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.

1 files changed, 18 insertions, 13 deletions

diff --git a/src/unexelf.c b/src/unexelf.c
index 286ba2e99c1..df99f92a466 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