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binutils-gdb/gdb/mips-tdep.c

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Initial revision
1991-03-29 00:26:26 +08:00
/* Work with core dump and executable files, for GDB on MIPS.
This code would be in core.c if it weren't machine-dependent. */
/* Low level interface to ptrace, for GDB when running under Unix.
Copyright (C) 1988, 1989, 1990 Free Software Foundation, Inc.
Contributed by Alessandro Forin(af@cs.cmu.edu) at CMU
and by Per Bothner(bothner@cs.wisc.edu) at U.Wisconsin.
This file is part of GDB.
GDB 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 1, or (at your option)
any later version.
GDB 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 GDB; see the file COPYING. If not, write to
the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */
/* FIXME: Can a MIPS porter/tester determine which of these include
files we still need? -- gnu@cygnus.com */
#include <stdio.h>
#include <mips/inst.h>
#include "defs.h"
#include "param.h"
#include "frame.h"
#include "inferior.h"
#include "symtab.h"
#include "value.h"
#include "gdbcmd.h"
#ifdef USG
#include <sys/types.h>
#endif
#include <sys/param.h>
#include <sys/dir.h>
#include <signal.h>
#include <sys/ioctl.h>
#include "gdbcore.h"
#ifndef MIPSMAGIC
#ifdef MIPSEL
#define MIPSMAGIC MIPSELMAGIC
#else
#define MIPSMAGIC MIPSEBMAGIC
#endif
#endif
#define VM_MIN_ADDRESS (unsigned)0x400000
#include <sys/user.h> /* After a.out.h */
#include <sys/file.h>
#include <sys/stat.h>
#define PROC_LOW_ADDR(proc) ((proc)->adr) /* least address */
#define PROC_HIGH_ADDR(proc) ((proc)->pad2) /* upper address bound */
#define PROC_FRAME_OFFSET(proc) ((proc)->framesize)
#define PROC_FRAME_REG(proc) ((proc)->framereg)
#define PROC_REG_MASK(proc) ((proc)->regmask)
#define PROC_FREG_MASK(proc) ((proc)->fregmask)
#define PROC_REG_OFFSET(proc) ((proc)->regoffset)
#define PROC_FREG_OFFSET(proc) ((proc)->fregoffset)
#define PROC_PC_REG(proc) ((proc)->pcreg)
#define PROC_SYMBOL(proc) (*(struct symbol**)&(proc)->isym)
#define _PROC_MAGIC_ 0x0F0F0F0F
#define PROC_DESC_IS_DUMMY(proc) ((proc)->isym == _PROC_MAGIC_)
#define SET_PROC_DESC_IS_DUMMY(proc) ((proc)->isym = _PROC_MAGIC_)
struct linked_proc_info
{
struct mips_extra_func_info info;
struct linked_proc_info *next;
} * linked_proc_desc_table = NULL;
#define READ_FRAME_REG(fi, regno) read_next_frame_reg((fi)->next, regno)
int
read_next_frame_reg(fi, regno)
FRAME fi;
int regno;
{
#define SIGFRAME_BASE sizeof(struct sigcontext)
#define SIGFRAME_PC_OFF (-SIGFRAME_BASE+ 2*sizeof(int))
#define SIGFRAME_SP_OFF (-SIGFRAME_BASE+32*sizeof(int))
#define SIGFRAME_RA_OFF (-SIGFRAME_BASE+34*sizeof(int))
for (; fi; fi = fi->next)
if (in_sigtramp(fi->pc, 0)) {
/* No idea if this code works. --PB. */
int offset;
if (regno == PC_REGNUM) offset = SIGFRAME_PC_OFF;
else if (regno == RA_REGNUM) offset = SIGFRAME_RA_OFF;
else if (regno == SP_REGNUM) offset = SIGFRAME_SP_OFF;
else return 0;
return read_memory_integer(fi->frame + offset, 4);
}
else if (regno == SP_REGNUM) return fi->frame;
else if (fi->saved_regs->regs[regno])
return read_memory_integer(fi->saved_regs->regs[regno], 4);
return read_register(regno);
}
int
mips_frame_saved_pc(frame)
FRAME frame;
{
mips_extra_func_info_t proc_desc = (mips_extra_func_info_t)frame->proc_desc;
int pcreg = proc_desc ? PROC_PC_REG(proc_desc) : RA_REGNUM;
if (proc_desc && PROC_DESC_IS_DUMMY(proc_desc))
return read_memory_integer(frame->frame - 4, 4);
#if 0
/* If in the procedure prologue, RA_REGNUM might not have been saved yet.
