glibc/sysdeps/alpha/dl-machine.h

/* Machine-dependent ELF dynamic relocation inline functions.  Alpha version.
   Copyright (C) 1996, 1997 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Richard Henderson <rth@tamu.edu>.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

/* This was written in the absence of an ABI -- don't expect
   it to remain unchanged.  */

#ifndef dl_machine_h
#define dl_machine_h 1

#define ELF_MACHINE_NAME "alpha"

#include <assert.h>
#include <string.h>


/* Return nonzero iff E_MACHINE is compatible with the running host.  */
static inline int
elf_machine_matches_host (Elf64_Word e_machine)
{
  return e_machine == EM_ALPHA;
}

/* Return the link-time address of _DYNAMIC.  The multiple-got-capable
   linker no longer allocates the first .got entry for this.  But not to
   worry, no special tricks are needed.  */
static inline Elf64_Addr
elf_machine_dynamic (void)
{
#ifndef NO_AXP_MULTI_GOT_LD
  return (Elf64_Addr) &_DYNAMIC;
#else
  register Elf64_Addr *gp __asm__ ("$29");
  return gp[-4096];
#endif
}

/* Return the run-time load address of the shared object.  */
static inline Elf64_Addr
elf_machine_load_address (void)
{
  /* NOTE: While it is generally unfriendly to put data in the text
     segment, it is only slightly less so when the "data" is an
     instruction.  While we don't have to worry about GLD just yet, an
     optimizing linker might decide that our "data" is an unreachable
     instruction and throw it away -- with the right switches, DEC's
     linker will do this.  What ought to happen is we should add
     something to GAS to allow us access to the new GPREL_HI32/LO32
     relocation types stolen from OSF/1 3.0.  */
  /* This code relies on the fact that BRADDR relocations do not
     appear in dynamic relocation tables.  Not that that would be very
     useful anyway -- br/bsr has a 4MB range and the shared libraries
     are usually many many terabytes away.  */

  Elf64_Addr dot;
  long zero_disp;

  asm("br %0, 1f\n\t"
      ".weak __load_address_undefined\n\t"
      "br $0, __load_address_undefined\n"
      "1:"
      : "=r"(dot));

  zero_disp = *(int *)dot;
  zero_disp = (zero_disp << 43) >> 41;

  return dot + 4 + zero_disp;
}

/* Set up the loaded object described by L so its unrelocated PLT
   entries will jump to the on-demand fixup code in dl-runtime.c.  */

static inline int
elf_machine_runtime_setup (struct link_map *l, int lazy)
{
  Elf64_Addr plt;
  extern void _dl_runtime_resolve (void);

  if (l->l_info[DT_JMPREL] && lazy)
    {
      /* The GOT entries for the functions in the PLT have not been
	 filled in yet.  Their initial contents are directed to the
	 PLT which arranges for the dynamic linker to be called.  */
      plt = l->l_addr + l->l_info[DT_PLTGOT]->d_un.d_ptr;

      /* This function will be called to perform the relocation.  */
      *(Elf64_Addr *)(plt + 16) = (Elf64_Addr) &_dl_runtime_resolve;

      /* Identify this shared object */
      *(Elf64_Addr *)(plt + 24) = (Elf64_Addr) l;

      /* If the first instruction of the plt entry is not
	 "br $28, plt0", we cannot do lazy relocation.  */
      lazy = (*(unsigned *)(plt + 32) == 0xc39ffff7);
    }

