[PATCH v2 04/11] s390: Represent FP/RA saved in register in SFrame

[Jens Remus]

On 27.05.2025 13:07, Jens Remus wrote:
> include/
> 	* sframe.h (SFRAME_S390X_OFFSET_IS_REGNUM): New s390x-specific
> 	macro to test whether an SFrame FP/RA offset is a DWARF register
> 	number.
> 	(SFRAME_S390X_OFFSET_ENCODE_REGNUM): New s390x-specific macro to
> 	encode a DWARF register number into an SFrame FP/RA offset.
> 	(SFRAME_S390X_OFFSET_DECODE_REGNUM): New s390x-specific macro to
> 	decode an SFrame FP/RA offset into a DWARF register number.
> 	* sframe-api.h (sframe_fre_get_fp_offset,
> 	sframe_fre_get_fp_offset): Add comment that for s390x the offset
> 	may be an encoded register number.
> 	(sframe_fre_get_ra_offset): Add comment that for s390x an offset
> 	value of SFRAME_FRE_RA_OFFSET_INVALID indicates that the RA is
> 	not saved.

SFRAME_FRE_RA_OFFSET_INVALID is introduced in the next patch.  I'll move
this accordingly in V3 of my series.

> libsframe/
> 	* sframe.c (sframe_fre_get_fp_offset, sframe_fre_get_fp_offset):
> 	Add comment that for s390x the offset may be an encoded register
> 	number.
> 	(sframe_fre_get_ra_offset): Add comment that for s390x an offset
> 	value of SFRAME_FRE_RA_OFFSET_INVALID indicates that the RA is
> 	not saved.

Ditto.

> 	* sframe-dump.c (is_sframe_abi_arch_s390x): New helper to test
> 	whether ABI/arch is s390x.
> 	(dump_sframe_func_with_fres): Use SFRAME_S390X_OFFSET_IS_REGNUM
> 	and SFRAME_S390X_OFFSET_DECODE_REGNUM to dump FP/RA saved in
> 	another register on s390x.
> 	* doc/sframe-spec.texi (s390x): Document s390x-specific
> 	representation of FP/RA saved in another register.

> Notes (jremus):
>     Changes in V2:
>     - Reword commit message (s390 to s390x). (Indu)
>     - Rename s390x-specific macros from *_S390_* to *_S390X_*. (Indu)
>     - Use "s390x" instead of "S390" in comments and SFrame spec. (Indu)
>     - Add comment on sframe_fre_get_{fp|ra}_offset that for s390x the offset
>       may be an encoded register number. (Indu)
>     - Add documentation that for s390x stack tracers need to implement
>       checks when restoring FP and RA from registers. (Indu)
>     - Add comment on sframe_fre_get_ra_offset that for s390x the offset may
>       be SFRAME_FRE_RA_OFFSET_INVALID when FP without RA saved.

Ditto.

>     - Reword test names.
>     - Adjust tests to commit bd9dc0a281a4 ("gas: sframe: reword diagnostic
>       to address ambiguity")
>     - Rename CFI SFrame test file names from s390 to s390x. (Indu)
>     - Reword test names.

> diff --git a/include/sframe-api.h b/include/sframe-api.h

> @@ -198,12 +198,20 @@ extern int32_t
>  sframe_fre_get_cfa_offset (sframe_decoder_ctx *dtcx,
>  			   sframe_frame_row_entry *fre, int *errp);
>  
> -/* Get the FP offset from the FRE.  If the offset is invalid, sets errp.  */
> +/* Get the FP offset from the FRE.  If the offset is invalid, sets errp.
> +
> +   For s390x the offset may be an encoded register number, indicated by
> +   LSB set to one, which is only valid in the topmost frame.  */
>  extern int32_t
>  sframe_fre_get_fp_offset (sframe_decoder_ctx *dctx,
>  			  sframe_frame_row_entry *fre, int *errp);
>  
> -/* Get the RA offset from the FRE.  If the offset is invalid, sets errp.  */
> +/* Get the RA offset from the FRE.  If the offset is invalid, sets errp.
> +
> +   For s390x a RA offset value of SFRAME_FRE_RA_OFFSET_INVALID indicates
> +   that the RA is not saved, which is only valid in the topmost frame.

Ditto.

> +   For s390x the offset may be an encoded register number, indicated by
> +   LSB set to one, which is only valid in the topmost frame.  */
>  extern int32_t
>  sframe_fre_get_ra_offset (sframe_decoder_ctx *dctx,
>  			  sframe_frame_row_entry *fre, int *errp);

> diff --git a/libsframe/sframe.c b/libsframe/sframe.c

> @@ -706,7 +709,12 @@ sframe_fre_get_fp_offset (sframe_decoder_ctx *dctx,
>    return sframe_get_fre_offset (fre, fp_offset_idx, errp);
>  }
>  
> -/* Get the RA offset from the FRE.  If the offset is invalid, sets errp.  */
> +/* Get the RA offset from the FRE.  If the offset is invalid, sets errp.
> +
> +   For s390x a RA offset value of SFRAME_FRE_RA_OFFSET_INVALID indicates
> +   that the RA is not saved, which is only valid in the topmost frame.

Ditto.

> +   For s390x the offset may be an encoded register number, indicated by
> +   LSB set to one, which is only valid in the topmost frame.  */
>  
>  int32_t
>  sframe_fre_get_ra_offset (sframe_decoder_ctx *dctx,

Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
+49-7031-16-1128 Office
jremus@de.ibm.com

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