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bfd: use the ELF linker to perform relocations in BPF targets

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This patch changes the eBPF linker to provide a relocate_section
function instead of relying on using special functions in relocation
howtos.

Tested in x86_64 host.
No regressions.

bfd/ChangeLog:

2019-08-07  Jose E. Marchesi  <jose.marchesi@oracle.com>

	* elf64-bpf.c (bpf_elf_relocate_section): New function.
	(bpf_elf_insn_disp_reloc): Delete function.
	(elf_backend_relocate_section): Define.
This commit is contained in:
Jose E. Marchesi 2019-08-07 11:33:13 +02:00
parent 97b031c5d6
commit fc8de8e227
2 changed files with 193 additions and 95 deletions
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6
bfd/ChangeLog
View File

@ -1,3 +1,9 @@
2019-08-07 Jose E. Marchesi <jose.marchesi@oracle.com>
* elf64-bpf.c (bpf_elf_relocate_section): New function.
(bpf_elf_insn_disp_reloc): Delete function.
(elf_backend_relocate_section): Define.
2019-08-07 Alan Modra <amodra@gmail.com>
PR 24644

282
bfd/elf64-bpf.c
View File

@ -31,96 +31,6 @@
#define BASEADDR(SEC) ((SEC)->output_section->vma + (SEC)->output_offset)
/* Handler for PC-relative relocations, which must be handled in
64-bit words. */
static bfd_reloc_status_type
bpf_elf_insn_disp_reloc (bfd *abfd,
arelent *reloc_entry,
asymbol *symbol,
void *data,
asection *input_section,
bfd *output_bfd,
char **error_message ATTRIBUTE_UNUSED)
{
bfd_signed_vma relocation;
bfd_signed_vma addend;
reloc_howto_type *howto = reloc_entry->howto;
/* This part is from bfd_elf_generic_reloc. */
if (output_bfd != NULL
&& (symbol->flags & BSF_SECTION_SYM) == 0
&& (! reloc_entry->howto->partial_inplace
|| reloc_entry->addend == 0))
{
reloc_entry->address += input_section->output_offset;
return bfd_reloc_ok;
}
/* This works because partial_inplace is FALSE. */
if (output_bfd != NULL)
return bfd_reloc_continue;
if (reloc_entry->address > bfd_get_section_limit (abfd, input_section))
return bfd_reloc_outofrange;
relocation = (symbol->value
+ symbol->section->output_section->vma
+ symbol->section->output_offset);
/* Make it PC relative. */
relocation -= (input_section->output_section->vma
+ input_section->output_offset);
relocation -= reloc_entry->address;
/* Make it 64-bit words. */
relocation = relocation / 8;
/* Get the addend from the instruction and apply it. */
switch (howto->bitsize)
{
default:
abort ();
break;
case 16:
addend = bfd_get_16 (abfd, (bfd_byte *) data + reloc_entry->address + 2);
break;
case 32:
addend = bfd_get_32 (abfd, (bfd_byte *) data + reloc_entry->address + 4);
break;
}
if ((addend & (((~howto->src_mask) >> 1) & howto->src_mask)) != 0)
addend -= (((~howto->src_mask) >> 1) & howto->src_mask) << 1;
relocation += addend;
/* Write out the relocated value. */
switch (howto->bitsize)
{
default:
abort ();
break;
case 16:
bfd_put_16 (abfd, relocation, (bfd_byte *) data + reloc_entry->address + 2);
break;
case 32:
bfd_put_32 (abfd, relocation, (bfd_byte *) data + reloc_entry->address + 4);
break;
}
/* Check for overflow. */
if (howto->complain_on_overflow == complain_overflow_signed)
{
bfd_signed_vma reloc_signed_max = (1 << (howto->bitsize - 1)) - 1;
bfd_signed_vma reloc_signed_min = ~reloc_signed_max;
