+\f
+/* This function handles relaxing for the PPC with option --mpc860c0[=<n>].
+
+ The MPC860, revision C0 or earlier contains a bug in the die.
+ If all of the following conditions are true, the next instruction
+ to be executed *may* be treated as a no-op.
+ 1/ A forward branch is executed.
+ 2/ The branch is predicted as not taken.
+ 3/ The branch is taken.
+ 4/ The branch is located in the last 5 words of a page.
+ (The EOP limit is 5 by default but may be specified as any value from 1-10.)
+
+ Our software solution is to detect these problematic branches in a
+ linker pass and modify them as follows:
+ 1/ Unconditional branches - Since these are always predicted taken,
+ there is no problem and no action is required.
+ 2/ Conditional backward branches - No problem, no action required.
+ 3/ Conditional forward branches - Ensure that the "inverse prediction
+ bit" is set (ensure it is predicted taken).
+ 4/ Conditional register branches - Ensure that the "y bit" is set
+ (ensure it is predicted taken).
+*/
+
+/* Sort sections by address. */
+
+static int
+ppc_elf_sort_rela (arg1, arg2)
+ const void *arg1;
+ const void *arg2;
+{
+ const Elf_Internal_Rela **rela1 = (const Elf_Internal_Rela**) arg1;
+ const Elf_Internal_Rela **rela2 = (const Elf_Internal_Rela**) arg2;
+
+ /* Sort by offset. */
+ return ((*rela1)->r_offset - (*rela2)->r_offset);
+}
+
+static boolean
+ppc_elf_relax_section (abfd, isec, link_info, again)
+ bfd *abfd;
+ asection *isec;
+ struct bfd_link_info *link_info;
+ boolean *again;
+{
+#define PAGESIZE 0x1000
+
+ bfd_byte *contents = NULL;
+ bfd_byte *free_contents = NULL;
+ Elf_Internal_Rela *internal_relocs = NULL;
+ Elf_Internal_Rela *free_relocs = NULL;
+ Elf_Internal_Rela **rela_comb = NULL;
+ int comb_curr, comb_count;
+
+ /* We never have to do this more than once per input section. */
+ *again = false;
+
+ /* If needed, initialize this section's cooked size. */
+ if (isec->_cooked_size == 0)
+ isec->_cooked_size = isec->_raw_size;
+
+ /* We're only interested in text sections which overlap the
+ troublesome area at the end of a page. */
+ if (link_info->mpc860c0 && (isec->flags & SEC_CODE) && isec->_cooked_size)
+ {
+ bfd_vma dot, end_page, end_section;
+ boolean section_modified;
+
+ /* Get the section contents. */
+ /* Get cached copy if it exists. */
+ if (elf_section_data (isec)->this_hdr.contents != NULL)
+ contents = elf_section_data (isec)->this_hdr.contents;
+ else
+ {
+ /* Go get them off disk. */
+ contents = (bfd_byte *) bfd_malloc (isec->_raw_size);
+ if (contents == NULL)
+ goto error_return;
+ free_contents = contents;
+
+ if (! bfd_get_section_contents (abfd, isec, contents,
+ (file_ptr) 0, isec->_raw_size))
+ goto error_return;
+ }
+
+ comb_curr = 0;
+ comb_count = 0;
+ if (isec->reloc_count)
+ {
+ unsigned n;
+
+ /* Get a copy of the native relocations. */
+ internal_relocs = _bfd_elf32_link_read_relocs (
+ abfd, isec, (PTR) NULL, (Elf_Internal_Rela *) NULL,
+ link_info->keep_memory);
+ if (internal_relocs == NULL)
+ goto error_return;
+ if (! link_info->keep_memory)
+ free_relocs = internal_relocs;
+
+ /* Setup a faster access method for the reloc info we need. */
+ rela_comb = (Elf_Internal_Rela**)
+ bfd_malloc (isec->reloc_count*sizeof (Elf_Internal_Rela*));
+ if (rela_comb == NULL)
+ goto error_return;
+ for (n = 0; n < isec->reloc_count; ++n)
+ {
+ long r_type;
+
+ r_type = ELF32_R_TYPE (internal_relocs[n].r_info);
+ if (r_type < 0 || r_type >= (int) R_PPC_max)
+ goto error_return;
+
+ /* Prologue constants are sometimes present in the ".text"
+ sections and they can be identified by their associated relocation.
+ We don't want to process those words and some others which
+ can also be identified by their relocations. However, not all
+ conditional branches will have a relocation so we will
+ only ignore words that 1) have a reloc, and 2) the reloc
+ is not applicable to a conditional branch.
