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[ARM-FDPIC 05/12] [ARM] Implement PLT for FDPIC.
- From: Christophe Lyon <christophe dot lyon at st dot com>
- To: <binutils at sourceware dot org>
- Date: Thu, 22 Mar 2018 15:38:23 +0100
- Subject: [ARM-FDPIC 05/12] [ARM] Implement PLT for FDPIC.
- References: <20180322143850.1766-1-christophe.lyon@st.com>
FDPIC requires special PLT entries, defined in this patch.
Note that lazy binding is not supported because of a race condition
for lack of an atomic 64-bits load instruction.
2018-XX-XX Christophe Lyon <christophe.lyon@st.com>
Mickaël Guêné <mickael.guene@st.com>
* elf32-arm.c (elf32_arm_fdpic_plt_entry): New.
(elf32_arm_create_dynamic_sections): Handle FDPIC.
(elf32_arm_allocate_plt_entry): Likewise.
(elf32_arm_populate_plt_entry): Likewise.
(elf32_arm_output_plt_map_1): Likewise.
---
bfd/elf32-arm.c | 152 ++++++++++++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 143 insertions(+), 9 deletions(-)
diff --git a/bfd/elf32-arm.c b/bfd/elf32-arm.c
index 5892255..d84edb1 100644
--- a/bfd/elf32-arm.c
+++ b/bfd/elf32-arm.c
@@ -2229,6 +2229,22 @@ static const unsigned long dl_tlsdesc_lazy_trampoline [] =
0x00000018, /* 4: .word _GLOBAL_OFFSET_TABLE_ - 2b - 8 */
};
+/* ARM FDPIC PLT entry. */
+/* The last 5 words contain PLT lazy fragment code and data. */
+static const bfd_vma elf32_arm_fdpic_plt_entry [] =
+ {
+ 0xe59fc008, /* ldr r12, .L1 */
+ 0xe08cc009, /* add r12, r12, r9 */
+ 0xe59c9004, /* ldr r9, [r12, #4] */
+ 0xe59cf000, /* ldr pc, [r12] */
+ 0x00000000, /* L1. .word foo(GOTOFFFUNCDESC) */
+ 0x00000000, /* L1. .word foo(funcdesc_value_reloc_offset) */
+ 0xe51fc00c, /* ldr r12, [pc, #-12] */
+ 0xe92d1000, /* push {r12} */
+ 0xe599c004, /* ldr r12, [r9, #4] */
+ 0xe599f000, /* ldr pc, [r9] */
+ };
+
#ifdef FOUR_WORD_PLT
/* The first entry in a procedure linkage table looks like
@@ -3856,6 +3872,14 @@ elf32_arm_create_dynamic_sections (bfd *dynobj, struct bfd_link_info *info)
htab->obfd = saved_obfd;
}
+ if (htab->fdpic_p) {
+ htab->plt_header_size = 0;
+ if (info->flags & DF_BIND_NOW)
+ htab->plt_entry_size = 4 * (ARRAY_SIZE(elf32_arm_fdpic_plt_entry) - 5);
+ else
+ htab->plt_entry_size = 4 * ARRAY_SIZE(elf32_arm_fdpic_plt_entry);
+ }
+
if (!htab->root.splt
|| !htab->root.srelplt
|| !htab->root.sdynbss
@@ -9392,8 +9416,22 @@ elf32_arm_allocate_plt_entry (struct bfd_link_info *info,
splt = htab->root.splt;
sgotplt = htab->root.sgotplt;
- /* Allocate room for an R_JUMP_SLOT relocation in .rel.plt. */
- elf32_arm_allocate_dynrelocs (info, htab->root.srelplt, 1);
+ if (htab->fdpic_p)
+ {
+ /* Allocate room for R_ARM_FUNCDESC_VALUE. */
+ /* For lazy binding, relocations will be put into .rel.plt, in
+ .rel.got otherwise. */
