aarch64: set sh_entsize of .plt to 0

On aarch64 the first PLT entry is 32 bytes, subsequent entries
are 16 bytes by default but can be 24 bytes with BTI or with
PAC-PLT.

sh_entsize of .plt was set to the PLT entry size, so in some
cases sh_size % sh_entsize != 0, which breaks some tools.

Note that PLT0 (and the TLSDESC stub code which is also in the
PLT) were historically not padded up to meet the sh_size
requirement, but to ensure that PLT stub code is aligned on
cache lines. Similar layout is present on other targets too
which just happens to make sh_size a multiple of sh_entsize and
it is not expected that sh_entsize of .plt is used for anything.

This patch sets sh_entsize of .plt to 0: the section does not
hold a table of fixed-size entries so other values are not
conforming in principle to the ELF spec.

bfd/ChangeLog:

	PR ld/26312
	* elfnn-aarch64.c (elfNN_aarch64_init_small_plt0_entry): Set sh_entsize
	to 0.
	(elfNN_aarch64_finish_dynamic_sections): Remove sh_entsize setting.

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 264e15a1fe5e2be9d7face0414554e28f0796381..e507a9d6c0f0ff32426427646f9ca73b5e403401 100644 (file)
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,10 @@
+2020-07-30  Szabolcs Nagy  <szabolcs.nagy@arm.com>
+
+       PR ld/26312
+       * elfnn-aarch64.c (elfNN_aarch64_init_small_plt0_entry): Set sh_entsize
+       to 0.
+       (elfNN_aarch64_finish_dynamic_sections): Remove sh_entsize setting.
+
 2020-07-30  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
 
        * bfd.m4 (BFD_SYS_PROCFS_H): New macro.

diff --git a/bfd/elfnn-aarch64.c b/bfd/elfnn-aarch64.c
index 2c88f288c3ac3b4f857fb4c8e07dde68b23e042b..a1c888722786b955b32fed490d56ab526173f215 100644 (file)
--- a/bfd/elfnn-aarch64.c
+++ b/bfd/elfnn-aarch64.c
@@ -9509,8 +9509,11 @@ elfNN_aarch64_init_small_plt0_entry (bfd *output_bfd ATTRIBUTE_UNUSED,
 
   memcpy (htab->root.splt->contents, htab->plt0_entry,
          htab->plt_header_size);
-  elf_section_data (htab->root.splt->output_section)->this_hdr.sh_entsize =
-    htab->plt_header_size;
+
+  /* PR 26312: Explicitly set the sh_entsize to 0 so that
+     consumers do not think that the section contains fixed
+     sized objects.  */
+  elf_section_data (htab->root.splt->output_section)->this_hdr.sh_entsize = 0;
 
   plt_got_2nd_ent = (htab->root.sgotplt->output_section->vma
                  + htab->root.sgotplt->output_offset
@@ -9612,10 +9615,6 @@ elfNN_aarch64_finish_dynamic_sections (bfd *output_bfd,
     {
       elfNN_aarch64_init_small_plt0_entry (output_bfd, htab);
 
-      elf_section_data (htab->root.splt->output_section)->
-       this_hdr.sh_entsize = htab->plt_entry_size;
-
-
       if (htab->root.tlsdesc_plt && !(info->flags & DF_BIND_NOW))
        {
          BFD_ASSERT (htab->root.tlsdesc_got != (bfd_vma)-1);