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Taking an undefined function's address in an executable
- From: Alan Modra <amodra at gmail dot com>
- To: binutils at sourceware dot org
- Date: Wed, 2 Jul 2014 18:15:28 +0930
- Subject: Taking an undefined function's address in an executable
- Authentication-results: sourceware.org; auth=none
doesn't always mean you need to define a function symbol on plt code.
If all references are in read-write sections, then using dynamic relocs
is OK. This is seen in powerpc64 ELFv2 crti.o where the address of
__gmon_start__ is taken in a .toc section to test whether a weak
__gmon_start__ is defined. Most other targets would implement this
sort of PIC test by arranging for the address to be in the GOT..
bfd/
* elf32-ppc.c (ppc_elf_adjust_dynamic_symbol): Clear
pointer_equality_needed when !readonly_dynrelocs.
* elf64-ppc.c (ppc64_elf_adjust_dynamic_symbol): Likewise.
ld/testsuite/
* ld-powerpc/ambiguousv1.d: Match symbol table too.
* ld-powerpc/ambiguousv2.d: Likewise.
* ld-powerpc/ambiguousv1b.d: New.
* ld-powerpc/ambiguousv2b.d: New.
* ld-powerpc/powerpc.exp: Run new tests.
diff --git a/bfd/elf32-ppc.c b/bfd/elf32-ppc.c
index 0a9c8f9..e20e804 100644
--- a/bfd/elf32-ppc.c
+++ b/bfd/elf32-ppc.c
@@ -5506,9 +5506,21 @@ ppc_elf_adjust_dynamic_symbol (struct bfd_link_info *info,
will go to this object, or will remain undefined. */
h->plt.plist = NULL;
h->needs_plt = 0;
+ h->pointer_equality_needed = 0;
}
else
{
+ /* Taking a function's address in a read/write section
+ doesn't require us to define the function symbol in the
+ executable on a global entry stub. A dynamic reloc can
+ be used instead. */
+ if (h->pointer_equality_needed
+ && !readonly_dynrelocs (h))
+ {
+ h->pointer_equality_needed = 0;
+ h->non_got_ref = 0;
+ }
+
/* After adjust_dynamic_symbol, non_got_ref set in the
non-shared case means that we have allocated space in
.dynbss for the symbol and thus dyn_relocs for this
@@ -5518,12 +5530,12 @@ ppc_elf_adjust_dynamic_symbol (struct bfd_link_info *info,
relocations against this symbol to the PLT entry. Allow
dynamic relocs if the reference is weak, and the dynamic
relocs will not cause text relocation. */
- if (!h->ref_regular_nonweak
- && h->non_got_ref
- && h->type != STT_GNU_IFUNC
- && !htab->is_vxworks
- && !ppc_elf_hash_entry (h)->has_sda_refs
- && !readonly_dynrelocs (h))
+ else if (!h->ref_regular_nonweak
+ && h->non_got_ref
+ && h->type != STT_GNU_IFUNC
+ && !htab->is_vxworks
+ && !ppc_elf_hash_entry (h)->has_sda_refs
+ && !readonly_dynrelocs (h))
h->non_got_ref = 0;
}
return TRUE;
diff --git a/bfd/elf64-ppc.c b/bfd/elf64-ppc.c
index 81e54a7..0efc602 100644
--- a/bfd/elf64-ppc.c
+++ b/bfd/elf64-ppc.c
@@ -6993,9 +6993,21 @@ ppc64_elf_adjust_dynamic_symbol (struct bfd_link_info *info,
{
h->plt.plist = NULL;
h->needs_plt = 0;
+ h->pointer_equality_needed = 0;
}
else if (abiversion (info->output_bfd) == 2)
{
+ /* Taking a function's address in a read/write section
+ doesn't require us to define the function symbol in the
+ executable on a global entry stub. A dynamic reloc can
+ be used instead. */
+ if (h->pointer_equality_needed
+ && !readonly_dynrelocs (h))
+ {
+ h->pointer_equality_needed = 0;
+ h->non_got_ref = 0;
+ }
+
