PR python/20190 - compute TLS symbol without a frame

PR python/20190 arose from an exception I noticed when trying to use
the Python unwinder for Spider Monkey in Firefox.

The problem is that the unwinder wants to examine the value of a
thread-local variable.  However, sympy_value rejects this because
symbol_read_needs_frame returns true for a TLS variable.

This problem arose once before, though in a different context:

https://sourceware.org/bugzilla/show_bug.cgi?id=11803

At the time Pedro and Daniel pointed out a simpler way to fix that bug
(see links in 20190 if you are interested); but for this new bug I
couldn't think of a similar fix and ended up implementing Daniel's
other suggestion:

https://sourceware.org/ml/gdb-patches/2010-07/msg00393.html

That is, this patch makes it possible to detect whether a symbol needs
a specific frame, or whether it just needs the inferior to have
registers.

Built and regtested on x86-64 Fedora 24.

2016-07-26  Tom Tromey  <tom@tromey.com>

	* symtab.c (register_symbol_computed_impl): Update.
	PR python/20190:
	* value.h (symbol_read_needs): Declare.
	(symbol_read_needs_frame): Add comment.
	* symtab.h (struct symbol_computed_ops) <read_variable>: Update
	comment.
	<get_symbol_read_needs>: Rename.  Change return type.
	* findvar.c (symbol_read_needs): New function.
	(symbol_read_needs_frame): Rewrite.
	(default_read_var_value): Use symbol_read_needs.
	* dwarf2loc.c (struct symbol_needs_baton): Rename.
	<needs>: Renamed from needs_frame.  Changed type.
	(needs_frame_read_addr_from_reg, symbol_needs_get_reg_value)
	(symbol_needs_read_mem, symbol_needs_frame_base)
	(symbol_needs_frame_cfa, symbol_needs_tls_address)
	(symbol_needs_dwarf_call): Rename.
	(needs_dwarf_reg_entry_value): Update.
	(symbol_needs_ctx_funcs, dwarf2_loc_desc_get_symbol_read_needs):
	Rename and update.
	(locexpr_get_symbol_read_needs, loclist_symbol_needs): Likewise.
	(dwarf2_locexpr_funcs, dwarf2_loclist_funcs): Update.
	* defs.h (enum symbol_needs_kind): New.

2016-07-26  Tom Tromey  <tom@tromey.com>

	PR python/20190:
	* gdb.threads/tls.exp (check_thread_local): Add python symbol
	test.
This commit is contained in:
Tom Tromey 2016-06-03 14:11:08 -06:00
parent 8484fb7587
commit 0b31a4bcec
9 changed files with 169 additions and 69 deletions

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@ -1,3 +1,28 @@
2016-07-26 Tom Tromey <tom@tromey.com>
* symtab.c (register_symbol_computed_impl): Update.
PR python/20190:
* value.h (symbol_read_needs): Declare.
(symbol_read_needs_frame): Add comment.
* symtab.h (struct symbol_computed_ops) <read_variable>: Update
comment.
<get_symbol_read_needs>: Rename. Change return type.
* findvar.c (symbol_read_needs): New function.
(symbol_read_needs_frame): Rewrite.
(default_read_var_value): Use symbol_read_needs.
* dwarf2loc.c (struct symbol_needs_baton): Rename.
<needs>: Renamed from needs_frame. Changed type.
(needs_frame_read_addr_from_reg, symbol_needs_get_reg_value)
(symbol_needs_read_mem, symbol_needs_frame_base)
(symbol_needs_frame_cfa, symbol_needs_tls_address)
(symbol_needs_dwarf_call): Rename.
(needs_dwarf_reg_entry_value): Update.
(symbol_needs_ctx_funcs, dwarf2_loc_desc_get_symbol_read_needs):
Rename and update.
(locexpr_get_symbol_read_needs, loclist_symbol_needs): Likewise.
(dwarf2_locexpr_funcs, dwarf2_loclist_funcs): Update.
* defs.h (enum symbol_needs_kind): New.
2016-07-26 Pedro Alves <palves@redhat.com>
* nat/linux-ptrace.c: Include "gregset.h".

