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cmd/link: ELF linker generates incorrect local dynamic symbol count #33358

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shachaf opened this issue Jul 30, 2019 · 5 comments
Closed

cmd/link: ELF linker generates incorrect local dynamic symbol count #33358

shachaf opened this issue Jul 30, 2019 · 5 comments
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FrozenDueToAge help wanted NeedsFix The path to resolution is known, but the work has not been done.
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Go1.14

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@shachaf
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shachaf commented Jul 30, 2019

When generating a dynamically-linked ELF file, the ".dynsym" section's info field specifies the number of local symbols. It currently seems to generate 0, but symbol 0 is reserved and always local, so the value should be at least 1. readelf (from GNU binutils 2.30) reports this warning.

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

$ go version
go version go1.10.4 linux/amd64

Does this issue reproduce with the latest release?

It is present in master at the time of writing.

See https://github.com/golang/go/blob/master/src/cmd/link/internal/ld/elf.go#L1934

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

linux_amd64

What did you do?

Build a program that uses dynamic linking. E.g.

package main

import "net"

func main() {
	net.Dial("", "")
}

And look at the .dynsym info field.

What did you expect to see?

.dynsym info field >= 1.

What did you see instead?

.dynsym info field 0, and no warnings from readelf.

  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [11] .dynsym           DYNSYM           000000000052c1e0  0012c1e0
       0000000000000390  0000000000000018   A      10     0     8
readelf: Warning: local symbol 0 found at index >= .dynsym's sh_info value of 0
@agnivade
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@ianlancetaylor

@agnivade agnivade changed the title ELF linker generates incorrect local dynamic symbol count cmd/link: ELF linker generates incorrect local dynamic symbol count Jul 30, 2019
@agnivade agnivade added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Jul 30, 2019
@ianlancetaylor ianlancetaylor added help wanted NeedsFix The path to resolution is known, but the work has not been done. labels Jul 30, 2019
@ianlancetaylor ianlancetaylor added this to the Go1.14 milestone Jul 30, 2019
@gopherbot gopherbot removed the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Jul 30, 2019
@ianlancetaylor
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Thanks. I agree that this should be fixed.

@gopherbot
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Change https://golang.org/cl/187979 mentions this issue: cmd/link: set .dynsym info field

@shachaf
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shachaf commented Aug 31, 2019

I suspect this won't happen if there's a .dynsym section, but I should mention that if there are no global symbols, this code won't set sh.info (it should be set to the local symbol count regardless).

tomocy pushed a commit to tomocy/go that referenced this issue Sep 1, 2019
@cuonglm @tomocy
cmd/link: set .dynsym info field
7771445 
.dynsym section info field is the index of first non-local symbol, mean
the number of local symbols.

The go linker have never ever set it before, so just set it.

Fixes golang#33358

Change-Id: Ifde2deb7c15471b04d565861f5d81daffb0c0d3d
Reviewed-on: https://go-review.googlesource.com/c/go/+/187979
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
@cuonglm cuonglm mentioned this issue Sep 1, 2019
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@cuonglm
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cuonglm commented Sep 1, 2019

@shachaf good catch, fixed in https://go-review.googlesource.com/c/go/+/192600

t4n6a1ka pushed a commit to t4n6a1ka/go that referenced this issue Sep 5, 2019
@cuonglm @t4n6a1ka
cmd/link: set .dynsym info field
f90c77f 
.dynsym section info field is the index of first non-local symbol, mean
the number of local symbols.

The go linker have never ever set it before, so just set it.

Fixes golang#33358

Change-Id: Ifde2deb7c15471b04d565861f5d81daffb0c0d3d
Reviewed-on: https://go-review.googlesource.com/c/go/+/187979
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
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