[PATCH] gold: scanning ARM relocations.
Doug Kwan (關振德)
dougkwan@google.com
Tue Jun 2 23:18:00 GMT 2009
This patch adds code to scan for global and local relocations in the
ARM (or more correctly Android) port of gold. This is part of a
bigger patch and was broken out to make review easier.
-Doug
2009-06-02 Doug Kwan <dougkwan@google.com>
* gold/arm.cc (Target_arm::Scan::Scan): Initialize
issued_non_pic_error_.
(class Target_arm::Scan): Declare new method check_non_pic.
Define new method symbol_needs_plt_entry.
Declare new data member issued_non_pic_error_.
(class Target_arm::Relocate): Declare new method
should_apply_static_reloc.
(Target_arm::may_need_copy_reloc): Handle STT_ARM_TFUNC.
(Target_arm::Scan::check_non_pic): Define new method.
(Target_arm::Scan::local): Handle a small subset of reloc types used
by Android.
(Target_arm::Scan::local): Same.
(Target_arm::Relocate::should_apply_statci_reloc): Define new method.
-------------- next part --------------
Index: gold/arm.cc
===================================================================
RCS file: /cvs/src/src/gold/arm.cc,v
retrieving revision 1.2
diff -u -u -p -r1.2 arm.cc
--- gold/arm.cc 30 May 2009 00:55:42 -0000 1.2
+++ gold/arm.cc 2 Jun 2009 23:08:21 -0000
@@ -75,8 +75,6 @@ class Output_data_plt_arm;
// R_ARM_PREL31
//
// Coming soon (pending patches):
-// - Local scanner
-// - Global scanner
// - Relocation
// - Defining section symbols __exidx_start and __exidx_stop.
// - Support interworking.
@@ -209,6 +207,7 @@ class Target_arm : public Sized_target<3
{
public:
Scan()
+ : issued_non_pic_error_(false)
{ }
inline void
@@ -237,6 +236,29 @@ class Target_arm : public Sized_target<3
static void
unsupported_reloc_global(Sized_relobj<32, big_endian>*,
unsigned int r_type, Symbol*);
+
+ void
+ check_non_pic(Relobj*, unsigned int r_type);
+
+ // Almost identical to Symbol::needs_plt_entry except that it also
+ // handles STT_ARM_TFUNC.
+ static bool
+ symbol_needs_plt_entry(const Symbol* sym)
+ {
+ // An undefined symbol from an executable does not need a PLT entry.
+ if (sym->is_undefined() && !parameters->options().shared())
+ return false;
+
+ return (!parameters->doing_static_link()
+ && (sym->type() == elfcpp::STT_FUNC
+ || sym->type() == elfcpp::STT_ARM_TFUNC)
+ && (sym->is_from_dynobj()
+ || sym->is_undefined()
+ || sym->is_preemptible()));
+ }
+
+ // Whether we have issued an error about a non-PIC compilation.
+ bool issued_non_pic_error_;
};
// The class which implements relocation.
@@ -249,6 +271,13 @@ class Target_arm : public Sized_target<3
~Relocate()
{ }
+ // Return whether the static relocation needs to be applied.
+ inline bool
+ should_apply_static_reloc(const Sized_symbol<32>* gsym,
+ int ref_flags,
+ bool is_32bit,
+ Output_section* output_section);
+
// Do a relocation. Return false if the caller should not issue
// any warnings about this relocation.
inline bool
@@ -306,7 +335,8 @@ class Target_arm : public Sized_target<3
{
return (!parameters->options().shared()
&& gsym->is_from_dynobj()
- && gsym->type() != elfcpp::STT_FUNC);
+ && gsym->type() != elfcpp::STT_FUNC
+ && gsym->type() != elfcpp::STT_ARM_TFUNC);
}
// Add a potential copy relocation.
@@ -669,18 +699,65 @@ Target_arm<big_endian>::Scan::unsupporte
object->name().c_str(), r_type);
}
+// We are about to emit a dynamic relocation of type R_TYPE. If the
+// dynamic linker does not support it, issue an error. The GNU linker
+// only issues a non-PIC error for an allocated read-only section.
+// Here we know the section is allocated, but we don't know that it is
+// read-only. But we check for all the relocation types which the
+// glibc dynamic linker supports, so it seems appropriate to issue an
+// error even if the section is not read-only.
+
+template<bool big_endian>
+void
+Target_arm<big_endian>::Scan::check_non_pic(Relobj* object,
+ unsigned int r_type)
+{
+ switch (r_type)
+ {
+ // These are the relocation types supported by glibc for ARM.
