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x86: shrink prefix related disassembler state fields

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By changing the values used for "artificial" prefix values,
all_prefixes[] can be shrunk to array of unsigned char. All that
additionally needs adjusting is the printing of possible apparently
standalone prefixes when recovering from longjmp(): Simply check
whether any prefixes were successfully decoded, to avoid converting
opcode bytes matching the "artificial" values to prefix mnemonics.

Similarly by re-arranging the bits assigned to PREFIX_* mask values
we can fit all segment register masks in a byte and hence shrink
active_seg_prefix to unsigned char.

Somewhat similarly with last_*_prefix representing offsets into the
opcode being disassembled, signed char is sufficient to hold all possible
values.
This commit is contained in:
Jan Beulich
2022-06-13 09:52:33 +02:00
parent 384e201e5a
commit eebc56d682
1 changed files with 28 additions and 27 deletions
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55
opcodes/i386-dis.c
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@ -175,21 +175,21 @@ struct instr_info
unsigned char *insn_codep; unsigned char *insn_codep;
unsigned char *codep; unsigned char *codep;
unsigned char *end_codep; unsigned char *end_codep;
int last_lock_prefix; signed char last_lock_prefix;
int last_repz_prefix; signed char last_repz_prefix;
int last_repnz_prefix; signed char last_repnz_prefix;
int last_data_prefix; signed char last_data_prefix;
int last_addr_prefix; signed char last_addr_prefix;
int last_rex_prefix; signed char last_rex_prefix;
int last_seg_prefix; signed char last_seg_prefix;
int fwait_prefix; signed char fwait_prefix;
/* The active segment register prefix. */ /* The active segment register prefix. */
int active_seg_prefix; unsigned char active_seg_prefix;
#define MAX_CODE_LENGTH 15 #define MAX_CODE_LENGTH 15
/* We can up to 14 ins->prefixes since the maximum instruction length is /* We can up to 14 ins->prefixes since the maximum instruction length is
15bytes. */ 15bytes. */
int all_prefixes[MAX_CODE_LENGTH - 1]; unsigned char all_prefixes[MAX_CODE_LENGTH - 1];
disassemble_info *info; disassemble_info *info;
struct struct
@ -276,13 +276,13 @@ struct instr_info
/* Flags stored in PREFIXES. */ /* Flags stored in PREFIXES. */
#define PREFIX_REPZ 1 #define PREFIX_REPZ 1
#define PREFIX_REPNZ 2 #define PREFIX_REPNZ 2
#define PREFIX_LOCK 4 #define PREFIX_CS 4
#define PREFIX_CS 8 #define PREFIX_SS 8
#define PREFIX_SS 0x10 #define PREFIX_DS 0x10
#define PREFIX_DS 0x20 #define PREFIX_ES 0x20
#define PREFIX_ES 0x40 #define PREFIX_FS 0x40
#define PREFIX_FS 0x80 #define PREFIX_GS 0x80
#define PREFIX_GS 0x100 #define PREFIX_LOCK 0x100
#define PREFIX_DATA 0x200 #define PREFIX_DATA 0x200
#define PREFIX_ADDR 0x400 #define PREFIX_ADDR 0x400
#define PREFIX_FWAIT 0x800 #define PREFIX_FWAIT 0x800
@ -8532,13 +8532,13 @@ static const struct dis386 rm_table[][8] = {
#define INTERNAL_DISASSEMBLER_ERROR _("<internal disassembler error>") #define INTERNAL_DISASSEMBLER_ERROR _("<internal disassembler error>")
/* We use the high bit to indicate different name for the same /* The values used here must be non-zero, fit in 'unsigned char', and not be
prefix. */ in conflict with actual prefix opcodes. */
#define REP_PREFIX (0xf3 | 0x100) #define REP_PREFIX 0x01
#define XACQUIRE_PREFIX (0xf2 | 0x200) #define XACQUIRE_PREFIX 0x02
#define XRELEASE_PREFIX (0xf3 | 0x400) #define XRELEASE_PREFIX 0x03
#define BND_PREFIX (0xf2 | 0x400) #define BND_PREFIX 0x04
#define NOTRACK_PREFIX (0x3e | 0x100) #define NOTRACK_PREFIX 0x05
static int static int
ckprefix (instr_info *ins) ckprefix (instr_info *ins)
@ -9519,14 +9519,15 @@ print_insn (bfd_vma pc, disassemble_info *info, int intel_syntax)
if (OPCODES_SIGSETJMP (priv.bailout) != 0) if (OPCODES_SIGSETJMP (priv.bailout) != 0)
{ {
const char *name;
/* Getting here means we tried for data but didn't get it. That /* Getting here means we tried for data but didn't get it. That
means we have an incomplete instruction of some sort. Just means we have an incomplete instruction of some sort. Just
print the first byte as a prefix or a .byte pseudo-op. */ print the first byte as a prefix or a .byte pseudo-op. */
if (ins.codep > priv.the_buffer) if (ins.codep > priv.the_buffer)
{ {
name = prefix_name (&ins, priv.the_buffer[0], priv.orig_sizeflag); const char *name = NULL;
if (ins.prefixes || ins.fwait_prefix >= 0 || (ins.rex & REX_OPCODE))
name = prefix_name (&ins, priv.the_buffer[0], priv.orig_sizeflag);
if (name != NULL) if (name != NULL)
i386_dis_printf (&ins, dis_style_mnemonic, "%s", name); i386_dis_printf (&ins, dis_style_mnemonic, "%s", name);
else else