* Assume non-leaf functions start with:
* addiu $sp,$sp,-frame_size
* sw $ra,ra_offset($sp)
* This if the pc is pointing at either of these instructions,
* then $ra hasn't been trashed.
* If the pc has advanced beyond these two instructions,
* then $ra has been saved.
* critical, and much more complex. Handling $ra is enough to get
* a stack trace, but some register values with be wrong.
*/
if (frame->proc_desc && frame->pc < PROC_LOW_ADDR(proc_desc) + 8)
return read_register(pcreg);
#endif
return read_next_frame_reg(frame, pcreg);
}
static struct mips_extra_func_info temp_proc_desc;
static struct frame_saved_regs temp_saved_regs;
CORE_ADDR heuristic_proc_start(pc)
CORE_ADDR pc;
{
CORE_ADDR start_pc = pc;
CORE_ADDR fence = start_pc - 10000;
if (fence < VM_MIN_ADDRESS) fence = VM_MIN_ADDRESS;
/* search back for previous return */
for (start_pc -= 4; ; start_pc -= 4)
if (start_pc < fence) return 0;
else if (ABOUT_TO_RETURN(start_pc))
break;
start_pc += 8; /* skip return, and its delay slot */
#if 0
/* skip nops (usually 1) 0 - is this */
while (start_pc < pc && read_memory_integer (start_pc, 4) == 0)
start_pc += 4;
#endif
return start_pc;
}
mips_extra_func_info_t
heuristic_proc_desc(start_pc, limit_pc, next_frame)
CORE_ADDR start_pc, limit_pc;
FRAME next_frame;
{
CORE_ADDR sp = next_frame ? next_frame->frame : read_register (SP_REGNUM);
CORE_ADDR cur_pc;
int frame_size;
int has_frame_reg = 0;
int reg30; /* Value of $r30. Used by gcc for frame-pointer */
unsigned long reg_mask = 0;
if (start_pc == 0) return NULL;
bzero(&temp_proc_desc, sizeof(temp_proc_desc));
bzero(&temp_saved_regs, sizeof(struct frame_saved_regs));
if (start_pc + 200 < limit_pc) limit_pc = start_pc + 200;
restart:
frame_size = 0;
for (cur_pc = start_pc; cur_pc < limit_pc; cur_pc += 4) {
unsigned long word;
int status;
status = read_memory_nobpt (cur_pc, &word, 4);
if (status) memory_error (status, cur_pc);
if ((word & 0xFFFF0000) == 0x27bd0000) /* addiu $sp,$sp,-i */
frame_size += (-word) & 0xFFFF;
else if ((word & 0xFFFF0000) == 0x23bd0000) /* addu $sp,$sp,-i */
frame_size += (-word) & 0xFFFF;
else if ((word & 0xFFE00000) == 0xafa00000) { /* sw reg,offset($sp) */
int reg = (word & 0x001F0000) >> 16;
reg_mask |= 1 << reg;
temp_saved_regs.regs[reg] = sp + (short)word;
}
else if ((word & 0xFFFF0000) == 0x27be0000) { /* addiu $30,$sp,size */
if ((unsigned short)word != frame_size)
reg30 = sp + (unsigned short)word;
else if (!has_frame_reg) {
int alloca_adjust;
has_frame_reg = 1;
reg30 = read_next_frame_reg(next_frame, 30);
alloca_adjust = reg30 - (sp + (unsigned short)word);
if (alloca_adjust > 0) {
/* FP > SP + frame_size. This may be because
/* of an alloca or somethings similar.
* Fix sp to "pre-alloca" value, and try again.
*/
sp += alloca_adjust;
goto restart;
}
}
}
else if ((word & 0xFFE00000) == 0xafc00000) { /* sw reg,offset($30) */
int reg = (word & 0x001F0000) >> 16;
reg_mask |= 1 << reg;
temp_saved_regs.regs[reg] = reg30 + (short)word;
}
}
if (has_frame_reg) {
PROC_FRAME_REG(&temp_proc_desc) = 30;
PROC_FRAME_OFFSET(&temp_proc_desc) = 0;
}
else {
PROC_FRAME_REG(&temp_proc_desc) = SP_REGNUM;
PROC_FRAME_OFFSET(&temp_proc_desc) = frame_size;
}
PROC_REG_MASK(&temp_proc_desc) = reg_mask;
PROC_PC_REG(&temp_proc_desc) = RA_REGNUM;
return &temp_proc_desc;
}
mips_extra_func_info_t
find_proc_desc(pc, next_frame)
CORE_ADDR pc;
FRAME next_frame;
{
mips_extra_func_info_t proc_desc;
extern struct block *block_for_pc();
struct block *b = block_for_pc(pc);
struct symbol *sym =
b ? lookup_symbol(".gdbinfo.", b, LABEL_NAMESPACE, 0, NULL) : NULL;
if (sym != NULL)
{
/* IF this is the topmost frame AND
* (this proc does not have debugging information OR
* the PC is in the procedure prologue)
* THEN create a "hueristic" proc_desc (by analyzing
* the actual code) to replace the "official" proc_desc.
