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Re: fix ppc32 long branch stubs
On Thu, Nov 06, 2003 at 02:19:24AM -0800, Eric Christopher wrote:
> re: comments - I believe that there was a reason for it, but it escapes
> me at the moment.
I'm taking it out. As we discussed on irc, it was likely due to trying
to keep code compiled with -fpic or -fPIC position independent when
linked static. That won't work anyway, due to lack of dynamic relocs,
non-pic crt* and probably other reasons.
Looking closer at the code, I discovered a number of other errors, so
have made quite a few fixes. Also made some improvements.
* elf32-ppc.c (ppc_elf_install_value): Delete.
(shared_stub_entry, stub_entry): Make them arrays of ints.
Remove initial branch.
(ppc_elf_relax_section): Write one branch around all trampolines
instead. Correct bogus R_PPC_PLTREL24 handling. Correct
branch range check. Only use shared_stub_entry when shared.
Test that branches can reach stubs. Write trampolines out at
end so that just one realloc is used. Handle little-endian
mode. Move relevant code from ppc_elf_install_value to here.
(ppc_elf_relocate_section): Move code handling RELAX32 from
ppc_elf_install_value to here.
Index: bfd/elf32-ppc.c
===================================================================
RCS file: /cvs/src/src/bfd/elf32-ppc.c,v
retrieving revision 1.105
diff -u -p -r1.105 elf32-ppc.c
--- bfd/elf32-ppc.c 6 Nov 2003 02:58:40 -0000 1.105
+++ bfd/elf32-ppc.c 6 Nov 2003 14:01:54 -0000
@@ -1625,84 +1625,26 @@ ppc_elf_howto_init (void)
}
}
-static bfd_reloc_status_type
-ppc_elf_install_value (bfd *abfd,
- bfd_byte *hit_addr,
- bfd_vma v,
- unsigned int r_type)
-{
- bfd_vma t0, t1;
-#ifdef BFD_HOST_U_64_BIT
- BFD_HOST_U_64_BIT val = (BFD_HOST_U_64_BIT) v;
-#else
- bfd_vma val = v;
-#endif
-
- switch (r_type)
- {
- case R_PPC_RELAX32:
- case R_PPC_RELAX32PC:
- t0 = bfd_get_32 (abfd, hit_addr);
- t1 = bfd_get_32 (abfd, hit_addr + 4);
-
- /* We're clearing the bits for R_PPC_ADDR16_HA
- and R_PPC_ADDR16_LO here. */
- t0 &= ~0xffff;
- t1 &= ~0xffff;
-
- /* t0 is HA, t1 is lo */
- t0 |= ((val + 0x8000) >> 16) & 0xffff;
- t1 |= val & 0xffff;
-
- bfd_put_32 (abfd, t0, hit_addr);
- bfd_put_32 (abfd, t1, hit_addr + 4);
- break;
+#define ARRAY_SIZE(a) (sizeof (a) / sizeof ((a)[0]))
- case R_PPC_REL24:
- case R_PPC_LOCAL24PC:
- case R_PPC_PLTREL24:
- t0 = bfd_get_32 (abfd, hit_addr);
- t0 &= ~0x3fffffc;
- t0 |= val & 0x3fffffc;
- bfd_put_32 (abfd, t0, hit_addr);
- break;
-
- case R_PPC_REL14:
- case R_PPC_REL14_BRTAKEN:
- case R_PPC_REL14_BRNTAKEN:
- t0 = bfd_get_32 (abfd, hit_addr);
- t0 &= ~0xfffc;
- t0 |= val & 0xfffc;
- bfd_put_32 (abfd, t0, hit_addr);
- break;
-
- default:
- return bfd_reloc_notsupported;
- }
-
- return bfd_reloc_ok;
-}
-
-static const bfd_byte shared_stub_entry[] =
+static const int shared_stub_entry[] =
{
- 0x48, 0x00, 0x00, 0x24, /* b .+36 */
- 0x7c, 0x08, 0x02, 0xa6, /* mflr 0 */
- 0x42, 0x9f, 0x00, 0x05, /* bcl 20, 31, .Lxxx */
- 0x7d, 0x68, 0x02, 0xa6, /* mflr 11 */
- 0x3d, 0x6b, 0x00, 0x00, /* addis 11, 11, (xxx-.Lxxx)@ha */
- 0x39, 0x6b, 0x00, 0x18, /* addi 11, 11, (xxx-.Lxxx)@l */
- 0x7c, 0x08, 0x03, 0xa6, /* mtlr 0 */
- 0x7d, 0x69, 0x03, 0xa6, /* mtctr 11 */
- 0x4e, 0x80, 0x04, 0x20, /* bctr */
+ 0x7c0802a6, /* mflr 0 */
+ 0x429f0005, /* bcl 20, 31, .Lxxx */
+ 0x7d6802a6, /* mflr 11 */
+ 0x3d6b0000, /* addis 11, 11, (xxx-.Lxxx)@ha */
