Re: [PATCH v3 09/15] gas: User readable warnings if SFrame FDE is not generated

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

On 4/12/24 07:47, 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:
> 

My intention below is to keep warning messages terse but useful.

> - skipping SFrame FDE due to .cfi_def_cfa defining non-SP/FP register
>    <regno> as CFA base register

.cfi_def_cfa _is_ used to specify the CFA base register. So I suggest we 
re-word this to following (and hence, removing the redundancy):

skipping SFrame FDE; non-SP/FP register <regno> in .cfi_def_cfa

or if (;) is unappetizing:

skipping SFrame FDE due to non-SP/FP register <regno> in .cfi_def_cfa

(replacing ; with "due to", if you prefer, applies to all comments below)

> - skipping SFrame FDE due to .cfi_def_cfa_register defining non-SP/FP
>    register <regno> as CFA base register

skipping SFrame FDE; non-SP/FP register <regno> in .cfi_def_cfa_register

> - skipping SFrame FDE due to .cfi_def_cfa_offset without CFA base
>    register in effect

skipping SFrame FDE; .cfi_def_cfa_offset specified when no CFA base 
register in effect

> - skipping SFrame FDE due to .cfi_def_cfa_offset with non-SP/FP register
>    <regno> as CFA base register in effect

I find this very confusing.  Can we not add this warning?  Such a case 
should not happen as we have handled the respective cases in 
sframe_xlate_do_def_cfa and sframe_xlate_do_def_cfa_register ?

