Mh, this is interesting. When I build a test binary with buildmode=pie, I even get an ELF section called `.data.rel.ro.gopclntab`.
However, in the containerd binary, this section does not exist.There also is no `.gosymtab` section, as that is easily wiped by the `ldflags`. > It is getting folded into the > .data.rel.ro <http://data.rel.ro/> section. You can still find the > information by looking > at the symbol table: the .gopclntab data is between runtime.pclntab > and runtime.epclntab. I'm not sure I follow. If I understand correctly, this means that what I see in my test binary as `.data.rel.ro <http://data.rel.ro/>.gopclntab` is a subsection "within" the `.data.rel.ro <http://data.rel.ro/>` section. Further, as the containerd binary has a `.data.rel.ro <http://data.rel.ro/>` section, at some offset within that data there should be a PCLN table? If so, two questions arise: - How do I find that offset? By looking for the magic string for the PCLN table? - Why is that subsection not listed / present in the containerd binary? Thanks a lot, this is a very interesting topic! Ramon PS: If you have some literature / documents on the Go specifics for this, I'd be curious to read them. > On 18 Sep 2022, at 04:51, Ian Lance Taylor <i...@golang.org> wrote: > > On Sat, Sep 17, 2022 at 2:48 PM 'Ramon Rüttimann' via golang-nuts > <golang-nuts@googlegroups.com <mailto:golang-nuts@googlegroups.com>> wrote: >> >> Sadly this does not seem to be the case, for example the nightly artifacts >> from containerd, which can be found here. >> A `go version -m <binary>` lists all deps & shows the Go version 1.19.1, >> but there is now PCLN table to be found... >> The binary seems to be created through the following go build command: >> >> go build -gcflags=-trimpath=/home/runner/work/containerd/containerd/src >> -buildmode=pie -o bin/containerd -ldflags '-X >> github.com/containerd/containerd/version.Version=290ef2b >> <http://github.com/containerd/containerd/version.Version=290ef2b> -X >> github.com/containerd/containerd/version.Revision=290ef2b43ff1b824e56d0adaebf621e053de6e86 >> >> <http://github.com/containerd/containerd/version.Revision=290ef2b43ff1b824e56d0adaebf621e053de6e86> >> -X >> github.com/containerd/containerd/version.Package=github.com/containerd/containerd >> >> <http://github.com/containerd/containerd/version.Package=github.com/containerd/containerd> >> -s -w ' -tags "urfave_cli_no_docs" ./cmd/containerd >> >> Local testing confirms that with `-buildmode=pie` ("Position Independent >> Executable") the PCLN table is not being added to the binary. Why? >> I'm not familiar with these executables, not sure how this would affect the >> PCLN. > > Interesting. I agree: with -buildmode=pie the .gopclntab section does > not appear in the final executable. It is getting folded into the > .data.rel.ro <http://data.rel.ro/> section. You can still find the > information by looking > at the symbol table: the .gopclntab data is between runtime.pclntab > and runtime.epclntab. > > Ian > > >> On Friday, September 16, 2022 at 9:36:53 PM UTC+2 Ian Lance Taylor wrote: >>> >>> On Fri, Sep 16, 2022 at 12:13 PM Ramon Rüttimann >>> <ramon.ru...@gmail.com> wrote: >>>> >>>> I am currently looking into what a built Go binary may contain and have >>>> found some confusing things around the `.gopclntab` ELF section, also >>>> known as the PCLN table. >>>> >>>> At first, I assumed that the PCLN table is present in all binaries, no >>>> matter how they are built. I've done some tests with stripped, trimmed and >>>> CGo binaries and have found it to be present. >>>> However, this article contains an interesting statement: >>>> >>>> For ordinary unstripped Go binaries, this debugging information is in the >>>> .gopclntab and .gosymtab ELF sections of the binary, and can be read out >>>> with debug/elf/File.Section() and Section.Data(). Unfortunately, Go >>>> binaries that use cgo do not have these Go ELF sections. As mentioned in >>>> Building a better Go linker: >>>> >>>> For “cgo” binaries, which may make arbitrary use of C libraries, the Go >>>> linker links all of the Go code into a single native object file and then >>>> invokes the system linker to produce the final binary. >>>> >>>> This linkage obliterates .gopclntab and .gosymtab as separate ELF >>>> sections. I believe that their data is still there in the final binary, >>>> but I don't know how to extract them. >>>> >>>> I have also found such binaries in the wild, like the `containerd` binary >>>> or some tools from Docker as well. I've tried to decipher how the >>>> containerd binary is being built (based on this Makefile), but I am not >>>> really familiar enough with Make to decipher this. >>>> >>>> This S/O post has asked the same question, but the answer doesn't match >>>> what I've seen and also what that article claims. >>>> >>>> Can someone shed some lights on how one can build CGo binaries without the >>>> `.pclntab` section? Also, what happens to stacktraces in such a case? >>> >>> I believe that at least as of Go 1.19 the .gopclntab section exists >>> even if the binary is built with cgo, and the .gosymtab section is >>> empty in any case. >>> >>> Ian >> >> -- >> You received this message because you are subscribed to the Google Groups >> "golang-nuts" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to golang-nuts+unsubscr...@googlegroups.com >> <mailto:golang-nuts+unsubscr...@googlegroups.com>. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/golang-nuts/a831b72f-6ecd-41e4-a5fd-e76b4b9fc7fbn%40googlegroups.com >> >> <https://groups.google.com/d/msgid/golang-nuts/a831b72f-6ecd-41e4-a5fd-e76b4b9fc7fbn%40googlegroups.com>. > > -- > You received this message because you are subscribed to a topic in the Google > Groups "golang-nuts" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/golang-nuts/oxseUnhRtXM/unsubscribe > <https://groups.google.com/d/topic/golang-nuts/oxseUnhRtXM/unsubscribe>. > To unsubscribe from this group and all its topics, send an email to > golang-nuts+unsubscr...@googlegroups.com > <mailto:golang-nuts+unsubscr...@googlegroups.com>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/CAOyqgcUoC3-9X%3DRBYMt%3DSNgbkXG_%3DJ3hKM8j-QMc%3DLaKcEj_Dg%40mail.gmail.com > > <https://groups.google.com/d/msgid/golang-nuts/CAOyqgcUoC3-9X%3DRBYMt%3DSNgbkXG_%3DJ3hKM8j-QMc%3DLaKcEj_Dg%40mail.gmail.com>. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. 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