+ 0x396b0018, /* addi 11, 11, (xxx-.Lxxx)@l */
+ 0x7c0803a6, /* mtlr 0 */
+ 0x7d6903a6, /* mtctr 11 */
+ 0x4e800420, /* bctr */
};
-static const bfd_byte stub_entry[] =
+static const int stub_entry[] =
{
- 0x48, 0x00, 0x00, 0x14, /* b .+20 */
- 0x3d, 0x60, 0x00, 0x00, /* lis 11,xxx@ha */
- 0x39, 0x6b, 0x00, 0x00, /* addi 11,11,xxx@l */
- 0x7d, 0x69, 0x03, 0xa6, /* mtctr 11 */
- 0x4e, 0x80, 0x04, 0x20, /* bctr */
+ 0x3d600000, /* lis 11,xxx@ha */
+ 0x396b0000, /* addi 11,11,xxx@l */
+ 0x7d6903a6, /* mtctr 11 */
+ 0x4e800420, /* bctr */
};
@@ -1726,9 +1668,9 @@ ppc_elf_relax_section (bfd *abfd,
Elf_Internal_Rela *internal_relocs = NULL;
Elf_Internal_Rela *irel, *irelend;
struct one_fixup *fixups = NULL;
- bfd_boolean changed_contents = FALSE;
- bfd_boolean changed_relocs = FALSE;
+ bfd_boolean changed;
struct ppc_elf_link_hash_table *ppc_info;
+ bfd_size_type trampoff;
*again = FALSE;
@@ -1743,6 +1685,10 @@ ppc_elf_relax_section (bfd *abfd,
if (isec->_cooked_size == 0)
isec->_cooked_size = isec->_raw_size;
+ trampoff = (isec->_cooked_size + 3) & (bfd_vma) -4;
+ /* Space for a branch around any trampolines. */
+ trampoff += 4;
+
symtab_hdr = &elf_tdata (abfd)->symtab_hdr;
/* Get a copy of the native relocations. */
@@ -1772,21 +1718,26 @@ ppc_elf_relax_section (bfd *abfd,
for (irel = internal_relocs; irel < irelend; irel++)
{
unsigned long r_type = ELF32_R_TYPE (irel->r_info);
- bfd_vma symaddr, reladdr, trampoff, toff, roff;
+ bfd_vma symaddr, reladdr, toff, roff;
asection *tsec;
- bfd_size_type amt;
struct one_fixup *f;
size_t insn_offset = 0;
- bfd_vma max_branch_offset;
+ bfd_vma max_branch_offset, val;
+ bfd_byte *hit_addr;
+ unsigned long t0;
switch (r_type)
{
case R_PPC_REL24:
case R_PPC_LOCAL24PC:
+ case R_PPC_PLTREL24:
+ max_branch_offset = 1 << 25;
+ break;
+
case R_PPC_REL14:
case R_PPC_REL14_BRTAKEN:
case R_PPC_REL14_BRNTAKEN:
- case R_PPC_PLTREL24:
+ max_branch_offset = 1 << 15;
break;
default:
@@ -1824,7 +1775,7 @@ ppc_elf_relax_section (bfd *abfd,
}
else
{
- /* Need dynamic symbol handling. */
+ /* Global symbol handling. */
unsigned long indx;
struct elf_link_hash_entry *h;
@@ -1835,62 +1786,34 @@ ppc_elf_relax_section (bfd *abfd,
|| h->root.type == bfd_link_hash_warning)
h = (struct elf_link_hash_entry *) h->root.u.i.link;
- if (r_type == R_PPC_PLTREL24)
+ if (r_type == R_PPC_PLTREL24
+ && ppc_info->plt != NULL
+ && h->plt.offset != (bfd_vma) -1)
{
- Elf_Internal_Sym *isym;
-
- if (h->plt.offset == (bfd_vma) -1
- || ppc_info->plt == NULL)
- {
-
- /* Read this BFD's local symbols. */
- if (isymbuf == NULL)
- {
- isymbuf = (Elf_Internal_Sym *) symtab_hdr->contents;
- if (isymbuf == NULL)
- isymbuf = bfd_elf_get_elf_syms (abfd, symtab_hdr,
- symtab_hdr->sh_info, 0,
- NULL, NULL, NULL);
- if (isymbuf == 0)
- goto error_return;
- }
- isym = isymbuf + ELF32_R_SYM (irel->r_info);
-
- if (isym->st_shndx == SHN_UNDEF)
- /* We can't do anthing with undefined symbols. */
- continue;
- else if (isym->st_shndx == SHN_ABS)
- tsec = bfd_abs_section_ptr;
- else if (isym->st_shndx == SHN_COMMON)
- tsec = bfd_com_section_ptr;
- else
- tsec = h->root.u.def.section;
-
- toff = h->root.u.def.value;
- }
- else
- {
- tsec = ppc_info->plt;
- toff = h->plt.offset;
- }
+ tsec = ppc_info->plt;
+ toff = h->plt.offset;
}
- else if (h->root.type == bfd_link_hash_undefined
- || h->root.type == bfd_link_hash_undefweak)
- continue;
