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From 63dd776220bb3a443e6b5c0766a389ec33dc4b69 Mon Sep 17 00:00:00 2001
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From: "Paul E. Murphy" <murp@ibm.com>
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Date: Wed, 16 Nov 2022 14:53:39 -0600
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Subject: [PATCH] [release-branch.go1.18] cmd/link/internal/ppc64: fix
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trampoline reuse distance calculation
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If a compatible trampoline has been inserted by a previously laid
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function in the same section, and is known to be sufficiently close,
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it can be reused.
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When testing if the trampoline can be reused, the addend of the direct
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call should be ignored. It is already encoded in the trampoline. If the
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addend is non-zero, and the target sufficiently far away, and just
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beyond direct call reach, this may cause the trampoline to be
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incorrectly reused.
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This was observed on go1.17.13 and openshift-installer commit f3c53b382
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building in release mode with the following error:
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github.com/aliyun/alibaba-cloud-sdk-go/services/cms.(*Client).DescribeMonitoringAgentAccessKeyWithChan.func1: direct call too far: runtime.duffzero+1f0-tramp0-1 -2000078
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Fixes #56833
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Change-Id: I54af957302506d4e3cd5d3121542c83fe980e912
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Reviewed-on: https://go-review.googlesource.com/c/go/+/451415
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Reviewed-by: Cherry Mui <cherryyz@google.com>
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Run-TryBot: Paul Murphy <murp@ibm.com>
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TryBot-Result: Gopher Robot <gobot@golang.org>
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Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>
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Reviewed-by: Than McIntosh <thanm@google.com>
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Reviewed-on: https://go-review.googlesource.com/c/go/+/451916
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Reviewed-by: Joedian Reid <joedian@golang.org>
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---
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.../testdata/script/trampoline_reuse_test.txt | 100 ++++++++++++++++++
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src/cmd/link/internal/ppc64/asm.go | 5 +-
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2 files changed, 103 insertions(+), 2 deletions(-)
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create mode 100644 src/cmd/go/testdata/script/trampoline_reuse_test.txt
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diff --git a/src/cmd/go/testdata/script/trampoline_reuse_test.txt b/src/cmd/go/testdata/script/trampoline_reuse_test.txt
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new file mode 100644
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index 0000000000000..bca897c16d054
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--- /dev/null
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+++ b/src/cmd/go/testdata/script/trampoline_reuse_test.txt
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@@ -0,0 +1,100 @@
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+# Verify PPC64 does not reuse a trampoline which is too far away.
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+# This tests an edge case where the direct call relocation addend should
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+# be ignored when computing the distance from the direct call to the
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+# already placed trampoline
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+[short] skip
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+[!ppc64] [!ppc64le] skip
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+[aix] skip
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+
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+# Note, this program does not run. Presumably, 'DWORD $0' is simpler to
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+# assembly 2^26 or so times.
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+#
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+# We build something which should be laid out as such:
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+#
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+# bar.Bar
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+# main.Func1
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+# bar.Bar+400-tramp0
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+# main.BigAsm
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+# main.Func2
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+# bar.Bar+400-tramp1
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+#
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+# bar.Bar needs to be placed far enough away to generate relocations
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+# from main package calls. and main.Func1 and main.Func2 are placed
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+# a bit more than the direct call limit apart, but not more than 0x400
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+# bytes beyond it (to verify the reloc calc).
