Hi everyone,
I've been wondering how to correctly build clang/LLVM for the AVR target
architecture. Unfortunately documentation is very scarce (or outdated or I
didn't find it) and while I've been able to build clang/LLVM for AVR
I'm still falling short of compiling an actual binary for the MCU. Here are
the steps I've undertaken so far:
git clone https://github.com/llvm/llvm-project
cd llvm-project
mkdir build && cd build
cmake -G "Unix Makefiles"
-DLLVM_ENABLE_PROJECTS="clang;libcxx;libcxxabi"
-DLLVM_TARGETS_TO_BUILD="AVR" -DCMAKE_BUILD_TYPE=Release ../llvm
make -j8
sudo make install
Next I created a pretty empty main.cpp and tried to compile that:
#include <stdint.h>
int main()
{
for(;;) { }
return 0;
}
Here's the result of attempting the compilation ...
$ clang++ --target=avr -mmcu=atmega328p -c main.cpp -o main.o -v
clang version 11.0.0 (https://github.com/llvm/llvm-project
177dd63c8d742250dac6ea365e7c30f0fbab3257)
Target: avr
Thread model: posix
InstalledDir: /usr/local/bin
Found candidate GCC installation: /usr/lib/gcc/avr/5.4.0
Selected GCC installation: /usr/lib/gcc/avr/5.4.0
(in-process)
"/usr/local/bin/clang-11" -cc1 -triple avr -emit-obj -mrelax-all
-disable-free -disable-llvm-verifier -discard-value-names -main-file-name
main.cpp -mrelocation-model static -mthread-model posix -mframe-pointer=all
-fmath-errno -fno-rounding-math -masm-verbose -mconstructor-aliases -target-cpu
atmega328p -dwarf-column-info -fno-split-dwarf-inlining -debugger-tuning=gdb -v
-resource-dir /usr/local/lib/clang/11.0.0 -fdeprecated-macro
-fdebug-compilation-dir /home/alex/tmp/clang-avr -ferror-limit 19
-fmessage-length 0 -fgnuc-version=4.2.1 -fobjc-runtime=gcc -fcxx-exceptions
-fexceptions -fdiagnostics-show-option -fcolor-diagnostics -faddrsig -o main.o
-x c++ main.cpp
clang -cc1 version 11.0.0 based upon LLVM 11.0.0git default target
x86_64-unknown-linux-gnu
#include "..." search starts here:
#include <...> search starts here:
/usr/local/include
/usr/local/lib/clang/11.0.0/include
/usr/include
End of search list.
In file included from main.cpp:1:
In file included from /usr/local/lib/clang/11.0.0/include/stdint.h:52:
/usr/include/stdint.h:26:10: fatal error: 'bits/libc-header-start.h'
file not found
#include <bits/libc-header-start.h>
^~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.
Looking for that file I can find it in the system
$ find /usr -iname libc-header-start.h
/usr/include/x86_64-linux-gnu/bits/libc-header-start.h
But adding it to the clang call via -isystem or -I does not help either.
$ clang --target=avr -mmcu=atmega328p -c main.cpp -o main.o -v
-I/usr/include/x86_64-linux-gnu
clang version 11.0.0 (https://github.com/llvm/llvm-project
177dd63c8d742250dac6ea365e7c30f0fbab3257)
Target: avr
Thread model: posix
InstalledDir: /usr/local/bin
(in-process)
"/usr/local/bin/clang-11" -cc1 -triple avr -emit-obj -mrelax-all
-disable-free -disable-llvm-verifier -discard-value-names -main-file-name
main.cpp -mrelocation-model static -mthread-model posix -mframe-pointer=all
-fmath-errno -fno-rounding-math -masm-verbose -mconstructor aliases -target-cpu
atmega328p -dwarf-column-info -fno-split-dwarf-inlining -debugger-tuning=gdb -v
-resource-dir /usr/local/lib/clang/11.0.0 -I /usr/include/x86_64-linux-gnu
-fdeprecated-macro -fdebug-compilation-dir /home/alex/tmp/clang-avr
-ferror-limit 19 -fmessage-length 0 -fgnuc-version=4.2.1 -fobjc-runtime=gcc
-fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics
-faddrsig -o main.o -x c++ main.cpp
clang -cc1 version 11.0.0 based upon LLVM 11.0.0git default target
x86_64-unknown-linux-gnu
#include "..." search starts here:
#include <...> search starts here:
/usr/include/x86_64-linux-gnu
/usr/local/include
/usr/local/lib/clang/11.0.0/include
/usr/include
End of search list.
