Globally enable linker dead-code elimination on Unix

[Copilot]

-ffunction-sections is set globally for non-MSVC builds in eng/native/configurecompiler.cmake, but the matching -Wl,--gc-sections / -Wl,-dead_strip is never passed to the linker, so on Linux/macOS unreferenced sections are not actually stripped. Windows is unaffected because /OPT:REF is set globally. This became visible in #126367 when apphost picked up a dn-containers link dependency and grew unexpectedly.

cc @dotnet/appmodel @jkotas

eng/native/configurecompiler.cmake:

• Compile: add -fdata-sections alongside the existing -ffunction-sections (Unix/WASI) so unreferenced data, not just functions, can be stripped.
• Link, Apple: -Wl,-dead_strip for Checked / Release / RelWithDebInfo.
• Link, other Unix (ELF, incl. Linux, BSDs, SunOS, Haiku, wasm-ld): -Wl,--gc-sections for the same three configurations.
• Debug: intentionally untouched — preserves full symbols, incremental linking, and the existing PAL -Wl,--no-gc-sections debug+sanitizers workaround.

Targets that need specific symbols retained can still opt out per-symbol via KEEP / __attribute__((used)) / export lists; -fvisibility=hidden plus existing export lists already cover the common cases.

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[Copilot]

Pull request overview

This PR updates the native build configuration (eng/native/configurecompiler.cmake) to enable link-time dead-code elimination (section GC) by default on non-Windows Unix builds, and ensures compilation places both functions and data into separate sections to make that elimination effective.

Changes:

• Add global non-Debug linker flags to strip unused sections (-Wl,-dead_strip on Apple, -Wl,--gc-sections elsewhere).
• Add -fdata-sections alongside the existing -ffunction-sections for Unix/WASI compilation.
• Update nearby comments to describe the function/data sectioning intent.

Show a summary per file

File	Description
eng/native/configurecompiler.cmake	Enables global link-time section GC on Unix non-Debug builds and adds -fdata-sections to support stripping unused data.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 3

[Copilot]

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 1

[elinor-fung]

@copilot what is the size delta on linux for runtime binaries (in particular coreclr and apphost) with this change?

[Copilot]

@copilot what is the size delta on linux for runtime binaries (in particular coreclr and apphost) with this change?

I'm unable to run a full Linux build in this environment to produce actual measurements. What I can say:

• apphost: PR Enable linker dead code elimination for apphost, dotnet, and nethost #128228 already measured the effect of --gc-sections on apphost in isolation (76,240 → 58,640 bytes, −23% stripped). Since this PR applies the same flags globally, apphost should see roughly the same benefit.
• coreclr (libcoreclr.so): This is the harder question and I can't provide a number without a real build. libcoreclr.so has a large, well-defined exported surface (EE exports, profiler APIs, DAC interfaces, etc.), and -fvisibility=hidden is already applied globally, so the linker's view of reachable symbols is constrained by the export lists. That said, internal dead code (e.g. unused static initializers, cold paths behind feature flags) could be stripped. I'd expect a smaller percentage reduction than apphost/dotnet, but still measurable.

If you can kick off a CI build or a local linux-x64 Release build comparing main vs. this branch with size/wc -c on the stripped binaries, that would give the definitive numbers. I'm happy to help interpret the results.

[Copilot]

Pull request overview

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[Copilot]

Pull request overview

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[Copilot]

Pull request overview

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[Copilot]

Pull request overview

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