Jakub Bogusz from pld-linux dot org writes:

Hello,

I managed to get ldso (and thus shared linking to uClibc) to work on
sparc (actually sparc64 kernel with 32-bit userspace), at least on
simple "hello world" program (more complex ones not tested).

Some notes on attached patch (against 0.9.26, would require some work
to apply on current CVS - but I tested 0.9.26, not CVS):

- ELF magic cannot be examined by _dl_strncmp so early, probably because of
  string constant, like on ppc/mips/sh
  (note that early SEND_STDERR still crashes when trying to do _dl_strlen
   - I suppose that string constants require relocation; but adding
   load_addr didn't help, just ELF header was displayed instead of crash)
- mmap() is syscall6 like on ppc/mips/sh, not old i386 mmap()
- for generic sparc (i.e. not sparcv8/sparcv9) gcc produces .udiv/.urem
  calls for unsigned integer / and % operators - so these operations
  must be avoided. I copied do_rem definition from arm header.
  But / and % are used also in _dl_simple_ltoa() and
  _dl_simple_ltoahex(); in ltoahex gcc optimizes it to shifts (but
  I think it's safer to use shifts explicitly, not rely on
  optimization...).
  I changed % in ltoa to do_rem, but as there was no do_div definition,
  I changed all "%d" specifiers to "%x" to avoid crashes (this changes
  wouldn't be needed if _dl_simple_ltoa() were fixed to not use
  division on sparc).
- "#define SOLARIS_COMPATIBLE" in ld_sysdep.h broke ldso on Linux
  because of redefining _dl_linux_resolve only in some places (it was
  still referenced in INIT_GOT before redefinition). So
  _dl_linux_resolve redefinition should be moved before INIT_GOT
  definition or removed.
- sparc64 kernel requires mmap() addresses to be aligned to 8192, not
  4096, otherwise mmap() call failed
- reloc_entry must be shifted by 10, not 12 (I found similar operation
  in glibc sources)

Aside of sparc-specific fixes:
- I moved some _dl_dprintf()s inside if(_dl_debug_*) conditions (to avoid
  debugging messages when LD_DEBUG is not defined)
- it seems that there was possible off-by-one in ltoa and ltoahex?
  they are called with char[22] as 1st argument, and then '\0' is stored
  in local[22] (_before_ p decrementation)... or am I missing something?
  If not, fix is included in patch.

1 files changed, 7 insertions, 3 deletions

diff --git a/ldso/ldso/sparc/elfinterp.c b/ldso/ldso/sparc/elfinterp.c
index 41bde4fa8..98435cbd4 100644
--- a/ldso/ldso/sparc/elfinterp.c
+++ b/ldso/ldso/sparc/elfinterp.c
@@ -72,7 +72,7 @@ unsigned int _dl_linux_resolver(unsigned int reloc_entry, unsigned int * plt)
   /*
    * Generate the correct relocation index into the .rela.plt section.
    */
-  reloc_entry = (reloc_entry >> 12) - 0xc;
+  reloc_entry = (reloc_entry >> 10) - 0xc;
 
   this_reloc = (Elf32_Rela *) ((char *) rel_addr + reloc_entry);
 
@@ -82,10 +82,14 @@ unsigned int _dl_linux_resolver(unsigned int reloc_entry, unsigned int * plt)
   symtab =  (Elf32_Sym *) (tpnt->dynamic_info[DT_SYMTAB] + tpnt->loadaddr);
   strtab = (char *) (tpnt->dynamic_info[DT_STRTAB] + tpnt->loadaddr);
 
+#ifdef __SUPPORT_LD_DEBUG__
+  if (_dl_debug_symbols) {
   _dl_dprintf(2, "tpnt = %x\n", tpnt);
   _dl_dprintf(2, "reloc = %x\n", this_reloc);
   _dl_dprintf(2, "symtab = %x\n", symtab);
   _dl_dprintf(2, "strtab = %x\n", strtab);
+  }
+#endif
 
 
   if (unlikely(reloc_type != R_SPARC_JMP_SLOT)) {
@@ -98,10 +102,10 @@ unsigned int _dl_linux_resolver(unsigned int reloc_entry, unsigned int * plt)
   instr_addr  = ((int)this_reloc->r_offset  + (int)tpnt->loadaddr);
   got_addr = (char **) instr_addr;
 
-  _dl_dprintf(2, "symtab_index %d\n", symtab_index);
-
 #ifdef __SUPPORT_LD_DEBUG__
   if (_dl_debug_symbols) {
+  _dl_dprintf(2, "symtab_index %x\n", symtab_index);
+
 	  _dl_dprintf(2, "Resolving symbol %s\n",
 			  strtab + symtab[symtab_index].st_name);
   }