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cmd/link: -buildmode=c-shared exports many functions, not just //export functions [1.15 backport] #43591

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gopherbot opened this issue Jan 8, 2021 · 14 comments
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cmd/link: -buildmode=c-shared exports many functions, not just //export functions [1.15 backport] #43591

gopherbot opened this issue Jan 8, 2021 · 14 comments
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CherryPickApproved Used during the release process for point releases FrozenDueToAge
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Go1.15.11

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@gopherbot
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gopherbot commented Jan 8, 2021 •
edited by dmitshur
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@networkimprov requested issue #30674 (fixed by 6f7b553 in Go 1.16) to be considered for backport to the next 1.15 minor release.

@gopherbot please backport to 1.15

buildmode=pie became the default in 1.15, so folks have to manually set buildmode=exe to work around this bug.
@gopherbot gopherbot added the CherryPickCandidate Used during the release process for point releases label Jan 8, 2021
@gopherbot gopherbot mentioned this issue Jan 8, 2021
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@gopherbot gopherbot added this to the Go1.15.7 milestone Jan 8, 2021
@networkimprov
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Filed in case fix for #40795 depends on this.

@dmitshur dmitshur modified the milestones: Go1.15.7, Go1.15.8 Jan 19, 2021
@cagedmantis cagedmantis modified the milestones: Go1.15.8, Go1.15.9 Feb 4, 2021
@dmitshur
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We've discussed this in a release meeting and it didn't seem like this is needed for #43592. CC @ianlancetaylor, @jeremyfaller.

@networkimprov If you still think that CL 262797 (fix for #30674) should be backported, please provide a rationale as described in the third paragraph of https://golang.org/wiki/MinorReleases. It seems to be about buildmode=c-shared, which doesn't match the current backport rationale.

@networkimprov
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You need to ask the authors of the fixes for this and #40795; somewhere I read this might be needed for its backport.

cc @qmuntal

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qmuntal commented Feb 18, 2021 •
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e463c28 adds a hardcoded dummy variable tagged with __declspec(dllexport) and removes the -Wl,--export-all-symbols flag from the linker arguments. This tells mingw-w64 to only add the symbols tagged with __declspec(dllexport) into the DLL export table. The dummy variable is necessary because the default behavior of mingw-w64 is to export everything, even if -Wl,--export-all-symbols is not present, unless there is a symbol tagged with __declspec(dllexport).

What 6f7b553 does is add the __declspec(dllexport) tag to all methods that should be exported.

Backporting e463c28 without either backporting 6f7b553 or setting again -Wl,--export-all-symbols for c-shared means that the generated binary won't honor the //export comment and that will only export the dummy variable (_cgo_dummy_export).

@qmuntal qmuntal mentioned this issue Feb 18, 2021
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@dmitshur
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dmitshur commented Mar 8, 2021 •
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Thank you for the rationale, it's very helpful.

We've discussed this candidate and agreed it is also okay to backport, so both e463c28 (#43592) and 6f7b553 (this issue) will be backported. Only Go 1.15 needs this backport.

@dmitshur dmitshur added CherryPickApproved Used during the release process for point releases and removed CherryPickCandidate Used during the release process for point releases labels Mar 8, 2021
@networkimprov
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FYI @alexbrainman @zx2c4

@toothrot toothrot modified the milestones: Go1.15.9, Go1.15.10 Mar 10, 2021
@gopherbot
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Change https://golang.org/cl/300693 mentions this issue: [release-branch.go1.15] [release-branch.go.1.15] cmd/link,cmd/cgo: avoid exporting all symbols on windows buildmode=c-shared/pie

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Change https://golang.org/cl/300694 mentions this issue: [release-branch.go1.15] cmd/cgo: remove unnecessary space in cgo export header

@cagedmantis cagedmantis modified the milestones: Go1.15.10, Go1.15.11 Mar 11, 2021
@networkimprov
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Should https://golang.org/cl/300692 reference this issue?

@dmitshur
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CL 300693 is a cherry-pick of CL 262797 and includes "Fixes #43591", the backport issue for CL 262797.
CL 300692 is a cherry-pick of CL 264459 and includes "Fixes #43592", the backport issue for CL 264459.

It seems okay to me that CL 300692 doesn't reference this issue, since CL 300693 does.

@networkimprov
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I'm referring to #40795 which this is the backport for.

@dmitshur
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I'm not sure what you mean. This is a 1.15 backport issue for #30674. The 1.15 backport issue for #40795 is #43592. If it's important, can you please leave a review comment on the affected CL?

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Closed by merging 5055314 to release-branch.go1.15.

gopherbot pushed a commit that referenced this issue Mar 31, 2021
@qmuntal @dmitshur
[release-branch.go1.15] cmd/cgo: avoid exporting all symbols on windo…
5055314 
…ws buildmode=c-shared

Disable default symbol auto-export behaviour by marking exported
function with the __declspec(dllexport) attribute. Old behaviour can
still be used by setting -extldflags=-Wl,--export-all-symbols.

See https://sourceware.org/binutils/docs/ld/WIN32.html for more info.

This change cuts 50kb of a "hello world" dll.

Updates #6853.
Updates #30674.
Fixes #43591.

Change-Id: I9c7fb09c677cc760f24d0f7d199740ae73981413
Reviewed-on: https://go-review.googlesource.com/c/go/+/262797
Run-TryBot: Ian Lance Taylor <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Alex Brainman <[email protected]>
Trust: Alex Brainman <[email protected]>
Reviewed-on: https://go-review.googlesource.com/c/go/+/300693
Trust: Dmitri Shuralyov <[email protected]>
Run-TryBot: Dmitri Shuralyov <[email protected]>
Reviewed-by: David Chase <[email protected]>
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gopherbot pushed a commit that referenced this issue Mar 31, 2021
@qmuntal @dmitshur
[release-branch.go1.15] cmd/cgo: remove unnecessary space in cgo expo…
1373d92 
…rt header

The cgo header has an unnecessary space in the exported function
definition on non-windows goos.

This was introduced in go1.16 so it would be good to fix it before
release.

Example:

// Current behavior, notice there is an unecessary space
// between extern and void
extern  void Foo();

// With this CL
extern void Foo();

Updates #43591.

Change-Id: Ic2c21f8d806fe35a7be7183dbfe35ac605b6e4f6
Reviewed-on: https://go-review.googlesource.com/c/go/+/283892
Reviewed-by: Ian Lance Taylor <[email protected]>
Trust: Katie Hockman <[email protected]>
Reviewed-on: https://go-review.googlesource.com/c/go/+/300694
Trust: Dmitri Shuralyov <[email protected]>
Trust: Emmanuel Odeke <[email protected]>
Run-TryBot: Dmitri Shuralyov <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: David Chase <[email protected]>
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