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@ -629,6 +629,25 @@ enum gdb_osabi
extern double atof (const char *); /* X3.159-1989 4.10.1.1 */
#endif
/* Enumerate the requirements a symbol has in order to be evaluated.
These are listed in order of "strength" -- a later entry subsumes
earlier ones. This fine-grained distinction is important because
it allows for the evaluation of a TLS symbol during unwinding --
when unwinding one has access to registers, but not the frame
itself, because that is being constructed. */
enum symbol_needs_kind
{
/* No special requirements -- just memory. */
SYMBOL_NEEDS_NONE,
/* The symbol needs registers. */
SYMBOL_NEEDS_REGISTERS,
/* The symbol needs a frame. */
SYMBOL_NEEDS_FRAME
};
/* Dynamic target-system-dependent parameters for GDB. */
#include "gdbarch.h"

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@ -2726,21 +2726,21 @@ dwarf2_compile_property_to_c (struct ui_file *stream,
}
/* Helper functions and baton for dwarf2_loc_desc_needs_frame. */
/* Helper functions and baton for dwarf2_loc_desc_get_symbol_read_needs. */
struct needs_frame_baton
struct symbol_needs_baton
{
int needs_frame;
enum symbol_needs_kind needs;
struct dwarf2_per_cu_data *per_cu;
};
/* Reads from registers do require a frame. */
static CORE_ADDR
needs_frame_read_addr_from_reg (void *baton, int regnum)
symbol_needs_read_addr_from_reg (void *baton, int regnum)
{
struct needs_frame_baton *nf_baton = (struct needs_frame_baton *) baton;
struct symbol_needs_baton *nf_baton = (struct symbol_needs_baton *) baton;
nf_baton->needs_frame = 1;
nf_baton->needs = SYMBOL_NEEDS_FRAME;
return 1;
}
@ -2748,61 +2748,64 @@ needs_frame_read_addr_from_reg (void *baton, int regnum)
Reads from registers do require a frame. */
static struct value *
needs_frame_get_reg_value (void *baton, struct type *type, int regnum)
symbol_needs_get_reg_value (void *baton, struct type *type, int regnum)
{
struct needs_frame_baton *nf_baton = (struct needs_frame_baton *) baton;
struct symbol_needs_baton *nf_baton = (struct symbol_needs_baton *) baton;
nf_baton->needs_frame = 1;
nf_baton->needs = SYMBOL_NEEDS_FRAME;
return value_zero (type, not_lval);
}
/* Reads from memory do not require a frame. */
static void
needs_frame_read_mem (void *baton, gdb_byte *buf, CORE_ADDR addr, size_t len)
symbol_needs_read_mem (void *baton, gdb_byte *buf, CORE_ADDR addr, size_t len)
{
memset (buf, 0, len);
}
/* Frame-relative accesses do require a frame. */
static void
needs_frame_frame_base (void *baton, const gdb_byte **start, size_t * length)
symbol_needs_frame_base (void *baton, const gdb_byte **start, size_t * length)
{
static gdb_byte lit0 = DW_OP_lit0;
struct needs_frame_baton *nf_baton = (struct needs_frame_baton *) baton;
struct symbol_needs_baton *nf_baton = (struct symbol_needs_baton *) baton;
*start = &lit0;
*length = 1;
nf_baton->needs_frame = 1;
nf_baton->needs = SYMBOL_NEEDS_FRAME;
}
/* CFA accesses require a frame. */
static CORE_ADDR
needs_frame_frame_cfa (void *baton)
symbol_needs_frame_cfa (void *baton)
{
struct needs_frame_baton *nf_baton = (struct needs_frame_baton *) baton;
struct symbol_needs_baton *nf_baton = (struct symbol_needs_baton *) baton;
nf_baton->needs_frame = 1;
nf_baton->needs = SYMBOL_NEEDS_FRAME;
return 1;
}
/* Thread-local accesses do require a frame. */
/* Thread-local accesses require registers, but not a frame. */
static CORE_ADDR
needs_frame_tls_address (void *baton, CORE_ADDR offset)
symbol_needs_tls_address (void *baton, CORE_ADDR offset)
{
struct needs_frame_baton *nf_baton = (struct needs_frame_baton *) baton;
struct symbol_needs_baton *nf_baton = (struct symbol_needs_baton *) baton;
nf_baton->needs_frame = 1;
if (nf_baton->needs <= SYMBOL_NEEDS_REGISTERS)
nf_baton->needs = SYMBOL_NEEDS_REGISTERS;
return 1;
}
/* Helper interface of per_cu_dwarf_call for dwarf2_loc_desc_needs_frame. */
/* Helper interface of per_cu_dwarf_call for
dwarf2_loc_desc_get_symbol_read_needs. */
static void
needs_frame_dwarf_call (struct dwarf_expr_context *ctx, cu_offset die_offset)
symbol_needs_dwarf_call (struct dwarf_expr_context *ctx, cu_offset die_offset)
{
struct needs_frame_baton *nf_baton = (struct needs_frame_baton *) ctx->baton;
struct symbol_needs_baton *nf_baton =
(struct symbol_needs_baton *) ctx->baton;
per_cu_dwarf_call (ctx, die_offset, nf_baton->per_cu,
ctx->funcs->get_frame_pc, ctx->baton);
@ -2815,9 +2818,10 @@ needs_dwarf_reg_entry_value (struct dwarf_expr_context *ctx,
enum call_site_parameter_kind kind,
union call_site_parameter_u kind_u, int deref_size)
{
struct needs_frame_baton *nf_baton = (struct needs_frame_baton *) ctx->baton;
struct symbol_needs_baton *nf_baton =
(struct symbol_needs_baton *) ctx->baton;
