955a04c7c7467e00ea42b704addb4a9c12b53a’ from master in GitHub - mavlink/mavlink: Marshalling / communication library for drones..

mavlink error: cast from const char* to const uint16_t* {aka const short unsigned int* } increases required alignment of target type [-Werror=cast-align]