*/
proc_desc = (struct mips_extra_func_info *)sym->value.value;
if (next_frame == NULL) {
struct symtab_and_line val;
struct symbol *proc_symbol =
PROC_DESC_IS_DUMMY(proc_desc) ? 0 : PROC_SYMBOL(proc_desc);
if (proc_symbol) {
val = find_pc_line (BLOCK_START
(SYMBOL_BLOCK_VALUE(proc_symbol)),
0);
val.pc = val.end ? val.end : pc;
}
if (!proc_symbol || pc < val.pc) {
mips_extra_func_info_t found_heuristic =
heuristic_proc_desc(PROC_LOW_ADDR(proc_desc),
pc, next_frame);
if (found_heuristic) proc_desc = found_heuristic;
}
}
}
else
{
register struct linked_proc_info *link;
for (link = linked_proc_desc_table; link; link = link->next)
if (PROC_LOW_ADDR(&link->info) <= pc
&& PROC_HIGH_ADDR(&link->info) > pc)
return &link->info;
proc_desc =
heuristic_proc_desc(heuristic_proc_start(pc), pc, next_frame);
}
return proc_desc;
}
mips_extra_func_info_t cached_proc_desc;
FRAME_ADDR mips_frame_chain(frame)
FRAME frame;
{
extern CORE_ADDR startup_file_start; /* From blockframe.c */
mips_extra_func_info_t proc_desc;
CORE_ADDR saved_pc = FRAME_SAVED_PC(frame);
if (startup_file_start)
{ /* has at least the __start symbol */
if (saved_pc == 0 || !outside_startup_file (saved_pc)) return 0;
}
else
{ /* This hack depends on the internals of __start. */
/* We also assume the breakpoints are *not* inserted */
if (read_memory_integer (saved_pc + 8, 4) & 0xFC00003F == 0xD)
return 0; /* break */
}
proc_desc = find_proc_desc(saved_pc, frame);
if (!proc_desc) return 0;
cached_proc_desc = proc_desc;
return read_next_frame_reg(frame, PROC_FRAME_REG(proc_desc))
+ PROC_FRAME_OFFSET(proc_desc);
}
void
init_extra_frame_info(fci)
struct frame_info *fci;
{
extern struct obstack frame_cache_obstack;
/* Use proc_desc calculated in frame_chain */
mips_extra_func_info_t proc_desc = fci->next ? cached_proc_desc :
find_proc_desc(fci->pc, fci->next);
fci->saved_regs = (struct frame_saved_regs*)
obstack_alloc (&frame_cache_obstack, sizeof(struct frame_saved_regs));
bzero(fci->saved_regs, sizeof(struct frame_saved_regs));
fci->proc_desc =
proc_desc == &temp_proc_desc ? (char*)NULL : (char*)proc_desc;
if (proc_desc)
{
int ireg;
CORE_ADDR reg_position;
unsigned long mask;
/* r0 bit means kernel trap */
int kernel_trap = PROC_REG_MASK(proc_desc) & 1;
/* Fixup frame-pointer - only needed for top frame */
/* This may not be quite right, if procedure has a real frame register */
if (fci->pc == PROC_LOW_ADDR(proc_desc))
fci->frame = read_register (SP_REGNUM);
else
fci->frame = READ_FRAME_REG(fci, PROC_FRAME_REG(proc_desc))
+ PROC_FRAME_OFFSET(proc_desc);
if (proc_desc == &temp_proc_desc)
*fci->saved_regs = temp_saved_regs;
else
{
/* find which general-purpose registers were saved */
reg_position = fci->frame + PROC_REG_OFFSET(proc_desc);
mask = kernel_trap ? 0xFFFFFFFF : PROC_REG_MASK(proc_desc);
for (ireg= 31; mask; --ireg, mask <<= 1)
if (mask & 0x80000000)
{
fci->saved_regs->regs[ireg] = reg_position;
reg_position -= 4;
}
/* find which floating-point registers were saved */
reg_position = fci->frame + PROC_FREG_OFFSET(proc_desc);
/* The freg_offset points to where the first *double* register is saved.
