[PATCH] naming GCC's profile data section

[David Taylor]

Our application is embedded.  And in addition to cold boot (reload
everything; start over from scratch), we support warm boot.  As part of
supporting warm boot, read-write data that needs to be initialized, is
initialized by code.  And we ensure at link time that the traditional
initialized read-write data sections (.data, .ldata, .sdata) are empty.

This presents a problem when attempting to use GCC based profiling as it
creates read-write data in the aforementioned data sections.

This patch adds a new command line option that allows you to specify the
name of the section where GCC puts the instrumentation data.

If the new option (-fprofile-data-section) is not specified, GCC behaves
as before.

What's missing?  Testsuite changes.  I haven't yet figured out how to do
automated testing of this.  To test it, I built our software, several
thousand files, and then did an 'objdump --headers', verified that
sections .data / .ldata / .sdata were either absent of empty, and that
the instrumentation section had the name that I specified.

We have a copyright assignment on file from before EMC was acquired by
Dell.  Our company lawyers assure me that it survived the acquisition
and is still valid.

I'm sending this from GNU/Linux rather than from Windows (to avoid
having the patch mangled), so I'm not sure what the headers will show
for my return address.  If you wish to email me, I can be reached at
dtaylor at emc dot com or David dot Taylor at dell dot com.  Or... you
can just send to the gcc-patches list as I'll be reading it.

Enough verbiage, here's the ChangeLog entry and the patch...

2019-10-23  David Taylor  <dtaylor@emc.com>

	* common.opt (fprofile-data-section): New command line switch.
	* coverage.c (build_var): Add support for -fprofile-data-section.
	(coverage_obj_finish): Ditto.
	* toplev.c (process_options): Issue warning if
	-fprofile-data-section is specified when it is not supported.
	* doc/invoke.texi (Option Summary): List -fprofile-data-section.
	(Instrumentation Options): Document -fprofile-data-section.

Index: gcc/common.opt
===================================================================
--- gcc/common.opt	(revision 277133)
+++ gcc/common.opt	(working copy)
@@ -2124,6 +2124,10 @@
 Common Joined RejectNegative Var(profile_note_location)
 Select the name for storing the profile note file.
 
+fprofile-data-section=
+Common Joined RejectNegative Var(profile_data_section_name)
+Specify the section name for initialized profile data.
+
 fprofile-correction
 Common Report Var(flag_profile_correction)
 Enable correction of flow inconsistent profile data input.
Index: gcc/coverage.c
===================================================================
--- gcc/coverage.c	(revision 277133)
+++ gcc/coverage.c	(working copy)
@@ -749,6 +749,9 @@
   fn_name_len = strlen (fn_name);
   buf = XALLOCAVEC (char, fn_name_len + 8 + sizeof (int) * 3);
 
+  TREE_STATIC (var) = 1;
+  if (profile_data_section_name)
+    set_decl_section_name (var, profile_data_section_name);
   if (counter < 0)
     strcpy (buf, "__gcov__");
   else
@@ -757,7 +760,6 @@
   buf[len - 1] = symbol_table::symbol_suffix_separator ();
   memcpy (buf + len, fn_name, fn_name_len + 1);
   DECL_NAME (var) = get_identifier (buf);
-  TREE_STATIC (var) = 1;
   TREE_ADDRESSABLE (var) = 1;
   DECL_NONALIASED (var) = 1;
   SET_DECL_ALIGN (var, TYPE_ALIGN (type));
@@ -1188,10 +1190,14 @@
   ASM_GENERATE_INTERNAL_LABEL (name_buf, "LPBX", 1);
   DECL_NAME (fn_info_ary) = get_identifier (name_buf);
   DECL_INITIAL (fn_info_ary) = build_constructor (fn_info_ary_type, ctor);
+  if (profile_data_section_name)
+    set_decl_section_name (fn_info_ary, profile_data_section_name);
   varpool_node::finalize_decl (fn_info_ary);
   
   DECL_INITIAL (gcov_info_var)
     = build_info (TREE_TYPE (gcov_info_var), fn_info_ary);
+  if (profile_data_section_name)
+    set_decl_section_name (gcov_info_var, profile_data_section_name);
   varpool_node::finalize_decl (gcov_info_var);
 }
 
Index: gcc/doc/invoke.texi
===================================================================
--- gcc/doc/invoke.texi	(revision 277133)
+++ gcc/doc/invoke.texi	(working copy)
@@ -496,7 +496,7 @@
 @item Program Instrumentation Options
 @xref{Instrumentation Options,,Program Instrumentation Options}.
 @gccoptlist{-p  -pg  -fprofile-arcs  --coverage  -ftest-coverage @gol
--fprofile-abs-path @gol
+-fprofile-abs-path -fprofile-data-section=@var{name} @gol
 -fprofile-dir=@var{path}  -fprofile-generate  -fprofile-generate=@var{path} @gol
 -fprofile-note=@var{path}  -fprofile-update=@var{method} @gol
 -fprofile-filter-files=@var{regex}  -fprofile-exclude-files=@var{regex} @gol
@@ -12483,6 +12483,14 @@
 generate test coverage data.  Coverage data matches the source files
 more closely if you do not optimize.
 
+@item -fprofile-data-section
+@opindex fprofile-data-section
+When profiling, sets the name of the section where GCC places the
+profiling data.  If not specified, then where the data is placed is
+target dependent, but is typically either @code{.data} or
+@code{.ldata}.  Only supported for targets that support named
+sections.
+
 @item -fprofile-abs-path
 @opindex fprofile-abs-path
 Automatically convert relative source file names to absolute path names
Index: gcc/toplev.c
===================================================================
--- gcc/toplev.c	(revision 277133)
+++ gcc/toplev.c	(working copy)
@@ -1665,6 +1665,12 @@
 		      "%<-fdata-sections%> not supported for this target");
 	  flag_data_sections = 0;
 	}
+      if (profile_data_section_name)
+	{
+	  warning_at (UNKNOWN_LOCATION, 0,
+		      "-fprofile-data-section= not supported for this target");
+	  profile_data_section_name = NULL;
+	}
     }
 
   if (flag_prefetch_loop_arrays > 0 && !targetm.code_for_prefetch)