[PATCH 5/8] ELF unexec: _OBJC_ symbols in bss sections

[Alan Modra]

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.

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

-- 
Alan Modra
Australia Development Lab, IBM