* So skip to the high-order word. */
reg_position += 4;
mask = kernel_trap ? 0xFFFFFFFF : PROC_FREG_MASK(proc_desc);
for (ireg = 31; mask; --ireg, mask <<= 1)
if (mask & 0x80000000)
{
fci->saved_regs->regs[32+ireg] = reg_position;
reg_position -= 4;
}
}
/* hack: if argument regs are saved, guess these contain args */
if ((PROC_REG_MASK(proc_desc) & 0xF0) == 0) fci->num_args = -1;
else if ((PROC_REG_MASK(proc_desc) & 0x80) == 0) fci->num_args = 4;
else if ((PROC_REG_MASK(proc_desc) & 0x40) == 0) fci->num_args = 3;
else if ((PROC_REG_MASK(proc_desc) & 0x20) == 0) fci->num_args = 2;
else if ((PROC_REG_MASK(proc_desc) & 0x10) == 0) fci->num_args = 1;
fci->saved_regs->regs[PC_REGNUM] = fci->saved_regs->regs[RA_REGNUM];
}
if (fci->next == 0)
supply_register(FP_REGNUM, &fci->frame);
}
CORE_ADDR mips_push_arguments(nargs, args, sp, struct_return, struct_addr)
int nargs;
value *args;
CORE_ADDR sp;
int struct_return;
CORE_ADDR struct_addr;
{
CORE_ADDR buf;
register i;
int accumulate_size = struct_return ? 4 : 0;
struct mips_arg { char *contents; int len; int offset; };
struct mips_arg *mips_args =
(struct mips_arg*)alloca(nargs * sizeof(struct mips_arg));
register struct mips_arg *m_arg;
for (i = 0, m_arg = mips_args; i < nargs; i++, m_arg++) {
extern value value_arg_coerce();
value arg = value_arg_coerce (args[i]);
m_arg->len = TYPE_LENGTH (VALUE_TYPE (arg));
/* This entire mips-specific routine is because doubles must be aligned
* on 8-byte boundaries. It still isn't quite right, because MIPS decided
* to align 'struct {int a, b}' on 4-byte boundaries (even though this
* breaks their varargs implementation...). A correct solution
* requires an simulation of gcc's 'alignof' (and use of 'alignof'
* in stdarg.h/varargs.h).
*/
if (m_arg->len > 4) accumulate_size = (accumulate_size + 7) & -8;
m_arg->offset = accumulate_size;
accumulate_size = (accumulate_size + m_arg->len + 3) & -4;
m_arg->contents = VALUE_CONTENTS(arg);
}
accumulate_size = (accumulate_size + 7) & (-8);
if (accumulate_size < 16) accumulate_size = 16;
sp -= accumulate_size;
for (i = nargs; m_arg--, --i >= 0; )
write_memory(sp + m_arg->offset, m_arg->contents, m_arg->len);
if (struct_return) {
buf = struct_addr;
write_memory(sp, &buf, sizeof(CORE_ADDR));
}
return sp;
}
/* MASK(i,j) == (1<<i) + (1<<(i+1)) + ... + (1<<j)). Assume i<=j<31. */
#define MASK(i,j) ((1 << (j)+1)-1 ^ (1 << (i))-1)
void
mips_push_dummy_frame()
{
int ireg;
struct linked_proc_info *link = (struct linked_proc_info*)
xmalloc(sizeof(struct linked_proc_info));
mips_extra_func_info_t proc_desc = &link->info;
CORE_ADDR sp = read_register (SP_REGNUM);
CORE_ADDR save_address;
REGISTER_TYPE buffer;
link->next = linked_proc_desc_table;
linked_proc_desc_table = link;
#define PUSH_FP_REGNUM 16 /* must be a register preserved across calls */
#define GEN_REG_SAVE_MASK MASK(1,16)|MASK(24,28)|(1<<31)
#define GEN_REG_SAVE_COUNT 22
#define FLOAT_REG_SAVE_MASK MASK(0,19)
#define FLOAT_REG_SAVE_COUNT 20
#define SPECIAL_REG_SAVE_COUNT 4
/*
* The registers we must save are all those not preserved across
* procedure calls. Dest_Reg (see tm-mips.h) must also be saved.
