RFR: 8372643: Warning message on macos when building the JDK - (arm64) /tmp/lto.o unable to open object file: No such file or directory

[Matthias Baesken]

On Fri, 28 Nov 2025 15:47:04 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

> When building the recent mainline JDK (26), I see the following warning messages:
> 
> warning: (arm64) /tmp/lto.o unable to open object file: No such file or directory
> warning: no debug symbols in executable (-arch arm64)
> 
> 
> The build completes normally even with these warnings.
> I am on macos aarch64, but I see the same warning on macos x64 and aarch64 in our CI.
> Seems we miss a linker flag for libs built with lto (libsplashscreen), because the Apple linker has the following issue
> 
> https://clang.llvm.org/docs/CommandGuide/clang.html
> Note
> 
> `
> On Darwin, when using [-flto](https://clang.llvm.org/docs/CommandGuide/clang.html#cmdoption-flto) along with [-g](https://clang.llvm.org/docs/CommandGuide/clang.html#cmdoption-g) and compiling and linking in separate steps, you also need to pass -Wl,-object_path_lto,<lto-filename>.o at the linking step to instruct the ld64 linker not to delete the temporary object file generated during Link Time Optimization (this flag is automatically passed to the linker by Clang if compilation and linking are done in a single step). This allows debugging the executable as well as generating the .dSYM bundle using dsymutil(1).`

I moved the special setting to Flags.gmk as suggested ,
The lto helper file goes now to the build dir; for example in my test setup 
`/priv/openjdk/build_mac/support/native/java.desktop/libsplashscreen/splashscreen_lto_helper.o`

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PR Comment: https://git.openjdk.org/jdk/pull/28559#issuecomment-3607397899