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[ARM] Implement PLT for FDPIC.

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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.

2018-04-25  Christophe Lyon  <christophe.lyon@st.com>
	Mickaël Guêné  <mickael.guene@st.com>

	bfd/
	* 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.
This commit is contained in:
Christophe Lyon
2018-03-20 10:55:20 +01:00
committed by Christophe Lyon
parent e8b09b8710
commit 7801f98f84
2 changed files with 152 additions and 9 deletions
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9
bfd/ChangeLog
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@ -1,3 +1,12 @@
2018-04-25 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.
2018-04-25 Christophe Lyon <christophe.lyon@st.com> 2018-04-25 Christophe Lyon <christophe.lyon@st.com>
Mickaël Guêné <mickael.guene@st.com> Mickaël Guêné <mickael.guene@st.com>

134
bfd/elf32-arm.c
View File

@ -2229,6 +2229,22 @@ static const unsigned long dl_tlsdesc_lazy_trampoline [] =
0x00000018, /* 4: .word _GLOBAL_OFFSET_TABLE_ - 2b - 8 */ 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 #ifdef FOUR_WORD_PLT
/* The first entry in a procedure linkage table looks like /* 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; 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 if (!htab->root.splt
|| !htab->root.srelplt || !htab->root.srelplt
|| !htab->root.sdynbss || !htab->root.sdynbss
@ -9392,8 +9416,22 @@ elf32_arm_allocate_plt_entry (struct bfd_link_info *info,
splt = htab->root.splt; splt = htab->root.splt;
sgotplt = htab->root.sgotplt; sgotplt = htab->root.sgotplt;
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. */ /* Allocate room for an R_JUMP_SLOT relocation in .rel.plt. */
elf32_arm_allocate_dynrelocs (info, htab->root.srelplt, 1); elf32_arm_allocate_dynrelocs (info, htab->root.srelplt, 1);
}
/* If this is the first .plt entry, make room for the special /* If this is the first .plt entry, make room for the special
first entry. */ first entry. */
@ -9417,6 +9455,10 @@ elf32_arm_allocate_plt_entry (struct bfd_link_info *info,
arm_plt->got_offset = sgotplt->size; arm_plt->got_offset = sgotplt->size;
else else
arm_plt->got_offset = sgotplt->size - 8 * htab->num_tls_desc; arm_plt->got_offset = sgotplt->size - 8 * htab->num_tls_desc;
if (htab->fdpic_p)
/* Function descriptor takes 64 bits in GOT. */
sgotplt->size += 8;
else
sgotplt->size += 4; sgotplt->size += 4;
} }
} }
@ -9526,6 +9568,10 @@ elf32_arm_populate_plt_entry (bfd *output_bfd, struct bfd_link_info *info,
in all the symbols for which we are making plt entries. in all the symbols for which we are making plt entries.
After the reserved .got.plt entries, all symbols appear in After the reserved .got.plt entries, all symbols appear in
the same order as in .plt. */ the same order as in .plt. */
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; plt_index = (got_offset - got_header_size) / 4;
/* Calculate the address of the GOT entry. */ /* Calculate the address of the GOT entry. */
@ -9634,6 +9680,42 @@ elf32_arm_populate_plt_entry (bfd *output_bfd, struct bfd_link_info *info,
| (tail_displacement & 0x00ffffff), | (tail_displacement & 0x00ffffff),
ptr + 12); 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)) else if (using_thumb_only (htab))
{ {
/* PR ld/16017: Generate thumb only PLT entries. */ /* PR ld/16017: Generate thumb only PLT entries. */
@ -9742,25 +9824,64 @@ elf32_arm_populate_plt_entry (bfd *output_bfd, struct bfd_link_info *info,
rel.r_info = ELF32_R_INFO (0, R_ARM_IRELATIVE); rel.r_info = ELF32_R_INFO (0, R_ARM_IRELATIVE);
initial_got_entry = sym_value; initial_got_entry = sym_value;
} }
else
{
/* 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 else
{ {
rel.r_info = ELF32_R_INFO (dynindx, R_ARM_JUMP_SLOT); rel.r_info = ELF32_R_INFO (dynindx, R_ARM_JUMP_SLOT);
initial_got_entry = (splt->output_section->vma initial_got_entry = (splt->output_section->vma
+ splt->output_offset); + splt->output_offset);
} }
}
/* Fill in the entry in the global offset table. */ /* Fill in the entry in the global offset table. */
bfd_put_32 (output_bfd, initial_got_entry, bfd_put_32 (output_bfd, initial_got_entry,
sgot->contents + got_offset); 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) if (dynindx == -1)
elf32_arm_add_dynreloc (output_bfd, info, srel, &rel); elf32_arm_add_dynreloc (output_bfd, info, srel, &rel);
else
{
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 else
{ {
loc = srel->contents + plt_index * RELOC_SIZE (htab); loc = srel->contents + plt_index * RELOC_SIZE (htab);
SWAP_RELOC_OUT (htab) (output_bfd, &rel, loc); SWAP_RELOC_OUT (htab) (output_bfd, &rel, loc);
} }
}
return TRUE; return TRUE;
} }
@ -17574,6 +17695,19 @@ elf32_arm_output_plt_map_1 (output_arch_syminfo *osi,
if (!elf32_arm_output_map_sym (osi, ARM_MAP_ARM, addr)) if (!elf32_arm_output_map_sym (osi, ARM_MAP_ARM, addr))
return FALSE; 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)) else if (using_thumb_only (htab))
{ {
if (!elf32_arm_output_map_sym (osi, ARM_MAP_THUMB, addr)) if (!elf32_arm_output_map_sym (osi, ARM_MAP_THUMB, addr))