[PATCH v2 #1/2] enable adjustment of return_pc debug attrs

[PATCH v2 #1/2] enable adjustment of return_pc debug attrs

[Alexandre Oliva, Alexandre Oliva]

This patch introduces infrastructure for targets to add an offset to
the label issued after the call_insn to set the call_return_pc
attribute.  This will be used on rs6000, that sometimes issues another
instruction after the call proper as part of a call insn.

Regstrapped on x86_64-linux-gnu and ppc64-linux-gnu.  Ok to install?


for  gcc/ChangeLog

	* target.def (call_offset_return_label): New hook.
	* gcc/doc/tm.texi.in (TARGET_CALL_OFFSET_RETURN_LABEL): Add
	placeholder.
	* gcc/doc/tm.texi: Rebuild.
	* dwarf2out.cc (struct call_arg_loc_node): Record call_insn
	instad of call_arg_loc_note.
	(add_AT_lbl_id): Add optional offset argument.
	(gen_call_site_die): Compute and pass on a return pc offset.
	(gen_subprogram_die): Move call_arg_loc_note computation...
	(dwarf2out_var_location): ... from here.  Set call_insn.
---
 gcc/doc/tm.texi    |    7 +++++++
 gcc/doc/tm.texi.in |    2 ++
 gcc/dwarf2out.cc   |   26 +++++++++++++++++---------
 gcc/target.def     |    9 +++++++++
 4 files changed, 35 insertions(+), 9 deletions(-)

diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index c4a92a5ebee90..44e4c18ad5c0a 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -5426,6 +5426,13 @@ except the last are treated as named.
 You need not define this hook if it always returns @code{false}.
 @end deftypefn
 
+@deftypefn {Target Hook} int TARGET_CALL_OFFSET_RETURN_LABEL (rtx_insn *@var{call_insn})
+While generating call-site debug info for a CALL insn, or a SEQUENCE
+insn starting with a CALL, this target hook is invoked to compute the
+offset to be added to the debug label emitted after the call to obtain
+the return address that should be recorded as the return PC.
+@end deftypefn
+
 @deftypefn {Target Hook} void TARGET_CALL_ARGS (rtx, @var{tree})
 While generating RTL for a function call, this target hook is invoked once
 for each argument passed to the function, either a register returned by
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index 4075e71624c04..68856978fe364 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -3785,6 +3785,8 @@ These machine description macros help implement varargs:
 
 @hook TARGET_STRICT_ARGUMENT_NAMING
 
+@hook TARGET_CALL_OFFSET_RETURN_LABEL
+
 @hook TARGET_CALL_ARGS
 
 @hook TARGET_END_CALL_ARGS
diff --git a/gcc/dwarf2out.cc b/gcc/dwarf2out.cc
index 1711ad2c2da31..d1db918c43900 100644
--- a/gcc/dwarf2out.cc
+++ b/gcc/dwarf2out.cc
@@ -3584,7 +3584,7 @@ typedef struct var_loc_list_def var_loc_list;
 
 /* Call argument location list.  */
 struct GTY ((chain_next ("%h.next"))) call_arg_loc_node {
-  rtx GTY (()) call_arg_loc_note;
+  rtx_insn * GTY (()) call_insn;
   const char * GTY (()) label;
   tree GTY (()) block;
   bool tail_call_p;
@@ -3768,7 +3768,8 @@ static void remove_addr_table_entry (addr_table_entry *);
 static void add_AT_addr (dw_die_ref, enum dwarf_attribute, rtx, bool);
 static inline rtx AT_addr (dw_attr_node *);
 static void add_AT_symview (dw_die_ref, enum dwarf_attribute, const char *);
-static void add_AT_lbl_id (dw_die_ref, enum dwarf_attribute, const char *);
+static void add_AT_lbl_id (dw_die_ref, enum dwarf_attribute, const char *,
+			   int = 0);
 static void add_AT_lineptr (dw_die_ref, enum dwarf_attribute, const char *);
 static void add_AT_macptr (dw_die_ref, enum dwarf_attribute, const char *);
 static void add_AT_range_list (dw_die_ref, enum dwarf_attribute,
@@ -5327,14 +5328,17 @@ add_AT_symview (dw_die_ref die, enum dwarf_attribute attr_kind,
 
 static inline void
 add_AT_lbl_id (dw_die_ref die, enum dwarf_attribute attr_kind,
-               const char *lbl_id)
+	       const char *lbl_id, int offset)
 {
   dw_attr_node attr;
 
