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cmd/asm: 386 assembler silently drops indices when indexing symbols #41286

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clausecker opened this issue Sep 9, 2020 · 1 comment
Open

cmd/asm: 386 assembler silently drops indices when indexing symbols #41286

clausecker opened this issue Sep 9, 2020 · 1 comment
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@clausecker
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@clausecker clausecker commented Sep 9, 2020

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

$ go version
go version go1.15 linux/amd64

Does this issue reproduce with the latest release?

Yes.

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

go env Output
$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build142714031=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Create an assembly file with the following content, assemble it for 386:

DATA bar<>(SB)/4, $0x0
GLOBL bar<>(SB), 0, $4

TEXT foo<>(SB), 4, $0
	MOVL bar<>(SB)(AX), AX

Then, dump the resulting object file.

What did you expect to see?

Something like

TEXT foo<1>(SB) gofile../.../bug.s
  bug.s:5		0x142			8b0500000000		MOVL 0(AX), AX		[2:6]R_ADDR:bar		

What did you see instead?

TEXT foo<1>(SB) gofile../.../bug.s
  bug.s:5		0x142			8b0500000000		MOVL 0, AX		[2:6]R_ADDR:bar		

It appears that the index register has been dropped silently. Please either fail this kind of code during assembly or add support for indexing into global symbols.

@cherrymui
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@cherrymui cherrymui commented Sep 9, 2020

Index into a global symbol is not a supported addressing mode. We should emit an error.

@andybons andybons added the NeedsFix label Sep 10, 2020
@andybons andybons added this to the Unplanned milestone Sep 10, 2020
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