[PATCH v2] Fix build error in binutils 2.36

[Michael Chang]

The following procedure to build xen/pvgrub is broken.

  git clone https://git.savannah.gnu.org/git/grub.git
  cd grub
  ./bootstrap
  mkdir build-xen
  cd build-xen
  ../configure --with-platform=xen
  make

It fails with the message:

  /usr/lib64/gcc/x86_64-suse-linux/10/../../../../x86_64-suse-linux/bin/ld:
  section .note.gnu.property VMA [0000000000400158,0000000000400187]
  overlaps section .bss VMA [000000000000f000,000000000041e1af]

The most significant factor is that new assembler (gnu as) generates the
.note.gnu.property section as default. This note section overlaps with
.bss because it doesn't reposition with -Wl,-Ttext,0 with which the base
address of .text section is set, rather the address of
.note.gnu.property is calculated for some reason from 0x400000 where the
elf executable defaults to start.

Using -Ttext-segment doesn't help either, though it is said to set the
address of the first byte of the text segment according to "man ld".
What it actually does is to override the default 0x400000, aka the image
base address, to something else. The entire process can be observed in
the default linker script used by gcc [1]. Therefore we can't expect it
to achieve the same thing as -Ttext given that the first segment where
.text resides is offset by SIZEOF_HEADERS plus some sections may be
preceding it within the first segment. The end result is .text always
has to start with non-zero address with -Wl,-Ttext-segment,0 if using
default linker script.

It is also worth mentioning that binutils upstream apparently doesn't
seem to consider this as a bug [2] and proposed to use
-Wl,-Ttext-segment,0 which's not fruitful as what has been tested by
gentoo [3].

As long as grub didn't use ISA information encoded in
.note.gnu.property, we can safely drop it via -Wa,-mx86-used-note=no
assembler option to fix the linker error above.

This is considered a better approach than using custom linker script to
drop the .note.gnu.property section because object file manipulation can
also be hampered one way or the other in that linker script may not be
helpful. See also this commit removing the section in the process of
objcopy.

  6643507ce build: Fix GRUB i386-pc build with Ubuntu gcc

[1] In /usr/lib64/ldscripts/elf_x86_64.x or use 'gcc -Wl,--verbose ...'
PROVIDE (__executable_start = SEGMENT_START("text-segment", 0x400000));
. = SEGMENT_START("text-segment", 0x400000) + SIZEOF_HEADERS;

[2] Ref: https://bugs.gentoo.org/787221
[3] Ref: https://sourceware.org/bugzilla/show_bug.cgi?id=27377

Signed-off-by: Michael Chang <mchang@suse.com>
---
 configure.ac | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/configure.ac b/configure.ac
index eeb5d2211..8d1c81a73 100644
--- a/configure.ac
+++ b/configure.ac
@@ -840,6 +840,20 @@ if ( test "x$target_cpu" = xi386 || test "x$target_cpu" = 
xx86_64 ) && test "x$p
   TARGET_CFLAGS="$TARGET_CFLAGS -mno-mmx -mno-sse -mno-sse2 -mno-sse3 
-mno-3dnow"
 fi
 
+if ( test "x$target_cpu" = xi386 || test "x$target_cpu" = xx86_64 ); then
+  AC_CACHE_CHECK([whether -Wa,-mx86-used-note works], 
[grub_cv_cc_mx86_used_note], [
+    CFLAGS="$TARGET_CFLAGS -Wa,-mx86-used-note=no -Werror"
+    AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]], [[]])],
+       [grub_cv_cc_mx86_used_note=yes],
+       [grub_cv_cc_mx86_used_note=no])
+  ])
+
+  if test "x$grub_cv_cc_mx86_used_note" = xyes; then
+    TARGET_CFLAGS="$TARGET_CFLAGS -Wa,-mx86-used-note=no"
+    TARGET_CCASFLAGS="$TARGET_CCASFLAGS -Wa,-mx86-used-note=no"
+  fi
+fi
+
 # GRUB doesn't use float or doubles at all. Yet some toolchains may decide
 # that floats are a good fit to run instead of what's written in the code.
 # Given that floating point unit is disabled (if present to begin with)
-- 
2.31.1