/* After adjust_dynamic_symbol, non_got_ref set in the
non-shared case means that we have allocated space in
.dynbss for the symbol and thus dyn_relocs for this
@@ -7005,10 +7017,10 @@ ppc64_elf_adjust_dynamic_symbol (struct bfd_link_info *info,
relocations against this symbol to the PLT entry. Allow
dynamic relocs if the reference is weak, and the dynamic
relocs will not cause text relocation. */
- if (!h->ref_regular_nonweak
- && h->non_got_ref
- && h->type != STT_GNU_IFUNC
- && !readonly_dynrelocs (h))
+ else if (!h->ref_regular_nonweak
+ && h->non_got_ref
+ && h->type != STT_GNU_IFUNC
+ && !readonly_dynrelocs (h))
h->non_got_ref = 0;
/* If making a plt entry, then we don't need copy relocs. */
diff --git a/ld/testsuite/ld-powerpc/ambiguousv1.d b/ld/testsuite/ld-powerpc/ambiguousv1.d
index 73beab9..458c554 100644
--- a/ld/testsuite/ld-powerpc/ambiguousv1.d
+++ b/ld/testsuite/ld-powerpc/ambiguousv1.d
@@ -1,12 +1,44 @@
#source: startv1.s
#source: funref.s
#as: -a64
-#ld: -melf64ppc
+#ld: -melf64ppc --emit-stub-syms
#ld_after_inputfiles: tmpdir/funv1.so
-#readelf: -r --wide
-# check that we do the right thing with funref.s that doesn't have
-# anything to mark it as ELFv1 or ELFv2
+#readelf: -rs --wide
+# Check that we do the right thing with funref.s that doesn't have
+# anything to mark it as ELFv1 or ELFv2. We should get a dynamic
+# reloc on the function address, and my_func should be undefined
+# dynamic with value zero.
Relocation section .* contains 1 entries:
.*
.* R_PPC64_ADDR64 +0+ my_func \+ 0
+
+Symbol table '\.dynsym' contains 5 entries:
+.*
+ 0: .*
+ 1: 0+00000000 0 FUNC GLOBAL DEFAULT UND my_func
+ 2: 0+10010390 0 NOTYPE GLOBAL DEFAULT 11 __bss_start
+ 3: 0+10010390 0 NOTYPE GLOBAL DEFAULT 11 _edata
+ 4: 0+10010390 0 NOTYPE GLOBAL DEFAULT 11 _end
+
+Symbol table '\.symtab' contains 19 entries:
+ Num: Value Size Type Bind Vis Ndx Name
+ 0: .*
+ 1: 0+10000158 0 SECTION LOCAL DEFAULT 1
+ 2: 0+10000170 0 SECTION LOCAL DEFAULT 2
+ 3: 0+10000198 0 SECTION LOCAL DEFAULT 3
+ 4: 0+10000210 0 SECTION LOCAL DEFAULT 4
+ 5: 0+10000248 0 SECTION LOCAL DEFAULT 5
+ 6: 0+10000260 0 SECTION LOCAL DEFAULT 6
+ 7: 0+10000264 0 SECTION LOCAL DEFAULT 7
+ 8: 0+10010268 0 SECTION LOCAL DEFAULT 8
+ 9: 0+10010368 0 SECTION LOCAL DEFAULT 9
+ 10: 0+10010370 0 SECTION LOCAL DEFAULT 10
+ 11: 0+10010388 0 SECTION LOCAL DEFAULT 11
+ 12: 0+10010268 0 OBJECT LOCAL DEFAULT 8 _DYNAMIC
+ 13: 0+10010368 0 NOTYPE GLOBAL DEFAULT 9 func_tab
+ 14: 0+00000000 0 FUNC GLOBAL DEFAULT UND my_func
+ 15: 0+10010370 0 FUNC GLOBAL DEFAULT 10 _start
+ 16: 0+10010390 0 NOTYPE GLOBAL DEFAULT 11 __bss_start
+ 17: 0+10010390 0 NOTYPE GLOBAL DEFAULT 11 _edata
+ 18: 0+10010390 0 NOTYPE GLOBAL DEFAULT 11 _end
diff --git a/ld/testsuite/ld-powerpc/ambiguousv1b.d b/ld/testsuite/ld-powerpc/ambiguousv1b.d
new file mode 100644
index 0000000..69bee95
--- /dev/null
+++ b/ld/testsuite/ld-powerpc/ambiguousv1b.d
@@ -0,0 +1,45 @@
+#source: startv1.s
+#source: funref2.s
+#as: -a64
+#ld: -melf64ppc --emit-stub-syms
+#ld_after_inputfiles: tmpdir/funv1.so
+#readelf: -rs --wide
+# Check that we do the right thing with funref2.s that doesn't have
+# anything to mark it as ELFv1 or ELFv2. Since my_func address is
+# taken in a read-only section we should get a copy reloc for the OPD
+# entry.
