configure: Add workaround for buggy binutils 2.35 [PR98811]

binutils since https://sourceware.org/bugzilla/show_bug.cgi?id=25612
changes from March last year until the
https://sourceware.org/pipermail/binutils/2020-August/112684.html
fix in early August emits incorrect .debug_info when assembling files
with --gdwarf-5.  Instead of emitting proper DWARF 5 .debug_info header,
it emits DWARF 4 .debug_info header with 5 as the dwarf version instead of
4.  This results e.g. in libgcc.a (morestack.o) having garbage in its
.debug_info sections and e.g. libbacktrace during pretty much all libgo
tests fails miserably.

The following patch adds a workaround for that, don't set
HAVE_AS_GDWARF_5_DEBUG_FLAG if readelf can't read the .debug_info back.

Built tested on x86_64-linux against both binutils 2.35 (buggy ones) and
latest binutils trunk, the former with the patch now has DWARF 3
.debug_line and DWARF 2 .debug_info in morestack.o, while the latter
as before correct DWARF 5 .debug_line and .debug_info.

2021-01-25  Jakub Jelinek  <jakub@redhat.com>

	PR debug/98811
	* configure.ac (HAVE_AS_GDWARF_5_DEBUG_FLAG): Only define if
	readelf -wi is able to read the emitted .debug_info back.
	* configure: Regenerated.

diff --git a/gcc/configure b/gcc/configure
index 41641c6..9bb436c 100755 (executable)
--- a/gcc/configure
+++ b/gcc/configure
@@ -29075,7 +29075,11 @@ fi
   $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
   test $ac_status = 0; }; }
     then
-       gcc_cv_as_gdwarf_5_flag=yes
+       if test x$gcc_cv_readelf != x \
+      && $gcc_cv_readelf -wi conftest.o 2>&1 \
+        | grep DW_TAG_compile_unit > /dev/null 2>&1; then
+     gcc_cv_as_gdwarf_5_flag=yes;
+   fi
     else
       echo "configure: failed program was" >&5
       cat conftest.s >&5

diff --git a/gcc/configure.ac b/gcc/configure.ac
index ff4d3dc..caa6119 100644 (file)
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -5416,8 +5416,12 @@ if test x"$insn" != x; then
 
  gcc_GAS_CHECK_FEATURE([--gdwarf-5 option],
   gcc_cv_as_gdwarf_5_flag,
-  [elf,2,36,0], [--gdwarf-5], [$insn],,
-  [AC_DEFINE(HAVE_AS_GDWARF_5_DEBUG_FLAG, 1,
+  [elf,2,36,0], [--gdwarf-5], [$insn],
+  [if test x$gcc_cv_readelf != x \
+      && $gcc_cv_readelf -wi conftest.o 2>&1 \
+        | grep DW_TAG_compile_unit > /dev/null 2>&1; then
+     gcc_cv_as_gdwarf_5_flag=yes;
+   fi],[AC_DEFINE(HAVE_AS_GDWARF_5_DEBUG_FLAG, 1,
 [Define if your assembler supports the --gdwarf-5 option.])])
 
  dwarf4_debug_info_size=0x46