+ /* FIXME: today we don't support lazy binding so put it in .rel.got */
+ if (info->flags & DF_BIND_NOW)
+ elf32_arm_allocate_dynrelocs (info, htab->root.srelgot, 1);
+ else
+ elf32_arm_allocate_dynrelocs (info, htab->root.srelplt, 1);
+ }
+ else
+ {
+ /* Allocate room for an R_JUMP_SLOT relocation in .rel.plt. */
+ elf32_arm_allocate_dynrelocs (info, htab->root.srelplt, 1);
+ }
/* If this is the first .plt entry, make room for the special
first entry. */
@@ -9417,7 +9455,11 @@ elf32_arm_allocate_plt_entry (struct bfd_link_info *info,
arm_plt->got_offset = sgotplt->size;
else
arm_plt->got_offset = sgotplt->size - 8 * htab->num_tls_desc;
- sgotplt->size += 4;
+ if (htab->fdpic_p)
+ /* Function descriptor takes 64 bits in GOT. */
+ sgotplt->size += 8;
+ else
+ sgotplt->size += 4;
}
}
@@ -9526,7 +9568,11 @@ elf32_arm_populate_plt_entry (bfd *output_bfd, struct bfd_link_info *info,
in all the symbols for which we are making plt entries.
After the reserved .got.plt entries, all symbols appear in
the same order as in .plt. */
- plt_index = (got_offset - got_header_size) / 4;
+ if (htab->fdpic_p)
+ /* Function descriptor takes 8 bytes. */
+ plt_index = (got_offset - got_header_size) / 8;
+ else
+ plt_index = (got_offset - got_header_size) / 4;
/* Calculate the address of the GOT entry. */
got_address = (sgot->output_section->vma
@@ -9634,6 +9680,42 @@ elf32_arm_populate_plt_entry (bfd *output_bfd, struct bfd_link_info *info,
| (tail_displacement & 0x00ffffff),
ptr + 12);
}
+ else if (htab->fdpic_p)
+ {
+ /* Fill-up Thumb stub if needed. */
+ if (elf32_arm_plt_needs_thumb_stub_p (info, arm_plt))
+ {
+ put_thumb_insn (htab, output_bfd,
+ elf32_arm_plt_thumb_stub[0], ptr - 4);
+ put_thumb_insn (htab, output_bfd,
+ elf32_arm_plt_thumb_stub[1], ptr - 2);
+ }
+ put_arm_insn(htab, output_bfd,
+ elf32_arm_fdpic_plt_entry[0], ptr + 0);
+ put_arm_insn(htab, output_bfd,
+ elf32_arm_fdpic_plt_entry[1], ptr + 4);
+ put_arm_insn(htab, output_bfd,
+ elf32_arm_fdpic_plt_entry[2], ptr + 8);
+ put_arm_insn(htab, output_bfd,
+ elf32_arm_fdpic_plt_entry[3], ptr + 12);
+ bfd_put_32 (output_bfd, got_offset, ptr + 16);
+
+ if (!(info->flags & DF_BIND_NOW))
+ {
+ /* funcdesc_value_reloc_offset. */
+ bfd_put_32 (output_bfd,
+ htab->root.srelplt->reloc_count * RELOC_SIZE (htab),
+ ptr + 20);
+ put_arm_insn(htab, output_bfd,
+ elf32_arm_fdpic_plt_entry[6], ptr + 24);
+ put_arm_insn(htab, output_bfd,
+ elf32_arm_fdpic_plt_entry[7], ptr + 28);
+ put_arm_insn(htab, output_bfd,
+ elf32_arm_fdpic_plt_entry[8], ptr + 32);
+ put_arm_insn(htab, output_bfd,
+ elf32_arm_fdpic_plt_entry[9], ptr + 36);
+ }
+ }
else if (using_thumb_only (htab))
{
/* PR ld/16017: Generate thumb only PLT entries. */
@@ -9744,22 +9826,61 @@ elf32_arm_populate_plt_entry (bfd *output_bfd, struct bfd_link_info *info,