* In addition, we must save the PC, and PUSH_FP_REGNUM.
* (Ideally, we should also save MDLO/-HI and FP Control/Status reg.)
*
* Dummy frame layout:
* (high memory)
* Saved PC
* Saved MMHI, MMLO, FPC_CSR
* Saved R31
* Saved R28
* ...
* Saved R1
* Saved D18 (i.e. F19, F18)
* ...
* Saved D0 (i.e. F1, F0)
* CALL_DUMMY (subroutine stub; see m-mips.h)
* Parameter build area (not yet implemented)
* (low memory)
*/
PROC_REG_MASK(proc_desc) = GEN_REG_SAVE_MASK;
PROC_FREG_MASK(proc_desc) = FLOAT_REG_SAVE_MASK;
PROC_REG_OFFSET(proc_desc) = /* offset of (Saved R31) from FP */
-sizeof(long) - 4 * SPECIAL_REG_SAVE_COUNT;
PROC_FREG_OFFSET(proc_desc) = /* offset of (Saved D18) from FP */
-sizeof(double) - 4 * (SPECIAL_REG_SAVE_COUNT + GEN_REG_SAVE_COUNT);
/* save general registers */
save_address = sp + PROC_REG_OFFSET(proc_desc);
for (ireg = 32; --ireg >= 0; )
if (PROC_REG_MASK(proc_desc) & (1 << ireg))
{
buffer = read_register (ireg);
write_memory (save_address, &buffer, sizeof(REGISTER_TYPE));
save_address -= 4;
}
/* save floating-points registers */
save_address = sp + PROC_FREG_OFFSET(proc_desc);
for (ireg = 32; --ireg >= 0; )
if (PROC_FREG_MASK(proc_desc) & (1 << ireg))
{
buffer = read_register (ireg);
write_memory (save_address, &buffer, 4);
save_address -= 4;
}
write_register (PUSH_FP_REGNUM, sp);
PROC_FRAME_REG(proc_desc) = PUSH_FP_REGNUM;
PROC_FRAME_OFFSET(proc_desc) = 0;
buffer = read_register (PC_REGNUM);
write_memory (sp - 4, &buffer, sizeof(REGISTER_TYPE));
buffer = read_register (HI_REGNUM);
write_memory (sp - 8, &buffer, sizeof(REGISTER_TYPE));
buffer = read_register (LO_REGNUM);
write_memory (sp - 12, &buffer, sizeof(REGISTER_TYPE));
buffer = read_register (FCRCS_REGNUM);
write_memory (sp - 16, &buffer, sizeof(REGISTER_TYPE));
sp -= 4 * (GEN_REG_SAVE_COUNT+FLOAT_REG_SAVE_COUNT+SPECIAL_REG_SAVE_COUNT);
write_register (SP_REGNUM, sp);
PROC_LOW_ADDR(proc_desc) = sp - CALL_DUMMY_SIZE + CALL_DUMMY_START_OFFSET;
PROC_HIGH_ADDR(proc_desc) = sp;
SET_PROC_DESC_IS_DUMMY(proc_desc);
PROC_PC_REG(proc_desc) = RA_REGNUM;
}
void
mips_pop_frame()
{ register int regnum;
FRAME frame = get_current_frame ();
CORE_ADDR new_sp = frame->frame;
mips_extra_func_info_t proc_desc = (mips_extra_func_info_t)frame->proc_desc;
if (PROC_DESC_IS_DUMMY(proc_desc))
{
struct linked_proc_info **ptr = &linked_proc_desc_table;;
for (; &ptr[0]->info != proc_desc; ptr = &ptr[0]->next )
if (ptr[0] == NULL) abort();
*ptr = ptr[0]->next;
free (ptr[0]);
write_register (HI_REGNUM, read_memory_integer(new_sp - 8, 4));
write_register (LO_REGNUM, read_memory_integer(new_sp - 12, 4));
write_register (FCRCS_REGNUM, read_memory_integer(new_sp - 16, 4));
}
write_register (PC_REGNUM, FRAME_SAVED_PC(frame));
if (frame->proc_desc) {
for (regnum = 32; --regnum >= 0; )
if (PROC_REG_MASK(proc_desc) & (1 << regnum))
write_register (regnum,
read_memory_integer (frame->saved_regs->regs[regnum], 4));
for (regnum = 64; --regnum >= 32; )
if (PROC_FREG_MASK(proc_desc) & (1 << regnum))
write_register (regnum,
read_memory_integer (frame->saved_regs->regs[regnum], 4));
}
write_register (SP_REGNUM, new_sp);
flush_cached_frames ();
set_current_frame (create_new_frame (new_sp, read_pc ()));
}
static mips_print_register(regnum, all)
int regnum, all;
{
unsigned char raw_buffer[8];
REGISTER_TYPE val;
read_relative_register_raw_bytes (regnum, raw_buffer);
