Missing vec_cvfo symbol on POWER9 when building downstream project with OpenCV 4.x/3.x

[hillwoodroc]

System Information

OpenCV version: 4.x / 3.x
Target architecture: ppc64le, POWER9
Compiler: GCC 13.x
Operating system: openSUSE Tumbleweed
VSX enabled: Yes (CV_VSX=ON)
Downstream project: ncnn

Detailed description

OpenCV builds successfully on POWER9 with VSX enabled.
However, when building a downstream project (such as ncnn) that uses OpenCV and links against it, the linker fails due to missing symbols related to vector conversion functions between float and double precision:

undefined reference to vec_cvfo(vector double const&)

This is because in vsx_utils.hpp, the functions:

VSX_REDIRECT_1RG(vec_float4,  vec_double2, vec_cvfo, vec_floate)
VSX_REDIRECT_1RG(vec_double2, vec_float4,  vec_cvfo, vec_doubleo)

are only valid if the underlying architecture supports POWER10-level VSX instructions for float64<->float32 conversion.

POWER9 lacks these instructions, but the macro doesn't guard against this, and there is no fallback definition. As a result, OpenCV compiles fine (no direct call), but consumers that indirectly rely on these intrinsics fail at link time.

Steps to reproduce

1. Use a POWER9 (ppc64le) system with VSX enabled (e.g., GCC defines VSX)
2. Build OpenCV 4.12.0 with default options (no error)
3. Build ncnn with OpenCV support enabled
4. Error:

