Better overflow checking for powerpc64 relocations

Alan Modra amodra@gmail.com
Sat Mar 8 02:32:00 GMT 2014


R_PPC64_ADDR16 is used in three contexts:
- .short data relocation
- 16-bit signed insn fields, eg. addi
- 16-bit unsigned insn fields, eg. ori
In the first case we want to allow both signed and unsigned 16-bit
values, the latter two ought to error if the field exceeds the range
of values allowed for 16-bit signed and unsigned integers
respectively.  These conflicting requirements meant that ld had to
choose the least restrictive overflow checks, and thus it is possible
to construct testcases where an addi field overflows but is not
reported by ld.  Many relocations dealing with 16-bit insn fields have
this problem.  What's more, some relocations that are only ever used
for signed fields of instructions woodenly copied the lax overflow
checking of R_PPC64_ADDR16.

bfd/
	* elf64-ppc.c (ppc64_elf_howto_raw): Use complain_overflow_signed
	for R_PPC64_ADDR14, R_PPC64_ADDR14_BRTAKEN, R_PPC64_ADDR14_BRNTAKEN,
	R_PPC64_SECTOFF, R_PPC64_ADDR16_DS, R_PPC64_SECTOFF_DS,
	R_PPC64_REL16 entries.  Use complain_overflow_dont for R_PPC64_TOC.
	(ppc64_elf_relocate_section): Modify overflow test for 16-bit
	fields in instructions to signed/unsigned according to whether
	the field takes a signed or unsigned value.
gold/
	* powerpc.cc (Powerpc_relocate_functions::Overflow_check): Add
	CHECK_UNSIGNED, CHECK_LOW_INSN, CHECK_HIGH_INSN.
	(Powerpc_relocate_functions::has_overflow_unsigned): New function.
	(Powerpc_relocate_functions::has_overflow_bitfield,
	overflowed): Use the above.
	(Target_powerpc::Relocate::relocate): Correct overflow checking
	for a number of relocations.  Modify overflow test for 16-bit
	fields in instructions to signed/unsigned according to whether
	the field takes a signed or unsigned value.

