PR25384, PowerPC64 ELFv1 copy relocs against function symbols

Function symbols of course don't normally want .dynbss copies but
with some old versions of gcc they are needed to copy the function
descriptor.  This patch restricts the cases where they are useful to
compilers using dot-symbols, and enables the warning regardless of
whether a PLT entry is emitted in the executable.  PLTs in shared
libraries are affected by a .dynbss copy in the executable.

bfd/
	PR 25384
	* elf64-ppc.c (ELIMINATE_COPY_RELOCS): Update comment.
	(ppc64_elf_adjust_dynamic_symbol): Don't allow .dynbss copies
	of function symbols unless dot symbols are present.  Do warn
	whenever one is created, regardles of whether a PLT entry is
	also emitted for the function symbol.
ld/
	* testsuite/ld-powerpc/ambiguousv1b.d: Adjust expected output.
	* testsuite/ld-powerpc/funref.s: Align func_tab.
	* testsuite/ld-powerpc/funref2.s: Likewise.
	* testsuite/ld-powerpc/funv1.s: Add dot symbols.

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 75099e91b223bea037f33225bc9ae66616e07331..21f6769ba4637bb578959c2680f4f2dea2404f70 100644 (file)
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,12 @@
+2020-01-15  Alan Modra  <amodra@gmail.com>
+
+       PR 25384
+       * elf64-ppc.c (ELIMINATE_COPY_RELOCS): Update comment.
+       (ppc64_elf_adjust_dynamic_symbol): Don't allow .dynbss copies
+       of function symbols unless dot symbols are present.  Do warn
+       whenever one is created, regardles of whether a PLT entry is
+       also emitted for the function symbol.
+
 2020-01-14  Alan Modra  <amodra@gmail.com>
 
        * som.c (som_bfd_count_ar_symbols): Error when file position

diff --git a/bfd/elf64-ppc.c b/bfd/elf64-ppc.c
index a451c4753ac9eb7e87ee5dda960081f384c8e998..8319a21940880020a543c7d40439b24418fd6b85 100644 (file)
--- a/bfd/elf64-ppc.c
+++ b/bfd/elf64-ppc.c
@@ -2788,20 +2788,20 @@ must_be_dyn_reloc (struct bfd_link_info *info,
 }
 
 /* If ELIMINATE_COPY_RELOCS is non-zero, the linker will try to avoid
-   copying dynamic variables from a shared lib into an app's dynbss
+   copying dynamic variables from a shared lib into an app's .dynbss
    section, and instead use a dynamic relocation to point into the
-   shared lib.  With code that gcc generates, it's vital that this be
-   enabled;  In the PowerPC64 ABI, the address of a function is actually
-   the address of a function descriptor, which resides in the .opd
-   section.  gcc uses the descriptor directly rather than going via the
-   GOT as some other ABI's do, which means that initialized function
-   pointers must reference the descriptor.  Thus, a function pointer
-   initialized to the address of a function in a shared library will
-   either require a copy reloc, or a dynamic reloc.  Using a copy reloc
-   redefines the function descriptor symbol to point to the copy.  This
-   presents a problem as a plt entry for that function is also
-   initialized from the function descriptor symbol and the copy reloc
-   may not be initialized first.  */
+   shared lib.  With code that gcc generates it is vital that this be
+   enabled;  In the PowerPC64 ELFv1 ABI the address of a function is
+   actually the address of a function descriptor which resides in the
+   .opd section.  gcc uses the descriptor directly rather than going
+   via the GOT as some other ABIs do, which means that initialized
+   function pointers reference the descriptor.  Thus, a function
+   pointer initialized to the address of a function in a shared
+   library will either require a .dynbss copy and a copy reloc, or a
+   dynamic reloc.  Using a .dynbss copy redefines the function
+   descriptor symbol to point to the copy.  This presents a problem as
+   a PLT entry for that function is also initialized from the function
+   descriptor symbol and the copy may not be initialized first.  */
 #define ELIMINATE_COPY_RELOCS 1
 
 /* Section name for stubs is the associated section name plus this
@@ -6462,13 +6462,23 @@ ppc64_elf_adjust_dynamic_symbol (struct bfd_link_info *info,
       || h->protected_def)
     return TRUE;
 
-  if (h->plt.plist != NULL)
+  if (h->type == STT_FUNC
+      || h->type == STT_GNU_IFUNC)
     {
-      /* We should never get here, but unfortunately there are versions
-        of gcc out there that improperly (for this ABI) put initialized
-        function pointers, vtable refs and suchlike in read-only
-        sections.  Allow them to proceed, but warn that this might
-        break at runtime.  */
+      /* .dynbss copies of function symbols only work if we have
+        ELFv1 dot-symbols.  ELFv1 compilers since 2004 default to not
+        use dot-symbols and set the function symbol size to the text
+        size of the function rather than the size of the descriptor.
+        That's wrong for copying a descriptor.  */
+      if (((struct ppc_link_hash_entry *) h)->oh == NULL
+         || !(h->size == 24 || h->size == 16))
+       return TRUE;
+
+      /* We should never get here, but unfortunately there are old
+        versions of gcc (circa gcc-3.2) that improperly for the
+        ELFv1 ABI put initialized function pointers, vtable refs and
+        suchlike in read-only sections.  Allow them to proceed, but
+        warn that this might break at runtime.  */
       info->callbacks->einfo
        (_("%P: copy reloc against `%pT' requires lazy plt linking; "
           "avoid setting LD_BIND_NOW=1 or upgrade gcc\n"),