if (relocation > reloc_signed_max || relocation < reloc_signed_min)
return bfd_reloc_overflow;
}
else
abort();
return bfd_reloc_ok;
}
/* Relocation tables. */
static reloc_howto_type bpf_elf_howto_table [] =
{
@ -192,7 +102,7 @@ static reloc_howto_type bpf_elf_howto_table [] =
TRUE, /* pc_relative */
32, /* bitpos */
complain_overflow_signed, /* complain_on_overflow */
bpf_elf_insn_disp_reloc, /* special_function */
bfd_elf_generic_reloc, /* special_function */
"R_BPF_INSN_DISP16", /* name */
FALSE, /* partial_inplace */
0xffff, /* src_mask */
@ -277,7 +187,7 @@ static reloc_howto_type bpf_elf_howto_table [] =
TRUE, /* pc_relative */
0, /* bitpos */
complain_overflow_signed, /* complain_on_overflow */
bpf_elf_insn_disp_reloc, /* special_function */
bfd_elf_generic_reloc, /* special_function */
"R_BPF_INSN_DISP32", /* name */
FALSE, /* partial_inplace */
0xffffffff, /* src_mask */
@ -336,9 +246,9 @@ static reloc_howto_type *
bpf_reloc_type_lookup (bfd * abfd ATTRIBUTE_UNUSED,
bfd_reloc_code_real_type code)
{
/* Note that the bpf_elf_howto_table is indxed by the R_
constants. Thus, the order that the howto records appear in the
table *must* match the order of the relocation types defined in
/* Note that the bpf_elf_howto_table is indexed by the R_ constants.
Thus, the order that the howto records appear in the table *must*
match the order of the relocation types defined in
include/elf/bpf.h. */
switch (code)
@ -419,6 +329,187 @@ bpf_info_to_howto (bfd *abfd, arelent *bfd_reloc,
return TRUE;
}
/* Relocate an eBPF ELF section.
The RELOCATE_SECTION function is called by the new ELF backend linker
to handle the relocations for a section.
The relocs are always passed as Rela structures; if the section
actually uses Rel structures, the r_addend field will always be
zero.
This function is responsible for adjusting the section contents as
necessary, and (if using Rela relocs and generating a relocatable
output file) adjusting the reloc addend as necessary.
This function does not have to worry about setting the reloc
address or the reloc symbol index.
LOCAL_SYMS is a pointer to the swapped in local symbols.
LOCAL_SECTIONS is an array giving the section in the input file
corresponding to the st_shndx field of each local symbol.
The global hash table entry for the global symbols can be found
via elf_sym_hashes (input_bfd).
When generating relocatable output, this function must handle
STB_LOCAL/STT_SECTION symbols specially. The output symbol is
going to be the section symbol corresponding to the output
section, which means that the addend must be adjusted
accordingly. */
#define sec_addr(sec) ((sec)->output_section->vma + (sec)->output_offset)
static bfd_boolean
bpf_elf_relocate_section (bfd *output_bfd ATTRIBUTE_UNUSED,
struct bfd_link_info *info,
bfd *input_bfd,
asection *input_section,
bfd_byte *contents,
Elf_Internal_Rela *relocs,
Elf_Internal_Sym *local_syms,
asection **local_sections)
{
Elf_Internal_Shdr *symtab_hdr;
struct elf_link_hash_entry **sym_hashes;
Elf_Internal_Rela *rel;
Elf_Internal_Rela *relend;
symtab_hdr = & elf_tdata (input_bfd)->symtab_hdr;
sym_hashes = elf_sym_hashes (input_bfd);
relend = relocs + input_section->reloc_count;
for (rel = relocs; rel < relend; rel ++)
{
reloc_howto_type * howto;
unsigned long r_symndx;
