section_table_xfer_memory: Replace section name with callback predicate

This patch is motivated by the need to be able to select sections
that section_table_xfer_memory_partial should consider for memory
transfers.  I'll use this facility in the next patch in this series.

section_table_xfer_memory_partial() can currently be passed a section
name which may be used to make name-based selections.  This is similar
to what I want to do, except that I want to be able to consider
section flags instead of the name.

I'm replacing the section name parameter with a predicate that,
when passed a pointer to a target_section struct, will return
true if that section should be further considered, or false which
indicates that it shouldn't.

I've converted the one existing use where a non-NULL section
name is passed to section_table_xfer_memory_partial().   Instead
of passing the section name, it now looks like this:

	  auto match_cb = [=] (const struct target_section *s)
	    {
	      return (strcmp (section_name, s->the_bfd_section->name) == 0);
	    };

	  return section_table_xfer_memory_partial (readbuf, writebuf,
						    memaddr, len, xfered_len,
						    table->sections,
						    table->sections_end,
						    match_cb);

The other callers all passed NULL; they've been simplified somewhat
in that they no longer need to pass NULL.

gdb/ChangeLog:

	* exec.h (section_table_xfer_memory): Revise declaration,
	replacing section name parameter with an optional callback
	predicate.
	* exec.c (section_table_xfer_memory): Likewise.
	* bfd-target.c, exec.c, target.c, corelow.c: Adjust all callers
	of section_table_xfer_memory.

gdb/ChangeLog

@@ -1,3 +1,12 @@
+2020-07-22  Kevin Buettner  <kevinb@redhat.com>
+
+	* exec.h (section_table_xfer_memory): Revise declaration,
+	replacing section name parameter with an optional callback
+	predicate.
+	* exec.c (section_table_xfer_memory): Likewise.
+	* bfd-target.c, exec.c, target.c, corelow.c: Adjust all callers
+	of section_table_xfer_memory.
+
 2020-07-22  Tom Tromey  <tromey@adacore.com>
 
 	* mi/mi-cmd-stack.c (list_args_or_locals): Use

gdb/bfd-target.c

@@ -77,8 +77,7 @@ target_bfd::xfer_partial (target_object object,
 	return section_table_xfer_memory_partial (readbuf, writebuf,
 						  offset, len, xfered_len,
 						  m_table.sections,
-						  m_table.sections_end,
-						  NULL);
+						  m_table.sections_end);
       }
     default:
       return TARGET_XFER_E_IO;

gdb/corelow.c

@@ -618,8 +618,7 @@ core_target::xfer_partial (enum target_object object, const char *annex,
 	      (readbuf, writebuf,
 	       offset, len, xfered_len,
 	       m_core_section_table.sections,
-	       m_core_section_table.sections_end,
-	       NULL));
+	       m_core_section_table.sections_end));
 
     case TARGET_OBJECT_AUXV:
       if (readbuf)

gdb/exec.c

@@ -956,7 +956,8 @@ section_table_xfer_memory_partial (gdb_byte *readbuf, const gdb_byte *writebuf,
 				   ULONGEST *xfered_len,
 				   struct target_section *sections,
 				   struct target_section *sections_end,
-				   const char *section_name)
+				   gdb::function_view<bool
+				     (const struct target_section *)> match_cb)
 {
   int res;
   struct target_section *p;
@@ -970,7 +971,7 @@ section_table_xfer_memory_partial (gdb_byte *readbuf, const gdb_byte *writebuf,
       struct bfd_section *asect = p->the_bfd_section;
       bfd *abfd = asect->owner;
 
-      if (section_name && strcmp (section_name, asect->name) != 0)
+      if (match_cb != nullptr && !match_cb (p))
 	continue;		/* not the section we need.  */
       if (memaddr >= p->addr)
         {
@@ -1043,8 +1044,7 @@ exec_target::xfer_partial (enum target_object object,
     return section_table_xfer_memory_partial (readbuf, writebuf,
 					      offset, len, xfered_len,
 					      table->sections,
-					      table->sections_end,
-					      NULL);
+					      table->sections_end);
   else
     return TARGET_XFER_E_IO;
 }

gdb/exec.h

@@ -65,8 +65,13 @@ extern enum target_xfer_status
    Request to transfer up to LEN 8-bit bytes of the target sections
    defined by SECTIONS and SECTIONS_END.  The OFFSET specifies the
    starting address.
-   If SECTION_NAME is not NULL, only access sections with that same
-   name.
+
+   The MATCH_CB predicate is optional; when provided it will be called
+   for each section under consideration.  When MATCH_CB evaluates as
+   true, the section remains under consideration; a false result
+   removes it from consideration for performing the memory transfers
+   noted above.  See memory_xfer_partial_1() in target.c for an
+   example.
 
    Return the number of bytes actually transfered, or zero when no
    data is available for the requested range.
@@ -83,7 +88,9 @@ extern enum target_xfer_status
 				     ULONGEST, ULONGEST, ULONGEST *,
 				     struct target_section *,
 				     struct target_section *,
-				     const char *);
+				     gdb::function_view<bool
+				       (const struct target_section *)> match_cb
+				         = nullptr);
 
 /* Read from mappable read-only sections of BFD executable files.
    Similar to exec_read_partial_read_only, but return

gdb/target.c

@@ -980,11 +980,17 @@ memory_xfer_partial_1 (struct target_ops *ops, enum target_object object,
 	  const char *section_name = section->the_bfd_section->name;
 
 	  memaddr = overlay_mapped_address (memaddr, section);
+
+	  auto match_cb = [=] (const struct target_section *s)
+	    {
+	      return (strcmp (section_name, s->the_bfd_section->name) == 0);
+	    };
+
 	  return section_table_xfer_memory_partial (readbuf, writebuf,
 						    memaddr, len, xfered_len,
 						    table->sections,
 						    table->sections_end,
-						    section_name);
+						    match_cb);
 	}
     }
 
@@ -1002,8 +1008,7 @@ memory_xfer_partial_1 (struct target_ops *ops, enum target_object object,
 	  return section_table_xfer_memory_partial (readbuf, writebuf,
 						    memaddr, len, xfered_len,
 						    table->sections,
-						    table->sections_end,
-						    NULL);
+						    table->sections_end);
 	}
     }