cmake: Errors not actually errors?

fanquake commented at 12:29 pm on August 7, 2025: member

Using current master (6a2bb0fd835977637e0f43db76121bbfd21565f6), if you configure with the following, CMake will “Error”:

 0# gcc --version
 1# gcc (Ubuntu 14.2.0-4ubuntu2~24.04) 14.2.0
 2
 3cmake -B build -DBUILD_KERNEL_LIB=ON -DCMAKE_INTERPROCEDURAL_OPTIMIZATION=ON
 4<snip>
 5Cross compiling ....................... FALSE
 6C++ compiler .......................... GNU 14.2.0, /usr/bin/c++
 7CMAKE_BUILD_TYPE ...................... RelWithDebInfo
 8Preprocessor defined macros ........... 
 9C++ compiler flags .................... -O2 -g -std=c++20 -fPIC -fno-extended-identifiers -fdebug-prefix-map=/root/ci_scratch/src=. -fmacro-prefix-map=/root/ci_scratch/src=. -fstack-reuse=none -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=3 -Wstack-protector -fstack-protector-all -fcf-protection=full -fstack-clash-protection -Wall -Wextra -Wformat -Wformat-security -Wvla -Wredundant-decls -Wdate-time -Wduplicated-branches -Wduplicated-cond -Wlogical-op -Woverloaded-virtual -Wsuggest-override -Wimplicit-fallthrough -Wunreachable-code -Wbidi-chars=any -Wundef -Wno-unused-parameter
10Linker flags .......................... -O2 -g -fstack-reuse=none -fstack-protector-all -fcf-protection=full -fstack-clash-protection -Wl,-z,relro -Wl,-z,now -Wl,-z,separate-code -fPIE -pie
11
12NOTE: The summary above may not exactly match the final applied build flags
13      if any additional CMAKE_* or environment variables have been modified.
14      To see the exact flags applied, build with the --verbose option.
15
16Treat compiler warnings as errors ..... OFF
17Use ccache for compiling .............. ON
18
19
20-- Configuring done (23.3s)
21CMake Error at src/kernel/CMakeLists.txt:11 (add_library):
22  CMake doesn't support IPO for current compiler
23
24
25-- Generating done (0.1s)
26CMake Generate step failed.  Build files cannot be regenerated correctly.

However you can just call cmake --build build, and compilation “works”:

 0cmake --build build -j14 --target bitcoinkernel
 1[  0%] Generating bitcoin-build-info.h
 2[  0%] Built target secp256k1_precomputed
 3[  0%] Built target crc32c
 4[ 14%] Built target bitcoin_crypto
 5[ 14%] Built target secp256k1
 6[ 42%] Built target leveldb
 7[ 42%] Built target generate_build_info
 8[ 42%] Built target bitcoin_clientversion
 9[100%] Built target bitcoinkernel
10
11# file build/lib/libbitcoinkernel.a 
12build/lib/libbitcoinkernel.a: current ar archive

It would be good if when CMake errors during configuration, it’s not actually possible to continue building, rather than silently ignoring errors.

Note that the presence of -Werror=dev when configuring, makes no difference here.

Also, the error string CMake is throwing, is also incorrect, as the compiler does support LTO.

fanquake added the label Build system on Aug 7, 2025

maflcko commented at 12:39 pm on August 7, 2025: member

in the Guix build, errors will just be silently ignored.

I think the guix build has set -e, so it should be fine and not proceed here.

hebasto commented at 12:44 pm on August 7, 2025: member

Using current master (6a2bb0f), if you configure with the following, CMake will “Error”

What version of CMake are you using?

fanquake commented at 1:08 pm on August 7, 2025: member

What version of CMake are you using?

Happens with 3.28.3 & 4.0.3.

fanquake commented at 1:12 pm on August 7, 2025: member

I think the guix build has set -e, so it should be fine and not proceed here.

Looks like this is the case, and tested the build does fail. So I guess it will just (potentially) silently ignore errors everywhere else.

hebasto commented at 3:22 pm on August 7, 2025: member

Also, the error string CMake is throwing, is also incorrect, as the compiler does support LTO.

CMake doesn’t blame the compiler, rather itself: “CMake doesn’t support IPO for current compiler”.

For some reason, this occurs with the “Unix Makefiles” generator but not with the “Ninja” generator.

hebasto commented at 3:22 pm on August 7, 2025: member

cc @purpleKarrot

hebasto commented at 3:34 pm on August 7, 2025: member

It seems that the $<TARGET_OBJECTS:..> added to bitcoinkernel sources in #33077 are causing the issue.

cc @theuni

cmake: Errors not actually errors? #33153