+
+Relocation section .* contains 1 entries:
+.*
+.* R_PPC64_COPY .* my_func \+ 0
+
+Symbol table '\.dynsym' contains 5 entries:
+.*
+ 0: .*
+ 1: 0+10010390 4 FUNC GLOBAL DEFAULT 12 my_func
+ 2: 0+10010390 0 NOTYPE GLOBAL DEFAULT 12 __bss_start
+ 3: 0+10010390 0 NOTYPE GLOBAL DEFAULT 11 _edata
+ 4: 0+10010398 0 NOTYPE GLOBAL DEFAULT 12 _end
+
+Symbol table '\.symtab' contains 20 entries:
+.*
+ 0: .*
+ 1: 0+10000158 0 SECTION LOCAL DEFAULT 1
+ 2: 0+10000170 0 SECTION LOCAL DEFAULT 2
+ 3: 0+10000198 0 SECTION LOCAL DEFAULT 3
+ 4: 0+10000210 0 SECTION LOCAL DEFAULT 4
+ 5: 0+10000248 0 SECTION LOCAL DEFAULT 5
+ 6: 0+10000260 0 SECTION LOCAL DEFAULT 6
+ 7: 0+10000264 0 SECTION LOCAL DEFAULT 7
+ 8: 0+1000026c 0 SECTION LOCAL DEFAULT 8
+ 9: 0+10010270 0 SECTION LOCAL DEFAULT 9
+ 10: 0+10010370 0 SECTION LOCAL DEFAULT 10
+ 11: 0+10010388 0 SECTION LOCAL DEFAULT 11
+ 12: 0+10010390 0 SECTION LOCAL DEFAULT 12
+ 13: 0+10010270 0 OBJECT LOCAL DEFAULT 9 _DYNAMIC
+ 14: 0+10000264 0 NOTYPE GLOBAL DEFAULT 7 func_tab
+ 15: 0+10010390 4 FUNC GLOBAL DEFAULT 12 my_func
+ 16: 0+10010370 0 FUNC GLOBAL DEFAULT 10 _start
+ 17: 0+10010390 0 NOTYPE GLOBAL DEFAULT 12 __bss_start
+ 18: 0+10010390 0 NOTYPE GLOBAL DEFAULT 11 _edata
+ 19: 0+10010398 0 NOTYPE GLOBAL DEFAULT 12 _end
diff --git a/ld/testsuite/ld-powerpc/ambiguousv2.d b/ld/testsuite/ld-powerpc/ambiguousv2.d
index 5cf047b..cfa5cb4 100644
--- a/ld/testsuite/ld-powerpc/ambiguousv2.d
+++ b/ld/testsuite/ld-powerpc/ambiguousv2.d
@@ -1,12 +1,51 @@
#source: startv2.s
#source: funref.s
#as: -a64
-#ld: -melf64ppc
+#ld: -melf64ppc --emit-stub-syms
#ld_after_inputfiles: tmpdir/funv2.so
-#readelf: -r --wide
-# check that we do the right thing with funref.s that doesn't have
-# anything to mark it as ELFv1 or ELFv2
+#readelf: -rs --wide
+# Check that we do the right thing with funref.s that doesn't have
+# anything to mark it as ELFv1 or ELFv2. We should get a dynamic
+# reloc on the function address, not have a global entry stub, and
+# my_func should be undefined dynamic with value zero.