diff --git a/bfd/elf64-ppc.c b/bfd/elf64-ppc.c
index 2c8171d..74c6e25 100644
--- a/bfd/elf64-ppc.c
+++ b/bfd/elf64-ppc.c
@@ -357,7 +357,7 @@ static reloc_howto_type ppc64_elf_howto_raw[] = {
 	 16,			/* bitsize */
 	 FALSE,			/* pc_relative */
 	 0,			/* bitpos */
-	 complain_overflow_bitfield, /* complain_on_overflow */
+	 complain_overflow_signed, /* complain_on_overflow */
 	 ppc64_elf_branch_reloc, /* special_function */
 	 "R_PPC64_ADDR14",	/* name */
 	 FALSE,			/* partial_inplace */
@@ -374,7 +374,7 @@ static reloc_howto_type ppc64_elf_howto_raw[] = {
 	 16,			/* bitsize */
 	 FALSE,			/* pc_relative */
 	 0,			/* bitpos */
-	 complain_overflow_bitfield, /* complain_on_overflow */
+	 complain_overflow_signed, /* complain_on_overflow */
 	 ppc64_elf_brtaken_reloc, /* special_function */
 	 "R_PPC64_ADDR14_BRTAKEN",/* name */
 	 FALSE,			/* partial_inplace */
@@ -391,7 +391,7 @@ static reloc_howto_type ppc64_elf_howto_raw[] = {
 	 16,			/* bitsize */
 	 FALSE,			/* pc_relative */
 	 0,			/* bitpos */
-	 complain_overflow_bitfield, /* complain_on_overflow */
+	 complain_overflow_signed, /* complain_on_overflow */
 	 ppc64_elf_brtaken_reloc, /* special_function */
 	 "R_PPC64_ADDR14_BRNTAKEN",/* name */
 	 FALSE,			/* partial_inplace */
@@ -632,7 +632,6 @@ static reloc_howto_type ppc64_elf_howto_raw[] = {
 	 32,			/* bitsize */
 	 TRUE,			/* pc_relative */
 	 0,			/* bitpos */
-	 /* FIXME: Verify.  Was complain_overflow_bitfield.  */
 	 complain_overflow_signed, /* complain_on_overflow */
 	 bfd_elf_generic_reloc,	/* special_function */
 	 "R_PPC64_REL32",	/* name */
@@ -727,7 +726,7 @@ static reloc_howto_type ppc64_elf_howto_raw[] = {
 	 16,			/* bitsize */
 	 FALSE,			/* pc_relative */
 	 0,			/* bitpos */
-	 complain_overflow_bitfield, /* complain_on_overflow */
+	 complain_overflow_signed, /* complain_on_overflow */
 	 ppc64_elf_sectoff_reloc, /* special_function */
 	 "R_PPC64_SECTOFF",	/* name */
 	 FALSE,			/* partial_inplace */
@@ -1015,7 +1014,7 @@ static reloc_howto_type ppc64_elf_howto_raw[] = {
 	 64,			/* bitsize */
 	 FALSE,			/* pc_relative */
 	 0,			/* bitpos */
-	 complain_overflow_bitfield, /* complain_on_overflow */
+	 complain_overflow_dont, /* complain_on_overflow */
 	 ppc64_elf_toc64_reloc,	/* special_function */
 	 "R_PPC64_TOC",		/* name */
 	 FALSE,			/* partial_inplace */
@@ -1103,7 +1102,7 @@ static reloc_howto_type ppc64_elf_howto_raw[] = {
 	 16,			/* bitsize */
 	 FALSE,			/* pc_relative */
 	 0,			/* bitpos */
-	 complain_overflow_bitfield, /* complain_on_overflow */
+	 complain_overflow_signed, /* complain_on_overflow */
 	 bfd_elf_generic_reloc,	/* special_function */
 	 "R_PPC64_ADDR16_DS",	/* name */
 	 FALSE,			/* partial_inplace */
@@ -1178,7 +1177,7 @@ static reloc_howto_type ppc64_elf_howto_raw[] = {
 	 16,			/* bitsize */
 	 FALSE,			/* pc_relative */
 	 0,			/* bitpos */
-	 complain_overflow_bitfield, /* complain_on_overflow */
+	 complain_overflow_signed, /* complain_on_overflow */
 	 ppc64_elf_sectoff_reloc, /* special_function */
 	 "R_PPC64_SECTOFF_DS",	/* name */
 	 FALSE,			/* partial_inplace */
@@ -1950,7 +1949,7 @@ static reloc_howto_type ppc64_elf_howto_raw[] = {
 	 16,			/* bitsize */
 	 TRUE,			/* pc_relative */
 	 0,			/* bitpos */
-	 complain_overflow_bitfield, /* complain_on_overflow */
+	 complain_overflow_signed, /* complain_on_overflow */
 	 bfd_elf_generic_reloc,	/* special_function */
 	 "R_PPC64_REL16",	/* name */
 	 FALSE,			/* partial_inplace */
@@ -12943,6 +12942,8 @@ ppc64_elf_relocate_section (bfd *output_bfd,
       bfd_vma max_br_offset;
       bfd_vma from;
       const Elf_Internal_Rela orig_rel = *rel;
+      reloc_howto_type *howto;
+      struct reloc_howto_struct alt_howto;
 
       r_type = ELF64_R_TYPE (rel->r_info);
       r_symndx = ELF64_R_SYM (rel->r_info);
@@ -14507,6 +14508,7 @@ ppc64_elf_relocate_section (bfd *output_bfd,
 	}
 