}
else
{
- rel.r_info = ELF32_R_INFO (dynindx, R_ARM_JUMP_SLOT);
- initial_got_entry = (splt->output_section->vma
- + splt->output_offset);
+ /* For FDPIC we will have to resolve a R_ARM_FUNCDESC_VALUE
+ used by PLT entry. */
+ if (htab->fdpic_p)
+ {
+ rel.r_info = ELF32_R_INFO (dynindx, R_ARM_FUNCDESC_VALUE);
+ initial_got_entry = 0;
+ }
+ else
+ {
+ rel.r_info = ELF32_R_INFO (dynindx, R_ARM_JUMP_SLOT);
+ initial_got_entry = (splt->output_section->vma
+ + splt->output_offset);
+ }
}
/* Fill in the entry in the global offset table. */
bfd_put_32 (output_bfd, initial_got_entry,
sgot->contents + got_offset);
+
+ if (htab->fdpic_p && !(info->flags & DF_BIND_NOW))
+ {
+ /* Setup initial funcdesc value. */
+ /* FIXME: we don't support lazy binding because there is a
+ race condition between both words getting written and
+ some other thread attempting to read them. The ARM
+ architecture does not have an atomic 64 bit load/store
+ instruction that could be used to prevent it; it is
+ recommended that threaded FDPIC applications run with the
+ LD_BIND_NOW environment variable set. */
+ bfd_put_32(output_bfd, plt_address + 0x18,
+ sgot->contents + got_offset);
+ bfd_put_32(output_bfd, -1 /*TODO*/,
+ sgot->contents + got_offset + 4);
+ }
}
if (dynindx == -1)
elf32_arm_add_dynreloc (output_bfd, info, srel, &rel);
else
{
- loc = srel->contents + plt_index * RELOC_SIZE (htab);
- SWAP_RELOC_OUT (htab) (output_bfd, &rel, loc);
+ if (htab->fdpic_p)
+ {
+ /* For FDPIC we put PLT relocationss into .rel.got when not
+ lazy binding otherwise we put them in .rel.plt. For now,
+ we don't support lazy binding so put it in .rel.got. */
+ if (info->flags & DF_BIND_NOW)
+ elf32_arm_add_dynreloc(output_bfd, info, htab->root.srelgot, &rel);
+ else
+ elf32_arm_add_dynreloc(output_bfd, info, htab->root.srelplt, &rel);
+ }
+ else
+ {
+ loc = srel->contents + plt_index * RELOC_SIZE (htab);
+ SWAP_RELOC_OUT (htab) (output_bfd, &rel, loc);
+ }
}
return TRUE;
@@ -17577,6 +17698,19 @@ elf32_arm_output_plt_map_1 (output_arch_syminfo *osi,
if (!elf32_arm_output_map_sym (osi, ARM_MAP_ARM, addr))
return FALSE;
}
+ else if (htab->fdpic_p)
+ {
+ if (elf32_arm_plt_needs_thumb_stub_p (osi->info, arm_plt))
+ if (!elf32_arm_output_map_sym (osi, ARM_MAP_THUMB, addr - 4))
+ return FALSE;
+ if (!elf32_arm_output_map_sym (osi, ARM_MAP_ARM, addr))
+ return FALSE;
+ if (!elf32_arm_output_map_sym (osi, ARM_MAP_DATA, addr + 16))
+ return FALSE;
+ if (htab->plt_entry_size == 4 * ARRAY_SIZE(elf32_arm_fdpic_plt_entry))
+ if (!elf32_arm_output_map_sym (osi, ARM_MAP_ARM, addr + 24))
+ return FALSE;
+ }
else if (using_thumb_only (htab))
{
if (!elf32_arm_output_map_sym (osi, ARM_MAP_THUMB, addr))
--
2.6.3