This is the mail archive of the
binutils@sources.redhat.com
mailing list for the binutils project.
[RFC PATCH] Readonly .eh_frame and .gcc_except_table
- From: Jakub Jelinek <jakub at redhat dot com>
- To: binutils at sources dot redhat dot com
- Date: Fri, 22 Nov 2002 21:58:28 +0100
- Subject: [RFC PATCH] Readonly .eh_frame and .gcc_except_table
- Reply-to: Jakub Jelinek <jakub at redhat dot com>
Hi!
While .eh_frame and .gcc_except_table used to have dynamic relocations
against it in the GCC 2 days, on most important arches it doesn't any
longer if DW_EH_PE_{pc,data,func,text}rel encodings are used
over the whole sections. But even when gcc makes sure to mark all .eh_frame
resp. all .gcc_except_table sections read-only if no dynamic relocations
will be against it, .eh_frame / .gcc_except_table stays in the read/write
segment since that is where linker script puts them.
If it is in RW segment, it can cause up to two pages wasted per process.
Either we can remove .eh_frame and .gcc_except_table from the linker script,
but we loose control on its exact placement and .eh_frame looses KEEP,
so that it can be garbage collected out of the binary/dso.
Or the following patch adds an linker script extension which allows to
keep control on where exactly is the output section placed, both if it
consists of all read-only sections only, or if it contains
at least one read-write section.
What do you think?
2002-11-22 Jakub Jelinek <jakub@redhat.com>
* ldgram.y (sect_constraint): New.
(ONLY_IF_RO, ONLY_IF_RW): New tokens.
(section): Add sect_constraint. Pass additional argument
to lang_enter_output_section_statement.
* mri.c (mri_draw_tree): Pass additional argument to
lang_enter_output_section_statement.
* emultempl/pe.em (place_orphan): Likewise.
(output_prev_sec_find): Disregard output section statements with
constraint == -1.
* emultempl/mmo.em (output_prev_sec_find): Likewise.
(mmo_place_orphan): Pass additional argument to
lang_enter_output_section_statement.
* emultempl/elf32.em (output_prev_sec_find): Disregard output section
statements with constraint == -1.
(place_orphan): Pass additional argument to
lang_enter_output_section_statement.
* ldlang.c (lang_enter_overlay_section): Likewise.
(lang_output_section_find_1): New.
(lang_output_section_find): Use it.
(lang_output_section_statement_lookup_1): New.
(lang_output_section_statement_lookup): Use it.
(check_section_callback, check_input_sections): New.
(map_input_to_output_sections): Check if all input sections
are readonly if ONLY_IF_RO or ONLY_IF_RW was seen.
(strip_excluded_output_sections): Disregard output section statements
with constraint == -1.
(lang_record_phdrs): Likewise.
(lang_enter_output_section_statement): Add constraint argument.
Use lang_output_section_statement_lookup_1.
* ldlang.h (lang_output_section_statement_type): Add constraint
and all_input_readonly fields.
(lang_enter_output_section_statement): Adjust prototype.
* ldlex.l (ONLY_IF_RO, ONLY_IF_RW): New tokens.
* scripttempl/elf.sc (.eh_frame, .gcc_except_table): Move into text
segment if all input sections are readonly.