+ case elfcpp::R_ARM_RELATIVE:
+ case elfcpp::R_ARM_COPY:
+ case elfcpp::R_ARM_GLOB_DAT:
+ case elfcpp::R_ARM_JUMP_SLOT:
+ case elfcpp::R_ARM_ABS32:
+ case elfcpp::R_ARM_PC24:
+ // FIXME: The following 3 types are not supported by Android's dynamic
+ // linker.
+ case elfcpp::R_ARM_TLS_DTPMOD32:
+ case elfcpp::R_ARM_TLS_DTPOFF32:
+ case elfcpp::R_ARM_TLS_TPOFF32:
+ return;
+
+ default:
+ // This prevents us from issuing more than one error per reloc
+ // section. But we can still wind up issuing more than one
+ // error per object file.
+ if (this->issued_non_pic_error_)
+ return;
+ object->error(_("requires unsupported dynamic reloc; "
+ "recompile with -fPIC"));
+ this->issued_non_pic_error_ = true;
+ return;
+
+ case elfcpp::R_ARM_NONE:
+ gold_unreachable();
+ }
+}
+
// Scan a relocation for a local symbol.
+// FIXME: This only handles a subset of relocation types used by Android
+// on ARM v5te devices.
template<bool big_endian>
inline void
Target_arm<big_endian>::Scan::local(const General_options&,
- Symbol_table* /* symtab */,
- Layout* /* layout */,
- Target_arm* /* target */,
+ Symbol_table* symtab,
+ Layout* layout,
+ Target_arm* target,
Sized_relobj<32, big_endian>* object,
- unsigned int /* data_shndx */,
- Output_section* /* output_section */,
- const elfcpp::Rel<32, big_endian>& /* reloc */,
+ unsigned int data_shndx,
+ Output_section* output_section,
+ const elfcpp::Rel<32, big_endian>& reloc,
unsigned int r_type,
const elfcpp::Sym<32, big_endian>&)
{
@@ -690,6 +767,77 @@ Target_arm<big_endian>::Scan::local(cons
case elfcpp::R_ARM_NONE:
break;
+ case elfcpp::R_ARM_ABS32:
+ // If building a shared library (or a position-independent
+ // executable), we need to create a dynamic relocation for
+ // this location. The relocation applied at link time will
+ // apply the link-time value, so we flag the location with
+ // an R_ARM_RELATIVE relocation so the dynamic loader can
+ // relocate it easily.
+ if (parameters->options().output_is_position_independent())
+ {
+ Reloc_section* rel_dyn = target->rel_dyn_section(layout);
+ unsigned int r_sym = elfcpp::elf_r_sym<32>(reloc.get_r_info());
+ // If we are to add more other reloc types than R_ARM_ABS32,
+ // we need to add check_non_pic(object, r_type) here.
+ rel_dyn->add_local_relative(object, r_sym, elfcpp::R_ARM_RELATIVE,
+ output_section, data_shndx,
+ reloc.get_r_offset());
+ }
+ break;
+
+ case elfcpp::R_ARM_REL32:
+ case elfcpp::R_ARM_THM_CALL:
+ case elfcpp::R_ARM_CALL:
+ case elfcpp::R_ARM_PREL31:
+ case elfcpp::R_ARM_JUMP24:
+ case elfcpp::R_ARM_PLT32:
+ break;
+
+ case elfcpp::R_ARM_GOTOFF32:
+ // We need a GOT section:
+ target->got_section(symtab, layout);
+ break;
+
+ case elfcpp::R_ARM_BASE_PREL:
+ // FIXME: What about this?
+ break;
+
+ case elfcpp::R_ARM_GOT_BREL:
+ {
+ // The symbol requires a GOT entry.
+ Output_data_got<32, big_endian>* got =
+ target->got_section(symtab, layout);
+ unsigned int r_sym = elfcpp::elf_r_sym<32>(reloc.get_r_info());
+ if (got->add_local(object, r_sym, GOT_TYPE_STANDARD))
+ {
+ // If we are generating a shared object, we need to add a
+ // dynamic RELATIVE relocation for this symbol's GOT entry.
+ if (parameters->options().output_is_position_independent())
+ {
+ Reloc_section* rel_dyn = target->rel_dyn_section(layout);
+ unsigned int r_sym = elfcpp::elf_r_sym<32>(reloc.get_r_info());
+ rel_dyn->add_local_relative(
+ object, r_sym, elfcpp::R_ARM_RELATIVE, got,
+ object->local_got_offset(r_sym, GOT_TYPE_STANDARD));
+ }
+ }
+ }
+ break;
+
+ case elfcpp::R_ARM_TARGET1:
+ // This should have been mapped to another type already.
+ // Fall through.