diff --git a/ld/ChangeLog b/ld/ChangeLog
index ee68a8c26d92ada267508ac2179220a994555b54..c68d92038c05527fe96b02081bca28103fbfaaa3 100644 (file)
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,10 @@
+2020-01-15  Alan Modra  <amodra@gmail.com>
+
+       * testsuite/ld-powerpc/ambiguousv1b.d: Adjust expected output.
+       * testsuite/ld-powerpc/funref.s: Align func_tab.
+       * testsuite/ld-powerpc/funref2.s: Likewise.
+       * testsuite/ld-powerpc/funv1.s: Add dot symbols.
+
 2020-01-14  Lili Cui <lili.cui@intel.com>
 
        * testsuite/ld-i386/align-branch-1.d: Updated for i686-pc-elf.

diff --git a/ld/testsuite/ld-powerpc/ambiguousv1b.d b/ld/testsuite/ld-powerpc/ambiguousv1b.d
index 9be1371e5ec9544b3028270a4f9963d67ca02987..205f7ea46f38f18d24992d285b9b68ab7fd20533 100644 (file)
--- a/ld/testsuite/ld-powerpc/ambiguousv1b.d
+++ b/ld/testsuite/ld-powerpc/ambiguousv1b.d
@@ -3,6 +3,7 @@
 #as: -a64
 #ld: -melf64ppc --emit-stub-syms
 #ld_after_inputfiles: tmpdir/funv1.so
+#warning: .*requires lazy plt linking.*
 #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
@@ -15,9 +16,9 @@ Relocation section .* contains 1 entry:
 
 Symbol table '\.dynsym' contains 2 entries:
 #...
-.*: 0*[1-9a-f][0-9a-f]*     4 FUNC    GLOBAL DEFAULT   1[23] my_func
+.*: 0*[1-9a-f][0-9a-f]* +24 FUNC +GLOBAL DEFAULT +1[23] my_func
 #...
 Symbol table '\.symtab' contains .* entries:
 #...
-.*: 0*[1-9a-f][0-9a-f]*     4 FUNC    GLOBAL DEFAULT   1[23] my_func
+.*: 0*[1-9a-f][0-9a-f]* +24 FUNC +GLOBAL DEFAULT +1[23] my_func
 #pass

diff --git a/ld/testsuite/ld-powerpc/funref.s b/ld/testsuite/ld-powerpc/funref.s
index 3f7de479ce5e00c65da2a9b68b9ca4c5ba63251d..27c1bcf6b1b4ec7605f28899b418877827a8fb4f 100644 (file)
--- a/ld/testsuite/ld-powerpc/funref.s
+++ b/ld/testsuite/ld-powerpc/funref.s
@@ -1,4 +1,5 @@
  .data
  .globl func_tab
+ .p2align 3
 func_tab:
  .dc.a my_func

diff --git a/ld/testsuite/ld-powerpc/funref2.s b/ld/testsuite/ld-powerpc/funref2.s
index a2bf9491264eeda9416f0df3eda05d5d413dda07..14c58f0123d7de8d5da8abf35434dab2dff2114f 100644 (file)
--- a/ld/testsuite/ld-powerpc/funref2.s
+++ b/ld/testsuite/ld-powerpc/funref2.s
@@ -1,4 +1,5 @@
  .section .rodata,"a",@progbits
  .globl func_tab
+ .p2align 3
 func_tab:
  .dc.a my_func

diff --git a/ld/testsuite/ld-powerpc/funv1.s b/ld/testsuite/ld-powerpc/funv1.s
index e79009d1d2110fc3c05531fda1f7ad606f8190c1..988ad0d8c14e8f09d45eaac897238149f24c2b69 100644 (file)
--- a/ld/testsuite/ld-powerpc/funv1.s
+++ b/ld/testsuite/ld-powerpc/funv1.s
@@ -1,10 +1,12 @@
- .globl my_func
- .type my_func,@function
- .section .opd,"aw",@progbits
+# old style ELFv1, with dot-symbols
+ .globl my_func, .my_func
+ .type .my_func, @function
+ .section .opd, "aw", @progbits
 my_func:
- .quad .Lmy_func, .TOC.@tocbase
+ .quad .my_func, .TOC.@tocbase, 0
+ .size my_func, . - my_func
 
  .text
-.Lmy_func:
+.my_func:
  blr
- .size my_func,.-.Lmy_func
+ .size .my_func, . - .my_func