   attr.dw_attr = attr_kind;
   attr.dw_attr_val.val_class = dw_val_class_lbl_id;
   attr.dw_attr_val.val_entry = NULL;
-  attr.dw_attr_val.v.val_lbl_id = xstrdup (lbl_id);
+  if (!offset)
+    attr.dw_attr_val.v.val_lbl_id = xstrdup (lbl_id);
+  else
+    attr.dw_attr_val.v.val_lbl_id = xasprintf ("%s%+i", lbl_id, offset);
   if (dwarf_split_debug_info)
     attr.dw_attr_val.val_entry
         = add_addr_table_entry (attr.dw_attr_val.v.val_lbl_id,
@@ -23405,7 +23409,9 @@ gen_call_site_die (tree decl, dw_die_ref subr_die,
   if (stmt_die == NULL)
     stmt_die = subr_die;
   die = new_die (dwarf_TAG (DW_TAG_call_site), stmt_die, NULL_TREE);
-  add_AT_lbl_id (die, dwarf_AT (DW_AT_call_return_pc), ca_loc->label);
+  add_AT_lbl_id (die, dwarf_AT (DW_AT_call_return_pc),
+		 ca_loc->label,
+		 targetm.calls.call_offset_return_label (ca_loc->call_insn));
   if (ca_loc->tail_call_p)
     add_AT_flag (die, dwarf_AT (DW_AT_call_tail_call), 1);
   if (ca_loc->symbol_ref)
@@ -24092,11 +24098,14 @@ gen_subprogram_die (tree decl, dw_die_ref context_die)
 	    {
 	      dw_die_ref die = NULL;
 	      rtx tloc = NULL_RTX, tlocc = NULL_RTX;
+	      rtx call_arg_loc_note
+		= find_reg_note (ca_loc->call_insn,
+				 REG_CALL_ARG_LOCATION, NULL_RTX);
 	      rtx arg, next_arg;
 	      tree arg_decl = NULL_TREE;
 
-	      for (arg = (ca_loc->call_arg_loc_note != NULL_RTX
-			  ? XEXP (ca_loc->call_arg_loc_note, 0)
+	      for (arg = (call_arg_loc_note != NULL_RTX
+			  ? XEXP (call_arg_loc_note, 0)
 			  : NULL_RTX);
 		   arg; arg = next_arg)
 		{
@@ -28125,8 +28134,7 @@ create_label:
 	= ggc_cleared_alloc<call_arg_loc_node> ();
       rtx_insn *prev = call_insn;
 
-      ca_loc->call_arg_loc_note
-	= find_reg_note (call_insn, REG_CALL_ARG_LOCATION, NULL_RTX);
+      ca_loc->call_insn = call_insn;
       ca_loc->next = NULL;
       ca_loc->label = last_label;
       gcc_assert (prev
diff --git a/gcc/target.def b/gcc/target.def
index f401fe148ee2d..94c0e22819687 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -4731,6 +4731,15 @@ not generate any instructions in this case.",
 	int *pretend_args_size, int second_time),
  default_setup_incoming_varargs)
 
+DEFHOOK
+(call_offset_return_label,
+ "While generating call-site debug info for a CALL insn, or a SEQUENCE\n\
+insn starting with a CALL, this target hook is invoked to compute the\n\
+offset to be added to the debug label emitted after the call to obtain\n\
+the return address that should be recorded as the return PC.",
+ int, (rtx_insn *call_insn),
+ hook_int_rtx_insn_0)
+
 DEFHOOK
 (call_args,
  "While generating RTL for a function call, this target hook is invoked once\n\

-- 
Alexandre Oliva, happy hacker                https://FSFLA.org/blogs/lxo/
   Free Software Activist                       GNU Toolchain Engineer
Disinformation flourishes because many people care deeply about injustice
but very few check the facts.  Ask me about <https://stallmansupport.org>

[PATCH v2 #2/2] [rs6000] adjust return_pc debug attrs

[Alexandre Oliva]

Some of the rs6000 call patterns, on some ABIs, issue multiple opcodes
out of a single call insn, but the call (bl) or jump (b) is not always
the last opcode in the sequence.

This does not seem to be a problem for exception handling tables, but
the return_pc attribute in the call graph output in dwarf2+ debug
information, that takes the address of a label output right after the
call, does not match the value of the link register even for non-tail
calls.  E.g., with ABI_AIX or ABI_ELFv2, such code as:

  foo ();

outputs:

  bl foo
  nop
 LVL#:
[...]
  .8byte .LVL#  # DW_AT_call_return_pc

but debug info consumers may rely on the return_pc address, and draw
incorrect conclusions from its off-by-4 value.