if (!(regnum & 1) && regnum >= FP0_REGNUM && regnum < FP0_REGNUM+32) {
read_relative_register_raw_bytes (regnum+1, raw_buffer+4);
printf_filtered ("(d%d: ", regnum&31);
val_print (builtin_type_double, raw_buffer, 0,
stdout, 0, 1, 0, Val_pretty_default);
printf_filtered ("); ", regnum&31);
}
fputs_filtered (reg_names[regnum], stdout);
#ifndef NUMERIC_REG_NAMES
if (regnum < 32)
printf_filtered ("(r%d): ", regnum);
else
#endif
printf_filtered (": ");
/* If virtual format is floating, print it that way. */
if (TYPE_CODE (REGISTER_VIRTUAL_TYPE (regnum)) == TYPE_CODE_FLT
&& ! INVALID_FLOAT (raw_buffer, REGISTER_VIRTUAL_SIZE(regnum))) {
val_print (REGISTER_VIRTUAL_TYPE (regnum), raw_buffer, 0,
stdout, 0, 1, 0, Val_pretty_default);
}
/* Else print as integer in hex. */
else
{
long val;
bcopy (raw_buffer, &val, sizeof (long));
if (val == 0)
printf_filtered ("0");
else if (all)
printf_filtered ("0x%x", val);
else
printf_filtered ("0x%x=%d", val, val);
}
}
mips_do_registers_info(regnum)
int regnum;
{
if (regnum != -1) {
mips_print_register (regnum, 0);
printf_filtered ("\n");
}
else {
for (regnum = 0; regnum < NUM_REGS; ) {
mips_print_register (regnum, 1);
regnum++;
if ((regnum & 3) == 0 || regnum == NUM_REGS)
printf_filtered (";\n");
else
printf_filtered ("; ");
}
}
}
/* Return number of args passed to a frame. described by FIP.
Can return -1, meaning no way to tell. */
mips_frame_num_args(fip)
FRAME fip;
{
#if 0
struct chain_info_t *p;
p = mips_find_cached_frame(FRAME_FP(fip));
if (p->valid)
return p->the_info.numargs;
#endif
return -1;
}
/* Bad floats: Returns 0 if P points to a valid IEEE floating point number,
1 if P points to a denormalized number or a NaN. LEN says whether this is
a single-precision or double-precision float */
#define SINGLE_EXP_BITS 8
#define DOUBLE_EXP_BITS 11
int
isa_NAN(p, len)
int *p, len;
{
int exponent;
if (len == 4)
{
exponent = *p;
exponent = exponent << 1 >> (32 - SINGLE_EXP_BITS - 1);
return ((exponent == -1) || (! exponent && *p));
}
else if (len == 8)
{
exponent = *(p+1);
exponent = exponent << 1 >> (32 - DOUBLE_EXP_BITS - 1);
return ((exponent == -1) || (! exponent && *p * *(p+1)));
}
else return 1;
}
/* To skip prologues, I use this predicate. Returns either PC
itself if the code at PC does not look like a function prologue,
PC+4 if it does (our caller does not need anything more fancy). */
CORE_ADDR mips_skip_prologue(pc)
CORE_ADDR pc;
{
struct symbol *f;
struct block *b;
unsigned long inst;
/* For -g modules and most functions anyways the
first instruction adjusts the stack. */
inst = read_memory_integer(pc, 4);
if ((inst & 0xffff0000) == 0x27bd0000)
return pc + 4;
/* Well, it looks like a frameless. Let's make sure.
Note that we are not called on the current PC,
but on the function`s start PC, and I have definitely
seen optimized code that adjusts the SP quite later */
b = block_for_pc(pc);
if (!b) return pc;
f = lookup_symbol(".gdbinfo.", b, LABEL_NAMESPACE, 0, NULL);
if (!f) return pc;
/* Ideally, I would like to use the adjusted info
from mips_frame_info(), but for all practical
purposes it will not matter (and it would require
a different definition of SKIP_PROLOGUE())
Actually, it would not hurt to skip the storing
of arguments on the stack as well. */
if (((struct mips_extra_func_info *)f->value.value)->framesize)
return pc + 4;
return pc;
}
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