-
- else
+ else if (h->root.type == bfd_link_hash_defined
+ || h->root.type == bfd_link_hash_defweak)
{
tsec = h->root.u.def.section;
toff = h->root.u.def.value;
}
+ else
+ continue;
}
+ /* If the branch and target are in the same section, you have
+ no hope of adding stubs. We'll error out later should the
+ branch overflow. */
+ if (tsec == isec)
+ continue;
+
+ toff += irel->r_addend;
if (tsec->sec_info_type == ELF_INFO_TYPE_MERGE)
toff = _bfd_merged_section_offset (abfd, &tsec,
elf_section_data (tsec)->sec_info,
- toff + irel->r_addend, 0);
- else
- toff += irel->r_addend;
+ toff, 0);
symaddr = tsec->output_section->vma + tsec->output_offset + toff;
@@ -1898,70 +1821,41 @@ ppc_elf_relax_section (bfd *abfd,
reladdr = (isec->output_section->vma
+ isec->output_offset
- + roff) & (bfd_vma) -4;
+ + roff);
/* If the branch is in range, no need to do anything. */
- max_branch_offset = 1 << 25;
- if (r_type != R_PPC_REL24
- && r_type != R_PPC_LOCAL24PC
- && r_type != R_PPC_PLTREL24)
- max_branch_offset = 1 << 15;
-
- if ((bfd_vma) (symaddr - reladdr) + max_branch_offset
- <= 2 * max_branch_offset)
+ if (symaddr - reladdr + max_branch_offset < 2 * max_branch_offset)
continue;
- /* If the branch and target are in the same section, you have
- no hope. We'll error out later. */
- if (tsec == isec)
- continue;
-
- /* Look for an existing fixup to this address.
- ??? What if the existing fixup is for a non-pic stub, and the
- new one requires a pic stub? This presumably could happen with
- a static link and a mix of R_PPC_LOCAL24PC and R_PPC_REL24
- relocs to a symbol needing long branch stubs.
- ??? Why do we require R_PPC_LOCAL24PC and branches to the plt
- to have a shared branch stub? Shared branch stubs should only
- be needed when info->shared. */
+ /* Look for an existing fixup to this address. */
for (f = fixups; f ; f = f->next)
if (f->tsec == tsec && f->toff == toff)
break;
if (f == NULL)
{
- const bfd_byte *stub;
size_t size;
unsigned long stub_rtype;
- if (link_info->shared
- || tsec == ppc_info->plt
- || r_type == R_PPC_LOCAL24PC)
- {
- stub = shared_stub_entry;
- size = sizeof (shared_stub_entry);
- insn_offset = 16;
+ val = trampoff - roff;
+ if (val >= max_branch_offset)
+ /* Oh dear, we can't reach a trampoline. Don't try to add
+ one. We'll report an error later. */
+ continue;
+
+ if (link_info->shared)
+ {
+ size = 4 * ARRAY_SIZE (shared_stub_entry);
+ insn_offset = 12;
stub_rtype = R_PPC_RELAX32PC;
}
else
{
- stub = stub_entry;
- size = sizeof (stub_entry);
- insn_offset = 4;
+ size = 4 * ARRAY_SIZE (stub_entry);
+ insn_offset = 0;
stub_rtype = R_PPC_RELAX32;
}
- /* Resize the current section to make room for the new branch. */
- trampoff = (isec->_cooked_size + 3) & (bfd_vma) - 4;
- amt = trampoff + size;
- contents = bfd_realloc (contents, amt);
- if (contents == NULL)
- abort ();
-
- isec->_cooked_size = amt;
-
- memcpy (contents + trampoff, stub, size);
-
/* Hijack the old relocation. Since we need two
relocations for this use a "composite" reloc. */
irel->r_info = ELF32_R_INFO (ELF32_R_SYM (irel->r_info),
@@ -1975,31 +1869,95 @@ ppc_elf_relax_section (bfd *abfd,
f->toff = toff;
f->trampoff = trampoff;
fixups = f;
+
+ trampoff += size;
}
else
{
+ val = f->trampoff - roff;
+ if (val >= max_branch_offset)
+ continue;
+
/* Nop out the reloc, since we're finalizing things here. */
irel->r_info = ELF32_R_INFO (0, R_PPC_NONE);