nf_baton->needs_frame = 1;
nf_baton->needs = SYMBOL_NEEDS_FRAME;
/* The expression may require some stub values on DWARF stack. */
dwarf_expr_push_address (ctx, 0, 0);
@ -2841,38 +2845,39 @@ needs_get_obj_addr (void *baton)
return 1;
}
/* Virtual method table for dwarf2_loc_desc_needs_frame below. */
/* Virtual method table for dwarf2_loc_desc_get_symbol_read_needs
below. */
static const struct dwarf_expr_context_funcs needs_frame_ctx_funcs =
static const struct dwarf_expr_context_funcs symbol_needs_ctx_funcs =
{
needs_frame_read_addr_from_reg,
needs_frame_get_reg_value,
needs_frame_read_mem,
needs_frame_frame_base,
needs_frame_frame_cfa,
needs_frame_frame_cfa, /* get_frame_pc */
needs_frame_tls_address,
needs_frame_dwarf_call,
symbol_needs_read_addr_from_reg,
symbol_needs_get_reg_value,
symbol_needs_read_mem,
symbol_needs_frame_base,
symbol_needs_frame_cfa,
symbol_needs_frame_cfa, /* get_frame_pc */
symbol_needs_tls_address,
symbol_needs_dwarf_call,
NULL, /* get_base_type */
needs_dwarf_reg_entry_value,
needs_get_addr_index,
needs_get_obj_addr
};
/* Return non-zero iff the location expression at DATA (length SIZE)
requires a frame to evaluate. */
/* Compute the correct symbol_needs_kind value for the location
expression at DATA (length SIZE). */
static int
dwarf2_loc_desc_needs_frame (const gdb_byte *data, size_t size,
struct dwarf2_per_cu_data *per_cu)
static enum symbol_needs_kind
dwarf2_loc_desc_get_symbol_read_needs (const gdb_byte *data, size_t size,
struct dwarf2_per_cu_data *per_cu)
{
struct needs_frame_baton baton;
struct symbol_needs_baton baton;
struct dwarf_expr_context *ctx;
int in_reg;
struct cleanup *old_chain;
struct objfile *objfile = dwarf2_per_cu_objfile (per_cu);
baton.needs_frame = 0;
baton.needs = SYMBOL_NEEDS_NONE;
baton.per_cu = per_cu;
ctx = new_dwarf_expr_context ();
@ -2884,7 +2889,7 @@ dwarf2_loc_desc_needs_frame (const gdb_byte *data, size_t size,
ctx->ref_addr_size = dwarf2_per_cu_ref_addr_size (per_cu);
ctx->offset = dwarf2_per_cu_text_offset (per_cu);
ctx->baton = &baton;
ctx->funcs = &needs_frame_ctx_funcs;
ctx->funcs = &symbol_needs_ctx_funcs;
dwarf_expr_eval (ctx, data, size);
@ -2903,7 +2908,9 @@ dwarf2_loc_desc_needs_frame (const gdb_byte *data, size_t size,
do_cleanups (old_chain);
return baton.needs_frame || in_reg;
if (in_reg)
baton.needs = SYMBOL_NEEDS_FRAME;
return baton.needs;
}
/* A helper function that throws an unimplemented error mentioning a
@ -3736,15 +3743,17 @@ locexpr_read_variable_at_entry (struct symbol *symbol, struct frame_info *frame)
dlbaton->size);
}
/* Return non-zero iff we need a frame to evaluate SYMBOL. */
static int
locexpr_read_needs_frame (struct symbol *symbol)
/* Implementation of get_symbol_read_needs from
symbol_computed_ops. */
static enum symbol_needs_kind
locexpr_get_symbol_read_needs (struct symbol *symbol)
{
struct dwarf2_locexpr_baton *dlbaton
= (struct dwarf2_locexpr_baton *) SYMBOL_LOCATION_BATON (symbol);
return dwarf2_loc_desc_needs_frame (dlbaton->data, dlbaton->size,
dlbaton->per_cu);
return dwarf2_loc_desc_get_symbol_read_needs (dlbaton->data, dlbaton->size,
dlbaton->per_cu);
}
/* Return true if DATA points to the end of a piece. END is one past
@ -4473,7 +4482,7 @@ locexpr_generate_c_location (struct symbol *sym, struct ui_file *stream,
const struct symbol_computed_ops dwarf2_locexpr_funcs = {
locexpr_read_variable,
locexpr_read_variable_at_entry,
locexpr_read_needs_frame,
locexpr_get_symbol_read_needs,
locexpr_describe_location,
0, /* location_has_loclist */
locexpr_tracepoint_var_ref,
@ -4530,9 +4539,11 @@ loclist_read_variable_at_entry (struct symbol *symbol, struct frame_info *frame)
return value_of_dwarf_block_entry (SYMBOL_TYPE (symbol), frame, data, size);
}
/* Return non-zero iff we need a frame to evaluate SYMBOL. */
static int
loclist_read_needs_frame (struct symbol *symbol)
/* Implementation of get_symbol_read_needs from
symbol_computed_ops. */
static enum symbol_needs_kind
loclist_symbol_needs (struct symbol *symbol)
{
/* If there's a location list, then assume we need to have a frame
to choose the appropriate location expression. With tracking of
@ -4540,7 +4551,7 @@ loclist_read_needs_frame (struct symbol *symbol)
is disabled in GCC at the moment until we figure out how to
represent it. */
return 1;
return SYMBOL_NEEDS_FRAME;
}
/* Print a natural-language description of SYMBOL to STREAM. This
@ -4684,7 +4695,7 @@ loclist_generate_c_location (struct symbol *sym, struct ui_file *stream,
const struct symbol_computed_ops dwarf2_loclist_funcs = {
loclist_read_variable,
loclist_read_variable_at_entry,
loclist_read_needs_frame,
loclist_symbol_needs,
loclist_describe_location,
1, /* location_has_loclist */
loclist_tracepoint_var_ref,