In file included from main.cpp:1:
In file included from /usr/local/lib/clang/11.0.0/include/stdint.h:52:
In file included from /usr/include/stdint.h:26:
In file included from
/usr/include/x86_64-linux-gnu/bits/libc-header-start.h:33:
In file included from /usr/include/features.h:448:
/usr/include/x86_64-linux-gnu/gnu/stubs.h:7:11: fatal error:
'gnu/stubs-32.h' file not found
# include <gnu/stubs-32.h>
^~~~~~~~~~~~~~~~
1 error generated.
Thinking that maybe the old version (5.4.0) of avr-gcc might be a problem
I've built a 9.2.0 version from sources
$ avr-gcc -v
Using built-in specs.
Reading specs from /opt/avr/avr-gcc/lib/gcc/avr/9.2.0/device-specs/specs-avr2
COLLECT_GCC=avr-gcc
COLLECT_LTO_WRAPPER=/opt/avr/avr-gcc/libexec/gcc/avr/9.2.0/lto-wrapper
Target: avr
Configured with: ../configure --prefix=/opt/avr/avr-gcc --target=avr
--enable-languages=c,c++ --disable-nls --disable-libssp --disable-libada
--with-dwarf2 --disable-shared --enable-static --enable-mingw-wildcard
Thread model: single
gcc version 9.2.0 (GCC)
But this didn't change anything, except that when running clang without file
arguments it does indicate that there is no avr-gcc in the system (although
there is, but probably not spliced in there where the clang/LLVM build process
expects it).
$ clang --target=avr -mmcu=atmega328p
clang-11: warning: no avr-gcc installation can be found on the system, cannot
link standard libraries [-Wavr-rtlib-linking-quirks]
clang-11: warning: standard library not linked and so no interrupt vector
table or compiler runtime routines will be linked [-Wavr-rtlib-linking-quirks]
clang-11: error: no input files
I'd greatly appreciate any input helping to solve these problems or a
pointer to working documentation.
With kind regards, Alex
> > In file included from main.cpp:1: > In file included from /usr/local/lib/clang/11.0.0/include/stdint.h:52: > /usr/include/stdint.h:26:10: fatal error: 'bits/libc-header-start.h' > file not found > #include <bits/libc-header-start.h> > ^~~~~~~~~~~~~~~~~~~~~~~~~~ > 1 error generated. >I had the same issue initially. The problem here is that it tries to include /usr/include/stdint.h, which it should not because that's the header for the host system not the AVR. To work around this you can use the -nostdlibinc flag. See: https://bugs.llvm.org/show_bug.cgi?id=39210 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20200325/3168da7b/attachment.html>
It looks like you’re cross-compiling for an embedded target, so you need to be careful about how you treat headers (like libc’s), as the x86 ones will not be compatible with the AVR ones. The clang driver can manage this for you, if you give it enough information: The first thing to try is adding the --gcc-toolchain argument to clang to point to the root of the avr gcc toolchain (I think in your case this will be /opt/avr/avr-gcc ). This should help the driver pick up the right include paths for AVR. Try that see how you get on. Sam> On 25 Mar 2020, at 12:01 pm, Alexander Entinger via llvm-dev <llvm-dev at lists.llvm.org> wrote: > > Hi everyone, > > I've been wondering how to correctly build clang/LLVM for the AVR target architecture. Unfortunately documentation is very scarce (or outdated or I didn't find it) and while I've been able to build clang/LLVM for AVR I'm still falling short of compiling an actual binary for the MCU. Here are the steps I've undertaken so far: > > git clone https://github.com/llvm/llvm-project > cd llvm-project > mkdir build && cd build > > cmake -G "Unix Makefiles" -DLLVM_ENABLE_PROJECTS="clang;libcxx;libcxxabi" -DLLVM_TARGETS_TO_BUILD="AVR" -DCMAKE_BUILD_TYPE=Release ../llvm > make -j8 > sudo make install > > Next I created a pretty empty main.cpp and tried to compile that: > > #include <stdint.h> > int main() > { > for(;;) { } > return 0; > } > > Here's the result of attempting the compilation ... > > $ clang++ --target=avr -mmcu=atmega328p -c main.cpp -o main.o -v > clang version 11.0.0 (https://github.com/llvm/llvm-project 177dd63c8d742250dac6ea365e7c30f0fbab3257) > Target: avr > Thread model: posix > InstalledDir: /usr/local/bin > Found candidate GCC installation: /usr/lib/gcc/avr/5.4.0 > Selected GCC installation: /usr/lib/gcc/avr/5.4.0 > (in-process) > "/usr/local/bin/clang-11" -cc1 -triple avr -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name main.cpp -mrelocation-model static -mthread-model posix -mframe-pointer=all -fmath-errno -fno-rounding-math -masm-verbose -mconstructor-aliases -target-cpu atmega328p -dwarf-column-info -fno-split-dwarf-inlining -debugger-tuning=gdb -v -resource-dir /usr/local/lib/clang/11.0.0 -fdeprecated-macro -fdebug-compilation-dir /home/alex/tmp/clang-avr -ferror-limit 19 -fmessage-length 0 -fgnuc-version=4.2.1 -fobjc-runtime=gcc -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -faddrsig -o main.o -x c++ main.cpp > clang -cc1 version 11.0.0 based upon LLVM 11.0.0git default target x86_64-unknown-linux-gnu > #include "..." search starts here: > #include <...> search starts here: > /usr/local/include > /usr/local/lib/clang/11.0.0/include > /usr/include > End of search list. > In file included from main.cpp:1: > In file included from /usr/local/lib/clang/11.0.0/include/stdint.h:52: > /usr/include/stdint.h:26:10: fatal error: 'bits/libc-header-start.h' file not found > #include <bits/libc-header-start.h> > ^~~~~~~~~~~~~~~~~~~~~~~~~~ > 1 error generated. > > Looking for that file I can find it in the system > > $ find /usr -iname libc-header-start.h > /usr/include/x86_64-linux-gnu/bits/libc-header-start.h > > But adding it to the clang call via -isystem or -I does not help either. > > $ clang --target=avr -mmcu=atmega328p -c main.cpp -o main.o -v -I/usr/include/x86_64-linux-gnu > clang version 11.0.0 (https://github.com/llvm/llvm-project 177dd63c8d742250dac6ea365e7c30f0fbab3257) > Target: avr > Thread model: posix > InstalledDir: /usr/local/bin > (in-process) > "/usr/local/bin/clang-11" -cc1 -triple avr -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name main.cpp -mrelocation-model static -mthread-model posix -mframe-pointer=all -fmath-errno -fno-rounding-math -masm-verbose -mconstructor aliases -target-cpu atmega328p -dwarf-column-info -fno-split-dwarf-inlining -debugger-tuning=gdb -v -resource-dir /usr/local/lib/clang/11.0.0 -I /usr/include/x86_64-linux-gnu -fdeprecated-macro -fdebug-compilation-dir /home/alex/tmp/clang-avr -ferror-limit 19 -fmessage-length 0 -fgnuc-version=4.2.1 -fobjc-runtime=gcc -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -faddrsig -o main.o -x c++ main.cpp > clang -cc1 version 11.0.0 based upon LLVM 11.0.0git default target x86_64-unknown-linux-gnu > #include "..." search starts here: > #include <...> search starts here: > /usr/include/x86_64-linux-gnu > /usr/local/include > /usr/local/lib/clang/11.0.0/include > /usr/include > End of search list. > In file included from main.cpp:1: > In file included from /usr/local/lib/clang/11.0.0/include/stdint.h:52: > In file included from /usr/include/stdint.h:26: > In file included from /usr/include/x86_64-linux-gnu/bits/libc-header-start.h:33: > In file included from /usr/include/features.h:448: > /usr/include/x86_64-linux-gnu/gnu/stubs.h:7:11: fatal error: 'gnu/stubs-32.h' file not found > # include <gnu/stubs-32.h> > ^~~~~~~~~~~~~~~~ > 1 error generated. > > Thinking that maybe the old version (5.4.0) of avr-gcc might be a problem I've built a 9.2.0 version from sources > > $ avr-gcc -v > Using built-in specs. > Reading specs from /opt/avr/avr-gcc/lib/gcc/avr/9.2.0/device-specs/specs-avr2 > COLLECT_GCC=avr-gcc > COLLECT_LTO_WRAPPER=/opt/avr/avr-gcc/libexec/gcc/avr/9.2.0/lto-wrapper > Target: avr > Configured with: ../configure --prefix=/opt/avr/avr-gcc --target=avr --enable-languages=c,c++ --disable-nls --disable-libssp --disable-libada --with-dwarf2 --disable-shared --enable-static --enable-mingw-wildcard > Thread model: single > gcc version 9.2.0 (GCC) > > But this didn't change anything, except that when running clang without file arguments it does indicate that there is no avr-gcc in the system (although there is, but probably not spliced in there where the clang/LLVM build process expects it). > > $ clang --target=avr -mmcu=atmega328p > clang-11: warning: no avr-gcc installation can be found on the system, cannot link standard libraries [-Wavr-rtlib-linking-quirks] > clang-11: warning: standard library not linked and so no interrupt vector table or compiler runtime routines will be linked [-Wavr-rtlib-linking-quirks] > clang-11: error: no input files > > I'd greatly appreciate any input helping to solve these problems or a pointer to working documentation. > > With kind regards, Alex > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev-- Sam Elliott Software Developer - LLVM and OpenTitan lowRISC CIC
