elflint: Add gnuld check when a NOBITS section falls inside a segment.

gnuld has a really bad bug where it can place a NOBITS section inside
a PT_LOAD segment. Normally that would not work. But it also makes sure
that the contents of the file is all zeros. So in practice it is actually
a PROGBITS section with all zero data. Except that other tools will think
there is an unused gap in the ELF file after the NOBITS section.

Recognize and check this pattern in elflint when --gnu is given.

Signed-off-by: Mark Wielaard <mjw@redhat.com>

diff --git a/src/ChangeLog b/src/ChangeLog
index a0c32fa247fb14d27d06a3ae009eef53f7bf4b0e..5be1075003f055fc91c65d086e4fb899f527ed87 100644 (file)
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,8 @@
+2015-08-11  Mark Wielaard  <mjw@redhat.com>
+
+       * elflint.c (check_sections): When gnuld and a NOBITS section falls
+       inside a segment make sure any ELF file contents is zero.
+
 2015-07-29  Mark Wielaard  <mjw@redhat.com>
 
        * unstrip.c (sections_flags_match): New function.

diff --git a/src/elflint.c b/src/elflint.c
index a916886234cbb00197002712f9f8e84d04fe4910..0d5f34d44d9780b5c40d870e6f6dc349eac4c238 100644 (file)
--- a/src/elflint.c
+++ b/src/elflint.c
@@ -3978,9 +3978,39 @@ section [%2zu] '%s' not fully contained in segment of program header entry %d\n"
                  {
                    if (shdr->sh_offset < phdr->p_offset + phdr->p_filesz
                        && !is_debuginfo)
-                     ERROR (gettext ("\
+                     {
+                       if (!gnuld)
+                         ERROR (gettext ("\
 section [%2zu] '%s' has type NOBITS but is read from the file in segment of program header entry %d\n"),
-                        cnt, section_name (ebl, cnt), pcnt);
+                                cnt, section_name (ebl, cnt), pcnt);
+                       else
+                         {
+                           /* This is truly horrible. GNU ld might put a
+                              NOBITS section in the middle of a PT_LOAD
+                              segment, assuming the next gap in the file
+                              actually consists of zero bits...
+                              So it really is like a PROGBITS section
+                              where the data is all zeros.  Check those
+                              zero bytes are really there.  */
+                           bool bad;
+                           Elf_Data *databits;
+                           databits = elf_getdata_rawchunk (ebl->elf,
+                                                            shdr->sh_offset,
+                                                            shdr->sh_size,
+                                                            ELF_T_BYTE);
+                           bad = (databits == NULL
+                                  || databits->d_size != shdr->sh_size);
+                           for (size_t idx = 0;
+                                idx < databits->d_size && ! bad;
+                                idx++)
+                             bad = ((char *) databits->d_buf)[idx] != 0;
+
+                           if (bad)
+                             ERROR (gettext ("\
+section [%2zu] '%s' has type NOBITS but is read from the file in segment of program header entry %d and file contents is non-zero\n"),
+                                    cnt, section_name (ebl, cnt), pcnt);
+                         }
+                     }
                  }
                else
                  {