fix: use real GN arg for linux shared-library TLS mode#1970
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#1911 tried to inject `V8_TLS_USED_IN_LIBRARY` into V8's compilation by writing `extra_cflags=["-DV8_TLS_USED_IN_LIBRARY"]` into args.gn, but `extra_cflags` isn't a declared top-level GN arg anywhere in chromium_build or V8 -- it's only used as an *invoker parameter* inside toolchain definitions in `build/toolchain/gcc_toolchain.gni`. GN silently accepts unknown args, so the define never reached the compiler. V8's thread-locals stayed in `local-exec` TLS model, and linking rusty_v8 into a downstream cdylib failed with: rust-lld: error: relocation R_X86_64_TPOFF32 against v8::internal::g_current_isolate_ cannot be used with -shared You can verify by grepping the generated `gn_out/obj/v8/v8_base_without_compiler.ninja` after a build -- `V8_TLS_USED_IN_LIBRARY` is absent from `defines = ...`. Switch to setting `v8_monolithic_for_shared_library=true`, which is a real declared GN arg in V8's BUILD.gn. The companion denoland/v8 patch (#TBD) wires that arg into `internal_config` so the define actually reaches V8 internal `.cc` files where the TLS variables live.
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👋 We ran into this issue while trying to link rusty_v8 into a Ruby native extension (cdylib) via |
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Hello! Is there any chance for this PR to be be merged soon? I have a library for Ruby similar to https://github.com/aglundahl/deno_rider I'd like to publish which depends on it |
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Summary
Fixes the shared-library TLS mode injection introduced in #1911 -- the previous implementation wrote
extra_cflags=["-DV8_TLS_USED_IN_LIBRARY"]intoargs.gn, butextra_cflagsis not a declared top-level GN arg anywhere in chromium_build or V8. It's only used as an invoker parameter inside toolchain definitions (build/toolchain/gcc_toolchain.gni:277). GN silently accepts unknown args, so the define never reached the compiler. V8's thread-locals stayed inlocal-execTLS model, and linking rusty_v8 into a downstream cdylib failed with:You can verify on
maintoday: build withV8_FROM_SOURCE=1, then grepgn_out/obj/v8/v8_base_without_compiler.ninja--V8_TLS_USED_IN_LIBRARYis absent from thedefines = ...line, despite being present inargs.gn.Change
Replace the
extra_cflags=[...]injection withv8_monolithic_for_shared_library=true, which is a real declared GN arg in V8'sBUILD.gn:379.Companion change in denoland/v8
This PR alone is not sufficient -- denoland/v8#20 is required to wire
v8_monolithic_for_shared_libraryinto V8'sinternal_configso the define actually reaches V8 internal.ccfiles (where the TLS variables live). Currently the arg only adds the define inside the:featuresconfig, which is consumed only by external embedders, not by V8 itself.This rusty_v8 PR should land after denoland/v8#20 has been picked up by the autoroll into
14.7-lkgr-denolandand the v8 submodule pointer here has been bumped to that commit.Test plan
V8_FROM_SOURCE=1 cargo buildsucceeds for a cdylib downstream (verified locally against Deno'sdenort_desktop).gn_out/obj/v8/v8_base_without_compiler.ninja--V8_TLS_USED_IN_LIBRARYis now indefines = ....