[   74s] /usr/include/opencv2/core/vsx_utils.hpp:260:1: error: ‘__builtin_vsx_xvcvdpsp’ was not declared in this scope; did you mean ‘__builtin_vsx_xscvdpsp’?
[   74s]   260 | VSX_REDIRECT_1RG(vec_float4,  vec_double2, vec_cvfo, __builtin_vsx_xvcvdpsp)
[   74s]       | ^~~~~~~~~~~~~~~~
[   74s] /usr/include/opencv2/core/vsx_utils.hpp: In function ‘vec_double2 vec_cvfo(const vec_float4&)’:
[   74s] /usr/include/opencv2/core/vsx_utils.hpp:261:1: error: ‘__builtin_vsx_xvcvspdp’ was not declared in this scope; did you mean ‘__builtin_vsx_xscvspdp’?
[   74s]   261 | VSX_REDIRECT_1RG(vec_double2, vec_float4,  vec_cvfo, __builtin_vsx_xvcvspdp)
[   74s]       | ^~~~~~~~~~~~~~~~
[   74s] In file included from /usr/include/opencv2/core/base.hpp:705,
[   74s]                  from /usr/include/opencv2/core.hpp:53,
[   74s]                  from /usr/include/opencv2/core/core.hpp:48,
[   74s]                  from /home/abuild/rpmbuild/BUILD/ncnn-20250503-build/ncnn-20250503/examples/squeezenet.cpp:21:
[   74s] /usr/include/opencv2/core/vsx_utils.hpp: In function ‘vec_float4 vec_cvfo(const vec_double2&)’:
[   74s] /usr/include/opencv2/core/vsx_utils.hpp:260:1: error: ‘__builtin_vsx_xvcvdpsp’ was not declared in this scope; did you mean ‘__builtin_vsx_xscvdpsp’?
[   74s]   260 | VSX_REDIRECT_1RG(vec_float4,  vec_double2, vec_cvfo, __builtin_vsx_xvcvdpsp)
[   74s]       | ^~~~~~~~~~~~~~~~
[   74s] In file included from /usr/include/opencv2/core/base.hpp:705,
[   74s]                  from /usr/include/opencv2/core.hpp:53,
[   74s]                  from /usr/include/opencv2/core/core.hpp:48,
[   74s]                  from /home/abuild/rpmbuild/BUILD/ncnn-20250503-build/ncnn-20250503/examples/yolov3.cpp:20:
[   74s] /usr/include/opencv2/core/vsx_utils.hpp: In function ‘vec_float4 vec_cvfo(const vec_double2&)’:
[   74s] /usr/include/opencv2/core/vsx_utils.hpp:260:1: error: ‘__builtin_vsx_xvcvdpsp’ was not declared in this scope; did you mean ‘__builtin_vsx_xscvdpsp’?
[   74s]   260 | VSX_REDIRECT_1RG(vec_float4,  vec_double2, vec_cvfo, __builtin_vsx_xvcvdpsp)
[   74s]       | ^~~~~~~~~~~~~~~~
[   74s] In file included from /usr/include/opencv2/core/base.hpp:705,
[   74s]                  from /usr/include/opencv2/core.hpp:53,
[   74s]                  from /usr/include/opencv2/core/core.hpp:48,
[   74s]                  from /home/abuild/rpmbuild/BUILD/ncnn-20250503-build/ncnn-20250503/examples/fasterrcnn.cpp:21:
[   74s] /usr/include/opencv2/core/vsx_utils.hpp: In function ‘vec_float4 vec_cvfo(const vec_double2&)’:
[   74s] /usr/include/opencv2/core/vsx_utils.hpp:260:1: error: ‘__builtin_vsx_xvcvdpsp’ was not declared in this scope; did you mean ‘__builtin_vsx_xscvdpsp’?
[   74s]   260 | VSX_REDIRECT_1RG(vec_float4,  vec_double2, vec_cvfo, __builtin_vsx_xvcvdpsp)
[   74s]       | ^~~~~~~~~~~~~~~~
[   74s] In file included from /usr/include/opencv2/core/base.hpp:705,
[   74s]                  from /usr/include/opencv2/core.hpp:53,
[   74s]                  from /usr/include/opencv2/core/core.hpp:48,
[   74s]                  from /home/abuild/rpmbuild/BUILD/ncnn-20250503-build/ncnn-20250503/examples/yolov2.cpp:20:
[   74s] /usr/include/opencv2/core/vsx_utils.hpp: In function ‘vec_float4 vec_cvfo(const vec_double2&)’:
[   74s] /usr/include/opencv2/core/vsx_utils.hpp:260:1: error: ‘__builtin_vsx_xvcvdpsp’ was not declared in this scope; did you mean ‘__builtin_vsx_xscvdpsp’?
[   74s]   260 | VSX_REDIRECT_1RG(vec_float4,  vec_double2, vec_cvfo, __builtin_vsx_xvcvdpsp)
[   74s]       | ^~~~~~~~~~~~~~~~
[   74s] In file included from /usr/include/opencv2/core/base.hpp:705,
[   74s]                  from /usr/include/opencv2/core.hpp:53,
[   74s]                  from /usr/include/opencv2/core/core.hpp:48,
