Hi Moritz
Thank you very much!
> On 22 Aug 2026, at 22:58, Moritz Hoffmann <[email protected]> wrote:
>
>
> If we want the warnings gone while keeping IPO, I would not disable the
> diagnostic globally. Per the manual sentence above the setting propagates at
> function granularity, so it is enough to put it on the affected files:
>
> ```cmake
> if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
> set_source_files_properties (
> interpreter/classes/StringClass.cpp
> interpreter/classes/StringClassBit.cpp
> interpreter/classes/StringClassConversion.cpp
> interpreter/classes/StringClassSub.cpp
> PROPERTIES COMPILE_OPTIONS -Wno-stringop-overflow)
> endif ()
> ```
>
> That keeps the diagnostic everywhere else. The manual also warns that inlining
> can move a region to another function's setting, so this wants a build to
> confirm rather than a claim from me.
>
I tested the CMake snippet above on WSL Ubuntu 22.04.5 LTS with GCC 11.4.0.
The warning is still there, even with a linker-specific option like this:
# Extra link library definitions
target_link_libraries(rexx rexxapi ${platform_interpreter_libs}
${CMAKE_REQUIRED_LIBRARIES})
if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
target_link_options(rexx PRIVATE
"-Wl,-plugin-opt=-Wno-stringop-overflow")
endif ()
Build log:
[322/360] : && /usr/bin/g++ -fPIC -O3 -O3 -DNDEBUG -flto -fno-fat-lto-objects
-Wl,-plugin-opt=-Wno-stringop-overflow -shared -Wl,-soname,librexx.so.4 -o
lib/librexx.so.4 CMakeFiles/rexx.dir/interpreter/classes/ArrayClass.cpp.o <cut>
CMakeFiles/rexx.dir/interpreter/platform/unix/RexxMain.cpp.o
-Wl,-rpath,/mnt/c/jlf/local/rexxlocal/oorexx/build/official/main/trunk/ubuntu-aarch64/gcc/release/build/lib:
lib/librexxapi.so.4 -ldl -lrt -lpthread -lcrypt -lnsl -lresolv && :
lto-wrapper: warning: using serial compilation of 22 LTRANS jobs
/local/rexx/oorexx/official/main/trunk/interpreter/classes/StringClass.cpp: In
member function "lower":
/local/rexx/oorexx/official/main/trunk/interpreter/classes/StringClass.cpp:1816:15:
warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
If Claude doesn't spot an error in my test and doesn't find a solution, I
propose disabling IPO/LTO for GCC < 17:
if (ORX_ENABLE_IPO AND NOT CMAKE_VERSION VERSION_LESS "3.9")
include (CheckIPOSupported)
check_ipo_supported (RESULT ipo_supported OUTPUT ipo_output)
if (ipo_supported)
# Don't use IPO with GCC version < 17 because of a false-positive
diagnostic from lto-wrapper:
# writing 1 byte into a region of size 0 [-Wstringop-overflow=]
if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU"
AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 17)
message (STATUS "IPO is supported but is not used with GCC < 17 because
lto-wrapper emits a false-positive diagnostic")
set(CMAKE_INTERPROCEDURAL_OPTIMIZATION FALSE)
# A Debug build wants to be debuggable, and cross-module inlining is the
# opposite of that.
elseif (CMAKE_BUILD_TYPE STREQUAL "Debug")
...
Test ok on WSL Ubuntu:
-- IPO is supported but is not used with GCC < 17 because lto-wrapper emits a
false-positive diagnostic
zero warning "writing 1 byte into a region of size ..."
Test ok on macOS:
-- IPO is supported and enabled
zero warning "writing 1 byte into a region of size ..."
Tested ok on Windows 11 ARM:
-- IPO is supported and enabled
zero warning "writing 1 byte into a region of size ..."
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