Re: [PATCH v2 8/9] gas: User readable warnings if SFrame FDE is not generated

[Indu Bhagat <indu.bhagat@oracle.com>]

On 2/23/24 09:07, Jens Remus wrote:
> The following generic warning message, which is printed whenever the
> assembler skips generation of SFrame FDE, is not very helpful for the
> user:
> 
>    skipping SFrame FDE due to DWARF CFI op <name> (0x<hexval>)
> 
> Whenever possible print meaningful warning messages, when the assembler
> skips generation of SFrame FDE:
> 
> - skipping SFrame FDE due to .cfi_def_cfa specifying CFA base register
>    other than SP or FP (<regno> instead of <SP-regno> or <FP-regno>)

I find that stating "<SP-regno> or <FP-regno>" is not necessary in the 
warning.  This information is identified unambiguously, given an ABI.

How about:
"skipping SFrame FDE due to .cfi_def_cfa defining CFA base reg to 
<regno>" or similar ?

> - skipping SFrame FDE due to .cfi_def_cfa_register specifying CFA base
>    register other than SP or FP (<regno> instead of <SP-regno> or
>    <FP-regno>)

Same thought as above.

> - skipping SFrame FDE due to .cfi_def_cfa_offset without CFA base
>    register in effect
> - skipping SFrame FDE due to .cfi_def_cfa_offset while CFA base register
>    other than SP or FP in effect (<regno> instead of <SP-regno> or
>    <FP-regno>)

Ditto.

> - skipping SFrame FDE due to .cfi_val_offset specifying {FP|RA} register
>    (<regno>)
> - skipping SFrame FDE due to .cfi_remember_state without SFrame FRE
>    state

I dont expect this warning to occur at all out in the field 
(uhand-written asm with errors is the only case that comes to mind). 
The testcase which triggers it simply happens to be just a testcase for 
checking corner case handling.

WDYT about skipping this warning altogether ?

> - skipping SFrame FDE due to .cfi_register specifying {SP|FP|RA}
>    register (<regno>)
> - skipping SFrame FDE due to non-default DWARF return column (<regno>
>    instead of <DWARF-def-ret-col-regno>)

I think this can be simply "skipping SFrame FDE due to non-default 
return addr reg <regno>".  IMO, stating the default DWARF return address 
register information in each warning msg does not add value.

