build: fix bundled protobuf headers being overridden by system-installed protobuf #28745
On macOS with Apple Clang 17, the compiler implicitly injects `/usr/local/include` as a high-priority user include (`-I`). The `SYSTEM` keyword in `target_include_directories` emits `-isystem` for the bundled protobuf path, which is searched after user `-I` paths, allowing a system-installed protobuf v4+ (which requires C++17 and abseil-cpp) to override the bundled headers.
Removing `SYSTEM` causes CMake to emit `-I` instead of `-isystem`, placing the bundled path before the implicit system include, restoring the intended header resolution order regardless of what protobuf version is installed on the host.
### Background
Apple Clang 17 (shipped with macOS 26 Tahoe Command Line Tools) changed the compiler driver behavior: it now unconditionally adds `-I/usr/local/include` to the search path, which is where Homebrew installs headers. Previous Apple Clang versions either omitted this path or added it as a lower-priority system include.
When Homebrew's `protobuf` is installed (v4+, e.g. `33.4_1`), its headers at `/usr/local/include/google/protobuf/` are resolved before the bundled `3rdparty/protobuf/src/` because `SYSTEM PUBLIC` in `target_include_directories` causes the bundled path to be emitted as `-isystem`, which ranks below `-I` in compiler search order. This was confirmed by inspecting the generated `flags.make`:
```
# before fix
-isystem /path/to/opencv/3rdparty/protobuf/src
# after fix
-I /path/to/opencv/3rdparty/protobuf/src (first in the include list)
```
The system protobuf v4+ headers require C++17 and abseil-cpp. Since OpenCV 4.x compiles with `-std=c++11`, every translation unit in `3rdparty/protobuf/` fails:
```
/usr/local/include/google/protobuf/port_def.inc: error: Protobuf only supports C++17 and newer.
/usr/local/include/absl/base/policy_checks.h: error: C++ versions less than C++17 are not supported.
```
Note that `include_directories(BEFORE ...)` on the line above was intended to prevent exactly this, but it was overridden by `target_include_directories(SYSTEM PUBLIC ...)` deduplicating the path into a single `-isystem` entry. This is essentially the same class of problem tracked in #13328.
### Impact
The change is a one-line diff. Removing `SYSTEM` has no effect on Linux or Windows since those toolchains do not inject `/usr/local/include` implicitly. Warning suppression for protobuf headers in dependent modules is unaffected because OpenCV already applies explicit `-Wno-*` flags for all protobuf-related warnings in `3rdparty/protobuf/CMakeLists.txt`.
### Tested on
- macOS 26.3 (Tahoe), Apple Clang 17.0.0 (`clang-1700.6.4.2`), Homebrew `protobuf 33.4_1`, full build passes with `BUILD_PROTOBUF=ON`.
Fixes#28743, related to #27886.
### Pull Request Readiness Checklist
See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request
- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake
According to GCC doc, -Wlong-long: Warn if long long type is used.
This is enabled by either -Wpedantic or -Wtraditional in ISO C90
and C++98 modes. To inhibit the warning messages, use -Wno-long-long.
OpenCV 4.x requires C++11. As result, this option is useless.
Ref: https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html
RISC-V/AArch64: disable CPU features detection #25901
This PR is the first step in fixing current issues with NEON/RVV, FP16, BF16 and other CPU features on AArch64 and RISC-V platforms.
On AArch64 and RISC-V platforms we usually have the platform set by default in the toolchain when we compile it or in the cmake toolchain file or in CMAKE_CXX_FLAGS by user. Then, there are two ways to set platform options: a) "-mcpu=<some_cpu>" ; b) "-march=<arch description>" (e.g. "rv64gcv"). Furthermore, there are no similar "levels" of optimizations as for x86_64, instead we have features (RVV, FP16,...) which can be enabled or disabled. So, for example, if a user has "rv64gc" set by the toolchain and we want to enable RVV. Then we need to somehow parse their current feature set and append "v" (vector optimizations) to this string. This task is quite hard and the whole procedure is prone to errors.