}
- /* Fix up the existing branch to hit the trampoline. Hope like
- hell this doesn't overflow too. */
- if (ppc_elf_install_value (abfd, contents + roff,
- f->trampoff - (roff & (bfd_vma) -3) + 4,
- r_type) != bfd_reloc_ok)
- abort ();
+ /* Fix up the existing branch to hit the trampoline. */
+ hit_addr = contents + roff;
+ switch (r_type)
+ {
+ case R_PPC_REL24:
+ case R_PPC_LOCAL24PC:
+ case R_PPC_PLTREL24:
+ t0 = bfd_get_32 (abfd, hit_addr);
+ t0 &= ~0x3fffffc;
+ t0 |= val & 0x3fffffc;
+ bfd_put_32 (abfd, t0, hit_addr);
+ break;
- changed_contents = TRUE;
- changed_relocs = TRUE;
+ case R_PPC_REL14:
+ case R_PPC_REL14_BRTAKEN:
+ case R_PPC_REL14_BRNTAKEN:
+ t0 = bfd_get_32 (abfd, hit_addr);
+ t0 &= ~0xfffc;
+ t0 |= val & 0xfffc;
+ bfd_put_32 (abfd, t0, hit_addr);
+ break;
+ }
}
- /* Clean up. */
- while (fixups)
+ /* Write out the trampolines. */
+ changed = fixups != NULL;
+ if (fixups != NULL)
{
- struct one_fixup *f = fixups;
- fixups = fixups->next;
- free (f);
+ const int *stub;
+ bfd_byte *dest;
+ bfd_vma val;
+ int i, size;
+
+ do
+ {
+ struct one_fixup *f = fixups;
+ fixups = fixups->next;
+ free (f);
+ }
+ while (fixups);
+
+ contents = bfd_realloc (contents, trampoff);
+ if (contents == NULL)
+ goto error_return;
+
+ isec->_cooked_size = (isec->_cooked_size + 3) & (bfd_vma) -4;
+ /* Branch around the trampolines. */
+ val = trampoff - isec->_cooked_size + 0x48000000;
+ dest = contents + isec->_cooked_size;
+ isec->_cooked_size = trampoff;
+ bfd_put_32 (abfd, val, dest);
+ dest += 4;
+
+ if (link_info->shared)
+ {
+ stub = shared_stub_entry;
+ size = ARRAY_SIZE (shared_stub_entry);
+ }
+ else
+ {
+ stub = stub_entry;
+ size = ARRAY_SIZE (stub_entry);
+ }
+
+ i = 0;
+ while (dest < contents + trampoff)
+ {
+ bfd_put_32 (abfd, stub[i], dest);
+ i++;
+ if (i == size)
+ i = 0;
+ dest += 4;
+ }
+ BFD_ASSERT (i == 0);
}
+
if (isymbuf != NULL
&& symtab_hdr->contents != (unsigned char *) isymbuf)
{
@@ -2015,7 +1973,7 @@ ppc_elf_relax_section (bfd *abfd,
if (contents != NULL
&& elf_section_data (isec)->this_hdr.contents != contents)
{
- if (!changed_contents && !link_info->keep_memory)
+ if (!changed && !link_info->keep_memory)
free (contents);
else
{
@@ -2026,13 +1984,13 @@ ppc_elf_relax_section (bfd *abfd,
if (elf_section_data (isec)->relocs != internal_relocs)
{
- if (!changed_relocs)
+ if (!changed)
free (internal_relocs);
else
elf_section_data (isec)->relocs = internal_relocs;
}
- *again = changed_contents || changed_relocs;
+ *again = changed;
return TRUE;
error_return:
@@ -5462,8 +5420,26 @@ ppc_elf_relocate_section (bfd *output_bf
+ rel->r_offset - 4);
/* Fall thru */
case R_PPC_RELAX32:
- ppc_elf_install_value (output_bfd, contents + rel->r_offset,
- relocation + addend, r_type);
+ {
+ unsigned long t0;
+ unsigned long t1;
+
+ t0 = bfd_get_32 (output_bfd, contents + rel->r_offset);
+ t1 = bfd_get_32 (output_bfd, contents + rel->r_offset + 4);
+
+ /* We're clearing the bits for R_PPC_ADDR16_HA
+ and R_PPC_ADDR16_LO here. */
+ t0 &= ~0xffff;
+ t1 &= ~0xffff;
+
+ /* t0 is HA, t1 is LO */
+ relocation += addend;
+ t0 |= ((relocation + 0x8000) >> 16) & 0xffff;
+ t1 |= relocation & 0xffff;
+
+ bfd_put_32 (output_bfd, t0, contents + rel->r_offset);
+ bfd_put_32 (output_bfd, t1, contents + rel->r_offset + 4);
+ }
continue;
/* Indirect .sdata relocation. */
--
Alan Modra
IBM OzLabs - Linux Technology Centre