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

[Jens Remus <jremus@linux.ibm.com>]

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 defining non-SP/FP register
  <regno> as CFA base register
- skipping SFrame FDE due to .cfi_def_cfa_register defining non-SP/FP
  register <regno> as CFA base register
- skipping SFrame FDE due to .cfi_def_cfa_offset without 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
- skipping SFrame FDE due to .cfi_val_offset specifying {FP|RA} register
- skipping SFrame FDE due to .cfi_remember_state without SFrame FRE
  state
- skipping SFrame FDE due to .cfi_register specifying {SP|FP|RA}
  register
- skipping SFrame FDE due to non-default return-address 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"));
+      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;
+      }
     }
 
+  /* 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 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
 #...
-- 
2.40.1