Thanks

> 
> gas/
> 	* gen-sframe.h (SFRAME_FRE_BASE_REG_INVAL): New macro for
> 	  invalid SFrame FRE CFA base register value of -1.
> 	* gen-sframe.c: User readable warnings if SFrame FDE is not
> 	  generated.
> 
> Reviewed-by: Andreas Krebbel <krebbel@linux.ibm.com>
> Signed-off-by: Jens Remus <jremus@linux.ibm.com>
> ---
>   gas/gen-sframe.c                              | 96 ++++++++++++++-----
>   gas/gen-sframe.h                              |  2 +
>   gas/testsuite/gas/cfi-sframe/common-empty-1.d |  2 +-
>   gas/testsuite/gas/cfi-sframe/common-empty-2.d |  2 +-
>   gas/testsuite/gas/cfi-sframe/common-empty-3.d |  2 +-
>   5 files changed, 79 insertions(+), 25 deletions(-)
> 
> diff --git a/gas/gen-sframe.c b/gas/gen-sframe.c
> index 28b49a2a8425..339f4412ca05 100644
> --- a/gas/gen-sframe.c
> +++ b/gas/gen-sframe.c
> @@ -867,7 +867,7 @@ sframe_row_entry_new (void)
>     struct sframe_row_entry *fre = XCNEW (struct sframe_row_entry);
>     /* Reset cfa_base_reg to -1.  A value of 0 will imply some valid register
>        for the supported arches.  */
> -  fre->cfa_base_reg = -1;
> +  fre->cfa_base_reg = SFRAME_FRE_BASE_REG_INVAL;
>     fre->merge_candidate = true;
>     /* Reset the mangled RA status bit to zero by default.  We will initialize it in
>        sframe_row_entry_initialize () with the sticky bit if set.  */
> @@ -922,6 +922,24 @@ sframe_row_entry_initialize (struct sframe_row_entry *cur_fre,
>     cur_fre->mangled_ra_p = prev_fre->mangled_ra_p;
>   }
>   
> +/* Return SFrame register name for SP, FP, and RA, or NULL if other.  */
> +
> +static const char *
> +sframe_register_name (unsigned int reg)
> +{
> +  if (reg == SFRAME_CFA_SP_REG)
> +    return "SP";
> +  else if (reg == SFRAME_CFA_FP_REG)
> +    return "FP";
> +#ifdef SFRAME_FRE_RA_TRACKING
> +  else if (sframe_ra_tracking_p ()
> +	   && (reg == SFRAME_CFA_RA_REG))
> +    return "RA";
> +#endif
> +  else
> +    return NULL;
> +}
> +
>   /* Translate DW_CFA_advance_loc into SFrame context.
>      Return SFRAME_XLATE_OK if success.  */
>   
> @@ -990,7 +1008,12 @@ sframe_xlate_do_def_cfa (struct sframe_xlate_ctx *xlate_ctx,
>        SFrame stack trace info for the function.  */
>     if (cfi_insn->u.r != SFRAME_CFA_SP_REG
>         && cfi_insn->u.r != SFRAME_CFA_FP_REG)
> -    return SFRAME_XLATE_ERR_NOTREPRESENTED; /* Not represented.  */
> +    {
> +      as_warn (_("skipping SFrame FDE due to .cfi_def_cfa specifying CFA base "
> +		 "register other than SP or FP (%u instead of %u or %u)"),
> +	       cfi_insn->u.r, SFRAME_CFA_SP_REG, SFRAME_CFA_FP_REG);
> +      return SFRAME_XLATE_ERR_NOTREPRESENTED; /* Not represented.  */
> +    }
>     sframe_fre_set_cfa_base_reg (cur_fre, cfi_insn->u.ri.reg);
>     sframe_fre_set_cfa_offset (cur_fre, cfi_insn->u.ri.offset);
>     cur_fre->merge_candidate = false;
> @@ -1015,7 +1038,12 @@ sframe_xlate_do_def_cfa_register (struct sframe_xlate_ctx *xlate_ctx,
>        skip creating SFrame stack trace info for the function.  */
>     if (cfi_insn->u.r != SFRAME_CFA_SP_REG
>         && cfi_insn->u.r != SFRAME_CFA_FP_REG)
> -    return SFRAME_XLATE_ERR_NOTREPRESENTED; /* Not represented.  */
> +    {
> +      as_warn (_("skipping SFrame FDE due to .cfi_def_cfa_register specifying "
> +		 "CFA base register other than SP or FP (%u instead of %u or %u)"),
> +	       cfi_insn->u.r, SFRAME_CFA_SP_REG, SFRAME_CFA_FP_REG);
