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x86: Regex support and known-movable symbols for relocs, fix _end

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This adds a new category of symbols to the relocs program: symbols
which are known to be relative, even though the linker emits them as
absolute; this is the case for symbols that live in the linker script,
which currently applies to _end.

Unfortunately the previous workaround of putting _end in its own empty
section was defeated by newer binutils, which remove empty sections
completely.

This patch also changes the symbol matching to use regular expressions
instead of hardcoded C for specific patterns.

This is a decidedly non-minimal patch: a modified version of the
relocs program is used as part of the Syslinux build, and this 	is
basically a backport to Linux of some of those changes; they have
thus been well tested.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
LKML-Reference: <4AF86211.3070103@zytor.com>
Acked-by: Michal Marek <mmarek@suse.cz>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
This commit is contained in:
H. Peter Anvin 2009-12-14 13:55:20 -08:00
parent 494c2ebfb2
commit 873b5271f8
2 changed files with 61 additions and 32 deletions
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89
arch/x86/boot/compressed/relocs.c
View File

@ -9,6 +9,9 @@
#include <byteswap.h>
#define USE_BSD
#include <endian.h>
#include <regex.h>
static void die(char *fmt, ...);
#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
static Elf32_Ehdr ehdr;
@ -30,25 +33,47 @@ static struct section *secs;
* the address for which it has been compiled. Don't warn user about
* absolute relocations present w.r.t these symbols.
*/
static const char* safe_abs_relocs[] = {
"xen_irq_disable_direct_reloc",
"xen_save_fl_direct_reloc",
};
static int is_safe_abs_reloc(const char* sym_name)
static const char abs_sym_regex[] =
"^(xen_irq_disable_direct_reloc$|"
"xen_save_fl_direct_reloc$|"
"VDSO|"
"__crc_)";
static regex_t abs_sym_regex_c;
static int is_abs_reloc(const char *sym_name)
{
int i;
return !regexec(&abs_sym_regex_c, sym_name, 0, NULL, 0);
}
for (i = 0; i < ARRAY_SIZE(safe_abs_relocs); i++) {
if (!strcmp(sym_name, safe_abs_relocs[i]))
/* Match found */
return 1;
}
if (strncmp(sym_name, "VDSO", 4) == 0)
return 1;
if (strncmp(sym_name, "__crc_", 6) == 0)
return 1;
return 0;
/*
* These symbols are known to be relative, even if the linker marks them
* as absolute (typically defined outside any section in the linker script.)
*/
static const char rel_sym_regex[] =
"^_end$";
static regex_t rel_sym_regex_c;
static int is_rel_reloc(const char *sym_name)
{
return !regexec(&rel_sym_regex_c, sym_name, 0, NULL, 0);
}
static void regex_init(void)
{
char errbuf[128];
int err;
err = regcomp(&abs_sym_regex_c, abs_sym_regex,
REG_EXTENDED|REG_NOSUB);
if (err) {
regerror(err, &abs_sym_regex_c, errbuf, sizeof errbuf);
die("%s", errbuf);
}
err = regcomp(&rel_sym_regex_c, rel_sym_regex,
REG_EXTENDED|REG_NOSUB);
if (err) {
regerror(err, &rel_sym_regex_c, errbuf, sizeof errbuf);
die("%s", errbuf);
}
}
static void die(char *fmt, ...)
@ -131,7 +156,7 @@ static const char *rel_type(unsigned type)
#undef REL_TYPE
};
const char *name = "unknown type rel type name";
if (type < ARRAY_SIZE(type_name)) {
if (type < ARRAY_SIZE(type_name) && type_name[type]) {
name = type_name[type];
}
return name;
@ -448,7 +473,7 @@ static void print_absolute_relocs(void)
* Before warning check if this absolute symbol
* relocation is harmless.
*/
if (is_safe_abs_reloc(name))
if (is_abs_reloc(name) || is_rel_reloc(name))
continue;
if (!printed) {
@ -501,21 +526,26 @@ static void walk_relocs(void (*visit)(Elf32_Rel *rel, Elf32_Sym *sym))
sym = &sh_symtab[ELF32_R_SYM(rel->r_info)];
r_type = ELF32_R_TYPE(rel->r_info);
/* Don't visit relocations to absolute symbols */
if (sym->st_shndx == SHN_ABS) {
if (sym->st_shndx == SHN_ABS &&
!is_rel_reloc(sym_name(sym_strtab, sym))) {
continue;
}
if (r_type == R_386_NONE || r_type == R_386_PC32) {
switch (r_type) {
case R_386_NONE:
case R_386_PC32:
/*
* NONE can be ignored and and PC relative
* relocations don't need to be adjusted.
*/
}
else if (r_type == R_386_32) {
break;
case R_386_32:
/* Visit relocations that need to be adjusted */
visit(rel, sym);
}
else {
die("Unsupported relocation type: %d\n", r_type);
break;
default:
die("Unsupported relocation type: %s (%d)\n",
rel_type(r_type), r_type);
break;
}
}
}
@ -571,16 +601,15 @@ static void emit_relocs(int as_text)
}
else {
unsigned char buf[4];
buf[0] = buf[1] = buf[2] = buf[3] = 0;
/* Print a stop */
printf("%c%c%c%c", buf[0], buf[1], buf[2], buf[3]);
fwrite("\0\0\0\0", 4, 1, stdout);
/* Now print each relocation */
for (i = 0; i < reloc_count; i++) {
buf[0] = (relocs[i] >> 0) & 0xff;
buf[1] = (relocs[i] >> 8) & 0xff;
buf[2] = (relocs[i] >> 16) & 0xff;
buf[3] = (relocs[i] >> 24) & 0xff;
printf("%c%c%c%c", buf[0], buf[1], buf[2], buf[3]);
fwrite(buf, 4, 1, stdout);
}
}
}
@ -598,6 +627,8 @@ int main(int argc, char **argv)
FILE *fp;
int i;
regex_init();
show_absolute_syms = 0;
show_absolute_relocs = 0;
as_text = 0;

4
arch/x86/kernel/vmlinux.lds.S
View File

@ -319,9 +319,7 @@ SECTIONS
__brk_limit = .;
}
.end : AT(ADDR(.end) - LOAD_OFFSET) {
_end = .;
}
_end = .;
STABS_DEBUG
DWARF_DEBUG