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Implement DWARF DW_CFA_val_expression for x86_64

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Ubuntu's libc-bin (2.15-0ubuntu20.2) on x86_64 uses DW_CFA_val_expression
in describing the pthread spinlock operations __lll_unlock_wake() and
__lll_lock_wait().  libunwind 1.1 doesn't understand that opcode and
so backtraces from those operations are truncated.

This changeset adds basic support for it, by adding a new type to
dwarf_loc_t that describes the register's actual contents rather than
its location.  I've only implemented the new type for x86_64, and
stubbed it out for all other architectures -- it looks like a lot
of that code is duplicated so oughtn't to be that hard, but I don't
have test cases for them.

Tested that DW_CFA_val_expression works on x86_64 (by using
https://code.google.com/p/gperftools/ on a lock-heavy program).
Build-tested on x86, x86_64 and arm.  The unit tests don't pass for me
on any of those archs, but this cset doesn't break anything that was
passing before.

Signed-off-by: Tim Deegan <tjd@phlegethon.org>
This commit is contained in:
Tim Deegan 2014-02-03 12:01:10 +01:00 committed by Arun Sharma
parent 11a7d98e39
commit 4eb880e1b5
4 changed files with 44 additions and 2 deletions
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2
include/dwarf.h
View file

@ -165,6 +165,7 @@ typedef enum
DW_CFA_offset_extended_sf = 0x11,
DW_CFA_def_cfa_sf = 0x12,
DW_CFA_def_cfa_offset_sf = 0x13,
DW_CFA_val_expression = 0x16,
DW_CFA_lo_user = 0x1c,
DW_CFA_MIPS_advance_loc8 = 0x1d,
DW_CFA_GNU_window_save = 0x2d,
@ -224,6 +225,7 @@ typedef enum
DWARF_WHERE_CFAREL, /* register saved at CFA-relative address */
DWARF_WHERE_REG, /* register saved in another register */
DWARF_WHERE_EXPR, /* register saved */
DWARF_WHERE_VAL_EXPR, /* register has computed value */
}
dwarf_where_t;

5
include/libunwind_i.h
View file

@ -351,6 +351,11 @@ static inline void invalidate_edi (struct elf_dyn_info *edi)
# define tdep_get_func_addr(as,addr,v) (*(v) = addr, 0)
#endif
#ifndef DWARF_VAL_LOC
# define DWARF_IS_VAL_LOC(l) 0
# define DWARF_VAL_LOC(c,v) DWARF_NULL_LOC
#endif
#define UNW_ALIGN(x,a) (((x)+(a)-1UL)&~((a)-1UL))
#endif /* libunwind_i_h */

15
include/tdep-x86_64/libunwind_i.h
View file

@ -109,25 +109,33 @@ dwarf_get_uc(const struct dwarf_cursor *cursor)
# define DWARF_IS_NULL_LOC(l) (DWARF_GET_LOC (l) == 0)
# define DWARF_LOC(r, t) ((dwarf_loc_t) { .val = (r) })
# define DWARF_IS_REG_LOC(l) 0
# define DWARF_IS_MEM_LOC(l) 1
# define DWARF_IS_VAL_LOC(l) 0
# define DWARF_REG_LOC(c,r) (DWARF_LOC((unw_word_t) \
x86_64_r_uc_addr(dwarf_get_uc(c), (r)), 0))
# define DWARF_MEM_LOC(c,m) DWARF_LOC ((m), 0)
# define DWARF_FPREG_LOC(c,r) (DWARF_LOC((unw_word_t) \
x86_64_r_uc_addr(dwarf_get_uc(c), (r)), 0))
# define DWARF_VAL_LOC(c,v) DWARF_NULL_LOC
#else /* !UNW_LOCAL_ONLY */
# define DWARF_LOC_TYPE_FP (1 << 0)
# define DWARF_LOC_TYPE_REG (1 << 1)
# define DWARF_LOC_TYPE_VAL (1 << 2)
# define DWARF_NULL_LOC DWARF_LOC (0, 0)
# define DWARF_IS_NULL_LOC(l) \
({ dwarf_loc_t _l = (l); _l.val == 0 && _l.type == 0; })
# define DWARF_LOC(r, t) ((dwarf_loc_t) { .val = (r), .type = (t) })
# define DWARF_IS_REG_LOC(l) (((l).type & DWARF_LOC_TYPE_REG) != 0)
# define DWARF_IS_FP_LOC(l) (((l).type & DWARF_LOC_TYPE_FP) != 0)
# define DWARF_IS_MEM_LOC(l) ((l).type == 0)
# define DWARF_IS_VAL_LOC(l) (((l).type & DWARF_LOC_TYPE_VAL) != 0)
# define DWARF_REG_LOC(c,r) DWARF_LOC((r), DWARF_LOC_TYPE_REG)
# define DWARF_MEM_LOC(c,m) DWARF_LOC ((m), 0)
# define DWARF_FPREG_LOC(c,r) DWARF_LOC((r), (DWARF_LOC_TYPE_REG \
| DWARF_LOC_TYPE_FP))
# define DWARF_VAL_LOC(c,v) DWARF_LOC ((v), DWARF_LOC_TYPE_VAL)
#endif /* !UNW_LOCAL_ONLY */
@ -158,14 +166,19 @@ dwarf_get (struct dwarf_cursor *c, dwarf_loc_t loc, unw_word_t *val)
if (DWARF_IS_REG_LOC (loc))
return (*c->as->acc.access_reg) (c->as, DWARF_GET_LOC (loc), val,
0, c->as_arg);
else
if (DWARF_IS_MEM_LOC (loc))
return (*c->as->acc.access_mem) (c->as, DWARF_GET_LOC (loc), val,
0, c->as_arg);
assert(DWARF_IS_VAL_LOC (loc));
*val = DWARF_GET_LOC (loc);
return 0;
}
static inline int
dwarf_put (struct dwarf_cursor *c, dwarf_loc_t loc, unw_word_t val)
{
assert(!DWARF_IS_VAL_LOC (loc));
if (DWARF_IS_NULL_LOC (loc))
return -UNW_EBADREG;

24
src/dwarf/Gparser.c
View file

@ -334,7 +334,22 @@ run_cfi_program (struct dwarf_cursor *c, dwarf_state_record_t *sr,
*addr += len;
break;
case DW_CFA_GNU_args_size:
case DW_CFA_val_expression:
if ((ret = read_regnum (as, a, addr, &regnum, arg)) < 0)
goto fail;
/* Save the address of the DW_FORM_block for later evaluation. */
set_reg (sr, regnum, DWARF_WHERE_VAL_EXPR, *addr);
if ((ret = dwarf_read_uleb128 (as, a, addr, &len, arg)) < 0)
goto fail;
Debug (15, "CFA_val_expression r%lu @ 0x%lx [%lu bytes]\n",
(long) regnum, (long) addr, (long) len);
*addr += len;
break;
case DW_CFA_GNU_args_size:
if ((ret = dwarf_read_uleb128 (as, a, addr, &val, arg)) < 0)
goto fail;
sr->args_size = val;
@ -785,6 +800,13 @@ apply_reg_state (struct dwarf_cursor *c, struct dwarf_reg_state *rs)
if ((ret = eval_location_expr (c, as, a, addr, c->loc + i, arg)) < 0)
return ret;
break;
case DWARF_WHERE_VAL_EXPR:
addr = rs->reg[i].val;
if ((ret = eval_location_expr (c, as, a, addr, c->loc + i, arg)) < 0)
return ret;
c->loc[i] = DWARF_VAL_LOC (c, DWARF_GET_LOC (c->loc[i]));
break;
}
}