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Enable real dynamic linking with -shared by default - #25930

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May 21, 2026
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Enable real dynamic linking with -shared by default#25930
sbc100 merged 6 commits into
emscripten-core:mainfrom
sbc100:shared_flag_part2

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@sbc100 sbc100 commented Dec 11, 2025 •
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This change essentially disables FAKE_DYLIBS by default, which in
turn means -shared will now produce dynamic libraries by default.

If you want the old behaviour you now need -sFAKE_DYLIBS.

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sbc100 commented Dec 11, 2025
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Comment thread cmake/Modules/Platform/Emscripten.cmake Resolved
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Comment thread site/source/docs/tools_reference/settings_reference.rst Resolved
Comment thread tools/building.py Resolved
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I wonder what would happen if we tested this with Binaryen. it doesn't seem prepared to force the Emscripten build to be static (assuming that's the behavior we actually want).

Comment thread test/test_core.py Resolved
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sbc100 force-pushed the shared_flag_part2 branch from 3b0addc to 2a98976 Compare May 12, 2026 01:15
@sbc100 sbc100 changed the title Disable FAKE_DYLIBS by default Enable real dynamic linking by default May 12, 2026
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Comment thread cmake/Modules/Platform/Emscripten.cmake Resolved
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sbc100 added a commit that referenced this pull request May 14, 2026
@sbc100
Improve test_multiply_defined_libsymbols (#26953)
c3736fb 
This test was first added in c735bb6. Hopefully these changes make it
more obvious what is being tested, and also test more commonly used
flags (`-shared` vs `-r`).

Split out from #25930.
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sbc100 commented May 15, 2026

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I wonder what would happen if we tested this with Binaryen. it doesn't seem prepared to force the Emscripten build to be static (assuming that's the behavior we actually want).

I actually ended up leaving the cmake TARGET_SUPPORTS_SHARED_LIBS setting as False until we resolve https://gitlab.kitware.com/cmake/cmake/-/work_items/27240

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OK, I think this change is in pretty good shape now

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sbc100 force-pushed the shared_flag_part2 branch from 19b4b57 to 28ec96d Compare May 15, 2026 19:31
@sbc100 sbc100 changed the title Enable real dynamic linking by default Enable real dynamic linking with -shared by default May 15, 2026
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sbc100 force-pushed the shared_flag_part2 branch from 28ec96d to 6b35408 Compare May 15, 2026 21:40
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sbc100 commented May 16, 2026

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@kripken @dschuff this change is pretty small now. No codesize changes anymore.

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lgtm % comment

Comment thread ChangeLog.md Resolved
@sbc100
sbc100 disabled auto-merge May 21, 2026 22:04
@sbc100
sbc100 merged commit bbc19e2 into emscripten-core:main May 21, 2026
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sbc100 deleted the shared_flag_part2 branch May 21, 2026 22:04
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hoodmane added a commit to pyodide/pyodide that referenced this pull request Jul 28, 2026
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Reduce patch to fix emscripten-core/emscripten#25930 regression (#6387)
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Reduce patch to fix emscripten-core/emscripten#25930 regression (#6387)
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hoodmane added a commit to pyodide/pyodide that referenced this pull request Jul 29, 2026
@hoodmane
Reduce patch to fix emscripten-core/emscripten#25930 regression (#6387)
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hoodmane added a commit to pyodide/pyodide that referenced this pull request Jul 31, 2026
@hoodmane
Reduce patch to fix emscripten-core/emscripten#25930 regression (#6387)
8d2dcc5
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sbc100 restored the shared_flag_part2 branch August 10, 2026 22:33
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sbc100 added a commit to sbc100/emscripten that referenced this pull request Oct 23, 2026
@sbc100
[dylink] Restore --whole-archive when linking with -sSIDE_MODULE=1
203a550 
In emscripten-core#25930, `-shared` was implemented by defaulting `SIDE_MODULE` to `1`
(which implies `LINKABLE=1`) and then special-casing `lld_flags` in
`tools/building.py` to avoid `--whole-archive`. That special case had
the unintended regression of also disabling `--whole-archive` for
explicit `-sSIDE_MODULE=1` builds, while still running `wasm-ld` twice
in `phase_link` for `-shared` due to `LINKABLE=1`.

Instead, default `SIDE_MODULE` to `2` when `-shared` is used so
`LINKABLE` remains disabled and `--whole-archive` is applied whenever
`LINKABLE` is set. This restores the pre-emscripten-core#25930 `--whole-archive`
behavior for `-sSIDE_MODULE=1` without enabling it for `-shared`.

To keep native linker semantics for `-shared`, avoid passing
`--no-export-dynamic` when `-shared` is specified so default-visibility
symbols in object files are still exported automatically (unlike
explicit `-sSIDE_MODULE=2`, which continues to DCE unexported symbols).

Supersedes emscripten-core#27430.

Fixes: emscripten-core#27403
sbc100 added a commit to sbc100/emscripten that referenced this pull request Oct 23, 2026
@sbc100
[dylink] Restore --whole-archive when linking with -sSIDE_MODULE=1
1ee38c3 
In emscripten-core#25930, `-shared` was implemented by defaulting `SIDE_MODULE` to `1`
(which implies `LINKABLE=1`) and then special-casing `lld_flags` in
`tools/building.py` to avoid `--whole-archive`. That special case had
the unintended regression of also disabling `--whole-archive` for
explicit `-sSIDE_MODULE=1` builds, while still running `wasm-ld` twice
in `phase_link` for `-shared` due to `LINKABLE=1`.