> - skipping SFrame FDE due to .cfi_val_offset specifying {FP|RA} register

skipping SFrame FDE; FP/RA register <regno> in .cfi_val_offset

> - skipping SFrame FDE due to .cfi_remember_state without SFrame FRE
>    state

skipping SFrame FDE; .cfi_remember_state without prior SFrame FRE state

> - skipping SFrame FDE due to .cfi_register specifying {SP|FP|RA}
>    register

skipping SFrame FDE; FP/RA register <regno> in .cfi_register

> - skipping SFrame FDE due to non-default return-address register <regno>

skipping SFrame FDE; non-default RA register <regno>

> 
> 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.
> 
> gas/testsuite/
> 	* gas/cfi-sframe/common-empty-1.d: Update generic SFrame test
> 	case to updated warning message texts.
> 	* gas/cfi-sframe/common-empty-2.d: Likewise.
> 	* gas/cfi-sframe/common-empty-3.d: Likewise.
> 
> Reviewed-by: Andreas Krebbel <krebbel@linux.ibm.com>
> Signed-off-by: Jens Remus <jremus@linux.ibm.com>
> ---
> 
> Notes (jremus):
>      Changes v2 -> v3:
>      - Updated SFrame warning message texts as suggested by Indu, except for
>        the .cfi_def_cfa[_register] ones. I think it would be helpful for the
>        user to know that the issue is caused by a non-SP/FP register. But
>        maybe that is because I am new to CFI and those that would actually
>        debug the cause for these warnings would not need this extra
>        information? Anyhow, Indu, if you still prefer your suggestions I
>        would go with yours.
>        The ".cfi_remember_state without SFrame FRE state" warning needs to
>        remain, as there would otherwise not be any warning at all. The reason
>        is that sframe_do_cfi_insn now expects any of its called CFI
>        processing functions to emit a warning, if they return with an error,
>        such as SFRAME_XLATE_ERR_NOTREPRESENTED. Silently skipping SFrame FDE
>        does not seem an acceptable approach to me.
>      - Do not test sframe_ra_tracking_p when determining the SFrame register
>        name in sframe_register_name. The RA register name does not depend on
>        whether RA tracking is used or not.
>      - Corrected formatting of ChangeLog in commit message.
> 
>   gas/gen-sframe.c                              | 95 ++++++++++++++-----
>   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, 75 insertions(+), 28 deletions(-)
> 
> diff --git a/gas/gen-sframe.c b/gas/gen-sframe.c
> index f47f51c7a354..a3b6f75cfe85 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 +922,23 @@ 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 (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 +1007,12 @@ 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 defining "
> +		 "non-SP/FP register %u as CFA base register"),
> +	       cfi_insn->u.r);
> +      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 +1037,12 @@ 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 defining "
> +		 "non-SP/FP register %u as CFA base register"),
> +	       cfi_insn->u.r);
> +      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 +1073,16 @@ 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 with "
> +		   "non-SP/FP register %u as CFA base register in effect"),
> +		 cur_fre->cfa_base_reg);
> +      return SFRAME_XLATE_ERR_NOTREPRESENTED;
> +    }
>   
>     return SFRAME_XLATE_OK;
>   }
> @@ -1096,13 +1132,16 @@ sframe_xlate_do_val_offset (struct sframe_xlate_ctx *xlate_ctx ATTRIBUTE_UNUSED,
>        register is not interesting (FP or RA reg), the current DW_CFA_val_offset
>        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.  */
> +  if (cfi_insn->u.r == SFRAME_CFA_FP_REG
>   #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.  */
> +      || (sframe_ra_tracking_p () && cfi_insn->u.r == SFRAME_CFA_RA_REG)
>   #endif
> +      )
> +    {
> +      as_warn (_("skipping SFrame FDE due to .cfi_val_offset specifying %s register"),
> +	       sframe_register_name (cfi_insn->u.r));
> +      return SFRAME_XLATE_ERR_NOTREPRESENTED; /* Not represented.  */
> +    }
>   
>     /* Safe to skip.  */
>     return SFRAME_XLATE_OK;
> @@ -1124,7 +1163,11 @@ sframe_xlate_do_register (struct sframe_xlate_ctx *xlate_ctx ATTRIBUTE_UNUSED,
>         || (cfi_insn->u.rr.reg1 == SFRAME_CFA_RA_REG)
>   #endif
>         || cfi_insn->u.rr.reg1 == SFRAME_CFA_FP_REG)
> -    return SFRAME_XLATE_ERR_NOTREPRESENTED;  /* Not represented.  */
> +    {
> +      as_warn (_("skipping SFrame FDE due to .cfi_register specifying %s register"),
> +	       sframe_register_name (cfi_insn->u.rr.reg1));
> +      return SFRAME_XLATE_ERR_NOTREPRESENTED;  /* Not represented.  */
> +    }
>   
>     /* Safe to skip.  */
>     return SFRAME_XLATE_OK;
> @@ -1142,7 +1185,10 @@ 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"));

"without SFrame FRE state" --> "without prior SFrame FRE state" ?

> +      return SFRAME_XLATE_ERR_INVAL;
> +    }
>   
>     if (!xlate_ctx->remember_fre)
>       xlate_ctx->remember_fre = sframe_row_entry_new ();
> @@ -1330,21 +1376,19 @@ 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;

<>/GCC/gcc-upstream/gcc/contrib/check_GNU_style.py patch gives:

=== ERROR type #1: blocks of 8 spaces should be replaced with tabs (1 
error(s)) ===
gas/gen-sframe.c:1386:0:        err = SFRAME_XLATE_ERR_NOTREPRESENTED;

I dont think it is a must-be-used-script for binutils project, but for 
my commits I have used this script to keep code base aligned to same 
formatting style.

PS: Not all errors reported by the script need to be fixed.

> +      }
>       }
>   
> +  /* Any error will cause no SFrame FDE later.  The user has already been
> +     warned.  */
>     return err;
>   }
>   
> @@ -1361,7 +1405,8 @@ sframe_do_fde (struct sframe_xlate_ctx *xlate_ctx,
>     /* SFrame format cannot represent a non-default DWARF return column reg.  */
>     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 return-address register %u"),
> +	       xlate_ctx->dw_fde->return_column);

return-address -> "return address" or even just RA.

>         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..5cc37d5ff440 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 return-address register 0
>   #objdump: --sframe=.sframe
>   #name: SFrame supports only default return column
>   #...