> +      return SFRAME_XLATE_ERR_NOTREPRESENTED; /* Not represented.  */
> +    }
>     sframe_fre_set_cfa_base_reg (cur_fre, cfi_insn->u.ri.reg);
>     sframe_fre_set_cfa_offset (cur_fre, last_fre->cfa_offset);
>     cur_fre->merge_candidate = false;
> @@ -1046,7 +1074,16 @@ sframe_xlate_do_def_cfa_offset (struct sframe_xlate_ctx *xlate_ctx,
>         cur_fre->merge_candidate = false;
>       }
>     else
> -    return SFRAME_XLATE_ERR_NOTREPRESENTED;
> +    {
> +      if (cur_fre->cfa_base_reg == SFRAME_FRE_BASE_REG_INVAL)
> +	as_warn (_("skipping SFrame FDE due to .cfi_def_cfa_offset without CFA "
> +		   "base register in effect"));
> +      else
> +	as_warn (_("skipping SFrame FDE due to .cfi_def_cfa_offset while CFA "
> +		   "base register other than SP or FP in effect (%u instead of %u or %u)"),
> +		 cur_fre->cfa_base_reg, SFRAME_CFA_SP_REG, SFRAME_CFA_FP_REG);
> +      return SFRAME_XLATE_ERR_NOTREPRESENTED;
> +    }
>   
>     return SFRAME_XLATE_OK;
>   }
> @@ -1097,11 +1134,19 @@ sframe_xlate_do_val_offset (struct sframe_xlate_ctx *xlate_ctx ATTRIBUTE_UNUSED,
>        instruction can be safely skipped without sacrificing the asynchronicity of
>        stack trace information.  */
>     if (cfi_insn->u.r == SFRAME_CFA_FP_REG)
> -    return SFRAME_XLATE_ERR_NOTREPRESENTED; /* Not represented.  */
> +    {
> +      as_warn (_("skipping SFrame FDE due to .cfi_val_offset specifying FP register (%u)"),
> +	       SFRAME_CFA_FP_REG);
> +      return SFRAME_XLATE_ERR_NOTREPRESENTED; /* Not represented.  */
> +    }
>   #ifdef SFRAME_FRE_RA_TRACKING
>     else if (sframe_ra_tracking_p ()
>   	   && cfi_insn->u.r == SFRAME_CFA_RA_REG)
> -    return SFRAME_XLATE_ERR_NOTREPRESENTED; /* Not represented.  */
> +    {
> +      as_warn (_("skipping SFrame FDE due to .cfi_val_offset specifying RA register (%u)"),
> +	       SFRAME_CFA_RA_REG);
> +      return SFRAME_XLATE_ERR_NOTREPRESENTED; /* Not represented.  */
> +    }
>   #endif
>   
>     /* Safe to skip.  */
> @@ -1120,7 +1165,10 @@ sframe_xlate_do_remember_state (struct sframe_xlate_ctx *xlate_ctx)
>        early with non-zero error code, this will cause no SFrame stack trace
>        info for the function involved.  */
>     if (!last_fre)
> -    return SFRAME_XLATE_ERR_INVAL;
> +    {
> +      as_warn (_("skipping SFrame FDE due to .cfi_remember_state without SFrame FRE state"));
> +      return SFRAME_XLATE_ERR_INVAL;
> +    }
>   
>     if (!xlate_ctx->remember_fre)
>       xlate_ctx->remember_fre = sframe_row_entry_new ();
> @@ -1307,7 +1355,12 @@ sframe_do_cfi_insn (struct sframe_xlate_ctx *xlate_ctx,
>   	  || cfi_insn->u.rr.reg1 == SFRAME_CFA_RA_REG
>   #endif
>   	  || cfi_insn->u.rr.reg1 == SFRAME_CFA_FP_REG)
> -	err = SFRAME_XLATE_ERR_NOTREPRESENTED;
> +	{
> +	  as_warn (_("skipping SFrame FDE due to .cfi_register specifying %s register (%u)"),
> +		   sframe_register_name (cfi_insn->u.rr.reg1),
> +		   cfi_insn->u.rr.reg1);
> +	  err = SFRAME_XLATE_ERR_NOTREPRESENTED;
> +	}
>         break;
>       case DW_CFA_undefined:
>       case DW_CFA_same_value:
> @@ -1315,21 +1368,19 @@ sframe_do_cfi_insn (struct sframe_xlate_ctx *xlate_ctx,
>       default:
>         /* Following skipped operations do, however, impact the asynchronicity:
>   	  - CFI_escape.  */
> -      err = SFRAME_XLATE_ERR_NOTREPRESENTED;
> -    }
> -
> -  /* An error here will cause no SFrame FDE later.  Warn the user because this
