sysprof/unwind.c

#include "elfparser.h"
#include "binparser.h"
#include <string.h>

/* FIXME: endianness, 64 bit */

static guint64
get_length (const guchar **data)
{
    guint64 len;

    len = *(guint32 *)*data;

    *data += 4;
    
    if (len == 0xffffffff)
    {
	len = *(guint64 *)data;
	*data += 8;
    }

    return len;
}

static guint64
decode_uleb128 (const guchar **data)
{
    guint64 result;
    int shift;
    guchar b;

    result = 0;
    shift = 0;
    do
    {
	b = *(*data)++;
	result |= (b & 0x7f) << shift;
	shift += 7;

    } while (b & 0x80);

    return result;
}

static gint64
decode_sleb128 (const guchar **data)
{
    gint64 result;
    int shift;
    guchar b;

    result = 0;
    shift = 0;
    do
    {
	b = *(*data)++;
	result |= (b & 0x7f) << shift;
	shift += 7;
    } while (b & 0x80);

    if (b & 0x40 && shift < 64)
	result |= - (1 << shift);

    return result;
}

static void
decode_block (const guchar **data)
{
    int len;
    
    /* FIXME */

    len = decode_uleb128 (data);

    (*data) += len;
}

static gulong
decode_address (const guchar **data)
{
    /* FIXME */
    gulong r;

    r = *(guint32 *)*data;
    (*data) += 4;
    return r;
}

static const char *
decode_instruction (const guchar **data)
{
    int opcode = *(*data)++;
    int high2 = (opcode & 0xc0) >> 6;
    int low6 = (opcode & 0x3f);

    if (high2 == 0x01)
    {
	return "DW_CFA_advance_loc";
    }
    else if (high2 == 0x02)
    {
	g_print ("register: %d\n", low6);
	g_print ("offset: %llu\n", decode_uleb128 (data));
	
	return "DW_CFA_offset";
    }
    else if (high2 == 0x03)
    {
	return "DW_CFA_restore";
    }
    else
    {
	g_assert ((opcode & 0xc0) == 0);
	
	switch (opcode)
	{
	case 0x0:
	    return "DW_CFA_nop";
	    
	case 0x01:
	    g_print ("addr: %p\n", (void *)decode_address (data));
	    return "DW_CFA_set_loc";

	case 0x02:
	    (*data)++;
	    return "DW_CFA_advance_loc1";

	case 0x03:
	    (*data) += 2;
	    return "DW_CFA_advance_loc2";

	case 0x04:
	    (*data) += 4;
	    return "DW_CFA_advance_loc4";

	case 0x05:
	    decode_uleb128 (data);
	    decode_uleb128 (data);
	    return "DW_CFA_offset_extended";

	case 0x06:
	    decode_uleb128 (data);
	    return "DW_CFA_restore_extended";

	case 0x07:
	    decode_uleb128 (data);
	    return "DW_CFA_undefined";

	case 0x08:
	    decode_uleb128 (data);
	    return "DW_CFA_same_value";

	case 0x09:
	    decode_uleb128 (data);
	    decode_uleb128 (data);
	    return "DW_CFA_register";

	case 0x0a:
	    return "DW_CFA_remember_state";

	case 0x0b:
	    return "DW_CFA_restore_state";

	case 0x0c:
	    g_print ("reg: %llu\n", decode_uleb128 (data));
	    g_print ("off: %llu\n", decode_uleb128 (data));
	    return "DW_CFA_def_cfa";

	case 0x0d:
	    decode_uleb128 (data);
	    return "DW_CFA_def_cfa_register";

	case 0x0e:
	    decode_uleb128 (data);
	    return "DW_CFA_def_cfa_offset";

	case 0x0f:
	    decode_block (data);
	    return "DW_CFA_def_cfa_expression";

	case 0x10:
	    decode_uleb128 (data);
	    decode_block (data);
	    return "DW_CFA_expression";

	case 0x11:
	    decode_uleb128 (data);
	    decode_sleb128 (data);
	    return "DW_CFA_offset_extended_sf";

	case 0x12:
	    decode_uleb128 (data);
	    decode_sleb128 (data);
	    return "DW_CFA_def_cfa_sf";

	case 0x13:
	    decode_sleb128 (data);
	    return "DW_CFA_def_cfa_offset_sf";

	case 0x14:
	    decode_uleb128 (data);
	    decode_uleb128 (data);
	    return "DW_CFA_val_offset";

	case 0x15:
	    decode_uleb128 (data);
	    decode_sleb128 (data);
	    return "DW_CFA_val_offset_sf";

	case 0x16:
	    decode_uleb128 (data);
	    decode_block (data);
	    return "DW_CFA_val_expression";

	case 0x1c:
	    return "DW_CFA_lo_user";

	case 0x3f:
	    return "DW_CFA_hi_user";

	default:
	    return "UNKNOWN INSTRUCTION";
	}
    }
}


static void
decode_entry (const guchar *data)
{
    guint64 len, aug_len;
    const guchar *end;
    gboolean has_augmentation;

    len = get_length (&data);

    end = data + len;
    
    g_print ("length: %llu\n", len);

    /* CIE_id is 0 for eh frames, and 0xffffffff/0xffffffffffffffff for .debug_frame */
    
    g_print ("id: %d\n", *(guint32 *)data);

    data += 4;

    g_print ("version: %d\n", *data);

    data += 1;

    g_print ("augmentation: %s\n", data);

    has_augmentation = strchr (data, 'z');
    
    data += strlen (data) + 1;

    g_print ("code alignment: %llu\n", decode_uleb128 (&data));

    g_print ("data alignment: %lld\n", decode_sleb128 (&data));

    g_print ("return register: %llu\n", decode_uleb128 (&data));

    if (has_augmentation)
    {
	g_print ("augmentation length: %llu\n", (aug_len = decode_uleb128 (&data)));

	data += aug_len;
    }
    
    while (data < end)
	g_print ("  %s\n", decode_instruction (&data));
}

/* The correct API is probably something like
 *
 *   gboolean
 *   unwind (ElfParser   *parser,
 *           gulong      *regs
 *	     int	  n_regs,
 *           MemoryReader reader,
 *           gpointer     data);
 *
 */
void
unwind (ElfParser *elf)
{
    const guchar *data;
    
    if ((data = elf_parser_get_debug_frame (elf)))
    {
	g_print ("Using .debug_frame\n");
    }
    else if ((data = elf_parser_get_eh_frame (elf)))
    {
	g_print ("Using .eh_frame\n");
    }
    else
    {
	g_print ("no debug info found\n");
	return;
    }

    decode_entry (data);
}