Re: BPF in linux-libre

[Mathieu Othacehe <othacehe@gnu.org>]

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Hello John,

> ld: /gnu/store/80y2wbx9lrhvwp41nnyjjsb4g9ff8avn-clang-toolchain-9.0.1/lib/libbfd.a(compress.o): undefined reference to symbol 'inflateEnd'
> ld: /gnu/store/80y2wbx9lrhvwp41nnyjjsb4g9ff8avn-clang-toolchain-9.0.1/lib/libz.so.1: error adding symbols: DSO missing from command line
>
> I added zlib to the inputs of bpftrace but still the same error.  Are
> there any CMake experts out there that can tell if there is a flag or
> option to use here? Is this an upstream issue?

By default, a dynamic version of bpftrace is built. However, as we do
not provide a libbpf.so, it falls back on libbpf.a.

There's a comment in FindLibBfd.cmake which says:

--8<---------------cut here---------------start------------->8---
# libbfd.a is not statically linked with libiberty.a or libz.a so we must manually
# do it. Furthermore, libbfd uses some libc symbols that we must manually
# link against if we're not using static libc (which includes such symbols).
--8<---------------cut here---------------end--------------->8---

So when STATIC_LINKING is ON, they add "libz" to the required
libraries. It would be preferable to avoid building a static bpftrace,
so I tried to provide a dynamic version of libbpf.

There's still a failure at validate-runpath phase that need to be
fixed, not sure why.

Thanks,

Mathieu

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diff --git a/gnu/packages/base.scm b/gnu/packages/base.scm
index 50e426fadf..42bba03b2a 100644
--- a/gnu/packages/base.scm
+++ b/gnu/packages/base.scm
@@ -601,6 +601,17 @@ included.")
      (inputs
      `(("gcc:lib" ,gcc "lib")))))
 
+(define-public binutils-shared
+  (package
+    (inherit binutils)
+    (name "binutils-shared")
+    (arguments
+     `(#:validate-runpath? #f
+       ,@(substitute-keyword-arguments (package-arguments binutils)
+         ((#:configure-flags flags)
+          `(cons "--enable-shared" ,flags)))))
+    (properties '())))
+
 (define* (make-ld-wrapper name #:key
                           (target (const #f))
                           binutils
diff --git a/gnu/packages/linux.scm b/gnu/packages/linux.scm
index 8f0b9ac018..7f30e3750c 100644
--- a/gnu/packages/linux.scm
+++ b/gnu/packages/linux.scm
@@ -7169,6 +7169,7 @@ persistent over reboots.")
          (list
           (string-append "PREFIX=''")
           (string-append "DESTDIR=" (assoc-ref %outputs "out"))
+          (string-append "LIBDIR=/lib")
           (string-append
            "CC=" (assoc-ref %build-inputs "gcc") "/bin/gcc"))
          #:phases
@@ -7272,8 +7273,11 @@ Linux 4.1 and above.")
       (inputs
        `(("bcc" ,bcc)
          ("bison" ,bison)
+         ("binutils" ,binutils-shared)
          ("clang-toolchain" ,clang-toolchain)
          ("elfutils" ,elfutils)
+         ("libiberty" ,libiberty)
+         ("libbpf" ,libbpf)
          ("flex" ,flex)
          ;; FIXME: Tests require googletest but not from system
          ;; ("googletest" ,googletest)
@@ -7282,7 +7286,8 @@ Linux 4.1 and above.")
        `(#:configure-flags
          '(;; FIXME: Make tests not clone the googletest repository
            "-DBUILD_TESTING=OFF"
-           "-DLIBBFD_DISASM_FOUR_ARGS_SIGNATURE=ON")))
+           "-DLIBBFD_DISASM_FOUR_ARGS_SIGNATURE=ON")
+         #:tests? #f))
       (home-page "https://github.com/iovisor/bpftrace")
       (synopsis "High-level tracing language for Linux eBPF")
       (description