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Symbolizing with GNU addr2line 2.40 records `??:?` as the filename of a location with no line info

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A pull request for this has already been merged.

  • #1045 by @TomerAberbach — merged
  • #1046 by @skyfireitdiy — closed without merging

Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
76/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
go
Domain
tooling

Research direction

The parsing lives in readFrame in internal/binutils/addr2liner.go, around lines 150-165, which currently clears the filename only for ??:0. Read that function and the existing addr2liner tests, then check how the : split handles a non-numeric line. Done when ??:? yields an empty filename like ??:0 and a test covers both forms.

Written by the indexing model from the issue text.

Description

When pprof symbolizes through GNU addr2line from binutils 2.40, it records ??:? as the filename of a location with no file and line info. addr2line 2.40 prints ??:? for an unknown location, but pprof recognizes only ??:0.

Reproduction

In golang:1.26-bookworm (GNU addr2line 2.40), with a heap profile from gperftools:

apt-get update -qq && apt-get install -y -qq google-perftools libgoogle-perftools-dev
go install github.com/google/pprof@latest

cat > t.c <<'C'
#include <stdlib.h>
#include <string.h>
__attribute__((noinline)) char *grow(int n) { char *p = malloc(n); memset(p, 1, n); return p; }
int main(void) { char *k[64] = {0}; for (int i = 0; i < 100000; i++) { free(k[i % 64]); k[i % 64] = grow(64 + i % 512); } return 0; }
C
gcc -O2 -o t t.c   # no -g
HEAPPROFILE=h LD_PRELOAD=$(find / -name libtcmalloc.so -print -quit) ./t
heap=$(ls h.*.heap | sort | tail -1)

addr2line -f -C -i -e ./t 0x$(nm ./t | awk '$3=="grow"{print $1}')
"$(go env GOPATH)/bin/pprof" -raw ./t "$heap" | sed -n '/^Locations/,/^Mappings/p'
Actual

addr2line reports the location as unknown:

grow
??:?

pprof records ??:? as the filename:

     1: 0xaaaae88f08f7 M=1 grow ??:?:0:0 s=0
     2: 0xaaaae88f0757 M=1 main ??:?:0:0 s=0
     4: 0xffff85df7817 M=6 __libc_start_main ??:?:0:0 s=0

A profile written with -proto contains ??:? as each function's filename, and tools reading it show ??:? as the source location.

Expected

An empty filename, as pprof produces for addr2line's ??:0. With llvm-symbolizer installed in the same image, pprof writes these locations with an empty filename (:0:0).

Environment
  • pprof v0.0.0-20261008003335-7bae8d8c4c9e (@latest)
  • GNU addr2line (GNU Binutils for Debian) 2.40
  • Debian bookworm, linux/arm64
Cause

readFrame empties the filename only for ??:0. For ??:?, the text after the last : is not a number, so the whole string stays as the filename:

https://github.com/google/pprof/blob/7bae8d8c4c9ebc3886a79f796fbde65b7e1316f8/internal/binutils/addr2liner.go#L150-L165

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Merged PRs (30d)
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