--- ld/ldgram.y.jj 2002-10-14 13:30:34.000000000 +0200
+++ ld/ldgram.y 2002-11-22 22:27:18.000000000 +0100
@@ -143,14 +143,14 @@ static int error_index;
%token ORIGIN FILL
%token LENGTH CREATE_OBJECT_SYMBOLS INPUT GROUP OUTPUT CONSTRUCTORS
%token ALIGNMOD AT PROVIDE
-%type <token> assign_op atype attributes_opt
+%type <token> assign_op atype attributes_opt sect_constraint
%type <name> filename
%token CHIP LIST SECT ABSOLUTE LOAD NEWLINE ENDWORD ORDER NAMEWORD ASSERT_K
%token FORMAT PUBLIC DEFSYMEND BASE ALIAS TRUNCATE REL
%token INPUT_SCRIPT INPUT_MRI_SCRIPT INPUT_DEFSYM CASE EXTERN START
%token <name> VERS_TAG VERS_IDENTIFIER
%token GLOBAL LOCAL VERSIONK INPUT_VERSION_SCRIPT
-%token KEEP
+%token KEEP ONLY_IF_RO ONLY_IF_RW
%token EXCLUDE_FILE
%type <versyms> vers_defns
%type <versnode> vers_tag
@@ -828,21 +828,28 @@ opt_at:
| { $$ = 0; }
;
+sect_constraint:
+ ONLY_IF_RO { $$ = ONLY_IF_RO; }
+ | ONLY_IF_RW { $$ = ONLY_IF_RW; }
+ | { $$ = 0; }
+ ;
+
section: NAME { ldlex_expression(); }
opt_exp_with_type
opt_at { ldlex_popstate (); ldlex_script (); }
+ sect_constraint
'{'
{
lang_enter_output_section_statement($1, $3,
sectype,
- 0, 0, 0, $4);
+ 0, 0, 0, $4, $6);
}
statement_list_opt
'}' { ldlex_popstate (); ldlex_expression (); }
memspec_opt memspec_at_opt phdr_opt fill_opt
{
ldlex_popstate ();
- lang_leave_output_section_statement ($14, $11, $13, $12);
+ lang_leave_output_section_statement ($15, $12, $14, $13);
}
opt_comma
{}
--- ld/mri.c.jj 2002-10-31 19:10:42.000000000 +0100
+++ ld/mri.c 2002-11-22 18:38:27.000000000 +0100
@@ -237,7 +237,7 @@ mri_draw_tree ()
lang_enter_output_section_statement (p->name, base,
p->ok_to_load ? 0 : noload_section,
1, align, subalign,
- (etree_type *) NULL);
+ (etree_type *) NULL, 0);
base = 0;
tmp = (struct wildcard_list *) xmalloc (sizeof *tmp);
tmp->next = NULL;
--- ld/emultempl/mmo.em.jj 2002-07-30 16:20:15.000000000 +0200
+++ ld/emultempl/mmo.em 2002-11-22 22:42:44.000000000 +0100
@@ -56,6 +56,8 @@ output_prev_sec_find (os)
u = lookup->next)
{
lookup = &u->output_section_statement;
+ if (lookup->constraint == -1)
+ continue;
if (lookup == os)
break;
if (lookup->bfd_section != NULL
@@ -141,7 +143,7 @@ mmo_place_orphan (file, s)
(bfd_vma) 0,
(etree_type *) NULL,
(etree_type *) NULL,
- (etree_type *) NULL);
+ (etree_type *) NULL, 0);
lang_add_section (&os->children, s, os, file);
--- ld/emultempl/pe.em.jj 2002-11-21 15:58:51.000000000 +0100
+++ ld/emultempl/pe.em 2002-11-22 22:43:02.000000000 +0100
@@ -1489,6 +1489,8 @@ output_prev_sec_find (os)
u = lookup->next)
{
lookup = &u->output_section_statement;
+ if (lookup->constraint == -1)
+ continue;
if (lookup == os)
return s;
@@ -1655,7 +1657,7 @@ gld_${EMULATION_NAME}_place_orphan (file
(bfd_vma) 0,
(etree_type *) NULL,
(etree_type *) NULL,
- (etree_type *) NULL);
+ (etree_type *) NULL, 0);
lang_add_section (&add_child, s, os, file);
--- ld/emultempl/elf32.em.jj 2002-10-31 19:10:44.000000000 +0100
+++ ld/emultempl/elf32.em 2002-11-22 22:42:16.000000000 +0100
@@ -1009,7 +1009,8 @@ output_rel_find (sec)
for (u = lang_output_section_statement.head; u; u = lookup->next)
{
lookup = &u->output_section_statement;
- if (strncmp (".rel", lookup->name, 4) == 0)
+ if (lookup->constraint != -1
+ && strncmp (".rel", lookup->name, 4) == 0)
{
/* Don't place after .rel.plt as doing so results in wrong
dynamic tags. Also, place allocated reloc sections before
@@ -1236,7 +1237,7 @@ gld${EMULATION_NAME}_place_orphan (file,
(bfd_vma) 0,
(etree_type *) NULL,
(etree_type *) NULL,
- (etree_type *) NULL);
+ (etree_type *) NULL, 0);