Elf_Internal_Sym * sym;
asection * sec;
struct elf_link_hash_entry * h;
bfd_vma relocation;
bfd_reloc_status_type r;
const char * name = NULL;
int r_type ATTRIBUTE_UNUSED;
r_type = ELF64_R_TYPE (rel->r_info);
r_symndx = ELF64_R_SYM (rel->r_info);
howto = bpf_elf_howto_table + ELF64_R_TYPE (rel->r_info);
h = NULL;
sym = NULL;
sec = NULL;
if (r_symndx < symtab_hdr->sh_info)
{
sym = local_syms + r_symndx;
sec = local_sections [r_symndx];
relocation = BASEADDR (sec) + sym->st_value;
name = bfd_elf_string_from_elf_section
(input_bfd, symtab_hdr->sh_link, sym->st_name);
name = (name == NULL) ? bfd_section_name (input_bfd, sec) : name;
}
else
{
bfd_boolean warned ATTRIBUTE_UNUSED;
bfd_boolean unresolved_reloc ATTRIBUTE_UNUSED;
bfd_boolean ignored ATTRIBUTE_UNUSED;
RELOC_FOR_GLOBAL_SYMBOL (info, input_bfd, input_section, rel,
r_symndx, symtab_hdr, sym_hashes,
h, sec, relocation,
unresolved_reloc, warned, ignored);
name = h->root.root.string;
}
if (sec != NULL && discarded_section (sec))
RELOC_AGAINST_DISCARDED_SECTION (info, input_bfd, input_section,
rel, 1, relend, howto, 0, contents);
if (bfd_link_relocatable (info))
continue;
switch (howto->type)
{
case R_BPF_INSN_DISP16:
case R_BPF_INSN_DISP32:
{
bfd_signed_vma addend;
/* Make the relocation PC-relative, and change its unit to
64-bit words. */
relocation -= sec_addr (input_section) + rel->r_offset;
/* Make it 64-bit words. */
relocation = relocation / 8;
/* Get the addend from the instruction and apply it. */
addend = bfd_get (howto->bitsize, input_bfd,
contents + rel->r_offset
+ (howto->bitsize == 16 ? 2 : 4));
if ((addend & (((~howto->src_mask) >> 1) & howto->src_mask)) != 0)
addend -= (((~howto->src_mask) >> 1) & howto->src_mask) << 1;
relocation += addend;
/* Write out the relocated value. */
bfd_put (howto->bitsize, input_bfd, relocation,
contents + rel->r_offset
+ (howto->bitsize == 16 ? 2 : 4));
r = bfd_reloc_ok;
break;
}
default:
r = _bfd_final_link_relocate (howto, input_bfd, input_section,
contents, rel->r_offset, relocation,
rel->r_addend);
}
if (r != bfd_reloc_ok)
{
const char * msg = NULL;
switch (r)
{
case bfd_reloc_overflow:
(*info->callbacks->reloc_overflow)
(info, (h ? &h->root : NULL), name, howto->name,
(bfd_vma) 0, input_bfd, input_section, rel->r_offset);
break;
case bfd_reloc_undefined:
(*info->callbacks->undefined_symbol)
(info, name, input_bfd, input_section, rel->r_offset, TRUE);
break;
case bfd_reloc_outofrange:
msg = _("internal error: out of range error");
break;
case bfd_reloc_notsupported:
if (sym != NULL) /* Only if it's not an unresolved symbol. */
msg = _("internal error: relocation not supported");
break;
case bfd_reloc_dangerous:
msg = _("internal error: dangerous relocation");
break;
default:
msg = _("internal error: unknown error");
break;
}
if (msg)
(*info->callbacks->warning) (info, msg, name, input_bfd,
input_section, rel->r_offset);
}
}
return TRUE;
}
/* Merge backend specific data from an object file to the output
object file when linking. */
@ -451,6 +542,7 @@ elf64_bpf_merge_private_bfd_data (bfd *ibfd, struct bfd_link_info *info)
#define elf_backend_may_use_rel_p 1
#define elf_backend_may_use_rela_p 0
#define elf_backend_default_use_rela_p 0
#define elf_backend_relocate_section bpf_elf_relocate_section
#define elf_backend_can_gc_sections 0