       /* Do any further special processing.  */
+      howto = ppc64_elf_howto_table[(int) r_type];
       switch (r_type)
 	{
 	default:
@@ -14581,7 +14583,7 @@ ppc64_elf_relocate_section (bfd *output_bfd,
 	      info->callbacks->einfo
 		(_("%P: %H: error: %s not a multiple of %u\n"),
 		 input_bfd, input_section, rel->r_offset,
-		 ppc64_elf_howto_table[r_type]->name,
+		 howto->name,
 		 mask + 1);
 	      bfd_set_error (bfd_error_bad_value);
 	      ret = FALSE;
@@ -14602,23 +14604,45 @@ ppc64_elf_relocate_section (bfd *output_bfd,
 	  info->callbacks->einfo
 	    (_("%P: %H: unresolvable %s against `%T'\n"),
 	     input_bfd, input_section, rel->r_offset,
-	     ppc64_elf_howto_table[(int) r_type]->name,
+	     howto->name,
 	     h->elf.root.root.string);
 	  ret = FALSE;
 	}
 
-      r = _bfd_final_link_relocate (ppc64_elf_howto_table[(int) r_type],
-				    input_bfd,
-				    input_section,
-				    contents,
-				    rel->r_offset,
-				    relocation,
-				    addend);
+      /* 16-bit fields in insns mostly have signed values, but a
+	 few insns have 16-bit unsigned values.  Really, we should
+	 have different reloc types.  */
+      if (howto->complain_on_overflow != complain_overflow_dont
+	  && howto->dst_mask == 0xffff
+	  && (input_section->flags & SEC_CODE) != 0)
+	{
+	  enum complain_overflow complain = complain_overflow_signed;
+
+	  insn = bfd_get_32 (input_bfd, contents + (rel->r_offset & ~3));
+	  if (howto->rightshift == 0
+	      ? ((insn & (0x3f << 26)) == 28u << 26 /* andi */
+		 || (insn & (0x3f << 26)) == 24u << 26 /* ori */
+		 || (insn & (0x3f << 26)) == 26u << 26 /* xori */
+		 || (insn & (0x3f << 26)) == 10u << 26 /* cmpli */)
+	      : ((insn & (0x3f << 26)) == 29u << 26 /* andis */
+		 || (insn & (0x3f << 26)) == 25u << 26 /* oris */
+		 || (insn & (0x3f << 26)) == 27u << 26 /* xoris */))
+	    complain = complain_overflow_unsigned;
+	  if (howto->complain_on_overflow != complain)
+	    {
+	      alt_howto = *howto;
+	      alt_howto.complain_on_overflow = complain;
+	      howto = &alt_howto;
+	    }
+	}
+
+      r = _bfd_final_link_relocate (howto, input_bfd, input_section, contents,
+				    rel->r_offset, relocation, addend);
 
       if (r != bfd_reloc_ok)
 	{
 	  char *more_info = NULL;
-	  const char *reloc_name = ppc64_elf_howto_table[r_type]->name;
+	  const char *reloc_name = howto->name;
 
 	  if (reloc_dest != DEST_NORMAL)
 	    {
@@ -14638,7 +14662,7 @@ ppc64_elf_relocate_section (bfd *output_bfd,
 		continue;
 	      if (h != NULL
 		  && h->elf.root.type == bfd_link_hash_undefweak
-		  && ppc64_elf_howto_table[r_type]->pc_relative)
+		  && howto->pc_relative)
 		{
 		  /* Assume this is a call protected by other code that
 		     detects the symbol is undefined.  If this is the case,
diff --git a/gold/ChangeLog b/gold/ChangeLog
index c3c3866..ddf18d6 100644
--- a/gold/ChangeLog
+++ b/gold/ChangeLog
@@ -1,3 +1,15 @@
+2014-03-07  Alan Modra  <amodra@gmail.com>
+
+	* powerpc.cc (Powerpc_relocate_functions::Overflow_check): Add
+	CHECK_UNSIGNED, CHECK_LOW_INSN, CHECK_HIGH_INSN.
+	(Powerpc_relocate_functions::has_overflow_unsigned): New function.
+	(Powerpc_relocate_functions::has_overflow_bitfield,
+	overflowed): Use the above.
+	(Target_powerpc::Relocate::relocate): Correct overflow checking
+	for a number of relocations.  Modify overflow test for 16-bit
+	fields in instructions to signed/unsigned according to whether
+	the field takes a signed or unsigned value.
+
 2014-03-05  Alan Modra  <amodra@gmail.com>
 