+ case elfcpp::R_ARM_COPY:
+ case elfcpp::R_ARM_GLOB_DAT:
+ case elfcpp::R_ARM_JUMP_SLOT:
+ case elfcpp::R_ARM_RELATIVE:
+ // These are relocations which should only be seen by the
+ // dynamic linker, and should never be seen here.
+ gold_error(_("%s: unexpected reloc %u in object file"),
+ object->name().c_str(), r_type);
+ break;
+
default:
unsupported_reloc_local(object, r_type);
break;
@@ -710,17 +858,19 @@ Target_arm<big_endian>::Scan::unsupporte
}
// Scan a relocation for a global symbol.
+// FIXME: This only handles a subset of relocation types used by Android
+// on ARM v5te devices.
template<bool big_endian>
inline void
Target_arm<big_endian>::Scan::global(const General_options&,
- Symbol_table* /* symtab */,
- Layout* /* layout */,
- Target_arm* /* target */,
+ Symbol_table* symtab,
+ Layout* layout,
+ Target_arm* target,
Sized_relobj<32, big_endian>* object,
- unsigned int /* data_shndx */,
- Output_section* /* output_section */,
- const elfcpp::Rel<32, big_endian>& /* reloc */,
+ unsigned int data_shndx,
+ Output_section* output_section,
+ const elfcpp::Rel<32, big_endian>& reloc,
unsigned int r_type,
Symbol* gsym)
{
@@ -730,6 +880,155 @@ Target_arm<big_endian>::Scan::global(con
case elfcpp::R_ARM_NONE:
break;
+ case elfcpp::R_ARM_ABS32:
+ {
+ // Make a dynamic relocation if necessary.
+ if (gsym->needs_dynamic_reloc(Symbol::ABSOLUTE_REF))
+ {
+ if (target->may_need_copy_reloc(gsym))
+ {
+ target->copy_reloc(symtab, layout, object,
+ data_shndx, output_section, gsym, reloc);
+ }
+ else if (gsym->can_use_relative_reloc(false))
+ {
+ // If we are to add more other reloc types than R_ARM_ABS32,
+ // we need to add check_non_pic(object, r_type) here.
+ Reloc_section* rel_dyn = target->rel_dyn_section(layout);
+ rel_dyn->add_global_relative(gsym, elfcpp::R_ARM_RELATIVE,
+ output_section, object,
+ data_shndx, reloc.get_r_offset());
+ }
+ else
+ {
+ // If we are to add more other reloc types than R_ARM_ABS32,
+ // we need to add check_non_pic(object, r_type) here.
+ Reloc_section* rel_dyn = target->rel_dyn_section(layout);
+ rel_dyn->add_global(gsym, r_type, output_section, object,
+ data_shndx, reloc.get_r_offset());
+ }
+ }
+ }
+ break;
+
+ case elfcpp::R_ARM_REL32:
+ case elfcpp::R_ARM_PREL31:
+ {
+ // Make a dynamic relocation if necessary.
+ int flags = Symbol::NON_PIC_REF;
+ if (gsym->needs_dynamic_reloc(flags))
+ {
+ if (target->may_need_copy_reloc(gsym))
+ {
+ target->copy_reloc(symtab, layout, object,
+ data_shndx, output_section, gsym, reloc);
+ }
+ else
+ {
+ check_non_pic(object, r_type);
+ Reloc_section* rel_dyn = target->rel_dyn_section(layout);
+ rel_dyn->add_global(gsym, r_type, output_section, object,
+ data_shndx, reloc.get_r_offset());
+ }
+ }
+ }
+ break;
+
+ case elfcpp::R_ARM_JUMP24:
+ case elfcpp::R_ARM_THM_CALL:
+ case elfcpp::R_ARM_CALL:
+ {
+ if (Target_arm<big_endian>::Scan::symbol_needs_plt_entry(gsym))
+ target->make_plt_entry(symtab, layout, gsym);
+ // Make a dynamic relocation if necessary.
+ int flags = Symbol::NON_PIC_REF;
+ if (gsym->type() == elfcpp::STT_FUNC
+ | gsym->type() == elfcpp::STT_ARM_TFUNC)
+ flags |= Symbol::FUNCTION_CALL;
+ if (gsym->needs_dynamic_reloc(flags))
+ {
+ if (target->may_need_copy_reloc(gsym))
+ {
+ target->copy_reloc(symtab, layout, object,
+ data_shndx, output_section, gsym,
+ reloc);
+ }
+ else
+ {
+ check_non_pic(object, r_type);
+ Reloc_section* rel_dyn = target->rel_dyn_section(layout);
+ rel_dyn->add_global(gsym, r_type, output_section, object,
+ data_shndx, reloc.get_r_offset());
+ }
+ }
+ }
+ break;
+
+ case elfcpp::R_ARM_PLT32:
+ // If the symbol is fully resolved, this is just a relative
+ // local reloc. Otherwise we need a PLT entry.
