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cmd/nm: bss symbols not correctly reported on linux/amd64 #77301

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cmd/nm: bss symbols not correctly reported on linux/amd64#77301
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BugReportIssues describing a possible bug in the Go implementation.FixPendingIssues that have a fix which has not yet been reviewed or submitted.compiler/runtimeIssues related to the Go compiler and/or runtime.
Milestone
Go1.27

Description

@egonelbre
egonelbre
opened on Jan 24, 2026

Go version

go1.26rc2

Output of go env in your module/workspace:

AR='ar'
CC='clang'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='clang++'
GCCGO='gccgo'
GO111MODULE=''
GOARCH='arm64'
GOARM64='v8.0'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/Users/egon/Library/Caches/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/Users/egon/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/1w/2x_sgq2j111d19xj1kpxkgp40000gn/T/go-build3668712380=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/dev/null'
GOMODCACHE='/Users/egon/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/egon/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/egon/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.26rc2'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

package main

var globalUninitialized int64     // should be in BSS
var globalInitialized int64 = 42  // should be in DATA

func main() {
    println(globalUninitialized)
    println(globalInitialized)
}

What did you see happen?

∫ GOOS=linux GOARCH=amd64 go build -o example example.go && go tool nm example | grep main.global
  534490 D main.globalInitialized
  55d510 D main.globalUninitialized

What did you expect to see?

∫ nm --version
llvm-nm, compatible with GNU nm
Apple LLVM version 17.0.0
  Optimized build.

∫ nm example | grep main.global
0000000000534490 D main.globalInitialized
000000000055d510 B main.globalUninitialized

Activity

  1. gopherbot
    added
    compiler/runtimeIssues related to the Go compiler and/or runtime.
    on Jan 24, 2026

  2. egonelbre commented on Jan 24, 2026

    @egonelbre
    egonelbre
    on Jan 24, 2026
    ContributorAuthor

    Debugging with AI pointed me to

    go/src/cmd/internal/objfile/elf.go

    Lines 48 to 55 in 1bd5dbf

    sect := f.elf.Sections[i]
    switch sect.Flags & (elf.SHF_WRITE | elf.SHF_ALLOC | elf.SHF_EXECINSTR) {
    case elf.SHF_ALLOC | elf.SHF_EXECINSTR:
    sym.Code = 'T'
    case elf.SHF_ALLOC:
    sym.Code = 'R'
    case elf.SHF_ALLOC | elf.SHF_WRITE:
    sym.Code = 'D'

    And suggested that it should check for:

    case elf.SHF_ALLOC | elf.SHF_WRITE:
	if sect.Type == elf.SHT_NOBITS {
		sym.Code = 'B'
	} else {
		sym.Code = 'D'
	}

    However, I do not have intimate knowledge with elf to know whether that is always correct.

  3. gabyhelp commented on Jan 24, 2026

    @gabyhelp
    gabyhelp
    on Jan 24, 2026

    Related Issues

    (Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)

  4. gabyhelp
    added
    BugReportIssues describing a possible bug in the Go implementation.
    on Jan 24, 2026

  5. ianlancetaylor commented on Jan 24, 2026

    @ianlancetaylor
    ianlancetaylor
    on Jan 24, 2026
    Contributor

    That is the correct fix. Sent CL 739080. Thanks.

  6. ianlancetaylor
    added
    FixPendingIssues that have a fix which has not yet been reviewed or submitted.
    on Jan 24, 2026

  7. gopherbot commented on Jan 24, 2026

    @gopherbot
    gopherbot
    on Jan 24, 2026
    Contributor

    Change https://go.dev/cl/739080 mentions this issue: cmd/internal/objfile: use 'B' code for symbols in ELF NOBITS sections

  8. prattmic
    added this to Go Compiler / Runtime / Commandon Jan 28, 2026
  9. mknyszek
    moved this to In Progress in Go Compiler / Runtime / Commandon Feb 4, 2026
  10. mknyszek
    added this to the Go1.27 milestone on Feb 4, 2026

  11. odeke-em commented on Jun 24, 2026

    @odeke-em
    odeke-em
    on Jun 24, 2026
    Member

    Thanks for the report @egonelbre! To investigate this further, I sent out a test in CL https://go-review.googlesource.com/c/go/+/794080 that I'll kindly nudge @ianlancetaylor to add to the fix CL and it turns out that it fails too on windows per windows-386-result and windows-amd64-result

  12. gopherbot
    closed this as completedin 5703e10on Jun 25, 2026
  13. github-project-automation
    moved this from In Progress to Done in Go Compiler / Runtime / Commandon Jun 25, 2026
  14. pull
    added a commit that references this issue on Jun 25, 2026

    cmd/internal/objfile: use 'B' code for ELF and PE BSS symbols

    5703e10
  15. dgilarranz-ik
    added a commit that references this issue on Jul 21, 2026

    cmd/internal/objfile: use 'B' code for ELF and PE BSS symbols

    6295f44
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