code review 9119043: cmd/ld: add .note.GNU-stack section for external linking

src/cmd/ld/elf.c

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 #include        "l.h"
 #include        "lib.h"
 #include        "../ld/elf.h"
 
 /*
  * We use the 64-bit data structures on both 32- and 64-bit machines
@@ skipping 912 matching lines @@
                         addstring(shstrtab, ".rel.text");
                         addstring(shstrtab, ".rel.rodata");
                         addstring(shstrtab, ".rel.typelink");
                         addstring(shstrtab, ".rel.gcdata");
                         addstring(shstrtab, ".rel.gcbss");
                         addstring(shstrtab, ".rel.gosymtab");
                         addstring(shstrtab, ".rel.gopclntab");
                         addstring(shstrtab, ".rel.noptrdata");
                         addstring(shstrtab, ".rel.data");
                 }
+                // add a .note.GNU-stack section to mark the stack as non-executable
+                addstring(shstrtab, ".note.GNU-stack");
         }
 
         if(!debug['s']) {
                 addstring(shstrtab, ".symtab");
                 addstring(shstrtab, ".strtab");
                 dwarfaddshstrings(shstrtab);
         }
         addstring(shstrtab, ".shstrtab");
 
         if(!debug['d']) {       /* -d suppresses dynamic loader format */
@@ skipping 453 matching lines @@
         for(sect=segtext.sect; sect!=nil; sect=sect->next)
                 elfshbits(sect);
         for(sect=segdata.sect; sect!=nil; sect=sect->next)
                 elfshbits(sect);
 
         if(linkmode == LinkExternal) {
                 for(sect=segtext.sect; sect!=nil; sect=sect->next)
                         elfshreloc(sect);
                 for(sect=segdata.sect; sect!=nil; sect=sect->next)
                         elfshreloc(sect);
+                // add a .note.GNU-stack section to mark the stack as non-executable
+                sh = elfshname(".note.GNU-stack");
+                sh->type = SHT_PROGBITS;
+                sh->addralign = 1;
+                sh->flags = 0;
         }
-                
+
         if(!debug['s']) {
                 sh = elfshname(".symtab");
                 sh->type = SHT_SYMTAB;
                 sh->off = symo;
                 sh->size = symsize;
                 sh->addralign = PtrSize;
                 sh->entsize = 8+2*PtrSize;
                 sh->link = elfshname(".strtab")->shnum;
                 sh->info = elfglobalsymndx;
 
@@ skipping 52 matching lines @@
                 if(HEADTYPE == Hnetbsd)
                         a += elfwritenetbsdsig();
                 if(HEADTYPE == Hopenbsd)
                         a += elfwriteopenbsdsig();
                 if(buildinfolen > 0)
                         a += elfwritebuildinfo();
         }
         if(a > ELFRESERVE)······
                 diag("ELFRESERVE too small: %d > %d", a, ELFRESERVE);
 }