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cmd/link: -buildmode=pie -linkshared generates large binaries #40416

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kiap opened this issue Jul 26, 2020 · 7 comments
Closed

cmd/link: -buildmode=pie -linkshared generates large binaries #40416

kiap opened this issue Jul 26, 2020 · 7 comments

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@kiap
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@kiap kiap commented Jul 26, 2020

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

$ go version

go version go1.15rc1 linux/amd64

Does this issue reproduce with the latest release?

Yes

This was working before on 1.14.6 and was working on every every version

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

go env Output
$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/usr/src/.cache"
GOENV="/root/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/usr/src/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/usr/src/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/src/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/src/go/pkg/tool/linux_amd64"
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-build647301757=/tmp/go-build -gno-record-gcc-switches"

What did you do?

go install -v -ldflags '-s -w' -gcflags '-trimpath /usr/src/go' -buildmode=shared -linkshared -pkgdir /usr/src/lib std

go install -v -ldflags '-s -w' -gcflags '-trimpath /usr/src/go' -buildmode=pie -linkshared -pkgdir /usr/src/lib prog

What did you expect to see?

The binary should be linked correctly and builds linked to standard library

What did you see instead?

static executable

@ianlancetaylor
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@ianlancetaylor ianlancetaylor commented Jul 26, 2020

@ianlancetaylor
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@ianlancetaylor ianlancetaylor commented Jul 26, 2020

Marking as a release blocker for 1.15. We should investigate this and decide whether it is a problem that needs to be addressed for 1.1.5

@cherrymui
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@cherrymui cherrymui commented Jul 27, 2020

Sorry, I cannot reproduce it on my machine:

$ go install -buildmode=shared -linkshared -pkgdir /tmp/lib std
$ go build -buildmode=pie -linkshared -pkgdir /tmp/lib hello.go 
$ file hello
hello: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=b2e8af86bc78040632dfe47c792077a16659905d, for GNU/Linux 3.2.0, not stripped
$ ldd hello | grep libstd
	libstd.so => /tmp/lib/libstd.so (0x00007ffa3ff33000)

The generated binary is dynamically linked and linked against libstd.so.

@kiap
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@kiap kiap commented Jul 27, 2020

Have you checked the executable file size?

despite ldd's output,

When I build hello world shared linked with 1.14.6 the size is 19 KB
with 1.15rc1 it is 4.8M if I use trimpath and ldflags; without them it is 9.4 MB

It seems the file also contains statically linked modules, try the same on 1.14.6 and compare executable file sizes and content of a simple hello world.

When I build statically the size is 2.3 MB

To the contrary the shared executable must be smaller in size

@aclements
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@aclements aclements commented Jul 27, 2020

@kiap , just the clarify, can you state the exact problem you're seeing more clearly? It's not clear from your original bug report. Is it specifically that the shared linkage executable is significantly larger than it used to be, indicating the linker included a lot of things it shouldn't have? Are you seeing problems besides the size? (When you say it "generates incorrect code", that suggests a crash or panic when you try to run it.)

@gopherbot
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@gopherbot gopherbot commented Jul 27, 2020

Change https://golang.org/cl/244839 mentions this issue: cmd/link: don't mark shared library symbols reachable unconditionally

@cherrymui
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@cherrymui cherrymui commented Jul 27, 2020

Thanks for the note about the size. It is not that we linked in a static copy, but we accidentally put a large number of symbols into the dynamic symbol table.

@aclements aclements changed the title cmd/link: -buildmode=pie -linkshared generates incorrect code cmd/link: -buildmode=pie -linkshared generates large binaries Jul 27, 2020
@gopherbot gopherbot closed this in 19a932c Jul 27, 2020
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