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cmd/link: add support for c-shared, plugin buildmodes on ppc64le #20756

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laboger opened this issue Jun 22, 2017 · 4 comments

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commented Jun 22, 2017

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

This is intended for go 1.10

What operating system and processor architecture are you using (go env)?

ppc64le Ubuntu, RH

These buildmodes are currently not supported on ppc64le. I've been working on plugin, and it seems to work but it needs some clean up.

I tried to enable c-shared but something's missing and I'm not sure what. When I try to run the tests from testcshared, some work but the one that does a dlopen on a cshared library is getting a segv in dl_open_worker.

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commented Aug 7, 2017

I found the problem with c-shared. The code in runtime/rt0_linux_ppc64le.s for _rt0_ppc64le_linux_lib is incorrect because it computes the callee's r2 at the beginning of the function and then saves it onto the caller's stack. This shouldn't be done because the caller should be saving and restoring its own r2 before and after the call.

Once this is corrected then c-shared works for ppc64le and can be enabled.

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commented Aug 9, 2017

Change https://golang.org/cl/53890 mentions this issue: cmd/build: support buildmode c-shared on ppc64le

gopherbot pushed a commit that referenced this issue Aug 9, 2017

cmd/go,cmd/link: support buildmode c-shared on ppc64le
This change enables buildmode c-shared on ppc64le.

A bug was fixed in runtime/rt0_linux_ppc64le.s that was necessary to
make this work.  In _rt0_ppc64le_linux_lib, there is code to store
the value of r2 onto the caller's stack.  However, if this file
is compiled using a build mode that maintains the TOC address in
r2, then instructions will be inserted at the beginning of this
function to generate the r2 value for the callee, not the caller.
That means the r2 value for the callee is stored onto the caller's
stack.  If caller and callee don't have the same r2 values, then
the caller will restore the wrong r2 value after it returns.  This
situation can happen when using dlopen since the caller of this
function will be in ld64.so and will definitely have a different
TOC.

Updates #20756

Change-Id: I6e165e0d0716e73721bbbcc520e8302e4856e3ba
Reviewed-on: https://go-review.googlesource.com/53890
Reviewed-by: Ian Lance Taylor <iant@golang.org>
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commented Aug 15, 2017

Change https://golang.org/cl/55850 mentions this issue: cmd/link: enable -buildmode=plugin for ppc64le

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commented Sep 11, 2017

Change https://golang.org/cl/62890 mentions this issue: cmd/compile: request r12 for indirect calls on ppc64le

gopherbot pushed a commit that referenced this issue Sep 11, 2017

cmd/compile: request r12 for indirect calls on ppc64le
On ppc64le, functions compiled with -shared expect r12 to
hold the function's address for indirect calls. Previously
this was enforced by generating a move instruction if the
address wasn't already in r12. This change avoids that extra
move by requesting r12 in the CALL ops that do indirect calls.

As a result of adding support for plugins on ppc64le, it was
discovered that there would be more cases where this extra
move was needed, so this seemed like a better solution.

Updates #20756

Change-Id: I6770885a46990f78c6d2902a715dcdaa822192a1
Reviewed-on: https://go-review.googlesource.com/62890
Run-TryBot: Lynn Boger <laboger@linux.vnet.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

@gopherbot gopherbot closed this in e9cbabb Sep 12, 2017

laboger added a commit to powertechpreview/go that referenced this issue Feb 2, 2018

cmd/link: enable -buildmode=c-shared for ppc64le
This enables -buildmode=c-shared on ppc64le.
It is described in golang issue golang#20756

@golang golang locked and limited conversation to collaborators Sep 12, 2018

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