From: Fabiano Rosas <farosas@suse.de>

Our linker script for optionroms specifies only the placement of the
.text section, leaving the linker free to place the remaining sections
at arbitrary places in the file.

Since at least binutils 2.39, the .note.gnu.build-id section is now
being placed at the start of the file, which causes label addresses to
be shifted. For linuxboot_dma.bin that means that the PnP header
(among others) will not be found when determining the type of ROM at
optionrom_setup():

(0x1c is the label _pnph, where the magic "PnP" is)

$ xxd /usr/share/qemu/linuxboot_dma.bin | grep "PnP"
00000010: 0000 0000 0000 0000 0000 1c00 2450 6e50  ............$PnP

$ xxd pc-bios/optionrom/linuxboot_dma.bin | grep "PnP"
00000010: 0000 0000 0000 0000 0000 4c00 2450 6e50  ............$PnP
                                   ^bad

Using a freshly built linuxboot_dma.bin ROM results in a broken boot:

  SeaBIOS (version rel-1.16.2-0-gea1b7a073390-prebuilt.qemu.org)
  Booting from Hard Disk...
  Boot failed: could not read the boot disk

  Booting from Floppy...
  Boot failed: could not read the boot disk

  No bootable device.

We're not using the build-id section, so pass the --build-id=none
option to the linker to remove it entirely.

Note: In theory, this same issue could happen with any other
section. The ideal solution would be to have all unused sections
discarded in the linker script. However that would be a larger change,
specially for the pvh rom which uses the .bss and COMMON sections so
I'm addressing only the immediate issue here.

Reported-by: Vasiliy Ulyanov <vulyanov@suse.de>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20230926192502.15986-1-farosas@suse.de>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 pc-bios/optionrom/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pc-bios/optionrom/Makefile b/pc-bios/optionrom/Makefile
index b1fff0ba6c8..30d07026c79 100644
--- a/pc-bios/optionrom/Makefile
+++ b/pc-bios/optionrom/Makefile
@@ -36,7 +36,7 @@ config-cc.mak: Makefile
 	    $(call cc-option,-Wno-array-bounds)) 3> config-cc.mak
 -include config-cc.mak
 
-override LDFLAGS = -nostdlib -Wl,-T,$(SRC_DIR)/flat.lds
+override LDFLAGS = -nostdlib -Wl,--build-id=none,-T,$(SRC_DIR)/flat.lds
 
 pvh.img: pvh.o pvh_main.o
 
-- 
2.41.0

03.10.2023 11:30, Paolo Bonzini wrote:
> From: Fabiano Rosas <farosas@suse.de>
> 
> Our linker script for optionroms specifies only the placement of the
> .text section, leaving the linker free to place the remaining sections
> at arbitrary places in the file.
..

> Cc: stable@vger.kernel.org

Are you sure you mean *that* stable? :)

/mjt