[PATCH] Correctly determine libc.so 'OUTPUT_FORMAT' when cross-compiling.

[Ludovic Courtès]

Commit 87d583c6e8cd0e49f64da76636ebeec033298b4d replaces the sed script
with an "objdump -f" invocation to determine the 'OUTPUT_FORMAT' bit of
the libc.so linker script.

However, when cross-compiling, for example from x86_64-linux-gnu to
aarch64-linux-gnu, "objdump -f" would report the wrong
format ("elf64-little").  Conversely, "aarch64-linux-gnu-objdump -f"
reports "elf64-littleaarch64" as expected.

This patch changes 'configure.ac' to use AC_CHECK_TOOL rather than
'$CC -print-prog-name=objdump' to determine the value of the OBJDUMP
variable.  That way, OBJDUMP is set to TRIPLET-objdump when
cross-compiling for TRIPLET.
---
 aclocal.m4   |  2 --
 configure    | 96 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 configure.ac |  1 +
 3 files changed, 94 insertions(+), 5 deletions(-)

diff --git a/aclocal.m4 b/aclocal.m4
index c195c4db56..13a791ffde 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -118,8 +118,6 @@ AS=`$CC -print-prog-name=as`
 LD=`$CC -print-prog-name=ld`
 AR=`$CC -print-prog-name=ar`
 AC_SUBST(AR)
-OBJDUMP=`$CC -print-prog-name=objdump`
-AC_SUBST(OBJDUMP)
 OBJCOPY=`$CC -print-prog-name=objcopy`
 AC_SUBST(OBJCOPY)
 GPROF=`$CC -print-prog-name=gprof`
diff --git a/configure b/configure
index 9619c10991..fe0eda1cd5 100755
--- a/configure
+++ b/configure
@@ -655,7 +655,6 @@ LD
 AS
 GPROF
 OBJCOPY
-OBJDUMP
 AR
 LN_S
 INSTALL_DATA
@@ -690,6 +689,7 @@ sysheaders
 ac_ct_CXX
 CXXFLAGS
 CXX
+OBJDUMP
 READELF
 CPP
 cross_compiling
@@ -2962,6 +2962,98 @@ else
   READELF="$ac_cv_prog_READELF"
 fi
 
+if test -n "$ac_tool_prefix"; then
+  # Extract the first word of "${ac_tool_prefix}objdump", so it can be a program name with args.
+set dummy ${ac_tool_prefix}objdump; ac_word=$2
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
+$as_echo_n "checking for $ac_word... " >&6; }
+if ${ac_cv_prog_OBJDUMP+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  if test -n "$OBJDUMP"; then
+  ac_cv_prog_OBJDUMP="$OBJDUMP" # Let the user override the test.
+else
+as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
+for as_dir in $PATH
+do
+  IFS=$as_save_IFS
+  test -z "$as_dir" && as_dir=.
+    for ac_exec_ext in '' $ac_executable_extensions; do
+  if as_fn_executable_p "$as_dir/$ac_word$ac_exec_ext"; then
+    ac_cv_prog_OBJDUMP="${ac_tool_prefix}objdump"
+    $as_echo "$as_me:${as_lineno-$LINENO}: found $as_dir/$ac_word$ac_exec_ext" >&5
+    break 2
+  fi
+done
+  done
+IFS=$as_save_IFS
+
+fi
+fi
+OBJDUMP=$ac_cv_prog_OBJDUMP
+if test -n "$OBJDUMP"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $OBJDUMP" >&5
+$as_echo "$OBJDUMP" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+
+fi
+if test -z "$ac_cv_prog_OBJDUMP"; then
+  ac_ct_OBJDUMP=$OBJDUMP
+  # Extract the first word of "objdump", so it can be a program name with args.
+set dummy objdump; ac_word=$2
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
+$as_echo_n "checking for $ac_word... " >&6; }
+if ${ac_cv_prog_ac_ct_OBJDUMP+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  if test -n "$ac_ct_OBJDUMP"; then
+  ac_cv_prog_ac_ct_OBJDUMP="$ac_ct_OBJDUMP" # Let the user override the test.
+else
+as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
+for as_dir in $PATH
+do
+  IFS=$as_save_IFS
+  test -z "$as_dir" && as_dir=.
+    for ac_exec_ext in '' $ac_executable_extensions; do
+  if as_fn_executable_p "$as_dir/$ac_word$ac_exec_ext"; then
+    ac_cv_prog_ac_ct_OBJDUMP="objdump"
+    $as_echo "$as_me:${as_lineno-$LINENO}: found $as_dir/$ac_word$ac_exec_ext" >&5
+    break 2
+  fi
+done
+  done
+IFS=$as_save_IFS
+
+fi
+fi
+ac_ct_OBJDUMP=$ac_cv_prog_ac_ct_OBJDUMP
+if test -n "$ac_ct_OBJDUMP"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_ct_OBJDUMP" >&5
+$as_echo "$ac_ct_OBJDUMP" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+  if test "x$ac_ct_OBJDUMP" = x; then
+    OBJDUMP="false"
+  else
+    case $cross_compiling:$ac_tool_warned in
+yes:)
+{ $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: using cross tools not prefixed with host triplet" >&5
+$as_echo "$as_me: WARNING: using cross tools not prefixed with host triplet" >&2;}
+ac_tool_warned=yes ;;
+esac
+    OBJDUMP=$ac_ct_OBJDUMP
+  fi
+else
+  OBJDUMP="$ac_cv_prog_OBJDUMP"
+fi
+
 
 # We need the C++ compiler only for testing.
 ac_ext=cpp
@@ -4553,8 +4645,6 @@ AS=`$CC -print-prog-name=as`
 LD=`$CC -print-prog-name=ld`
 AR=`$CC -print-prog-name=ar`
 
-OBJDUMP=`$CC -print-prog-name=objdump`
-
 OBJCOPY=`$CC -print-prog-name=objcopy`
 
 GPROF=`$CC -print-prog-name=gprof`
diff --git a/configure.ac b/configure.ac
index 34ecbba540..924af12738 100644
--- a/configure.ac
+++ b/configure.ac
@@ -52,6 +52,7 @@ fi
 AC_SUBST(cross_compiling)
 AC_PROG_CPP
 AC_CHECK_TOOL(READELF, readelf, false)
+AC_CHECK_TOOL(OBJDUMP, objdump, false)
 
 # We need the C++ compiler only for testing.
 AC_PROG_CXX

base-commit: eb68d7d23cc411acdf68a60f194343a6774d6194
-- 
2.32.0