lang_add_section (&os->children, s, os, file);
--- ld/scripttempl/elf.sc.jj 2002-09-25 11:21:42.000000000 +0200
+++ ld/scripttempl/elf.sc 2002-11-22 22:35:47.000000000 +0100
@@ -280,6 +280,8 @@ cat <<EOF
${CREATE_SHLIB-${SBSS2}}
${OTHER_READONLY_SECTIONS}
.eh_frame_hdr : { *(.eh_frame_hdr) }
+ .eh_frame ${RELOCATING-0} : ONLY_IF_RO { KEEP (*(.eh_frame)) }
+ .gcc_except_table ${RELOCATING-0} : ONLY_IF_RO { *(.gcc_except_table) }
/* Adjust the address for the data segment. We want to adjust up to
the same address within the page on the next page up. */
@@ -312,8 +314,8 @@ cat <<EOF
.data1 ${RELOCATING-0} : { *(.data1) }
.tdata ${RELOCATING-0} : { *(.tdata${RELOCATING+ .tdata.* .gnu.linkonce.td.*}) }
.tbss ${RELOCATING-0} : { *(.tbss${RELOCATING+ .tbss.* .gnu.linkonce.tb.*})${RELOCATING+ *(.tcommon)} }
- .eh_frame ${RELOCATING-0} : { KEEP (*(.eh_frame)) }
- .gcc_except_table ${RELOCATING-0} : { *(.gcc_except_table) }
+ .eh_frame ${RELOCATING-0} : ONLY_IF_RW { KEEP (*(.eh_frame)) }
+ .gcc_except_table ${RELOCATING-0} : ONLY_IF_RW { *(.gcc_except_table) }
${WRITABLE_RODATA+${RODATA}}
${OTHER_READWRITE_SECTIONS}
${TEXT_DYNAMIC-${DYNAMIC}}
--- ld/ldlang.h.jj 2002-10-10 00:53:07.000000000 +0200
+++ ld/ldlang.h 2002-11-22 22:27:37.000000000 +0100
@@ -132,6 +132,8 @@ typedef struct lang_output_section_state
int subsection_alignment; /* alignment of components */
int section_alignment; /* alignment of start of section */
+ int constraint;
+ boolean all_input_readonly;
union etree_union *load_base;
@@ -385,7 +387,7 @@ extern lang_output_section_statement_typ
bfd_vma block_value,
etree_type *align,
etree_type *subalign,
- etree_type *));
+ etree_type *, int));
extern void lang_final PARAMS ((void));
extern void lang_process PARAMS ((void));
extern void lang_section_start PARAMS ((const char *, union etree_union *));
--- ld/ldlang.c.jj 2002-11-14 14:06:22.000000000 +0100
+++ ld/ldlang.c 2002-11-22 22:41:51.000000000 +0100
@@ -71,6 +71,10 @@ static void lang_for_each_statement_work
static lang_input_statement_type *new_afile
PARAMS ((const char *, lang_input_file_enum_type, const char *, boolean));
static lang_memory_region_type *lang_memory_default PARAMS ((asection *));
+static lang_output_section_statement_type * lang_output_section_find_1
+ PARAMS ((const char *, int));
+static lang_output_section_statement_type *
+ lang_output_section_statement_lookup_1 PARAMS ((const char *, int));
static void lang_map_flags PARAMS ((flagword));
static void init_os PARAMS ((lang_output_section_statement_type *));
static void exp_init_os PARAMS ((etree_type *));
@@ -86,6 +90,9 @@ static lang_statement_union_type *wild_s
static void output_section_callback
PARAMS ((lang_wild_statement_type *, struct wildcard_list *, asection *,
lang_input_statement_type *, PTR));
+static void check_section_callback
+ PARAMS ((lang_wild_statement_type *, struct wildcard_list *, asection *,
+ lang_input_statement_type *, PTR));
static lang_input_statement_type *lookup_name PARAMS ((const char *));
static boolean load_symbols
PARAMS ((lang_input_statement_type *, lang_statement_list_type *));
@@ -98,6 +105,9 @@ static void open_input_bfds PARAMS ((lan
static void lang_reasonable_defaults PARAMS ((void));
static void insert_undefined PARAMS ((const char *));
static void lang_place_undefineds PARAMS ((void));
+static void check_input_sections
+ PARAMS ((lang_statement_union_type *,
+ lang_output_section_statement_type *));
static void map_input_to_output_sections
PARAMS ((lang_statement_union_type *, const char *,
lang_output_section_statement_type *));
