Add segment index to segment labels

This change is needed to support analyzing embedded
microcontroller ELF files, which leverage segments to place
code and data in either flash or RAM.

Author: keir

src/elf.cc

@@ -1117,7 +1117,20 @@ static void DoReadELFSegments(RangeSink* sink, ReportSegmentsBy report_by) {
                    continue;
                  }
 
-                 std::string name = "LOAD [";
+                 // Include the segment index in the label, to support embedded.
+                 //
+                 // Including the index in the segment label differentiates
+                 // segments with the same access control (e.g. RWX vs RW). In
+                 // ELF files built for embedded microcontroller projects, a
+                 // segment is used for each distinct type of memory. In simple
+                 // cases, there is a segment for the flash (which will store
+                 // code and read-only data) and a segment for RAM (which
+                 // usually stores globals, stacks, and maybe a heap). In more
+                 // involved projects, there may be special segments for faster
+                 // RAM (e.g. core coupled RAM or CCRAM), or there may even be
+                 // memory overlays to support manual paging of code from flash
+                 // (which may be slow) into RAM.
+                 std::string name(absl::StrCat("LOAD #", i, " ["));
 
                  if (header.p_flags & PF_R) {
                    name += 'R';