This patch uses the infrastructure for targets to add an offset to the
label issued after the call_insn to set the call_return_pc attribute,
on rs6000, to account for opcodes issued after actual call opcode as
part of call insns output patterns.

Regstrapped on x86_64-linux-gnu and ppc64-linux-gnu.  Ok to install?


for  gcc/ChangeLog

	* config/rs6000/rs6000.cc (TARGET_CALL_OFFSET_RETURN_LABEL):
	Override.
	(rs6000_call_offset_return_label): New.
---
 gcc/config/rs6000/rs6000.cc |   19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
index 8e0b0d022db2f..e55117159b270 100644
--- a/gcc/config/rs6000/rs6000.cc
+++ b/gcc/config/rs6000/rs6000.cc
@@ -1760,6 +1760,9 @@ static const struct attribute_spec rs6000_attribute_table[] =
 
 #undef TARGET_UPDATE_IPA_FN_TARGET_INFO
 #define TARGET_UPDATE_IPA_FN_TARGET_INFO rs6000_update_ipa_fn_target_info
+
+#undef TARGET_CALL_OFFSET_RETURN_LABEL
+#define TARGET_CALL_OFFSET_RETURN_LABEL rs6000_call_offset_return_label
 \f
 
 /* Processor table.  */
@@ -14593,6 +14596,22 @@ rs6000_assemble_integer (rtx x, unsigned int size, int aligned_p)
   return default_assemble_integer (x, size, aligned_p);
 }
 
+/* Return the offset to be added to the label output after CALL_INSN
+   to compute the address to be placed in DW_AT_call_return_pc.  */
+
+static int
+rs6000_call_offset_return_label (rtx_insn *call_insn)
+{
+  /* All rs6000 CALL_INSN output patterns start with a b or bl, always
+     a 4-byte instruction, but some output patterns issue other
+     opcodes afterwards.  The return label is issued after the entire
+     call insn, including any such post-call opcodes.  Instead of
+     figuring out which cases need adjustments, we compute the offset
+     back to the address of the call opcode proper, then add the
+     constant 4 bytes, to get the address after that opcode.  */
+  return 4 - get_attr_length (call_insn);
+}
+
 /* Return a template string for assembly to emit when making an
    external call.  FUNOP is the call mem argument operand number.  */
 

-- 
Alexandre Oliva, happy hacker                https://FSFLA.org/blogs/lxo/
   Free Software Activist                       GNU Toolchain Engineer
Disinformation flourishes because many people care deeply about injustice
but very few check the facts.  Ask me about <https://stallmansupport.org>

Re: [PATCH v2 #1/2] enable adjustment of return_pc debug attrs

[Alexandre Oliva]

On Mar 23, 2023, Alexandre Oliva <oliva@adacore.com> wrote:

> This patch introduces infrastructure for targets to add an offset to
> the label issued after the call_insn to set the call_return_pc
> attribute.  This will be used on rs6000, that sometimes issues another
> instruction after the call proper as part of a call insn.

Ping?
https://gcc.gnu.org/pipermail/gcc-patches/2023-March/614452.html
https://gcc.gnu.org/pipermail/gcc-patches/2023-March/614453.html

This is a new feature, but it's needed to avoid regressions with the
recently-released GDB on ppc64.

-- 
Alexandre Oliva, happy hacker                https://FSFLA.org/blogs/lxo/
   Free Software Activist                       GNU Toolchain Engineer
Disinformation flourishes because many people care deeply about injustice
but very few check the facts.  Ask me about <https://stallmansupport.org>

Re: [PATCH v2 #1/2] enable adjustment of return_pc debug attrs

[Alexandre Oliva]

On Apr 14, 2023, Alexandre Oliva <oliva@adacore.com> wrote:

> On Mar 23, 2023, Alexandre Oliva <oliva@adacore.com> wrote:
>> This patch introduces infrastructure for targets to add an offset to
>> the label issued after the call_insn to set the call_return_pc
>> attribute.  This will be used on rs6000, that sometimes issues another
>> instruction after the call proper as part of a call insn.

> Ping?
> https://gcc.gnu.org/pipermail/gcc-patches/2023-March/614452.html
> https://gcc.gnu.org/pipermail/gcc-patches/2023-March/614453.html

Ping?

-- 
Alexandre Oliva, happy hacker                https://FSFLA.org/blogs/lxo/
   Free Software Activist                       GNU Toolchain Engineer
Disinformation flourishes because many people care deeply about injustice
but very few check the facts.  Ask me about <https://stallmansupport.org>