Instead, default `SIDE_MODULE` to `2` when `-shared` is used so
`LINKABLE` remains disabled and `--whole-archive` is applied whenever
`LINKABLE` is set. This restores the pre-emscripten-core#25930 `--whole-archive`
behavior for `-sSIDE_MODULE=1` without enabling it for `-shared`.

To keep native linker semantics for `-shared`, avoid passing
`--no-export-dynamic` when `-shared` is specified so default-visibility
symbols in object files are still exported automatically (unlike
explicit `-sSIDE_MODULE=2`, which continues to DCE unexported symbols).

Supersedes emscripten-core#27430.

Fixes: emscripten-core#27403
sbc100 added a commit to sbc100/emscripten that referenced this pull request Oct 23, 2026
@sbc100
[dylink] Restore --whole-archive when linking with -sSIDE_MODULE=1
849e531 
In emscripten-core#25930, `-shared` was implemented by defaulting `SIDE_MODULE` to `1`
(which implies `LINKABLE=1`) and then special-casing `lld_flags` in
`tools/building.py` to avoid `--whole-archive`. That special case had
the unintended regression of also disabling `--whole-archive` for
explicit `-sSIDE_MODULE=1` builds, while still running `wasm-ld` twice
in `phase_link` for `-shared` due to `LINKABLE=1`.

Instead, default `SIDE_MODULE` to `2` when `-shared` is used so
`LINKABLE` remains disabled and `--whole-archive` is applied whenever
`LINKABLE` is set. This restores the pre-emscripten-core#25930 `--whole-archive`
behavior for `-sSIDE_MODULE=1` without enabling it for `-shared`.

To keep native linker semantics for `-shared`, avoid passing
`--no-export-dynamic` when `-shared` is specified so default-visibility
symbols in object files are still exported automatically (unlike
explicit `-sSIDE_MODULE=2`, which continues to DCE unexported symbols).

Supersedes emscripten-core#27430.

Fixes: emscripten-core#27403
sbc100 added a commit to sbc100/emscripten that referenced this pull request Oct 23, 2026
@sbc100
[dylink] Restore --whole-archive when linking with -sSIDE_MODULE=1
6f27d59 
In emscripten-core#25930, `-shared` was implemented by defaulting `SIDE_MODULE` to `1`
(which implies `LINKABLE=1`) and then special-casing `lld_flags` in
`tools/building.py` to avoid `--whole-archive`. That special case had
the unintended regression of also disabling `--whole-archive` for
explicit `-sSIDE_MODULE=1` builds, while still running `wasm-ld` twice
in `phase_link` for `-shared` due to `LINKABLE=1`.

Instead, default `SIDE_MODULE` to `2` when `-shared` is used so
`LINKABLE` remains disabled and `--whole-archive` is applied whenever
`LINKABLE` is set. This restores the pre-emscripten-core#25930 `--whole-archive`
behavior for `-sSIDE_MODULE=1` without enabling it for `-shared`.

To keep native linker semantics for `-shared`, avoid passing
`--no-export-dynamic` when `-shared` is specified so default-visibility
symbols in object files are still exported automatically (unlike
explicit `-sSIDE_MODULE=2`, which continues to DCE unexported symbols).

Supersedes emscripten-core#27430.

Fixes: emscripten-core#27403
sbc100 added a commit to sbc100/emscripten that referenced this pull request Oct 27, 2026
@sbc100
[dylink] Restore --whole-archive when linking with -sSIDE_MODULE=1
7cd837f 
In emscripten-core#25930, `-shared` was implemented by defaulting `SIDE_MODULE` to `1`
(which implies `LINKABLE=1`) and then special-casing `lld_flags` in
`tools/building.py` to avoid `--whole-archive`. That special case had
the unintended regression of also disabling `--whole-archive` for
explicit `-sSIDE_MODULE=1` builds, while still running `wasm-ld` twice
in `phase_link` for `-shared` due to `LINKABLE=1`.

Instead, default `SIDE_MODULE` to `2` when `-shared` is used so
`LINKABLE` remains disabled and `--whole-archive` is applied whenever
`LINKABLE` is set. This restores the pre-emscripten-core#25930 `--whole-archive`
behavior for `-sSIDE_MODULE=1` without enabling it for `-shared`.

To keep native linker semantics for `-shared`, avoid passing
`--no-export-dynamic` when `-shared` is specified so default-visibility
symbols in object files are still exported automatically (unlike
explicit `-sSIDE_MODULE=2`, which continues to DCE unexported symbols).

Supersedes emscripten-core#27430.

Fixes: emscripten-core#27403
sbc100 added a commit that referenced this pull request Oct 27, 2026
@sbc100
[dylink] Restore --whole-archive when linking with -sSIDE_MODULE=1 (
e9aeb39 
#28055)

In #25930, `-shared` was implemented by defaulting `SIDE_MODULE` to `1`
(which implies `LINKABLE=1`) and then special-casing `lld_flags` in
`tools/building.py` to avoid `--whole-archive`. That special case had
the unintended regression of also disabling `--whole-archive` for
explicit `-sSIDE_MODULE=1` builds, while still running `wasm-ld` twice
in `phase_link` for `-shared` due to `LINKABLE=1`.

Instead, default `SIDE_MODULE` to `2` when `-shared` is used so
`LINKABLE` remains disabled and `--whole-archive` is applied whenever
`LINKABLE` is set. This restores the pre-#25930 `--whole-archive`
behavior for `-sSIDE_MODULE=1` without enabling it for `-shared`.

To keep native linker semantics for `-shared`, avoid passing
`--no-export-dynamic` when `-shared` is specified so default-visibility
symbols in object files are still exported automatically (unlike
explicit `-sSIDE_MODULE=2`, which continues to DCE unexported symbols).

Supersedes #27430.

Fixes: #27403
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