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@ -337,14 +337,13 @@ address_to_signed_pointer (struct gdbarch *gdbarch, struct type *type,
store_signed_integer (buf, TYPE_LENGTH (type), byte_order, addr);
}
/* Will calling read_var_value or locate_var_value on SYM end
up caring what frame it is being evaluated relative to? SYM must
be non-NULL. */
int
symbol_read_needs_frame (struct symbol *sym)
/* See value.h. */
enum symbol_needs_kind
symbol_read_needs (struct symbol *sym)
{
if (SYMBOL_COMPUTED_OPS (sym) != NULL)
return SYMBOL_COMPUTED_OPS (sym)->read_needs_frame (sym);
return SYMBOL_COMPUTED_OPS (sym)->get_symbol_read_needs (sym);
switch (SYMBOL_CLASS (sym))
{
@ -358,7 +357,7 @@ symbol_read_needs_frame (struct symbol *sym)
case LOC_REF_ARG:
case LOC_REGPARM_ADDR:
case LOC_LOCAL:
return 1;
return SYMBOL_NEEDS_FRAME;
case LOC_UNDEF:
case LOC_CONST:
@ -374,9 +373,17 @@ symbol_read_needs_frame (struct symbol *sym)
case LOC_CONST_BYTES:
case LOC_UNRESOLVED:
case LOC_OPTIMIZED_OUT:
return 0;
return SYMBOL_NEEDS_NONE;
}
return 1;
return SYMBOL_NEEDS_FRAME;
}
/* See value.h. */
int
symbol_read_needs_frame (struct symbol *sym)
{
return symbol_read_needs (sym) == SYMBOL_NEEDS_FRAME;
}
/* Private data to be used with minsym_lookup_iterator_cb. */
@ -575,6 +582,7 @@ default_read_var_value (struct symbol *var, const struct block *var_block,
struct value *v;
struct type *type = SYMBOL_TYPE (var);
CORE_ADDR addr;
enum symbol_needs_kind sym_need;
/* Call check_typedef on our type to make sure that, if TYPE is
a TYPE_CODE_TYPEDEF, its length is set to the length of the target type
@ -583,8 +591,11 @@ default_read_var_value (struct symbol *var, const struct block *var_block,
set the returned value type description correctly. */
check_typedef (type);
if (symbol_read_needs_frame (var))
sym_need = symbol_read_needs (var);
if (sym_need == SYMBOL_NEEDS_FRAME)
gdb_assert (frame != NULL);
else if (sym_need == SYMBOL_NEEDS_REGISTERS && !target_has_registers)
error (_("Cannot read `%s' without registers"), SYMBOL_PRINT_NAME (var));
if (frame != NULL)
frame = get_hosting_frame (var, var_block, frame);