Thank you for both of your input. Yes, I try to cross-compile for AVR, the simple ATMEGA328P used in every Arduino Uno. My main motivation being that I hope to be able to use a couple of STL containers, <functional> and <type_traits> on the MCU. Not sure though if this can be reached by going via the clang route. Getting back to the compilation: when I run clang with both both -nostdlibinc (which makes it necessary to point clang to the header file location via -isystem /opt/avr/avr-libc/avr/include) and --gcc-toolchain I can compile the minimum example code. clang++ --target=avr -nostdlibinc -isystem /opt/avr/avr-libc/avr/include --gcc-toolchain=/opt/avr/avr-gcc -mmcu=atmega328p -c main.cpp -o main.o However, when I'm running a compilation on a more complicated embedded programm I get a lot of troubling warnings, e.g. warning: unknown attribute '__progmem__' ignored [-Wunknown-attributes] (which are troubling me, because if all those string constants are put in RAM instead of Flash the RAM will be pretty soon empty ;) ). But those warnings aside I run ultimately into problems when getting to the linking step where it appears there are trouble providing implementations for avr-gcc built-in functions which I believe are located within the avr-gcc MCU specific libraries /opt/avr/avr-libc/avr/include/util/delay.h:187: undefined reference to `__builtin_avr_delay_cycles(unsigned long)' as well as troubles which seem to be originating from my C++ usage within the firmware undefined reference to `vtable for __cxxabiv1::__class_type_info' Kind regards, Alex ________________________________________ Von: Sam Elliott [selliott at lowrisc.org] Gesendet: Mittwoch, 25. März 2020 13:17 An: Alexander Entinger Cc: llvm-dev at lists.llvm.org Betreff: Re: [llvm-dev] Build Clang/LLVM for AVR It looks like you’re cross-compiling for an embedded target, so you need to be careful about how you treat headers (like libc’s), as the x86 ones will not be compatible with the AVR ones. The clang driver can manage this for you, if you give it enough information: The first thing to try is adding the --gcc-toolchain argument to clang to point to the root of the avr gcc toolchain (I think in your case this will be /opt/avr/avr-gcc ). This should help the driver pick up the right include paths for AVR. Try that see how you get on. Sam> On 25 Mar 2020, at 12:01 pm, Alexander Entinger via llvm-dev <llvm-dev at lists.llvm.org> wrote: > > Hi everyone, > > I've been wondering how to correctly build clang/LLVM for the AVR target architecture. Unfortunately documentation is very scarce (or outdated or I didn't find it) and while I've been able to build clang/LLVM for AVR I'm still falling short of compiling an actual binary for the MCU. Here are the steps I've undertaken so far: > > git clone https://github.com/llvm/llvm-project > cd llvm-project > mkdir build && cd build > > cmake -G "Unix Makefiles" -DLLVM_ENABLE_PROJECTS="clang;libcxx;libcxxabi" -DLLVM_TARGETS_TO_BUILD="AVR" -DCMAKE_BUILD_TYPE=Release ../llvm > make -j8 > sudo make install > > Next I created a pretty empty main.cpp and tried to compile that: > > #include <stdint.h> > int main() > { > for(;;) { } > return 0; > } > > Here's the result of attempting the compilation ... > > $ clang++ --target=avr -mmcu=atmega328p -c main.cpp -o main.o -v > clang version 11.0.0 (https://github.com/llvm/llvm-project 177dd63c8d742250dac6ea365e7c30f0fbab3257) > Target: avr > Thread model: posix > InstalledDir: /usr/local/bin > Found candidate GCC installation: /usr/lib/gcc/avr/5.4.0 > Selected GCC installation: /usr/lib/gcc/avr/5.4.0 > (in-process) > "/usr/local/bin/clang-11" -cc1 -triple avr -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name main.cpp -mrelocation-model static -mthread-model posix -mframe-pointer=all -fmath-errno -fno-rounding-math -masm-verbose -mconstructor-aliases -target-cpu atmega328p -dwarf-column-info -fno-split-dwarf-inlining -debugger-tuning=gdb -v -resource-dir /usr/local/lib/clang/11.0.0 -fdeprecated-macro -fdebug-compilation-dir /home/alex/tmp/clang-avr -ferror-limit 19 -fmessage-length 0 -fgnuc-version=4.2.1 -fobjc-runtime=gcc -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -faddrsig -o main.o -x c++ main.cpp > clang -cc1 version 11.0.0 based upon LLVM 11.0.0git default target x86_64-unknown-linux-gnu > #include "..." search starts here: > #include <...