Re: BUG: bfd/elf allows only 2 PT_LOAD phdrs

[Bhavesh P. Davda]

Hi Nick,

Attached are the following files:

1. test.c, the source code for an example for requiring 3 PT_LOAD
segments
2. ld_map, the linker script used to append to the default linker script
3. Makefile, to build test.c

I am also attaching a alternative patch to bfd/elf.c, since
address@hidden, the binutils maintainer for RedHat refused to apply my
original patch. His concern was valid: the original patch would grow the
program headers for all elf binaries, whether or not you needed 2 or
more PT_LOAD segments.

The new patch only creates additional PT_LOAD segments and grows the
program header if it needs to, i.e. going through the output sections,
it encounters a case that requires a new PT_LOAD segment be created. The
above example shows one such case...

Thanks

- Bhavesh


Nick Clifton wrote:
> 
> Hi Bhavesh,
> 
> > IMHO, the following is too restrictive in bfd/elf.c:
> 
> >   /* Assume we will need exactly two PT_LOAD segments: one for text
> >      and one for data.  */
> >   segs = 2;
> 
> > I tried allowing 3 PT_LOAD segments, and it works for both the normal 2
> > PT_LOAD segments case and the 3 PT_LOAD segments case.
> >
> > The final ELF executable produced with this change was identical to that
> > produced without this change for the normal case.
> 
> Do you have a small test case which needs 3 PT_LOAD segments, which
> we could incorporate into the linker testsuite ?
> 
> Cheers
>         Nick

int cda_data[4096] __attribute__ ((section(".cda")));

int main()
{
        cda_data[0] = 0;
        cda_data[500] = 500;
        while (1) ;
        return 0;
}

SECTIONS {
        .cda_bss 0x10000000 : {
                *(.cda)
        }
}

all: test

test.o: test.c
        gcc -g3 -O0 -c test.c

test: test.o
        /usr/bin/ld --dynamic-linker /lib/ld-linux.so.2 -o test /usr/lib/crt1.o 
/usr/lib/crti.o /usr/lib/gcc-lib/i686-pc-linux-gnu/2.95.2/crtbegin.o 
-L/usr/lib/gcc-lib/i686-pc-linux-gnu/2.95.2 test.o ld_map -lgcc -lc -lgcc 
/usr/lib/gcc-lib/i686-pc-linux-gnu/2.95.2/crtend.o /usr/lib/crtn.o

diff -Naur orig/src/bfd/elf.c new/src/bfd/elf.c
--- orig/src/bfd/elf.c  Sat Nov 30 01:39:37 2002
+++ new/src/bfd/elf.c   Fri Dec  6 19:11:30 2002
@@ -3639,20 +3639,13 @@
     return TRUE;
 
   /* If we already counted the number of program segments, make sure
-     that we allocated enough space.  This happens when SIZEOF_HEADERS
+     that we allocate enough space.  This happens when SIZEOF_HEADERS
      is used in a linker script.  */
   alloc = elf_tdata (abfd)->program_header_size / bed->s->sizeof_phdr;
-  if (alloc != 0 && count > alloc)
+  if ((alloc != 0 && count > alloc) || (alloc == 0))
     {
-      ((*_bfd_error_handler)
-       (_("%s: Not enough room for program headers (allocated %u, need %u)"),
-       bfd_get_filename (abfd), alloc, count));
-      bfd_set_error (bfd_error_bad_value);
-      return FALSE;
+       alloc = count;
     }
-
-  if (alloc == 0)
-    alloc = count;
 
   amt = alloc * sizeof (Elf_Internal_Phdr);
   phdrs = (Elf_Internal_Phdr *) bfd_alloc (abfd, amt);