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nehaljwani opened this issue Jun 13, 2022 · 6 comments
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cmd/compile: incomplete relocation support on ppc64le #53345

nehaljwani opened this issue Jun 13, 2022 · 6 comments
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@pmur
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arch-ppc64x compiler/runtime Issues related to the Go compiler and/or runtime. FeatureRequest Issues asking for a new feature that does not need a proposal. FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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Go1.20

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@nehaljwani
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nehaljwani commented Jun 13, 2022 •
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Since 2c4f389c I am unable to compile go with CGO_ENABLED=1 on ppc64le with GCC 10.3.0 and binutils 2.36.1

I see errors like:

/path/to/go/pkg/linux_ppc64le/a/b/c/d.a(_x???.o): unknown relocation type <>; compiled without -fpic?

Where <> are numbers: 31, 60, 119, 120. I am not sure if I am reading this correctly, but these correspond to:
R_PPC_PLT16_HA, R_PPC64_PLT16_LO_DS, R_POWERPC_PLTSEQ, R_POWERPC_PLTCALL and references to these are missing in:

src/cmd/link/internal/loadelf/ldelf.go
src/cmd/link/internal/ppc64/asm.go
src/debug/elf/elf.go
@nehaljwani nehaljwani mentioned this issue Jun 13, 2022
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@mengzhuo mengzhuo changed the title Incomplete relocation support on ppc64le cmd/compile: incomplete relocation support on ppc64le Jun 13, 2022
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@golang/ppc64 @laboger

@mengzhuo mengzhuo added the FeatureRequest Issues asking for a new feature that does not need a proposal. label Jun 13, 2022
@pmur
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pmur commented Jun 13, 2022

Hi @nehaljwani, thank you for reporting. Would you be able to share the gcc flags used to compile the C code? A simplified test case would help me. I suspect it just needs to make libc call with the compiler options used on the project.

I am still digging through the linked CI logs trying to understand how the linked utility is being compiled.

A trivial workaround is to explicitly request external linking on ppc64le. This was the behavior prior 1.18 with any cgo usage. I will try to implement these relocs. They are fairly new (introduced with ELFv2 1.5), but I suspect we need to handle with newer GCC.

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pmur commented Jun 13, 2022

@nehaljwani is one of the CFLAG options -fno-plt, or similar option to optimize library calls in C/C++? I can reproduce a similar error using this option.

@nehaljwani
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Hello @pmur, we use:

CGO_CFLAGS=-ftree-vectorize -fPIC -fstack-protector-strong -fno-plt -O3 -pipe

@thanm thanm added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Jun 15, 2022
@pmur pmur self-assigned this Jun 16, 2022
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Change https://go.dev/cl/412715 mentions this issue: cmd/link: optimize PPC64 inline plt sequences if local

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Change https://go.dev/cl/412714 mentions this issue: debug/elf, cmd/link: support -fno-plt compiled gcc objects on ppc64le

@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Jul 13, 2022
@mknyszek mknyszek moved this to Triage Backlog in Go Compiler / Runtime Jul 15, 2022
@pmur pmur mentioned this issue Aug 8, 2022
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@seankhliao seankhliao added this to the Unplanned milestone Aug 20, 2022
Repository owner moved this from Triage Backlog to Done in Go Compiler / Runtime Sep 15, 2022
@dmitshur dmitshur modified the milestones: Unplanned, Go1.20 Sep 26, 2022
gopherbot pushed a commit that referenced this issue Oct 5, 2022
@pmur
cmd/link: optimize PPC64 inline plt sequences if local
c318f19 
Indirect branches are much more expensive than direct. If the call is
known to be local, we can replace most of the operations with a nop,
and call directly.

Updates #53345

Change-Id: Icfff9ec1f6c7f8e4181f0f28976033308d2f53eb
Reviewed-on: https://go-review.googlesource.com/c/go/+/412715
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
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arch-ppc64x compiler/runtime Issues related to the Go compiler and/or runtime. FeatureRequest Issues asking for a new feature that does not need a proposal. FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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