+ The array rela_comb is built here for use in the EOP scan loop. */
+ switch (r_type)
+ {
+ case R_PPC_ADDR14_BRNTAKEN: /* absolute, predicted not taken */
+ case R_PPC_REL14: /* relative cond. br. */
+ case R_PPC_REL14_BRNTAKEN: /* rel. cond. br., predicted not taken */
+ /* We should check the instruction. */
+ break;
+ default:
+ /* The word is not a conditional branch - ignore it. */
+ rela_comb[comb_count++] = &internal_relocs[n];
+ break;
+ }
+ }
+ if (comb_count > 1)
+ qsort (rela_comb, (size_t) comb_count, sizeof (int), ppc_elf_sort_rela);
+ }
+
+ /* Enumerate each EOP region that overlaps this section. */
+ end_section = isec->vma + isec->_cooked_size;
+ dot = end_page = (isec->vma | (PAGESIZE - 1)) + 1;
+ dot -= link_info->mpc860c0;
+ section_modified = false;
+ if (dot < isec->vma) /* Increment the start position if this section */
+ dot = isec->vma; /* begins in the middle of its first EOP region. */
+ for (;
+ dot < end_section;
+ dot += PAGESIZE, end_page += PAGESIZE)
+ {
+
+ /* Check each word in this EOP region. */
+ for (; dot < end_page; dot += 4)
+ {
+ bfd_vma isec_offset;
+ unsigned long insn;
+ boolean skip, modified;
+
+ /* Don't process this word if there is a relocation for it and
+ the relocation indicates the word is not a conditional branch. */
+ skip = false;
+ isec_offset = dot - isec->vma;
+ for (; comb_curr<comb_count; ++comb_curr)
+ {
+ bfd_vma r_offset;
+
+ r_offset = rela_comb[comb_curr]->r_offset;
+ if (r_offset >= isec_offset)
+ {
+ if (r_offset == isec_offset) skip = true;
+ break;
+ }
+ }
+ if (skip) continue;
+
+ /* Check the current word for a problematic conditional branch. */
+#define BO0(insn) ((insn) & 0x02000000)
+#define BO2(insn) ((insn) & 0x00800000)
+#define BO4(insn) ((insn) & 0x00200000)
+ insn = (unsigned long) bfd_get_32 (abfd, contents + isec_offset);
+ modified = false;
+ if ((insn & 0xFc000000) == 0x40000000)
+ {
+ /* Instruction is BCx */
+ if ((!BO0(insn) || !BO2(insn)) && !BO4(insn))
+ {
+ bfd_vma target;
+ /* This branch is predicted as "normal".
+ If this is a forward branch, it is problematic. */
+
+ target = insn & 0x0000Fffc; /*extract*/
+ target = (target ^ 0x8000) - 0x8000; /*sign extend*/
+ if ((insn & 0x00000002) == 0)
+ target += dot; /*convert to abs*/
+ if (target > dot)
+ {
+ insn |= 0x00200000; /* set the prediction bit */
+ modified = true;
+ }
+ }
+ }
+ else if ((insn & 0xFc00Fffe) == 0x4c000420)
+ {
+ /* Instruction is BCCTRx */
+ if ((!BO0(insn) || !BO2(insn)) && !BO4(insn))
+ {
+ /* This branch is predicted as not-taken.
+ If this is a forward branch, it is problematic.
+ Since we can't tell statically if it will branch forward,
+ always set the prediction bit. */
+ insn |= 0x00200000; /* set the prediction bit */
+ modified = true;
+ }
+ }
+ else if ((insn & 0xFc00Fffe) == 0x4c000020)
+ {
+ /* Instruction is BCLRx */
+ if ((!BO0(insn) || !BO2(insn)) && !BO4(insn))
+ {
+ /* This branch is predicted as not-taken.
+ If this is a forward branch, it is problematic.
+ Since we can't tell statically if it will branch forward,
+ always set the prediction bit. */
+ insn |= 0x00200000; /* set the prediction bit */
+ modified = true;
+ }
+ }
+#undef BO0
+#undef BO2
+#undef BO4
+ if (modified)
+ {
+ bfd_put_32 (abfd, insn, contents + isec_offset);
+ section_modified = true;
+ }
+ }
+ }
+ if (section_modified)
+ {
+ elf_section_data (isec)->this_hdr.contents = contents;
+ free_contents = NULL;
+ }
+ }
+
+ if (rela_comb != NULL)
+ {
+ free (rela_comb);
+ rela_comb = NULL;
+ }
+
+ if (free_relocs != NULL)
+ {
+ free (free_relocs);
+ free_relocs = NULL;
+ }
+
+ if (free_contents != NULL)
+ {
+ if (! link_info->keep_memory)
+ free (free_contents);
+ else
+ {
+ /* Cache the section contents for elf_link_input_bfd. */
+ elf_section_data (isec)->this_hdr.contents = contents;
+ }
+ free_contents = NULL;
+ }
+
+ return true;
projects / deliverable / binutils-gdb.git / blobdiff