> -     will affect the overall coverage and hence, asynchronicity.  */
> -  if (err)
> -    {
> -      const char *cfi_name = sframe_get_cfi_name (op);
> -
> -      if (!cfi_name)
> -	cfi_name = _("(unknown)");
> -      as_warn (_("skipping SFrame FDE due to DWARF CFI op %s (%#x)"),
> -	       cfi_name, op);
> +      {
> +	const char *cfi_name = sframe_get_cfi_name (op);
> +
> +	if (!cfi_name)
> +	  cfi_name = _("(unknown)");
> +	as_warn (_("skipping SFrame FDE due to DWARF CFI op %s (%#x)"),
> +		 cfi_name, op);
> +        err = SFRAME_XLATE_ERR_NOTREPRESENTED;
> +      }
>       }
>   
> +  /* Any error will cause no SFrame FDE later.  The user has already been
> +     warned.  */
>     return err;
>   }
>   
> @@ -1346,7 +1397,8 @@ sframe_do_fde (struct sframe_xlate_ctx *xlate_ctx,
>     /* If the return column is not RIP, SFrame format cannot represent it.  */
>     if (xlate_ctx->dw_fde->return_column != DWARF2_DEFAULT_RETURN_COLUMN)
>       {
> -      as_warn (_("skipping SFrame FDE due to non-default DWARF return column"));
> +      as_warn (_("skipping SFrame FDE due to non-default DWARF return column (%u instead of %u)"),
> +	       xlate_ctx->dw_fde->return_column, DWARF2_DEFAULT_RETURN_COLUMN);
>         return SFRAME_XLATE_ERR_NOTREPRESENTED;
>       }
>   
> diff --git a/gas/gen-sframe.h b/gas/gen-sframe.h
> index fbe2fd5d9368..8ed46dbb087b 100644
> --- a/gas/gen-sframe.h
> +++ b/gas/gen-sframe.h
> @@ -24,6 +24,8 @@
>   #define SFRAME_FRE_ELEM_LOC_REG		0
>   #define SFRAME_FRE_ELEM_LOC_STACK	1
>   
> +#define SFRAME_FRE_BASE_REG_INVAL	((unsigned int)-1)
> +
>   /* SFrame Frame Row Entry (FRE).
>   
>      A frame row entry is a slice of the frame and can be valid for a set of
> diff --git a/gas/testsuite/gas/cfi-sframe/common-empty-1.d b/gas/testsuite/gas/cfi-sframe/common-empty-1.d
> index d7756302b559..08731b069229 100644
> --- a/gas/testsuite/gas/cfi-sframe/common-empty-1.d
> +++ b/gas/testsuite/gas/cfi-sframe/common-empty-1.d
> @@ -1,5 +1,5 @@
>   #as: --gsframe
> -#warning: skipping SFrame FDE due to DWARF CFI op DW_CFA_remember_state \(0xa\)
> +#warning: skipping SFrame FDE due to \.cfi_remember_state without SFrame FRE state
>   #objdump: --sframe=.sframe
>   #name: Uninteresting cfi directives generate an empty SFrame section
>   #...
> diff --git a/gas/testsuite/gas/cfi-sframe/common-empty-2.d b/gas/testsuite/gas/cfi-sframe/common-empty-2.d
> index 20282c7854e8..e759cddfcc20 100644
> --- a/gas/testsuite/gas/cfi-sframe/common-empty-2.d
> +++ b/gas/testsuite/gas/cfi-sframe/common-empty-2.d
> @@ -1,5 +1,5 @@
>   #as: --gsframe
> -#warning: skipping SFrame FDE due to DWARF CFI op DW_CFA_def_cfa_offset \(0xe\)
> +#warning: skipping SFrame FDE due to \.cfi_def_cfa_offset without CFA base register in effect
>   #objdump: --sframe=.sframe
>   #name: SFrame supports only FP/SP based CFA
>   #...
> diff --git a/gas/testsuite/gas/cfi-sframe/common-empty-3.d b/gas/testsuite/gas/cfi-sframe/common-empty-3.d
> index d17521dd88ea..9a46b016a9ba 100644
> --- a/gas/testsuite/gas/cfi-sframe/common-empty-3.d
> +++ b/gas/testsuite/gas/cfi-sframe/common-empty-3.d
> @@ -1,5 +1,5 @@
>   #as: --gsframe
> -#warning: skipping SFrame FDE due to non-default DWARF return column
> +#warning: skipping SFrame FDE due to non-default DWARF return column \(0 instead of \d+\)
>   #objdump: --sframe=.sframe
>   #name: SFrame supports only default return column
>   #...