+# FIXME someday: No need for a plt entry.
-Relocation section .*contains 1 entries:
+Relocation section .* contains 1 entries:
+.*
+.* R_PPC64_ADDR64 .* my_func \+ 0
+
+Relocation section .* contains 1 entries:
.*
.* R_PPC64_JMP_SLOT .* my_func \+ 0
+
+Symbol table '\.dynsym' contains 5 entries:
+.*
+ 0: .*
+ 1: 0+00000000 0 FUNC GLOBAL DEFAULT UND my_func
+ 2: 0+10010438 0 NOTYPE GLOBAL DEFAULT 12 __bss_start
+ 3: 0+10010438 0 NOTYPE GLOBAL DEFAULT 11 _edata
+ 4: 0+10010450 0 NOTYPE GLOBAL DEFAULT 12 _end
+
+Symbol table '\.symtab' contains 21 entries:
+.*
+ 0: .*
+ 1: 0+10000158 0 SECTION LOCAL DEFAULT 1
+ 2: 0+10000170 0 SECTION LOCAL DEFAULT 2
+ 3: 0+10000198 0 SECTION LOCAL DEFAULT 3
+ 4: 0+10000210 0 SECTION LOCAL DEFAULT 4
+ 5: 0+10000248 0 SECTION LOCAL DEFAULT 5
+ 6: 0+10000260 0 SECTION LOCAL DEFAULT 6
+ 7: 0+10000278 0 SECTION LOCAL DEFAULT 7
+ 8: 0+100002c4 0 SECTION LOCAL DEFAULT 8
+ 9: 0+100102c8 0 SECTION LOCAL DEFAULT 9
+ 10: 0+10010428 0 SECTION LOCAL DEFAULT 10
+ 11: 0+10010430 0 SECTION LOCAL DEFAULT 11
+ 12: 0+10010438 0 SECTION LOCAL DEFAULT 12
+ 13: 0+100102c8 0 OBJECT LOCAL DEFAULT 9 _DYNAMIC
+ 14: 0+10000288 0 NOTYPE LOCAL DEFAULT 7 __glink_PLTresolve
+ 15: 0+10010428 0 NOTYPE GLOBAL DEFAULT 10 func_tab
+ 16: 0+00000000 0 FUNC GLOBAL DEFAULT UND my_func
+ 17: 0+10000278 0 NOTYPE GLOBAL DEFAULT 7 _start
+ 18: 0+10010438 0 NOTYPE GLOBAL DEFAULT 12 __bss_start
+ 19: 0+10010438 0 NOTYPE GLOBAL DEFAULT 11 _edata
+ 20: 0+10010450 0 NOTYPE GLOBAL DEFAULT 12 _end
diff --git a/ld/testsuite/ld-powerpc/ambiguousv2b.d b/ld/testsuite/ld-powerpc/ambiguousv2b.d
new file mode 100644
index 0000000..a95faa7
--- /dev/null
+++ b/ld/testsuite/ld-powerpc/ambiguousv2b.d
@@ -0,0 +1,47 @@
+#source: startv2.s
+#source: funref2.s
+#as: -a64
+#ld: -melf64ppc --emit-stub-syms
+#ld_after_inputfiles: tmpdir/funv2.so
+#readelf: -rs --wide
+# Check that we do the right thing with funref2.s that doesn't have
+# anything to mark it as ELFv1 or ELFv2. Since my_func address is
+# taken in a read-only section we should get a plt entry, a global
+# entry stub, and my_func should be undefined dynamic with non-zero
+# value.