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+
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+go build
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+
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+-- go.mod --
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+
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+module foo
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+
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+go 1.19
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+
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+-- main.go --
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+
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+package main
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+
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+import "foo/bar"
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+
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+func Func1()
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+
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+func main() {
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+ Func1()
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+ bar.Bar2()
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+}
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+
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+-- foo.s --
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+
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+TEXT main·Func1(SB),0,$0-0
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+ CALL bar·Bar+0x400(SB)
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+ CALL main·BigAsm(SB)
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+// A trampoline will be placed here to bar.Bar
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+
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+// This creates a gap sufficiently large to prevent trampoline reuse
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+#define NOP64 DWORD $0; DWORD $0; DWORD $0; DWORD $0; DWORD $0; DWORD $0; DWORD $0; DWORD $0;
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+#define NOP256 NOP64 NOP64 NOP64 NOP64
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+#define NOP2S10 NOP256 NOP256 NOP256 NOP256
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+#define NOP2S12 NOP2S10 NOP2S10 NOP2S10 NOP2S10
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+#define NOP2S14 NOP2S12 NOP2S12 NOP2S12 NOP2S12
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+#define NOP2S16 NOP2S14 NOP2S14 NOP2S14 NOP2S14
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+#define NOP2S18 NOP2S16 NOP2S16 NOP2S16 NOP2S16
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+#define NOP2S20 NOP2S18 NOP2S18 NOP2S18 NOP2S18
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+#define NOP2S22 NOP2S20 NOP2S20 NOP2S20 NOP2S20
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+#define NOP2S24 NOP2S22 NOP2S22 NOP2S22 NOP2S22
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+#define BIGNOP NOP2S24 NOP2S24
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+TEXT main·BigAsm(SB),0,$0-0
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+ // Fill to the direct call limit so Func2 must generate a new trampoline.
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+ // As the implicit trampoline above is just barely unreachable.
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+ BIGNOP
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+ MOVD $main·Func2(SB), R3
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+
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+TEXT main·Func2(SB),0,$0-0
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+ CALL bar·Bar+0x400(SB)
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+// Another trampoline should be placed here.
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+
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+-- bar/bar.s --
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+
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+#define NOP64 DWORD $0; DWORD $0; DWORD $0; DWORD $0; DWORD $0; DWORD $0; DWORD $0; DWORD $0;
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+#define NOP256 NOP64 NOP64 NOP64 NOP64
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+#define NOP2S10 NOP256 NOP256 NOP256 NOP256
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+#define NOP2S12 NOP2S10 NOP2S10 NOP2S10 NOP2S10
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+#define NOP2S14 NOP2S12 NOP2S12 NOP2S12 NOP2S12
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+#define NOP2S16 NOP2S14 NOP2S14 NOP2S14 NOP2S14
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+#define NOP2S18 NOP2S16 NOP2S16 NOP2S16 NOP2S16
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+#define NOP2S20 NOP2S18 NOP2S18 NOP2S18 NOP2S18
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+#define NOP2S22 NOP2S20 NOP2S20 NOP2S20 NOP2S20
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+#define NOP2S24 NOP2S22 NOP2S22 NOP2S22 NOP2S22
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+#define BIGNOP NOP2S24 NOP2S24 NOP2S10
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+// A very big not very interesting function.
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+TEXT bar·Bar(SB),0,$0-0
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+ BIGNOP
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+
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+-- bar/bar.go --
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+
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+package bar
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+
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+func Bar()
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+
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+func Bar2() {
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+}
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diff --git a/src/cmd/link/internal/ppc64/asm.go b/src/cmd/link/internal/ppc64/asm.go
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index 73c2718a3369f..879adaa965050 100644
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--- a/src/cmd/link/internal/ppc64/asm.go
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+++ b/src/cmd/link/internal/ppc64/asm.go
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@@ -809,8 +809,9 @@ func trampoline(ctxt *ld.Link, ldr *loader.Loader, ri int, rs, s loader.Sym) {
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if ldr.SymValue(tramp) == 0 {
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break
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}
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-
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- t = ldr.SymValue(tramp) + r.Add() - (ldr.SymValue(s) + int64(r.Off()))
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+ // Note, the trampoline is always called directly. The addend of the original relocation is accounted for in the
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+ // trampoline itself.
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+ t = ldr.SymValue(tramp) - (ldr.SymValue(s) + int64(r.Off()))
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// With internal linking, the trampoline can be used if it is not too far.
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// With external linking, the trampoline must be in this section for it to be reused.
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