  return lazy;
}

/* This code is used in dl-runtime.c to call the `fixup' function
   and then redirect to the address it returns.  */
#define ELF_MACHINE_RUNTIME_TRAMPOLINE asm ( \
"/* Trampoline for _dl_runtime_resolver */
	.globl _dl_runtime_resolve
	.ent _dl_runtime_resolve
_dl_runtime_resolve:
	lda	$sp, -168($sp)
	.frame	$sp, 168, $26
	/* Preserve all registers that C normally doesn't.  */
	stq	$26, 0($sp)
	stq	$0, 8($sp)
	stq	$1, 16($sp)
	stq	$2, 24($sp)
	stq	$3, 32($sp)
	stq	$4, 40($sp)
	stq	$5, 48($sp)
	stq	$6, 56($sp)
	stq	$7, 64($sp)
	stq	$8, 72($sp)
	stq	$16, 80($sp)
	stq	$17, 88($sp)
	stq	$18, 96($sp)
	stq	$19, 104($sp)
	stq	$20, 112($sp)
	stq	$21, 120($sp)
	stq	$22, 128($sp)
	stq	$23, 136($sp)
	stq	$24, 144($sp)
	stq	$25, 152($sp)
	stq	$29, 160($sp)
	.mask	0x27ff01ff, -168
	/* Set up our $gp */
	br	$gp, 0f
0:	ldgp	$gp, 0($gp)
	.prologue 1
	/* Set up the arguments for _dl_runtime_resolve. */
	/* $16 = link_map out of plt0 */
	/* $17 = offset of reloc entry = ($28 - $27 - 20) /12 * 24 */
	subq	$28, $27, $17
	ldq	$16, 8($27)
	subq	$17, 20, $17
	addq	$17, $17, $17
	/* Do the fixup */
	bsr	$26, fixup..ng
	/* Move the destination address into position.  */
	mov	$0, $27
	/* Restore program registers.  */
	ldq	$26, 0($sp)
	ldq	$0, 8($sp)
	ldq	$1, 16($sp)
	ldq	$2, 24($sp)
	ldq	$3, 32($sp)
	ldq	$4, 40($sp)
	ldq	$5, 48($sp)
	ldq	$6, 56($sp)
	ldq	$7, 64($sp)
	ldq	$8, 72($sp)
	ldq	$16, 80($sp)
	ldq	$17, 88($sp)
	ldq	$18, 96($sp)
	ldq	$19, 104($sp)
	ldq	$20, 112($sp)
	ldq	$21, 120($sp)
	ldq	$22, 128($sp)
	ldq	$23, 136($sp)
	ldq	$24, 144($sp)
	ldq	$25, 152($sp)
	ldq	$29, 160($sp)
	/* Flush the Icache after having modified the .plt code.  */
	imb
	/* Clean up and turn control to the destination */
	lda	$sp, 168($sp)
	jmp	$31, ($27)
	.end _dl_runtime_resolve");

/* The PLT uses Elf64_Rela relocs.  */
#define elf_machine_relplt elf_machine_rela

/* Initial entry point code for the dynamic linker.
   The C function `_dl_start' is the real entry point;
   its return value is the user program's entry point.  */

#define RTLD_START asm ("\
.text
	.globl _start
	.ent _start
_start:
	br	$gp, 0f
0:	ldgp	$gp, 0($gp)
	/* Pass pointer to argument block to _dl_start.  */
	mov	$sp, $16
	bsr	$26, _dl_start..ng
	.end _start
	/* FALLTHRU */
	.globl _dl_start_user
	.ent _dl_start_user
_dl_start_user:
	/* Save the user entry point address in s0.  */
	mov	$0, $9
	/* See if we were run as a command with the executable file
	   name as an extra leading argument.  If so, adjust the stack
	   pointer to skip _dl_skip_args words.  */
	ldl	$1, _dl_skip_args
	beq	$1, 0f
	ldq	$2, 0($sp)
	subq	$2, $1, $2
	s8addq	$1, $sp, $sp
	stq	$2, 0($sp)
	/* Load _dl_default_scope[2] into s1 to pass to _dl_init_next.  */
0:	ldq	$10, _dl_default_scope+16
	/* Call _dl_init_next to return the address of an initializer
	   function to run.  */
1:	mov	$10, $16
	jsr	$26, _dl_init_next
	ldgp	$gp, 0($26)
	beq	$0, 2f
	mov	$0, $27
	jsr	$26, ($0)
	ldgp	$gp, 0($26)
	br	1b
2:	/* Clear the startup flag.  */
	.set at
	stl	$31, _dl_starting_up
	.set noat
	/* Pass our finalizer function to the user in $0. */
	lda	$0, _dl_fini
	/* Jump to the user's entry point.  */
	mov	$9, $27
	jmp	($9)
	.end _dl_start_user");