+
+Relocation section .* contains 1 entries:
+.*
+.* R_PPC64_JMP_SLOT .* my_func \+ 0
+
+Symbol table '\.dynsym' contains 5 entries:
+.*
+ 0: .*
+ 1: 0+100002b8 0 FUNC GLOBAL DEFAULT UND my_func
+ 2: 0+10010408 0 NOTYPE GLOBAL DEFAULT 11 __bss_start
+ 3: 0+10010408 0 NOTYPE GLOBAL DEFAULT 10 _edata
+ 4: 0+10010420 0 NOTYPE GLOBAL DEFAULT 11 _end
+
+Symbol table '\.symtab' contains 21 entries:
+.*
+ 0: .*
+ 1: 0+10000158 0 SECTION LOCAL DEFAULT 1
+ 2: 0+10000170 0 SECTION LOCAL DEFAULT 2
+ 3: 0+10000198 0 SECTION LOCAL DEFAULT 3
+ 4: 0+10000210 0 SECTION LOCAL DEFAULT 4
+ 5: 0+10000248 0 SECTION LOCAL DEFAULT 5
+ 6: 0+10000260 0 SECTION LOCAL DEFAULT 6
+ 7: 0+100002c8 0 SECTION LOCAL DEFAULT 7
+ 8: 0+100002d0 0 SECTION LOCAL DEFAULT 8
+ 9: 0+100102d0 0 SECTION LOCAL DEFAULT 9
+ 10: 0+10010400 0 SECTION LOCAL DEFAULT 10
+ 11: 0+10010408 0 SECTION LOCAL DEFAULT 11
+ 12: 0+100102d0 0 OBJECT LOCAL DEFAULT 9 _DYNAMIC
+ 13: 0+100002b8 0 NOTYPE LOCAL DEFAULT 6 00000011\.global_entry\.my_func
+ 14: 0+10000270 0 NOTYPE LOCAL DEFAULT 6 __glink_PLTresolve
+ 15: 0+100002c8 0 NOTYPE GLOBAL DEFAULT 7 func_tab
+ 16: 0+100002b8 0 FUNC GLOBAL DEFAULT UND my_func
+ 17: 0+10000260 0 NOTYPE GLOBAL DEFAULT 6 _start
+ 18: 0+10010408 0 NOTYPE GLOBAL DEFAULT 11 __bss_start
+ 19: 0+10010408 0 NOTYPE GLOBAL DEFAULT 10 _edata
+ 20: 0+10010420 0 NOTYPE GLOBAL DEFAULT 11 _end
diff --git a/ld/testsuite/ld-powerpc/funref2.s b/ld/testsuite/ld-powerpc/funref2.s
new file mode 100644
index 0000000..a2bf949
--- /dev/null
+++ b/ld/testsuite/ld-powerpc/funref2.s
@@ -0,0 +1,4 @@
+ .section .rodata,"a",@progbits
+ .globl func_tab
+func_tab:
+ .dc.a my_func
diff --git a/ld/testsuite/ld-powerpc/powerpc.exp b/ld/testsuite/ld-powerpc/powerpc.exp
index 1eaedaa..08a7e2b 100644
--- a/ld/testsuite/ld-powerpc/powerpc.exp
+++ b/ld/testsuite/ld-powerpc/powerpc.exp
@@ -275,7 +275,9 @@ if [ supports_ppc64 ] then {
run_dump_test "elfv2-2so"
run_dump_test "elfv2-2exe"
run_dump_test "ambiguousv1"
+ run_dump_test "ambiguousv1b"
run_dump_test "ambiguousv2"
+ run_dump_test "ambiguousv2b"
}
if { [istarget "powerpc*-eabi*"] } {
--
Alan Modra
Australia Development Lab, IBM