[v2] mini-os: use -m elf_i386 for final linking

[PATCH v2] mini-os: use -m elf_i386 for final linking

Posted by Juergen Gross 4 years ago

Using the standard -m elf_x86_64 for 64-bit mini-os results in the
first section (.text) to start only at offset 2MB in the binary file.

Quoting Andrew Cooper on that topic:

  Specifically, 64bit emulation appears to include "align primary
  sections to 2M so your OS can make better use of superpages even when
  mmap()ing", with no way I can spot to override this in the linker
  file.

Using -m elf_i386 avoids that problem without any visible disadvantage.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 arch/x86/arch.mk | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/arch.mk b/arch/x86/arch.mk
index c87885f..00028a0 100644
--- a/arch/x86/arch.mk
+++ b/arch/x86/arch.mk
@@ -26,3 +26,5 @@ ifeq ($(CONFIG_PARAVIRT),n)
 ARCH_LDFLAGS_FINAL := --oformat=elf32-i386
 ARCH_AS_DEPS += x86_hvm.S
 endif
+
+ARCH_LDFLAGS_FINAL += -m elf_i386
-- 
2.16.4

Re: [PATCH v2] mini-os: use -m elf_i386 for final linking

Posted by Wei Liu 4 years ago

On Thu, Apr 16, 2020 at 03:17:15PM +0200, Juergen Gross wrote:
> Using the standard -m elf_x86_64 for 64-bit mini-os results in the
> first section (.text) to start only at offset 2MB in the binary file.
> 
> Quoting Andrew Cooper on that topic:
> 
>   Specifically, 64bit emulation appears to include "align primary
>   sections to 2M so your OS can make better use of superpages even when
>   mmap()ing", with no way I can spot to override this in the linker
>   file.
> 
> Using -m elf_i386 avoids that problem without any visible disadvantage.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>

Applied with Samuel's Rb from v1.

Wei.