/* Nonzero iff TYPE describes relocation of a PLT entry, so
   PLT entries should not be allowed to define the value.  */
#define elf_machine_lookup_noplt_p(type)  ((type) == R_ALPHA_JMP_SLOT)

/* Nonzero iff TYPE should not be allowed to resolve to one of
   the main executable's symbols, as for a COPY reloc, which we don't use.  */
#define elf_machine_lookup_noexec_p(type)  (0)

/* A reloc type used for ld.so cmdline arg lookups to reject PLT entries.  */
#define ELF_MACHINE_RELOC_NOPLT	 R_ALPHA_JMP_SLOT

/* The alpha never uses Elf64_Rel relocations.  */
#define ELF_MACHINE_NO_REL 1

#endif /* !dl_machine_h */

#ifdef RESOLVE

/* Fix up the instructions of a PLT entry to invoke the function
   rather than the dynamic linker.  */
static inline void
elf_alpha_fix_plt(struct link_map *l,
		  const Elf64_Rela *reloc,
		  Elf64_Addr got_addr,
		  Elf64_Addr value)
{
  const Elf64_Rela *rela_plt;
  Elf64_Word *plte;
  long edisp;

  /* Recover the PLT entry address by calculating reloc's index into the
     .rela.plt, and finding that entry in the .plt.  */

  rela_plt = (void *)(l->l_addr + l->l_info[DT_JMPREL]->d_un.d_ptr);

  plte = (void *)(l->l_addr + l->l_info[DT_PLTGOT]->d_un.d_ptr + 32);
  plte += 3 * (reloc - rela_plt);

  /* Find the displacement from the plt entry to the function.  */

  edisp = (long)(value - (Elf64_Addr)&plte[3]) / 4;

  if (edisp >= -0x100000 && edisp < 0x100000)
    {
      /* If we are in range, use br to perfect branch prediction and
	 elide the dependency on the address load.  This case happens,
	 e.g., when a shared library call is resolved to the same library.  */

      int hi, lo;
      hi = value - (Elf64_Addr)&plte[0];
      lo = (short)hi;
      hi = (hi - lo) >> 16;

      /* Emit "lda $27,L($27)" */
      plte[1] = 0x237b0000 | (lo & 0xffff);

      /* Emit "br $31,function" */
      plte[2] = 0xc3e00000 | (edisp & 0x1fffff);

      /* Think about thread-safety -- the previous instructions must be
	 committed to memory before the first is overwritten.  */
      __asm__ __volatile__("wmb" : : : "memory");

      /* Emit "ldah $27,H($27)" */
      plte[0] = 0x277b0000 | (hi & 0xffff);
    }
  else
    {
      /* Don't bother with the hint since we already know the hint is
	 wrong.  Eliding it prevents the wrong page from getting pulled
	 into the cache.  */

      int hi, lo;
      hi = got_addr - (Elf64_Addr)&plte[0];
      lo = (short)hi;
      hi = (hi - lo) >> 16;

      /* Emit "ldq $27,L($27)" */
      plte[1] = 0xa77b0000 | (lo & 0xffff);

      /* Emit "jmp $31,($27)" */
      plte[2] = 0x6bfb0000;

      /* Think about thread-safety -- the previous instructions must be
	 committed to memory before the first is overwritten.  */
      __asm__ __volatile__("wmb" : : : "memory");

