lddtree: keep relativeness of invoked program in elf wrapper

This makes clang's resource dir relative when we pass
-no-canonical-prefixes flag like below.
$ chromium/.cros_cache/chrome-sdk/tarballs/$BOARD+$VERSION+target_toolchain/usr/bin/clang -no-canonical-prefixes -###
Chromium OS 7.0_pre328903_p20180425-r5 clang version 7.0.0 (/var/cache/chromeos-cache/distfiles/host/egit-src/clang.git e7408fe366bb18923fa360b069b4e4566203f34f) (/var/cache/chromeos-cache/distfiles/host/egit-src/llvm.git 95561668f063fbcb8195bde05ecede721ece4ba4) (based on LLVM 7.0.0svn)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: chromium/.cros_cache/chrome-sdk/tarballs/kevin+10750.0.0+target_toolchain/usr/bin

Without this patch, -no-canonical-prefixes has no meaning.
$ chromium/.cros_cache/chrome-sdk/tarballs/$BOARD+$VERSION+target_toolchain/usr/bin/clang -no-canonical-prefixes -###
Chromium OS 7.0_pre328903_p20180425-r5 clang version 7.0.0 (/var/cache/chromeos-cache/distfiles/host/egit-src/clang.git e7408fe366bb18923fa360b069b4e4566203f34f) (/var/cache/chromeos-cache/distfiles/host/egit-src/llvm.git 95561668f063fbcb8195bde05ecede721ece4ba4) (based on LLVM 7.0.0svn)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: $HOME/chromium/.cros_cache/chrome-sdk/tarballs/kevin+10750.0.0+target_toolchain/usr/bin

This is a part of effort for build cache sharing when using goma by
removing absolute path from compile result.

Instead of enforcing relative path, I keep relativeness of compiler
path.

I confirmed this works as following with a debug line to show ${base}.elf.
(sdk daisy R70-11005.0.0) tikuta@tikuta ~/chromium/src $ ln -s build/cros_cache/chrome-sdk/tarballs/daisy+11005.0.0+target_toolchain/usr/bin/clang-7 clang
(sdk daisy R70-11005.0.0) tikuta@tikuta ~/chromium/src $ ./clang
${base}.elf: './build/cros_cache/chrome-sdk/tarballs/daisy+11005.0.0+target_toolchain/usr/bin/clang-7.elf'
clang-7: error: no input files

In previous versions of this change, it ran like below:
(sdk daisy R70-11005.0.0) tikuta@tikuta ~/chromium/src $ ./clang
${base}.elf: '/usr/local/google/home/tikuta/chromium/src/build/cros_cache/chrome-sdk/tarballs/daisy+11005.0.0+target_toolchain/usr/bin/clang-7.elf'
clang-7: error: no input files

I confirmed this can build base_unittests on daisy and amd64-generic
after creating a new CrOS SDK with chromiumos-sdk-tryjob.

Bug: https://crbug.com/846610
Bug: https://crbug.com/876604
Signed-off-by: Takuto Ikuta <tikuta@chromium.org>
Signed-off-by: Mike Frysinger <vapier@chromium.org>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/lddtree.py b/lddtree.py
index 80808fc..bbf9df9 100755
--- a/lddtree.py
+++ b/lddtree.py
@@ -182,8 +182,12 @@ def GenerateLdsoWrapper(
         "argv0_arg": '--argv0 "$0"' if interp_supports_argv0(root + interp) else "",
         "preload_arg": f'--preload "{preload}"' if preload else "",
     }
+
+    # Keep path relativeness of argv0 (in ${base}.elf). This allows tools to
+    # remove absolute paths from build outputs and enables directory independent
+    # cache sharing in distributed build systems.
     wrapper = """#!/bin/sh
-if ! base=$(realpath "$0" 2>/dev/null); then
+if ! base=$(dirname "$0")/$(readlink "$0" 2>/dev/null); then
   case $0 in
   /*) base=$0;;
   *)  base=${PWD:-`pwd`}/$0;;