build: fix linking against -latomic when building for riscv #20938

pull fanquake wants to merge 2 commits into bitcoin:master from fanquake:fix_riscv_atomic_usage changing 2 files +4 −0

fanquake commented at 3:01 AM on January 15, 2021: member

Since the merge of #19937, riscv builds have been failing, due to a link issue with std::atomic_exchange in bitcoin-util:

  CXXLD    bitcoin-util
bitcoin_util-bitcoin-util.o: In function `grind_task':
/home/ubuntu/build/bitcoin/distsrc-riscv64-linux-gnu/src/bitcoin-util.cpp:98: undefined reference to `__atomic_exchange_1'
collect2: error: ld returned 1 exit status

We have a macro that tries to determine when -latomic is required, however it doesn't quite work well enough, as it's currently determining it isn't needed:

./autogen.sh
./configure --prefix=/home/ubuntu/bitcoin/depends/riscv64-linux-gnu
...
checking whether std::atomic can be used without link library... yes

This PR adds a call to std::atomic_exchange to the macro, which will get us properly linked against -latomic on riscv:

checking whether std::atomic can be used without link library... no
checking whether std::atomic needs -latomic... yes

Also adds an <atomic> include to bitcoin-util.cpp.

add std::atomic include to bitcoin-util.cpp 2c010b9c56

build: improve macro for testing -latomic requirement

riscv builds are currently failing because -latomic isn't being linked
against, when it is needed:
```bash
/home/ubuntu/build/bitcoin/distsrc-riscv64-linux-gnu/src/bitcoin-util.cpp:98: undefined reference to `__atomic_exchange_1'
```

This exteneds our macro to ensure that -latomic is linked against when
required.

54ce4fac80

fanquake added the label Build system on Jan 15, 2021
fanquake renamed this:
~~Fix linking against -latomic when building for riscv~~
build: fix linking against -latomic when building for riscv
on Jan 15, 2021
MarcoFalke added the label Needs gitian build on Jan 15, 2021
laanwj commented at 11:40 AM on January 18, 2021: member
Testing this. Doing a compile on the SiFive Unleashed is a bit slow, so give it some time.

Master without this PR:
```
configure:5619: checking whether std::atomic can be used without link library
configure:5637: g++ -std=c++17 -o conftest -g -O2   conftest.cpp  >&5
configure:5637: $? = 0
configure:5639: result: yes
```
Now trying a build of master to see if it fails. Will then try with this PR.

Edit: this clang issue seems related: https://reviews.llvm.org/D69869 . The conclusion is the same—RISC-V GCC needs libatomic for some atomic operations, but not others.

Edit2: i got some awful, unrelated DWARF error during linking, i think my build toolchain is messed up

Edit3: reproduced
```
/usr/bin/ld: bitcoin_util-bitcoin-util.o: in function `.L0 ':
/data/src/bitcoin/src/bitcoin-util.cpp:102: undefined reference to `__atomic_exchange_1'
collect2: error: ld returned 1 exit status
gmake[2]: *** [Makefile:5562: bitcoin-util] Error 1
gmake[2]: *** Waiting for unfinished jobs....
```
laanwj commented at 5:32 PM on January 18, 2021: member

Tested ACK 54ce4fac80689621dcbcc76169b2b00b179ee743
laanwj merged this on Jan 18, 2021
laanwj closed this on Jan 18, 2021
MarcoFalke removed the label Needs gitian build on Jan 18, 2021
sidhujag referenced this in commit f2485c00b8 on Jan 20, 2021
fanquake deleted the branch on Feb 6, 2021
luke-jr referenced this in commit 594eb77f73 on Jun 27, 2021
furszy referenced this in commit f2b45fded0 on Jan 9, 2022
DrahtBot locked this on Aug 16, 2022

Contributors

fanquake

laanwj

Labels

Build system

Linked (view graph)

#19937 signet mining utility