+ if (gsym->final_value_is_known())
+ break;
+ // If building a shared library, we can also skip the PLT entry
+ // if the symbol is defined in the output file and is protected
+ // or hidden.
+ if (gsym->is_defined()
+ && !gsym->is_from_dynobj()
+ && !gsym->is_preemptible())
+ break;
+ target->make_plt_entry(symtab, layout, gsym);
+ break;
+
+ case elfcpp::R_ARM_GOTOFF32:
+ // We need a GOT section.
+ target->got_section(symtab, layout);
+ break;
+
+ case elfcpp::R_ARM_BASE_PREL:
+ // FIXME: What about this?
+ break;
+
+ case elfcpp::R_ARM_GOT_BREL:
+ {
+ // The symbol requires a GOT entry.
+ Output_data_got<32, big_endian>* got =
+ target->got_section(symtab, layout);
+ if (gsym->final_value_is_known())
+ got->add_global(gsym, GOT_TYPE_STANDARD);
+ else
+ {
+ // If this symbol is not fully resolved, we need to add a
+ // GOT entry with a dynamic relocation.
+ Reloc_section* rel_dyn = target->rel_dyn_section(layout);
+ if (gsym->is_from_dynobj()
+ || gsym->is_undefined()
+ || gsym->is_preemptible())
+ got->add_global_with_rel(gsym, GOT_TYPE_STANDARD,
+ rel_dyn, elfcpp::R_ARM_GLOB_DAT);
+ else
+ {
+ if (got->add_global(gsym, GOT_TYPE_STANDARD))
+ rel_dyn->add_global_relative(
+ gsym, elfcpp::R_ARM_RELATIVE, got,
+ gsym->got_offset(GOT_TYPE_STANDARD));
+ }
+ }
+ }
+ break;
+
+ case elfcpp::R_ARM_TARGET1:
+ // This should have been mapped to another type already.
+ // Fall through.
+ case elfcpp::R_ARM_COPY:
+ case elfcpp::R_ARM_GLOB_DAT:
+ case elfcpp::R_ARM_JUMP_SLOT:
+ case elfcpp::R_ARM_RELATIVE:
+ // These are relocations which should only be seen by the
+ // dynamic linker, and should never be seen here.
+ gold_error(_("%s: unexpected reloc %u in object file"),
+ object->name().c_str(), r_type);
+ break;
+
default:
unsupported_reloc_global(object, r_type, gsym);
break;
@@ -855,6 +1154,46 @@ Target_arm<big_endian>::do_finalize_sect
this->copy_relocs_.emit(this->rel_dyn_section(layout));
}
+// Return whether a direct absolute static relocation needs to be applied.
+// In cases where Scan::local() or Scan::global() has created
+// a dynamic relocation other than R_ARM_RELATIVE, the addend
+// of the relocation is carried in the data, and we must not
+// apply the static relocation.
+
+template<bool big_endian>
+inline bool
+Target_arm<big_endian>::Relocate::should_apply_static_reloc(
+ const Sized_symbol<32>* gsym,
+ int ref_flags,
+ bool is_32bit,
+ Output_section* output_section)
+{
+ // If the output section is not allocated, then we didn't call
+ // scan_relocs, we didn't create a dynamic reloc, and we must apply
+ // the reloc here.
+ if ((output_section->flags() & elfcpp::SHF_ALLOC) == 0)
+ return true;
+
+ // For local symbols, we will have created a non-RELATIVE dynamic
+ // relocation only if (a) the output is position independent,
+ // (b) the relocation is absolute (not pc- or segment-relative), and
+ // (c) the relocation is not 32 bits wide.
+ if (gsym == NULL)
+ return !(parameters->options().output_is_position_independent()
+ && (ref_flags & Symbol::ABSOLUTE_REF)
+ && !is_32bit);
+
+ // For global symbols, we use the same helper routines used in the
+ // scan pass. If we did not create a dynamic relocation, or if we
+ // created a RELATIVE dynamic relocation, we should apply the static
+ // relocation.
+ bool has_dyn = gsym->needs_dynamic_reloc(ref_flags);
+ bool is_rel = (ref_flags & Symbol::ABSOLUTE_REF)
+ && gsym->can_use_relative_reloc(ref_flags
+ & Symbol::FUNCTION_CALL);
+ return !has_dyn || is_rel;
+}
+
// Perform a relocation.
template<bool big_endian>
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