@@ -700,9 +710,10 @@ lang_memory_default (section)
return lang_memory_region_lookup ("*default*");
}
-lang_output_section_statement_type *
-lang_output_section_find (name)
+static lang_output_section_statement_type *
+lang_output_section_find_1 (name, constraint)
const char *const name;
+ int constraint;
{
lang_statement_union_type *u;
lang_output_section_statement_type *lookup;
@@ -712,7 +723,9 @@ lang_output_section_find (name)
u = lookup->next)
{
lookup = &u->output_section_statement;
- if (strcmp (name, lookup->name) == 0)
+ if (strcmp (name, lookup->name) == 0
+ && lookup->constraint != -1
+ && (constraint == 0 || constraint == lookup->constraint))
{
return lookup;
}
@@ -721,12 +734,20 @@ lang_output_section_find (name)
}
lang_output_section_statement_type *
-lang_output_section_statement_lookup (name)
+lang_output_section_find (name)
+ const char *const name;
+{
+ return lang_output_section_find_1 (name, 0);
+}
+
+static lang_output_section_statement_type *
+lang_output_section_statement_lookup_1 (name, constraint)
const char *const name;
+ int constraint;
{
lang_output_section_statement_type *lookup;
- lookup = lang_output_section_find (name);
+ lookup = lang_output_section_find_1 (name, constraint);
if (lookup == (lang_output_section_statement_type *) NULL)
{
@@ -741,6 +762,7 @@ lang_output_section_statement_lookup (na
lookup->next = (lang_statement_union_type *) NULL;
lookup->bfd_section = (asection *) NULL;
lookup->processed = false;
+ lookup->constraint = constraint;
lookup->sectype = normal_section;
lookup->addr_tree = (etree_type *) NULL;
lang_list_init (&lookup->children);
@@ -760,6 +782,13 @@ lang_output_section_statement_lookup (na
return lookup;
}
+lang_output_section_statement_type *
+lang_output_section_statement_lookup (name)
+ const char *const name;
+{
+ return lang_output_section_statement_lookup_1 (name, 0);
+}
+
static void
lang_map_flags (flag)
flagword flag;
@@ -1434,6 +1463,31 @@ output_section_callback (ptr, sec, secti
}
}
+/* Check if all sections in a wild statement for a particular FILE
+ are readonly. */
+
+static void
+check_section_callback (ptr, sec, section, file, output)
+ lang_wild_statement_type *ptr ATTRIBUTE_UNUSED;
+ struct wildcard_list *sec ATTRIBUTE_UNUSED;
+ asection *section;
+ lang_input_statement_type *file ATTRIBUTE_UNUSED;
+ PTR output;
+{
+ /* Exclude sections that match UNIQUE_SECTION_LIST. */
+ if (unique_section_p (bfd_get_section_name (file->the_bfd, section)))
+ return;
+
+ if (section->output_section == NULL)
+ {
+ flagword flags = bfd_get_section_flags (section->owner, section);
+
+ if ((flags & SEC_READONLY) == 0)
+ ((lang_output_section_statement_type *) output)->all_input_readonly
+ = false;
+ }
+}
+
/* This is passed a file name which must have been seen already and
added to the statement tree. We will see if it has been opened
already and had its symbols read. If not then we'll read it. */
@@ -2099,6 +2153,41 @@ lang_place_undefineds ()
}
}
+/* Check for all readonly or some readwrite sections. */
+
+static void
+check_input_sections (s, output_section_statement)
+ lang_statement_union_type *s;
+ lang_output_section_statement_type *output_section_statement;
+{
+ for (; s != (lang_statement_union_type *) NULL; s = s->header.next)
+ {
+ switch (s->header.type)
+ {
+ case lang_wild_statement_enum:
+ walk_wild (&s->wild_statement, check_section_callback,
+ output_section_statement);
+ if (! output_section_statement->all_input_readonly)
+ return;
+ break;
+ case lang_constructors_statement_enum:
