old-cross-binutils/ld/ldexp.h
Alan Modra 0e5fabeb2c Rewrite relro adjusting code
The linker tries to put the end of the last section in the relro
segment exactly on a page boundary, because the relro segment itself
must end on a page boundary.  If for any reason this can't be done,
padding is inserted.  Since the end of the relro segment is typically
between .got and .got.plt, padding effectively increases the size of
the GOT.  This isn't nice for targets and code models with limited GOT
addressing.

The problem with the current code is that it doesn't cope very well
with aligned sections in the relro segment.  When making .got aligned
to a 256 byte boundary for PowerPC64, I found that often the initial
alignment attempt failed and the fallback attempt to be less than
adequate.  This is a particular problem for PowerPC64 since the
distance between .got and .plt affects the size of plt call stubs,
leading to "stubs don't match calculated size" errors.

So this rewrite takes a direct approach to calculating a new relro
base.  Starting from the last section in the segment, we calculate
where it must start to position its end on the boundary, or as near as
possible considering alignment requirements.  The new start then
becomes the goal for the previous section to end, and so on for all
sections.  This of course ignores the possibility that user scripts
will place . = ALIGN(xxx); in the relro segment, or provide section
address expressions.  In those cases we might fail, but the old code
probably did too, and a fallback is provided.

ld/
	* ldexp.h (struct ldexp_control): Delete dataseg.min_base.  Add
	data_seg.relro_offset.
	* ldexp.c (fold_binary <DATA_SEGMENT_ALIGN>): Don't set min_base.
	(fold_binary <DATA_SEGMENT_RELRO_END>): Do set relro_offset.
	* ldlang.c (lang_size_sections): Rewrite code adjusting relro
	segment base to line up last section on page boundary.
ld/testsuite/
	* ld-x86-64/pr18176.d: Update.
2015-04-22 23:19:59 +09:30

227 lines
5.6 KiB
C

/* ldexp.h -
Copyright (C) 1991-2015 Free Software Foundation, Inc.
This file is part of the GNU Binutils.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
MA 02110-1301, USA. */
#ifndef LDEXP_H
#define LDEXP_H
/* The result of an expression tree */
typedef struct {
bfd_vma value;
char *str;
asection *section;
bfd_boolean valid_p;
} etree_value_type;
enum node_tree_enum {
etree_binary,
etree_trinary,
etree_unary,
etree_name,
etree_assign,
etree_provide,
etree_provided,
etree_value,
etree_assert,
etree_rel
};
typedef struct {
int node_code;
unsigned int lineno;
const char *filename;
enum node_tree_enum node_class;
} node_type;
typedef union etree_union {
node_type type;
struct {
node_type type;
union etree_union *lhs;
union etree_union *rhs;
} binary;
struct {
node_type type;
union etree_union *cond;
union etree_union *lhs;
union etree_union *rhs;
} trinary;
struct {
node_type type;
const char *dst;
union etree_union *src;
bfd_boolean defsym;
bfd_boolean hidden;
} assign;
struct {
node_type type;
union etree_union *child;
} unary;
struct {
node_type type;
const char *name;
} name;
struct {
node_type type;
bfd_vma value;
char *str;
} value;
struct {
node_type type;
asection *section;
bfd_vma value;
} rel;
struct {
node_type type;
union etree_union *child;
const char *message;
} assert_s;
} etree_type;
/* Expression evaluation control. */
typedef enum
{
/* Parsing linker script. Will only return "valid" for expressions
that evaluate to a constant. */
lang_first_phase_enum,
/* Prior to section sizing. */
lang_mark_phase_enum,
/* During section sizing. */
lang_allocating_phase_enum,
/* During assignment of symbol values when relaxation in progress. */
lang_assigning_phase_enum,
/* Final assignment of symbol values. */
lang_final_phase_enum
} lang_phase_type;
union lang_statement_union;
enum phase_enum {
/* We step through the first four states here as we see the
associated linker script tokens. */
exp_dataseg_none,
exp_dataseg_align_seen,
exp_dataseg_relro_seen,
exp_dataseg_end_seen,
/* The last three states are final, and affect the value returned
by DATA_SEGMENT_ALIGN. */
exp_dataseg_relro_adjust,
exp_dataseg_adjust,
exp_dataseg_done
};
enum relro_enum {
exp_dataseg_relro_none,
exp_dataseg_relro_start,
exp_dataseg_relro_end,
};
struct ldexp_control {
/* Modify expression evaluation depending on this. */
lang_phase_type phase;
/* Principally used for diagnostics. */
bfd_boolean assigning_to_dot;
/* If evaluating an assignment, the destination. Cleared if an
etree_name NAME matches this, to signal a self-assignment.
Note that an etree_name DEFINED does not clear this field, nor
does the false branch of a trinary expression. */
const char *assign_name;
/* Working results. */
etree_value_type result;
bfd_vma dot;
/* Current dot and section passed to ldexp folder. */
bfd_vma *dotp;
asection *section;
/* State machine and results for DATASEG. */
struct {
enum phase_enum phase;
bfd_vma base, relro_offset, relro_end, end, pagesize, maxpagesize;
enum relro_enum relro;
union lang_statement_union *relro_start_stat;
union lang_statement_union *relro_end_stat;
} dataseg;
};
extern struct ldexp_control expld;
/* A maps from a segment name to a base address. */
typedef struct segment_struct {
/* The next segment in the linked list. */
struct segment_struct *next;
/* The name of the sgement. */
const char *name;
/* The base address for the segment. */
bfd_vma value;
/* True if a SEGMENT_START directive corresponding to this segment
has been seen. */
bfd_boolean used;
} segment_type;
/* The segments specified by the user on the command-line. */
extern segment_type *segments;
typedef struct _fill_type fill_type;
etree_type *exp_intop
(bfd_vma);
etree_type *exp_bigintop
(bfd_vma, char *);
etree_type *exp_relop
(asection *, bfd_vma);
void exp_fold_tree
(etree_type *, asection *, bfd_vma *);
void exp_fold_tree_no_dot
(etree_type *);
etree_type *exp_binop
(int, etree_type *, etree_type *);
etree_type *exp_trinop
(int,etree_type *, etree_type *, etree_type *);
etree_type *exp_unop
(int, etree_type *);
etree_type *exp_nameop
(int, const char *);
etree_type *exp_assign
(const char *, etree_type *, bfd_boolean);
etree_type *exp_defsym
(const char *, etree_type *);
etree_type *exp_provide
(const char *, etree_type *, bfd_boolean);
etree_type *exp_assert
(etree_type *, const char *);
void exp_print_tree
(etree_type *);
bfd_vma exp_get_vma
(etree_type *, bfd_vma, char *);
int exp_get_value_int
(etree_type *, int, char *);
fill_type *exp_get_fill
(etree_type *, fill_type *, char *);
bfd_vma exp_get_abs_int
(etree_type *, int, char *);
void ldexp_init (void);
void ldexp_finish (void);
#endif