> search starts here: > /usr/local/include > /usr/local/lib/clang/11.0.0/include > /usr/include > End of search list. > In file included from main.cpp:1: > In file included from /usr/local/lib/clang/11.0.0/include/stdint.h:52: > /usr/include/stdint.h:26:10: fatal error: 'bits/libc-header-start.h' file not found > #include <bits/libc-header-start.h> > ^~~~~~~~~~~~~~~~~~~~~~~~~~ > 1 error generated. > > Looking for that file I can find it in the system > > $ find /usr -iname libc-header-start.h > /usr/include/x86_64-linux-gnu/bits/libc-header-start.h > > But adding it to the clang call via -isystem or -I does not help either. > > $ clang --target=avr -mmcu=atmega328p -c main.cpp -o main.o -v -I/usr/include/x86_64-linux-gnu > clang version 11.0.0 (https://github.com/llvm/llvm-project 177dd63c8d742250dac6ea365e7c30f0fbab3257) > Target: avr > Thread model: posix > InstalledDir: /usr/local/bin > (in-process) > "/usr/local/bin/clang-11" -cc1 -triple avr -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name main.cpp -mrelocation-model static -mthread-model posix -mframe-pointer=all -fmath-errno -fno-rounding-math -masm-verbose -mconstructor aliases -target-cpu atmega328p -dwarf-column-info -fno-split-dwarf-inlining -debugger-tuning=gdb -v -resource-dir /usr/local/lib/clang/11.0.0 -I /usr/include/x86_64-linux-gnu -fdeprecated-macro -fdebug-compilation-dir /home/alex/tmp/clang-avr -ferror-limit 19 -fmessage-length 0 -fgnuc-version=4.2.1 -fobjc-runtime=gcc -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -faddrsig -o main.o -x c++ main.cpp > clang -cc1 version 11.0.0 based upon LLVM 11.0.0git default target x86_64-unknown-linux-gnu > #include "..." search starts here: > #include <...> search starts here: > /usr/include/x86_64-linux-gnu > /usr/local/include > /usr/local/lib/clang/11.0.0/include > /usr/include > End of search list. > In file included from main.cpp:1: > In file included from /usr/local/lib/clang/11.0.0/include/stdint.h:52: > In file included from /usr/include/stdint.h:26: > In file included from /usr/include/x86_64-linux-gnu/bits/libc-header-start.h:33: > In file included from /usr/include/features.h:448: > /usr/include/x86_64-linux-gnu/gnu/stubs.h:7:11: fatal error: 'gnu/stubs-32.h' file not found > # include <gnu/stubs-32.h> > ^~~~~~~~~~~~~~~~ > 1 error generated. > > Thinking that maybe the old version (5.4.0) of avr-gcc might be a problem I've built a 9.2.0 version from sources > > $ avr-gcc -v > Using built-in specs. > Reading specs from /opt/avr/avr-gcc/lib/gcc/avr/9.2.0/device-specs/specs-avr2 > COLLECT_GCC=avr-gcc > COLLECT_LTO_WRAPPER=/opt/avr/avr-gcc/libexec/gcc/avr/9.2.0/lto-wrapper > Target: avr > Configured with: ../configure --prefix=/opt/avr/avr-gcc --target=avr --enable-languages=c,c++ --disable-nls --disable-libssp --disable-libada --with-dwarf2 --disable-shared --enable-static --enable-mingw-wildcard > Thread model: single > gcc version 9.2.0 (GCC) > > But this didn't change anything, except that when running clang without file arguments it does indicate that there is no avr-gcc in the system (although there is, but probably not spliced in there where the clang/LLVM build process expects it). > > $ clang --target=avr -mmcu=atmega328p > clang-11: warning: no avr-gcc installation can be found on the system, cannot link standard libraries [-Wavr-rtlib-linking-quirks] > clang-11: warning: standard library not linked and so no interrupt vector table or compiler runtime routines will be linked [-Wavr-rtlib-linking-quirks] > clang-11: error: no input files > > I'd greatly appreciate any input helping to solve these problems or a pointer to working documentation. > > With kind regards, Alex > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev-- Sam Elliott Software Developer - LLVM and OpenTitan lowRISC CIC