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@ -6092,7 +6092,7 @@ register_symbol_computed_impl (enum address_class aclass,
gdb_assert (ops != NULL);
gdb_assert (ops->tracepoint_var_ref != NULL);
gdb_assert (ops->describe_location != NULL);
gdb_assert (ops->read_needs_frame != NULL);
gdb_assert (ops->get_symbol_read_needs != NULL);
gdb_assert (ops->read_variable != NULL);
return result;

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@ -629,7 +629,8 @@ struct symbol_computed_ops
frame FRAME. If the variable has been optimized out, return
zero.
Iff `read_needs_frame (SYMBOL)' is zero, then FRAME may be zero. */
Iff `read_needs_frame (SYMBOL)' is not SYMBOL_NEEDS_FRAME, then
FRAME may be zero. */
struct value *(*read_variable) (struct symbol * symbol,
struct frame_info * frame);
@ -640,8 +641,11 @@ struct symbol_computed_ops
struct value *(*read_variable_at_entry) (struct symbol *symbol,
struct frame_info *frame);
/* Return non-zero if we need a frame to find the value of the SYMBOL. */
int (*read_needs_frame) (struct symbol * symbol);
/* Find the "symbol_needs_kind" value for the given symbol. This
value determines whether reading the symbol needs memory (e.g., a
global variable), just registers (a thread-local), or a frame (a
local variable). */
enum symbol_needs_kind (*get_symbol_read_needs) (struct symbol * symbol);
/* Write to STREAM a natural-language description of the location of
SYMBOL, in the context of ADDR. */

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@ -1,3 +1,9 @@
2016-07-26 Tom Tromey <tom@tromey.com>
PR python/20190:
* gdb.threads/tls.exp (check_thread_local): Add python symbol
test.
2016-07-26 Markus Metzger <markus.t.metzger@intel.com>
* gdb.btrace/record_goto.exp: se is_amd64_regs_target for

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@ -14,6 +14,8 @@
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>. */
load_lib gdb-python.exp
standard_testfile tls.c tls2.c
if [istarget "*-*-linux"] then {
@ -70,6 +72,17 @@ proc check_thread_local {number} {
"= $expected_value" \
"${number} thread local storage"
if {![skip_python_tests]} {
gdb_test_no_output \
"python sym = gdb.lookup_symbol('a_thread_local')\[0\]" \
"${number} look up a_thread_local symbol"
# We intentionally do not pass a frame to "value" here. If a
# TLS variable requires a frame, this will fail. However, if
# it does not require a frame, then it will succeed.
gdb_test "python print(sym.value())" "$expected_value" \
"${number} get symbol value without frame"
}
gdb_test "p K::another_thread_local" \
"= $me_variable" \
"${number} another thread local storage"
@ -139,6 +152,10 @@ proc check_thread_stack {number spin_threads spin_threads_level} {
}
clean_restart ${binfile}
gdb_test "print a_thread_local" \
"Cannot read .a_thread_local. without registers"
if ![runto_main] then {
fail "Can't run to main"
return 0

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@ -672,6 +672,13 @@ extern struct value *value_of_register (int regnum, struct frame_info *frame);
struct value *value_of_register_lazy (struct frame_info *frame, int regnum);
/* Return the symbol's reading requirement. */
extern enum symbol_needs_kind symbol_read_needs (struct symbol *);
/* Return true if the symbol needs a frame. This is a wrapper for
symbol_read_needs that simply checks for SYMBOL_NEEDS_FRAME. */
extern int symbol_read_needs_frame (struct symbol *);
extern struct value *read_var_value (struct symbol *var,