introduce ELFShim#rpath, refactor keg_relocate to use the same.

refines PatchELF #runpath, #rpath #soname #interpreter
to return nil.
let Brew hard exits on PatchELF::PatchError.

Co-authored-by: Shaun Jackman <sjackman@gmail.com>
Co-authored-by: Mike McQuaid <mike@mikemcquaid.com>

Library/Homebrew/extend/os/linux/keg_relocate.rb

@@ -20,27 +20,21 @@ class Keg
 
     patchelf = DevelopmentTools.locate "patchelf"
     odie "Could not locate patchelf, please: brew install patchelf." if patchelf.nil?
+    cmd = [patchelf]
 
-    cmd_rpath = [patchelf, "--print-rpath", file]
-    old_rpath = Utils.popen_read(*cmd_rpath, err: :out).strip
-
-    # patchelf requires that the ELF file have a .dynstr section.
-    # Skip ELF files that do not have a .dynstr section.
-    return if ["cannot find section .dynstr", "strange: no string table"].include?(old_rpath)
-
-    unless $CHILD_STATUS.success?
-      raise ErrorDuringExecution.new(cmd_rpath, status: $CHILD_STATUS, output: [[:stderr, old_rpath]])
-    end
-
-    rpath = old_rpath
-            .split(":")
+    old_rpath = file.rpath
+    new_rpath = if old_rpath
+      rpath = old_rpath.split(":")
                        .map { |x| x.sub(old_prefix, new_prefix) }
                        .select { |x| x.start_with?(new_prefix, "$ORIGIN") }
 
       lib_path = "#{new_prefix}/lib"
       rpath << lib_path unless rpath.include? lib_path
       new_rpath = rpath.join(":")
-    cmd = [patchelf, "--force-rpath", "--set-rpath", new_rpath]
+      cmd.push  "--force-rpath", "--set-rpath", new_rpath
+
+      new_rpath
+    end
 
     old_interpreter = file.interpreter
     new_interpreter = if old_interpreter.nil?

Library/Homebrew/os/linux/elf.rb

@@ -1,7 +1,45 @@
 # frozen_string_literal: true
 
+if HOMEBREW_PATCHELF_RB
+  require "utils/gems"
+  Homebrew.install_bundler_gems!
+  require "patchelf"
+
+  module PatchELF
+    refine Patcher do
+      # patchelf.rb throws exception when the requested entry is missing in the ELF file.
+      # We prefer an API that returns nil.
+
+      def rpath
+        super
+      rescue PatchELF::MissingTagError
+        nil
+      end
+
+      def runpath
+        super
+      rescue PatchELF::MissingTagError
+        nil
+      end
+
+      def soname
+        super
+      rescue PatchELF::MissingTagError
+        nil
+      end
+
+      def interpreter
+        super
+      rescue PatchELF::MissingSegmentError
+        nil
+      end
+    end
+  end
+end
+
 # @see https://en.wikipedia.org/wiki/Executable_and_Linkable_Format#File_header
 module ELFShim
+  using PatchELF if HOMEBREW_PATCHELF_RB
   MAGIC_NUMBER_OFFSET = 0
   MAGIC_NUMBER_ASCII = "\x7fELF"
 
@@ -68,16 +106,21 @@ module ELFShim
     elf_type == :executable
   end
 
+  def rpath
+    return @rpath if defined? @rpath
+
+    @rpath = if HOMEBREW_PATCHELF_RB
+      rpath_using_patchelf_rb
+    else
+      rpath_using_patchelf
+    end
+  end
+
   def interpreter
     return @interpreter if defined? @interpreter
 
     @interpreter = if HOMEBREW_PATCHELF_RB
-      begin
       patchelf_patcher.interpreter
-      rescue PatchELF::PatchError => e
-        opoo e unless e.to_s.start_with? "No interpreter found"
-        nil
-      end
     elsif (patchelf = DevelopmentTools.locate "patchelf")
       interp = Utils.popen_read(patchelf, "--print-interpreter", to_s, err: :out).strip
       $CHILD_STATUS.success? ? interp : nil
@@ -147,21 +190,7 @@ module ELFShim
 
     def needed_libraries_using_patchelf_rb(path)
       patcher = path.patchelf_patcher
-      return [nil, []] unless patcher
-
-      soname = begin
-        patcher.soname
-      rescue PatchELF::PatchError => e
-        opoo e unless e.to_s.start_with? "Entry DT_SONAME not found, not a shared library?"
-        nil
-      end
-      needed = begin
-        patcher.needed
-      rescue PatchELF::PatchError => e
-        opoo e
-        []
-      end
-      [soname, needed]
+      [patcher.soname, patcher.needed]
     end
 
     def needed_libraries_using_patchelf(path)
@@ -198,14 +227,32 @@ module ELFShim
     end
   end
 
+  def rpath_using_patchelf_rb
+    patchelf_patcher.runpath || patchelf_patcher.rpath
+  end
+
+  def rpath_using_patchelf
+    patchelf = DevelopmentTools.locate "patchelf"
+    odie "Could not locate patchelf, please: brew install patchelf." if patchelf.nil?
+
+    cmd_rpath = [patchelf, "--print-rpath", to_s]
+    rpath = Utils.popen_read(*cmd_rpath, err: :out).strip
+
+    # patchelf requires that the ELF file have a .dynstr section.
+    # Skip ELF files that do not have a .dynstr section.
+    return if ["cannot find section .dynstr", "strange: no string table"].include?(rpath)
+
+    unless $CHILD_STATUS.success?
+      raise ErrorDuringExecution.new(cmd_rpath, status: $CHILD_STATUS, output: [[:stderr, rpath]])
+    end
+
+    rpath
+  end
+
   def patchelf_patcher
     return unless HOMEBREW_PATCHELF_RB
 
-    @patchelf_patcher ||= begin
-      Homebrew.install_bundler_gems!
-      require "patchelf"
-      PatchELF::Patcher.new to_s, logging: false
-    end
+    @patchelf_patcher ||= PatchELF::Patcher.new to_s, logging: false
   end
 
   def metadata