On 2/27/25 6:10 AM, Jens Remus wrote:
> The function start address in a SFrame FDE (sfde_func_start_address) is
> a signed offset, that is relative to the (1) FDE in object files and
> (2) SFrame section in executables and shared libraries after final link.
> Internal in the GNU linker it is relative to the (3) FDE in linker
> generated FDE for PLT0 and (4) PLT0 in linker generated FDE for PLTn.
>
> While at it fix a typo in SFD_INFO and remove commented out debugging
> code.
>
> bfd/
> * elf-sframe.c (_bfd_elf_merge_section_sframe): Add comments on
> FDE function start address.
> (sframe_decoder_set_func_reloc_index): Correct typo in comment.
>
> libsframe/doc/
> * sframe-spec.texi (sfde_func_start_address): Enhance
> documentation on FDE function start address.
>
> Signed-off-by: Jens Remus <jremus@linux.ibm.com>
> ---
> bfd/elf-sframe.c | 13 ++++++++-----
> libsframe/doc/sframe-spec.texi | 6 ++++--
> 2 files changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/bfd/elf-sframe.c b/bfd/elf-sframe.c
> index 97e007345152..e3c7c52a548f 100644
> --- a/bfd/elf-sframe.c
> +++ b/bfd/elf-sframe.c
> @@ -93,7 +93,7 @@ sframe_decoder_set_func_reloc_index (struct sframe_dec_info *sfd_info,
> sfd_info->sfd_func_bfdinfo[func_idx].func_reloc_index = reloc_index;
> }
>
> -/* Initialize the set of additional information in CFD_INFO,
> +/* Initialize the set of additional information in SFD_INFO,
> needed for linking SEC. Returns TRUE if setup is done successfully. */
>
> static bool
> @@ -475,16 +475,19 @@ _bfd_elf_merge_section_sframe (bfd *abfd,
> }
> }
>
> - /* Get the SFrame FDE function start address after relocation. */
> + /* Get the SFrame FDE function start address after relocation.
> + In object files it is the signed function offset from FDE.
> + For linker generated FDE for PLT0 it is the PLT0 offset
> + from FDE and for PLTn it is the PLTn offset from PLT0. */
> address = sframe_read_value (abfd, contents, r_offset, 4);
> + /* For PLTn add the PLTn offset from PLT0. */
> if (pltn_reloc_by_hand)
> address += sframe_read_value (abfd, contents,
> pltn_r_offset, 4);
> + /* Fixup offset to be from SFrame section instead of FDE, by
> + adding the FDE offset from SFrame output section. */
> address += (sec->output_offset + r_offset);
>
> - /* FIXME For testing only. Cleanup later. */
> - // address += (sec->output_section->vma);
> -
> func_start_addr = address;
> }
>
> diff --git a/libsframe/doc/sframe-spec.texi b/libsframe/doc/sframe-spec.texi
> index ae115705ca73..7f30d33cf4ef 100644
> --- a/libsframe/doc/sframe-spec.texi
> +++ b/libsframe/doc/sframe-spec.texi
> @@ -460,8 +460,10 @@ Following table describes each component of the SFrame FDE structure:
> @tab @code{sfde_func_start_address}
> @tab Signed 32-bit integral field denoting the virtual memory address of the
> described function, for which the SFrame FDE applies. The value encoded in
> -the @code{sfde_func_start_address} field is the offset in bytes of the
> -function's start address, from the SFrame section.
> +the @code{sfde_func_start_address} field is the signed offset in bytes to the
> +function's start address. For object files from the FDE (using a 32-bit
> +PC-relative relocation). For executables and shared libraries after final
> +link, from the SFrame section.
>
This indicates some problem. Something else needs fixing, I am checking
a few things in the current implementation in GAS/ld. Will get back soon.
Thanks
Indu