modpost: Update 64k section support for binutils 2.18.50

Binutils 2.18.50 made a backwards-incompatible change in the way it
writes ELF objects with over 65280 sections, to improve conformance
with the ELF specification and interoperability with other ELF tools.
Specifically, it no longer adds 256 to section indices SHN_LORESERVE
and higher to skip over the reserved range SHN_LORESERVE through
SHN_HIRESERVE; those values are only considered special in the
st_shndx field, and not in other places where section indices are
stored.  See:

http://sourceware.org/bugzilla/show_bug.cgi?id=5900
http://groups.google.com/group/generic-abi/browse_thread/thread/e8bb63714b072e67/6c63738f12cc8a17

Signed-off-by: Anders Kaseorg <andersk@ksplice.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

scripts/mod/modpost.c

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index cd104af..413c536 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -420,11 +420,10 @@
 		return 0;
 	}
 
-	if (hdr->e_shnum == 0) {
+	if (hdr->e_shnum == SHN_UNDEF) {
 		/*
 		 * There are more than 64k sections,
 		 * read count from .sh_size.
-		 * note: it doesn't need shndx2secindex()
 		 */
 		info->num_sections = TO_NATIVE(sechdrs[0].sh_size);
 	}
@@ -432,8 +431,7 @@
 		info->num_sections = hdr->e_shnum;
 	}
 	if (hdr->e_shstrndx == SHN_XINDEX) {
-		info->secindex_strings =
-		    shndx2secindex(TO_NATIVE(sechdrs[0].sh_link));
+		info->secindex_strings = TO_NATIVE(sechdrs[0].sh_link);
 	}
 	else {
 		info->secindex_strings = hdr->e_shstrndx;
@@ -489,7 +487,7 @@
 			    sechdrs[i].sh_offset;
 			info->symtab_stop  = (void *)hdr +
 			    sechdrs[i].sh_offset + sechdrs[i].sh_size;
-			sh_link_idx = shndx2secindex(sechdrs[i].sh_link);
+			sh_link_idx = sechdrs[i].sh_link;
 			info->strtab       = (void *)hdr +
 			    sechdrs[sh_link_idx].sh_offset;
 		}
@@ -516,11 +514,9 @@
 
 	if (symtab_shndx_idx != ~0U) {
 		Elf32_Word *p;
-		if (symtab_idx !=
-		    shndx2secindex(sechdrs[symtab_shndx_idx].sh_link))
+		if (symtab_idx != sechdrs[symtab_shndx_idx].sh_link)
 			fatal("%s: SYMTAB_SHNDX has bad sh_link: %u!=%u\n",
-			      filename,
-			      shndx2secindex(sechdrs[symtab_shndx_idx].sh_link),
+			      filename, sechdrs[symtab_shndx_idx].sh_link,
 			      symtab_idx);
 		/* Fix endianness */
 		for (p = info->symtab_shndx_start; p < info->symtab_shndx_stop;
@@ -1446,7 +1442,7 @@
 				    Elf_Shdr *sechdr, Elf_Rela *r)
 {
 	Elf_Shdr *sechdrs = elf->sechdrs;
-	int section = shndx2secindex(sechdr->sh_info);
+	int section = sechdr->sh_info;
 
 	return (void *)elf->hdr + sechdrs[section].sh_offset +
 		r->r_offset;

scripts/mod/modpost.h

diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
index 0388cfcc..2031119 100644
--- a/scripts/mod/modpost.h
+++ b/scripts/mod/modpost.h
@@ -145,33 +145,22 @@
 	return i != SHN_XINDEX && i >= SHN_LORESERVE && i <= SHN_HIRESERVE;
 }
 
-/* shndx is in [0..SHN_LORESERVE) U (SHN_HIRESERVE, 0xfffffff], thus:
- * shndx == 0               <=> sechdrs[0]
- * ......
- * shndx == SHN_LORESERVE-1 <=> sechdrs[SHN_LORESERVE-1]
- * shndx == SHN_HIRESERVE+1 <=> sechdrs[SHN_LORESERVE]
- * shndx == SHN_HIRESERVE+2 <=> sechdrs[SHN_LORESERVE+1]
- * ......
- * fyi: sym->st_shndx is uint16, SHN_LORESERVE = ff00, SHN_HIRESERVE = ffff,
- * so basically we map  0000..feff -> 0000..feff
- *                      ff00..ffff -> (you are a bad boy, dont do it)
- *                     10000..xxxx -> ff00..(xxxx-0x100)
+/*
+ * Move reserved section indices SHN_LORESERVE..SHN_HIRESERVE out of
+ * the way to -256..-1, to avoid conflicting with real section
+ * indices.
  */
-static inline unsigned int shndx2secindex(unsigned int i)
-{
-	if (i <= SHN_HIRESERVE)
-		return i;
-	return i - (SHN_HIRESERVE + 1 - SHN_LORESERVE);
-}
+#define SPECIAL(i) ((i) - (SHN_HIRESERVE + 1))
 
 /* Accessor for sym->st_shndx, hides ugliness of "64k sections" */
 static inline unsigned int get_secindex(const struct elf_info *info,
 					const Elf_Sym *sym)
 {
+	if (is_shndx_special(sym->st_shndx))
+		return SPECIAL(sym->st_shndx);
 	if (sym->st_shndx != SHN_XINDEX)
 		return sym->st_shndx;
-	return shndx2secindex(info->symtab_shndx_start[sym -
-						       info->symtab_start]);
+	return info->symtab_shndx_start[sym - info->symtab_start];
 }
 
 /* file2alias.c */