bneradt commented on code in PR #13936:
URL: https://github.com/apache/trafficserver/pull/13936#discussion_r4415994848
##########
cmake/Findunwind.cmake:
##########
@@ -28,10 +28,21 @@
# unwind::unwind
#
-find_library(unwind_LIBRARY NAMES unwind)
find_library(unwind_ptrace_LIBRARY NAMES unwind-ptrace)
find_library(unwind_generic_LIBRARY NAMES unwind-generic)
-find_path(unwind_INCLUDE_DIR NAMES libunwind.h libunwind/libunwind.h)
+# LLVM's unwinder also installs a libunwind.so and libunwind.h, which may be
+# earlier in the search path but lack the remote unwinding API. Take the ones
+# installed alongside libunwind-ptrace.
+if(unwind_ptrace_LIBRARY)
+ get_filename_component(_unwind_library_dir "${unwind_ptrace_LIBRARY}"
DIRECTORY)
+ find_library(
+ unwind_LIBRARY
+ NAMES unwind
+ PATHS "${_unwind_library_dir}"
+ NO_DEFAULT_PATH
+ )
+endif()
+find_path(unwind_INCLUDE_DIR NAMES libunwind-ptrace.h
libunwind/libunwind-ptrace.h)
Review Comment:
The minimal fix is to invalidate only incompatible cached selections before
the existing searches:
```cmake
# Immediately after computing _unwind_library_dir:
if(unwind_LIBRARY)
get_filename_component(_unwind_cached_dir "${unwind_LIBRARY}" DIRECTORY)
if(NOT _unwind_cached_dir STREQUAL _unwind_library_dir)
unset(unwind_LIBRARY CACHE)
endif()
endif()
# Immediately before find_path(unwind_INCLUDE_DIR ...):
if(unwind_INCLUDE_DIR
AND NOT EXISTS "${unwind_INCLUDE_DIR}/libunwind-ptrace.h"
AND NOT EXISTS "${unwind_INCLUDE_DIR}/libunwind/libunwind-ptrace.h"
)
unset(unwind_INCLUDE_DIR CACHE)
endif()
```
I see that 8801856a09b5 now implements exactly this approach. I checked the
updated finder with a minimal CMake fixture containing competing LLVM and
remote-unwinding installations: it repairs caches with both paths stale, only
the library stale, or only the include directory stale. A fresh configure also
selects the intended installation, and a subsequent configure leaves the valid
cache unchanged. This addresses my finding; no further patch is needed for it.
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