[PATCH v2] bfd: Add minimal support to handle note that describes xsave layout

[Jan Beulich]

On 29.09.2025 04:10, Vignesh Balasubramanian wrote:
> This note section is already supported by Linux kernel.
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/x86/kernel/fpu/xstate.c?id=ba386777a30b38dabcc7fb8a89ec2869a09915f7
> 
> Co-Authored-By: Jini Susan George <jinisusan.george@amd.com>
> ---
>  bfd/elf-bfd.h        |  2 ++
>  bfd/elf.c            | 24 +++++++++++++++++++++++-
>  binutils/readelf.c   |  2 ++
>  include/elf/common.h |  2 ++
>  4 files changed, 29 insertions(+), 1 deletion(-)

While this looks all plausible, can you please clarify what was changed in
v2?

Jan

> diff --git a/bfd/elf-bfd.h b/bfd/elf-bfd.h
> index 9ce81ebd314..2877d82b907 100644
> --- a/bfd/elf-bfd.h
> +++ b/bfd/elf-bfd.h
> @@ -2926,6 +2926,8 @@ extern char *elfcore_write_prxfpreg
>    (bfd *, char *, int *, const void *, int);
>  extern char *elfcore_write_xstatereg
>    (bfd *, char *, int *, const void *, int);
> +extern char *elfcore_write_xsave_layout
> +  (bfd *, char *, int *, const void *, int);
>  extern char *elfcore_write_x86_segbases
>    (bfd *, char *, int *, const void *, int);
>  extern char *elfcore_write_i386_tls
> diff --git a/bfd/elf.c b/bfd/elf.c
> index bde7414ee21..07e672f07a5 100644
> --- a/bfd/elf.c
> +++ b/bfd/elf.c
> @@ -114,6 +114,7 @@ SECTION
>  #define NOTE_PSEUDO_SECTION_X86_SEGBASES 	".reg-x86-segbases"
>  #define NOTE_PSEUDO_SECTION_XFP          	".reg-xfp"
>  #define NOTE_PSEUDO_SECTION_XSTATE       	".reg-xstate"
> +#define NOTE_PSEUDO_SECTION_XSAVE_LAYOUT	".reg-xsave-layout"
>  
>  static int elf_sort_sections (const void *, const void *);
>  static bool assign_file_positions_except_relocs (bfd *, struct bfd_link_info *);
> @@ -10492,6 +10493,14 @@ elfcore_grok_sspreg (bfd *abfd, Elf_Internal_Note *note)
>    return elfcore_make_note_pseudosection (abfd, NOTE_PSEUDO_SECTION_SSP, note);
>  }
>  
> +/* Linux dumps the XSAVE Layout description in a note named "LINUX"
> +   with a note type of NT_X86_XSAVE_LAYOUT. */
> +static bool
> +elfcore_grok_xsave_layout_desc (bfd *abfd, Elf_Internal_Note *note)
> +{
> +  return elfcore_make_note_pseudosection (abfd, NOTE_PSEUDO_SECTION_XSAVE_LAYOUT, note);
> +}
> +
>  static bool
>  elfcore_grok_ppc_vmx (bfd *abfd, Elf_Internal_Note *note)
>  {
> @@ -11211,6 +11220,7 @@ elfcore_grok_note (bfd *abfd, Elf_Internal_Note *note)
>  	case NT_S390_VXRS_LOW:	return elfcore_grok_s390_vxrs_low (abfd, note);
>  	case NT_X86_SHSTK:	return elfcore_grok_sspreg (abfd, note);
>  	case NT_X86_XSTATE:	return elfcore_grok_xstatereg (abfd, note);
> +	case NT_X86_XSAVE_LAYOUT: return elfcore_grok_xsave_layout_desc (abfd, note);
>  	default: break;
>  	}
>      }
> @@ -12390,6 +12400,17 @@ elfcore_write_xstatereg (bfd *abfd, char *buf, int *bufsiz,
>  			     note_name, NT_X86_XSTATE, xfpregs, size);
>  }
>  
> +char *
> +elfcore_write_xsave_layout (bfd *abfd, char *buf, int *bufsiz,
> +			    const void *xsave_layout, int size)
> +{
> +  return elfcore_write_note (abfd, buf, bufsiz,
> +			     NOTE_NAME_LINUX,
> +			     NT_X86_XSAVE_LAYOUT,
> +			     xsave_layout,
> +			     size);
> +}
> +
>  static char *
>  elfcore_write_sspreg (bfd *abfd, char *buf, int *bufsiz,
>  		      const void *ssp, int size)
> @@ -13035,7 +13056,8 @@ elfcore_write_register_note (bfd *abfd,
>        { NOTE_PSEUDO_SECTION_TDESC,            elfcore_write_gdb_tdesc},
>        { NOTE_PSEUDO_SECTION_X86_SEGBASES,     elfcore_write_x86_segbases},
>        { NOTE_PSEUDO_SECTION_XFP,              elfcore_write_prxfpreg},
> -      { NOTE_PSEUDO_SECTION_XSTATE,           elfcore_write_xstatereg} /* NB/ No comma.  */
> +      { NOTE_PSEUDO_SECTION_XSTATE,           elfcore_write_xstatereg},
> +      { NOTE_PSEUDO_SECTION_XSAVE_LAYOUT,     elfcore_write_xsave_layout} /* NB/ No comma.  */
>      };
>  
>    int i;
> diff --git a/binutils/readelf.c b/binutils/readelf.c
> index fd9722c8afc..16f50318da9 100644
> --- a/binutils/readelf.c
> +++ b/binutils/readelf.c
> @@ -21375,6 +21375,8 @@ get_note_type (Filedata * filedata, unsigned e_type)
>  	return _("NT_386_IOPERM (x86 I/O permissions)");
>        case NT_X86_XSTATE:
>  	return _("NT_X86_XSTATE (x86 XSAVE extended state)");
> +      case NT_X86_XSAVE_LAYOUT:
> +	return _("NT_X86_XSAVE_LAYOUT (x86 XSAVE Layout description)");
>        case NT_X86_CET:
>  	return _("NT_X86_CET (x86 CET state)");
>        case NT_X86_SHSTK:
> diff --git a/include/elf/common.h b/include/elf/common.h
> index 5d0f93ebf56..c0894870fc5 100644
> --- a/include/elf/common.h
> +++ b/include/elf/common.h
> @@ -696,6 +696,8 @@
>  #define NT_X86_SHSTK	0x204		/* x86 SHSTK state.  */
>  					/* This replaces NT_X86_CET (0x203).  */
>  					/*   note name must be "LINUX".  */
> +#define NT_X86_XSAVE_LAYOUT	0x205	/* XSAVE layout description */
> +					/*   note name must be "LINUX".  */
>  #define NT_S390_HIGH_GPRS 0x300		/* S/390 upper halves of GPRs  */
>  					/*   note name must be "LINUX".  */
>  #define NT_S390_TIMER	0x301		/* S390 timer */