 	Update copyright years.
diff --git a/gold/powerpc.cc b/gold/powerpc.cc
index 6e9ddd6..0589d0c 100644
--- a/gold/powerpc.cc
+++ b/gold/powerpc.cc
@@ -1446,7 +1446,10 @@ public:
   {
     CHECK_NONE,
     CHECK_SIGNED,
-    CHECK_BITFIELD
+    CHECK_UNSIGNED,
+    CHECK_BITFIELD,
+    CHECK_LOW_INSN,
+    CHECK_HIGH_INSN
   };
 
   enum Status
@@ -1472,12 +1475,20 @@ private:
 
   template<int valsize>
   static inline bool
-  has_overflow_bitfield(Address value)
+  has_overflow_unsigned(Address value)
   {
     Address limit = static_cast<Address>(1) << ((valsize - 1) >> 1);
     limit <<= ((valsize - 1) >> 1);
     limit <<= ((valsize - 1) - 2 * ((valsize - 1) >> 1));
-    return value > (limit << 1) - 1 && value + limit > (limit << 1) - 1;
+    return value > (limit << 1) - 1;
+  }
+
+  template<int valsize>
+  static inline bool
+  has_overflow_bitfield(Address value)
+  {
+    return (has_overflow_unsigned<valsize>(value)
+	    && has_overflow_signed<valsize>(value));
   }
 
   template<int valsize>
@@ -1489,6 +1500,11 @@ private:
 	if (has_overflow_signed<valsize>(value))
 	  return STATUS_OVERFLOW;
       }
+    else if (overflow == CHECK_UNSIGNED)
+      {
+	if (has_overflow_unsigned<valsize>(value))
+	  return STATUS_OVERFLOW;
+      }
     else if (overflow == CHECK_BITFIELD)
       {
 	if (has_overflow_bitfield<valsize>(value))
@@ -7259,6 +7275,7 @@ Target_powerpc<size, big_endian>::Relocate::relocate(
     }
 
   typename Reloc::Overflow_check overflow = Reloc::CHECK_NONE;
+  elfcpp::Shdr<size, big_endian> shdr(relinfo->data_shdr);
   switch (r_type)
     {
     case elfcpp::R_POWERPC_ADDR32:
@@ -7272,16 +7289,19 @@ Target_powerpc<size, big_endian>::Relocate::relocate(
 	overflow = Reloc::CHECK_SIGNED;
       break;
 
-    case elfcpp::R_POWERPC_ADDR24:
-    case elfcpp::R_POWERPC_ADDR16:
     case elfcpp::R_POWERPC_UADDR16:
-    case elfcpp::R_PPC64_ADDR16_DS:
-    case elfcpp::R_POWERPC_ADDR14:
-    case elfcpp::R_POWERPC_ADDR14_BRTAKEN:
-    case elfcpp::R_POWERPC_ADDR14_BRNTAKEN:
       overflow = Reloc::CHECK_BITFIELD;
       break;
 