      /* Emit "ldah $27,H($27)" */
      plte[0] = 0x277b0000 | (hi & 0xffff);
    }

  /* At this point, if we've been doing runtime resolution, Icache is dirty.
     This will be taken care of in _dl_runtime_resolve.  If instead we are
     doing this as part of non-lazy startup relocation, that bit of code
     hasn't made it into Icache yet, so there's nothing to clean up.  */
}

/* Perform the relocation specified by RELOC and SYM (which is fully resolved).
   MAP is the object containing the reloc.  */
static inline void
elf_machine_rela (struct link_map *map,
		  const Elf64_Rela *reloc,
		  const Elf64_Sym *sym,
		  const struct r_found_version *version)
{
  Elf64_Addr * const reloc_addr = (void *)(map->l_addr + reloc->r_offset);
  unsigned long const r_type = ELF64_R_TYPE (reloc->r_info);

#ifndef RTLD_BOOTSTRAP
  /* This is defined in rtld.c, but nowhere in the static libc.a; make the
     reference weak so static programs can still link.  This declaration
     cannot be done when compiling rtld.c (i.e.  #ifdef RTLD_BOOTSTRAP)
     because rtld.c contains the common defn for _dl_rtld_map, which is
     incompatible with a weak decl in the same file.  */
  weak_extern (_dl_rtld_map);
#endif

  /* We cannot use a switch here because we cannot locate the switch
     jump table until we've self-relocated.  */

  if (r_type == R_ALPHA_RELATIVE)
    {
#ifndef RTLD_BOOTSTRAP
      /* Already done in dynamic linker.  */
      if (map != &_dl_rtld_map)
#endif
	*reloc_addr += map->l_addr;
    }
  else if (r_type == R_ALPHA_NONE)
    return;
  else
    {
      Elf64_Addr loadbase, sym_value;

      loadbase = RESOLVE (&sym, version, r_type);
      sym_value = sym ? loadbase + sym->st_value : 0;

      if (r_type == R_ALPHA_GLOB_DAT)
	*reloc_addr = sym_value;
      else if (r_type == R_ALPHA_JMP_SLOT)
	{
	  *reloc_addr = sym_value;
	  elf_alpha_fix_plt (map, reloc, (Elf64_Addr) reloc_addr, sym_value);
	}
      else if (r_type == R_ALPHA_REFQUAD)
	{
	  sym_value += *reloc_addr;
#ifndef RTLD_BOOTSTRAP
	  if (map == &_dl_rtld_map)
	    {
	      /* Undo the relocation done here during bootstrapping.
		 Now we will relocate anew, possibly using a binding
		 found in the user program or a loaded library rather
		 than the dynamic linker's built-in definitions used
		 while loading those libraries.  */
	      const Elf64_Sym *const dlsymtab
		= (void *)(map->l_addr + map->l_info[DT_SYMTAB]->d_un.d_ptr);
	      sym_value -= map->l_addr;
	      sym_value -= dlsymtab[ELF64_R_SYM(reloc->r_info)].st_value;
	    }
	  else
#endif
	    sym_value += reloc->r_addend;
	  *reloc_addr = sym_value;
	}
      else
	assert (! "unexpected dynamic reloc type");
    }
}

static inline void
elf_machine_lazy_rel (struct link_map *map, const Elf64_Rela *reloc)
{
  Elf64_Addr * const reloc_addr = (void *)(map->l_addr + reloc->r_offset);
  unsigned long const r_type = ELF64_R_TYPE (reloc->r_info);

  if (r_type == R_ALPHA_JMP_SLOT)
    {
      /* Perform a RELATIVE reloc on the .got entry that transfers
	 to the .plt.  */
      *reloc_addr += map->l_addr;
    }
  else if (r_type == R_ALPHA_NONE)
    return;
  else
    assert (! "unexpected PLT reloc type");
}

#endif /* RESOLVE */