From 8c30fba366c6814c7bb1795fdda16265eb48efb0 Mon Sep 17 00:00:00 2001
From: Alan Modra <amodra@gmail.com>
Date: Sun, 8 Nov 2015 09:29:00 -0800
Subject: [PATCH 06/11] ELF unexec: _OBJC_ symbols in bss sections

This code assumed that there was only one bss section.  Rather than
checking for a particular index, check the section type.  Also, handle
the possibility that the section was SHT_NOBITS originally and is
unchanged, in which case no clearing is needed (and sh_offset isn't
necessarily valid, which can lead to a wild memset).

* unexelf.c (unexec): Properly handle _OBJC_ symbols in bss sections.
---
 src/unexelf.c | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/src/unexelf.c b/src/unexelf.c
index 286ba2e..df99f92 100644
--- a/src/unexelf.c
+++ b/src/unexelf.c
@@ -1176,20 +1176,25 @@ temacs:
 		       "_OBJC_", sizeof ("_OBJC_") - 1) == 0)
 	    {
 	      ElfW (Shdr) *new_shdr = &NEW_SECTION_H (symp->st_shndx);
-	      ptrdiff_t reladdr = symp->st_value - new_shdr->sh_addr;
-	      ptrdiff_t newoff = reladdr + new_shdr->sh_offset;
-
-	      /* "Unpatch" index.  */
-	      nn = symp->st_shndx;
-	      if (nn > old_bss_index)
-		nn--;
-	      if (nn == old_bss_index)
-		memset (new_base + newoff, 0, symp->st_size);
-	      else
+	      if (new_shdr->sh_type != SHT_NOBITS)
 		{
-		  ElfW (Shdr) *old_shdr = &OLD_SECTION_H (nn);
-		  ptrdiff_t oldoff = reladdr + old_shdr->sh_offset;
-		  memcpy (new_base + newoff, old_base + oldoff, symp->st_size);
+		  ElfW (Shdr) *old_shdr;
+		  ptrdiff_t reladdr = symp->st_value - new_shdr->sh_addr;
+		  ptrdiff_t newoff = reladdr + new_shdr->sh_offset;
+
+		  /* "Unpatch" index.  */
+		  nn = symp->st_shndx;
+		  if (nn > old_bss_index)
+		    nn--;
+		  old_shdr = &OLD_SECTION_H (nn);
+		  if (old_shdr->sh_type == SHT_NOBITS)
+		    memset (new_base + newoff, 0, symp->st_size);
+		  else
+		    {
+		      ptrdiff_t oldoff = reladdr + old_shdr->sh_offset;
+		      memcpy (new_base + newoff, old_base + oldoff,
+			      symp->st_size);
+		    }
 		}
 	    }
 #endif
-- 
2.7.4