https://sourceware.org/bugzilla/show_bug.cgi?id=33172
Bug ID: 33172
Summary: RFE: eu-stacktrace adjacent tool to generate sampled
call-graph profile info
Product: elfutils
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: tools
Assignee: unassigned at sourceware dot org
Reporter: fche at redhat dot com
CC: elfutils-devel at sourceware dot org
Target Milestone: ---
There is the need for a *lightweight* (in terms of usage complexity, build
dependency) tool that generates dynamic callgraph profiles of uninstrumented
programs, in a format that linkers can use to guide PGO optimization. (There
are other uses for this sort of data, such as compiler LTO.)
The format I propose is the llvm sampled profile text format as accepted by
llvm-profdata and lld, and generated by autofdo's create_llvm_prof.
Conceptually it's kinda sorta similar to "gprof -b", but lacking basic-block
level edge data one would get from instrumentation. "gprofng" may be
arm-twisted into producing such a report too, maybe. (On the production side,
sediment and llvm-prof-gen on the other hand presuppose LBR perfctr hardware
instead of unwinding, so unhelpful on much hardware.)
One such file would have to be output for each binary of interest (i.e.,
separate for solibs).
I imagine the tool invoking some default set of perfctr events (sth. like "perf
record --call-graph $SOMETHING -c $COUNT -e branches" and optional extra
events), and piping the data into eu-stacktrace's unwinder. For each perf
record, it'd need to do only a couple of rounds of unwinding, just enough to
get through inlining and out to a normal function. The data then needs to be
turned to symbols (mangled function names; ideally also source-level
function-definition-relative line numbers of the pc addresses), tabulated in a
tree, then eventually printed.
(It may be possible to prototype it in systemtap.)
https://github.com/google/autofdo/blob/master/testdata/callgraph_with_cycles.txt
https://sourceware.org/pipermail/binutils/2025-July/142644.html
https://x.com/i/grok/share/1gPL7JSBCimEn9rFPr6Ze4Tlh [format description]
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