I propose to use "CPU_BASELINE=DETECT" by default on AArch64 and RISC-V platforms. And somehow remove other features or make them read-only/detect-only, so that OpenCV wouldn't add any extra "-march" flags to the default configuration. We would rely only on the flags provided by the compiler and cmake toolchain file. We can have some predefined configurations in our cmake toolchain files.
Changes made by this PR:
- `CMakeLists.txt`:
- use `CMAKE_CROSSCOMPILING` instead of `CMAKE_TOOLCHAIN_FILE` to detect cross-compilation. This might be useful in cases of native compilation with a toolchain file
- removed obsolete variables `ENABLE_NEON` and `ENABLE_VFPV3`, the first one have been turned ON by default on AArch64 platform which caused setting `CPU_BASELINE=NEON`
- raise minimum cmake version allowed to 3.7 to allow using `CMAKE_CXX_FLAGS_INIT` in toolchain files
- added separate files with arch flags for native compilation on AArch64 and RISC-V, these files will be used in our toolchain files and in regular cmake
- use `DETECT` as default value for `CPU_BASELINE` also allow `NATIVE`, warn user if other values were used (only for AArch64 and RISC-V)
- for each feature listed in `CPU_DISPATCH` check if corresponding `CPU_${opt}_FLAGS_ON` has been provided, warn user if it is empty (only for AArch64 and RISC-V)
- use `CPU_BASELINE_DISABLE` variable to actually turn off macros responsible for corresponding features even if they are enabled by compiler
- removed Aarch64 feature merge procedure (it didn't support `-mcpu` and built-in `-march`)
- reworked AArch64 and two RISC-V cmake toolchain files (does not affect Android/OSX/iOS/Win):
- use `CMAKE_CXX_FLAGS_INIT` to set compiler flags
- use variables `ENABLE_BF16`, `ENABLE_DOTPROD`, `ENABLE_RVV`, `ENABLE_FP16` to control `-march`
- AArch64: removed other compiler and linker flags
- `-fdata-sections`, `-fsigned-char`, `-Wl,--no-undefined`, `-Wl,--gc-sections` - already set by OpenCV
- `-Wa,--noexecstack`, `-Wl,-z,noexecstack`, `-Wl,-z,relro`, `-Wl,-z,now` - can be enabled by OpenCV via `ENABLE_HARDENING`
- `-Wno-psabi` - this option used to disable some warnings on older ARM platforms, shouldn't harm
- ARM: removed same common flags as for AArch64, but left `-mthumb` and `--fix-cortex-a8`, `-z nocopyreloc`
FAILED: lib/libopencv_core.so.13.0
...
ld: error: undefined symbol: __cxa_atexit
Do not try to use --no-undefined on OpenBSD. OpenBSD does not link
shared libraries with libc and thus linkage with --no-undefined is
expected to fail.
* Added NEON support in builds for Windows on ARM
* Fixed `HAVE_CPU_NEON_SUPPORT` display broken during compiler test
* Fixed a build error prior to Visual Studio 2022
* [build][option] Introduce `OPENCV_DISABLE_THREAD_SUPPORT` option.
The option forces the library to build without thread support.
* update handling of OPENCV_DISABLE_THREAD_SUPPORT
- reduce amount of #if conditions
* [to squash] cmake: apply mode vars in toolchains too
Co-authored-by: Alexander Alekhin <alexander.a.alekhin@gmail.com>
* add -Wno-psabi when using GCC 6
* add -Wundef for CUDA 10
* add -Wdeprecated-declarations when using GCC 7
* add -Wstrict-aliasing and -Wtautological-compare for GCC 7
* replace cudaThreadSynchronize with cudaDeviceSynchronize
- builds with CMAKE_SKIP_RPATH=ON should properly find project .so files from <build>/lib directory
- $ORIGIN doesn't work properly in cross-compilation mode
Jesus Armando Anaya
Alexander Smorkalov
Letu Ren
Maksim Shabunin
Brad Smith
ashadrina
不鱼儿
Alexander Smorkalov
Andrey Senyaev
Alexander Alekhin
Tatsuro Shibamura
Dale Phurrough
Francesco Petrogalli
Alexander Alekhin
Peter Würtz
Tomoaki Teshima