+ check_input_sections (constructor_list.head,
+ output_section_statement);
+ if (! output_section_statement->all_input_readonly)
+ return;
+ break;
+ case lang_group_statement_enum:
+ check_input_sections (s->group_statement.children.head,
+ output_section_statement);
+ if (! output_section_statement->all_input_readonly)
+ return;
+ break;
+ default:
+ break;
+ }
+ }
+}
+
/* Open input files and attatch to output sections. */
static void
@@ -2120,6 +2209,23 @@ map_input_to_output_sections (s, target,
output_section_statement);
break;
case lang_output_section_statement_enum:
+ if (s->output_section_statement.constraint)
+ {
+ if (s->output_section_statement.constraint == -1)
+ break;
+ s->output_section_statement.all_input_readonly = true;
+ check_input_sections (s->output_section_statement.children.head,
+ &s->output_section_statement);
+ if ((s->output_section_statement.all_input_readonly
+ && s->output_section_statement.constraint == ONLY_IF_RW)
+ || (!s->output_section_statement.all_input_readonly
+ && s->output_section_statement.constraint == ONLY_IF_RO))
+ {
+ s->output_section_statement.constraint = -1;
+ break;
+ }
+ }
+
map_input_to_output_sections (s->output_section_statement.children.head,
target,
&s->output_section_statement);
@@ -2190,6 +2296,8 @@ strip_excluded_output_sections ()
asection *s;
os = &u->output_section_statement;
+ if (os->constraint == -1)
+ continue;
s = os->bfd_section;
if (s != NULL && (s->flags & SEC_EXCLUDE) != 0)
{
@@ -4056,7 +4164,7 @@ topower (x)
lang_output_section_statement_type *
lang_enter_output_section_statement (output_section_statement_name,
address_exp, sectype, block_value,
- align, subalign, ebase)
+ align, subalign, ebase, constraint)
const char *output_section_statement_name;
etree_type *address_exp;
enum section_type sectype;
@@ -4064,12 +4172,14 @@ lang_enter_output_section_statement (out
etree_type *align;
etree_type *subalign;
etree_type *ebase;
+ int constraint;
{
lang_output_section_statement_type *os;
current_section =
os =
- lang_output_section_statement_lookup (output_section_statement_name);
+ lang_output_section_statement_lookup_1 (output_section_statement_name,
+ constraint);
/* Add this statement to tree. */
#if 0
@@ -4784,6 +4894,8 @@ lang_record_phdrs ()
struct lang_output_section_phdr_list *pl;
os = &u->output_section_statement;
+ if (os->constraint == -1)
+ continue;
pl = os->phdrs;
if (pl != NULL)
@@ -4844,7 +4956,8 @@ lang_record_phdrs ()
{
struct lang_output_section_phdr_list *pl;
- if (u->output_section_statement.bfd_section == NULL)
+ if (u->output_section_statement.constraint == -1
+ || u->output_section_statement.bfd_section == NULL)
continue;
for (pl = u->output_section_statement.phdrs;
@@ -4914,7 +5027,7 @@ lang_enter_overlay_section (name)
etree_type *size;
lang_enter_output_section_statement (name, overlay_vma, normal_section,
- 0, 0, 0, 0);
+ 0, 0, 0, 0, 0);
/* If this is the first section, then base the VMA of future
sections on this one. This will work correctly even if `.' is
--- ld/ldlex.l.jj 2002-10-31 19:10:42.000000000 +0100
+++ ld/ldlex.l 2002-11-22 17:29:14.000000000 +0100
@@ -303,6 +303,8 @@ V_IDENTIFIER [*?.$_a-zA-Z\[\]\-\!\^]([*?
<EXPRESSION,BOTH,SCRIPT>"COPY" { RTOKEN(COPY);}
<EXPRESSION,BOTH,SCRIPT>"INFO" { RTOKEN(INFO);}
<EXPRESSION,BOTH,SCRIPT>"OVERLAY" { RTOKEN(OVERLAY);}
+<EXPRESSION,BOTH,SCRIPT>"ONLY_IF_RO" { RTOKEN(ONLY_IF_RO); }
+<EXPRESSION,BOTH,SCRIPT>"ONLY_IF_RW" { RTOKEN(ONLY_IF_RW); }
<BOTH,SCRIPT>"o" { RTOKEN(ORIGIN);}
<BOTH,SCRIPT>"org" { RTOKEN(ORIGIN);}
<BOTH,SCRIPT>"l" { RTOKEN( LENGTH);}
Jakub