+    case elfcpp::R_POWERPC_ADDR16:
+      // We really should have three separate relocations,
+      // one for 16-bit data, one for insns with 16-bit signed fields,
+      // and one for insns with 16-bit unsigned fields.
+      overflow = Reloc::CHECK_BITFIELD;
+      if ((shdr.get_sh_flags() & elfcpp::SHF_EXECINSTR) != 0)
+	overflow = Reloc::CHECK_LOW_INSN;
+      break;
+
     case elfcpp::R_POWERPC_ADDR16_HI:
     case elfcpp::R_POWERPC_ADDR16_HA:
     case elfcpp::R_POWERPC_GOT16_HI:
@@ -7308,17 +7328,31 @@ Target_powerpc<size, big_endian>::Relocate::relocate(
     case elfcpp::R_POWERPC_GOT_DTPREL16_HA:
     case elfcpp::R_POWERPC_REL16_HI:
     case elfcpp::R_POWERPC_REL16_HA:
-      if (size == 32)
-	break;
-    case elfcpp::R_POWERPC_REL24:
-    case elfcpp::R_PPC_PLTREL24:
-    case elfcpp::R_PPC_LOCAL24PC:
+      if (size != 32)
+	overflow = Reloc::CHECK_HIGH_INSN;
+      break;
+
     case elfcpp::R_POWERPC_REL16:
     case elfcpp::R_PPC64_TOC16:
     case elfcpp::R_POWERPC_GOT16:
     case elfcpp::R_POWERPC_SECTOFF:
     case elfcpp::R_POWERPC_TPREL16:
     case elfcpp::R_POWERPC_DTPREL16:
+    case elfcpp::R_POWERPC_GOT_TLSGD16:
+    case elfcpp::R_POWERPC_GOT_TLSLD16:
+    case elfcpp::R_POWERPC_GOT_TPREL16:
+    case elfcpp::R_POWERPC_GOT_DTPREL16:
+      overflow = Reloc::CHECK_LOW_INSN;
+      break;
+
+    case elfcpp::R_POWERPC_ADDR24:
+    case elfcpp::R_POWERPC_ADDR14:
+    case elfcpp::R_POWERPC_ADDR14_BRTAKEN:
+    case elfcpp::R_POWERPC_ADDR14_BRNTAKEN:
+    case elfcpp::R_PPC64_ADDR16_DS:
+    case elfcpp::R_POWERPC_REL24:
+    case elfcpp::R_PPC_PLTREL24:
+    case elfcpp::R_PPC_LOCAL24PC:
     case elfcpp::R_PPC64_TPREL16_DS:
     case elfcpp::R_PPC64_DTPREL16_DS:
     case elfcpp::R_PPC64_TOC16_DS:
@@ -7327,14 +7361,28 @@ Target_powerpc<size, big_endian>::Relocate::relocate(
     case elfcpp::R_POWERPC_REL14:
     case elfcpp::R_POWERPC_REL14_BRTAKEN:
     case elfcpp::R_POWERPC_REL14_BRNTAKEN:
-    case elfcpp::R_POWERPC_GOT_TLSGD16:
-    case elfcpp::R_POWERPC_GOT_TLSLD16:
-    case elfcpp::R_POWERPC_GOT_TPREL16:
-    case elfcpp::R_POWERPC_GOT_DTPREL16:
       overflow = Reloc::CHECK_SIGNED;
       break;
     }
 
+  if (overflow == Reloc::CHECK_LOW_INSN
+      || overflow == Reloc::CHECK_HIGH_INSN)
+    {
+      Insn* iview = reinterpret_cast<Insn*>(view - 2 * big_endian);
+      Insn insn = elfcpp::Swap<32, big_endian>::readval(iview);
+
+      overflow = Reloc::CHECK_SIGNED;
+      if (overflow == Reloc::CHECK_LOW_INSN
+	  ? ((insn & (0x3f << 26)) == 28u << 26 /* andi */
+	     || (insn & (0x3f << 26)) == 24u << 26 /* ori */
+	     || (insn & (0x3f << 26)) == 26u << 26 /* xori */
+	     || (insn & (0x3f << 26)) == 10u << 26 /* cmpli */)
+	  : ((insn & (0x3f << 26)) == 29u << 26 /* andis */
+	     || (insn & (0x3f << 26)) == 25u << 26 /* oris */
+	     || (insn & (0x3f << 26)) == 27u << 26 /* xoris */))
+	overflow = Reloc::CHECK_UNSIGNED;
+    }
+
   typename Powerpc_relocate_functions<size, big_endian>::Status status
     = Powerpc_relocate_functions<size, big_endian>::STATUS_OK;
   switch (r_type)

-- 
Alan Modra
Australia Development Lab, IBM



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