[   74s]                  from /home/abuild/rpmbuild/BUILD/ncnn-20250503-build/ncnn-20250503/examples/rfcn.cpp:21:
[   74s] /usr/include/opencv2/core/vsx_utils.hpp: In function ‘vec_float4 vec_cvfo(const vec_double2&)’:
[   74s] /usr/include/opencv2/core/vsx_utils.hpp:260:1: error: ‘__builtin_vsx_xvcvdpsp’ was not declared in this scope; did you mean ‘__builtin_vsx_xscvdpsp’?
[   74s]   260 | VSX_REDIRECT_1RG(vec_float4,  vec_double2, vec_cvfo, __builtin_vsx_xvcvdpsp)
[   74s]       | ^~~~~~~~~~~~~~~~
[   74s] /usr/include/opencv2/core/vsx_utils.hpp: In function ‘vec_double2 vec_cvfo(const vec_float4&)’:
[   74s] /usr/include/opencv2/core/vsx_utils.hpp:261:1: error: ‘__builtin_vsx_xvcvspdp’ was not declared in this scope; did you mean ‘__builtin_vsx_xscvspdp’?
[   74s]   261 | VSX_REDIRECT_1RG(vec_double2, vec_float4,  vec_cvfo, __builtin_vsx_xvcvspdp)
[   74s]       | ^~~~~~~~~~~~~~~~
[   74s] /usr/include/opencv2/core/vsx_utils.hpp: In function ‘vec_double2 vec_cvfo(const vec_float4&)’:
[   74s] /usr/include/opencv2/core/vsx_utils.hpp:261:1: error: ‘__builtin_vsx_xvcvspdp’ was not declared in this scope; did you mean ‘__builtin_vsx_xscvspdp’?
[   74s]   261 | VSX_REDIRECT_1RG(vec_double2, vec_float4,  vec_cvfo, __builtin_vsx_xvcvspdp)
[   74s]       | ^~~~~~~~~~~~~~~~
[   74s] /usr/include/opencv2/core/vsx_utils.hpp: In function ‘vec_double2 vec_cvfo(const vec_float4&)’:
[   74s] /usr/include/opencv2/core/vsx_utils.hpp:261:1: error: ‘__builtin_vsx_xvcvspdp’ was not declared in this scope; did you mean ‘__builtin_vsx_xscvspdp’?
[   74s]   261 | VSX_REDIRECT_1RG(vec_double2, vec_float4,  vec_cvfo, __builtin_vsx_xvcvspdp)
[   74s]       | ^~~~~~~~~~~~~~~~
[   74s] /usr/include/opencv2/core/vsx_utils.hpp: In function ‘vec_double2 vec_cvfo(const vec_float4&)’:
[   74s] /usr/include/opencv2/core/vsx_utils.hpp:261:1: error: ‘__builtin_vsx_xvcvspdp’ was not declared in this scope; did you mean ‘__builtin_vsx_xscvspdp’?
[   74s]   261 | VSX_REDIRECT_1RG(vec_double2, vec_float4,  vec_cvfo, __builtin_vsx_xvcvspdp)
[   74s]       | ^~~~~~~~~~~~~~~~
[   74s] In file included from /usr/include/opencv2/core/base.hpp:705,
[   74s]                  from /usr/include/opencv2/core.hpp:53,
[   74s]                  from /usr/include/opencv2/core/core.hpp:48,
[   74s]                  from /home/abuild/rpmbuild/BUILD/ncnn-20250503-build/ncnn-20250503/examples/yolov5.cpp:21:
[   74s] /usr/include/opencv2/core/vsx_utils.hpp: In function ‘vec_float4 vec_cvfo(const vec_double2&)’:
[   74s] /usr/include/opencv2/core/vsx_utils.hpp:260:1: error: ‘__builtin_vsx_xvcvdpsp’ was not declared in this scope; did you mean ‘__builtin_vsx_xscvdpsp’?
[   74s]   260 | VSX_REDIRECT_1RG(vec_float4,  vec_double2, vec_cvfo, __builtin_vsx_xvcvdpsp)
[   74s]       | ^~~~~~~~~~~~~~~~
[   74s] /usr/include/opencv2/core/vsx_utils.hpp: In function ‘vec_double2 vec_cvfo(const vec_float4&)’:
[   74s] /usr/include/opencv2/core/vsx_utils.hpp:261:1: error: ‘__builtin_vsx_xvcvspdp’ was not declared in this scope; did you mean ‘__builtin_vsx_xscvspdp’?
[   74s]   261 | VSX_REDIRECT_1RG(vec_double2, vec_float4,  vec_cvfo, __builtin_vsx_xvcvspdp)
[   74s]       | ^~~~~~~~~~~~~~~~
[   74s] /usr/include/opencv2/core/vsx_utils.hpp: In function ‘vec_double2 vec_cvfo(const vec_float4&)’:
[   74s] /usr/include/opencv2/core/vsx_utils.hpp:261:1: error: ‘__builtin_vsx_xvcvspdp’ was not declared in this scope; did you mean ‘__builtin_vsx_xscvspdp’?
[   74s]   261 | VSX_REDIRECT_1RG(vec_double2, vec_float4,  vec_cvfo, __builtin_vsx_xvcvspdp)

Suggested Fix

#27633

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues, forum.opencv.org, Stack Overflow, etc and have not found any solution
• I updated to the latest OpenCV version and the issue is still there
• There is reproducer code and related data files (videos, images, onnx, etc)