From a519e8ffe2b0f008deaef1517562090d9eaadccc Mon Sep 17 00:00:00 2001 From: Tom Tromey Date: Fri, 10 Sep 2021 12:40:54 -0600 Subject: [PATCH] Add lval_funcs::is_optimized_out This adds an is_optimized_out function pointer to lval_funcs, and changes value_optimized_out to call it. This new function lets gdb determine if a value is optimized out without necessarily fetching the value. This is needed for a subsequent patch, where an attempt to access a lazy value would fail due to the value size limit -- however, the access was only needed to determine the optimized-out state. --- gdb/dwarf2/expr.c | 56 +++++++++++++++++++++++++++++++++++++---------- gdb/dwarf2/loc.c | 1 + gdb/opencl-lang.c | 1 + gdb/value.c | 17 +++++++++++--- gdb/value.h | 6 +++++ 5 files changed, 66 insertions(+), 15 deletions(-) diff --git a/gdb/dwarf2/expr.c b/gdb/dwarf2/expr.c index 0e62de22aff..0f05f889e2a 100644 --- a/gdb/dwarf2/expr.c +++ b/gdb/dwarf2/expr.c @@ -149,10 +149,13 @@ allocate_piece_closure (dwarf2_per_cu_data *per_cu, /* Read or write a pieced value V. If FROM != NULL, operate in "write mode": copy FROM into the pieces comprising V. If FROM == NULL, operate in "read mode": fetch the contents of the (lazy) value V by - composing it from its pieces. */ + composing it from its pieces. If CHECK_OPTIMIZED is true, then no + reading or writing is done; instead the return value of this + function is true if any piece is optimized out. When + CHECK_OPTIMIZED is true, FROM must be nullptr. */ -static void -rw_pieced_value (value *v, value *from) +static bool +rw_pieced_value (value *v, value *from, bool check_optimized) { int i; LONGEST offset = 0, max_offset; @@ -163,6 +166,7 @@ rw_pieced_value (value *v, value *from) gdb::byte_vector buffer; bool bits_big_endian = type_byte_order (value_type (v)) == BFD_ENDIAN_BIG; + gdb_assert (!check_optimized || from == nullptr); if (from != nullptr) { from_contents = value_contents (from); @@ -174,7 +178,10 @@ rw_pieced_value (value *v, value *from) internal_error (__FILE__, __LINE__, _("Should not be able to create a lazy value with " "an enclosing type")); - v_contents = value_contents_raw (v); + if (check_optimized) + v_contents = nullptr; + else + v_contents = value_contents_raw (v); from_contents = nullptr; } @@ -240,17 +247,22 @@ rw_pieced_value (value *v, value *from) buffer, &optim, &unavail)) { if (optim) - mark_value_bits_optimized_out (v, offset, - this_size_bits); - if (unavail) + { + if (check_optimized) + return true; + mark_value_bits_optimized_out (v, offset, + this_size_bits); + } + if (unavail && !check_optimized) mark_value_bits_unavailable (v, offset, this_size_bits); break; } - copy_bitwise (v_contents, offset, - buffer.data (), bits_to_skip % 8, - this_size_bits, bits_big_endian); + if (!check_optimized) + copy_bitwise (v_contents, offset, + buffer.data (), bits_to_skip % 8, + this_size_bits, bits_big_endian); } else { @@ -286,6 +298,9 @@ rw_pieced_value (value *v, value *from) case DWARF_VALUE_MEMORY: { + if (check_optimized) + break; + bits_to_skip += p->offset; CORE_ADDR start_addr = p->v.mem.addr + bits_to_skip / 8; @@ -355,6 +370,9 @@ rw_pieced_value (value *v, value *from) case DWARF_VALUE_STACK: { + if (check_optimized) + break; + if (from != nullptr) { mark_value_bits_optimized_out (v, offset, this_size_bits); @@ -384,6 +402,9 @@ rw_pieced_value (value *v, value *from) case DWARF_VALUE_LITERAL: { + if (check_optimized) + break; + if (from != nullptr) { mark_value_bits_optimized_out (v, offset, this_size_bits); @@ -418,6 +439,8 @@ rw_pieced_value (value *v, value *from) break; case DWARF_VALUE_OPTIMIZED_OUT: + if (check_optimized) + return true; mark_value_bits_optimized_out (v, offset, this_size_bits); break; @@ -428,18 +451,26 @@ rw_pieced_value (value *v, value *from) offset += this_size_bits; bits_to_skip = 0; } + + return false; } static void read_pieced_value (value *v) { - rw_pieced_value (v, nullptr); + rw_pieced_value (v, nullptr, false); } static void write_pieced_value (value *to, value *from) { - rw_pieced_value (to, from); + rw_pieced_value (to, from, false); +} + +static bool +is_optimized_out_pieced_value (value *v) +{ + return rw_pieced_value (v, nullptr, true); } /* An implementation of an lval_funcs method to see whether a value is @@ -617,6 +648,7 @@ free_pieced_value_closure (value *v) static const struct lval_funcs pieced_value_funcs = { read_pieced_value, write_pieced_value, + is_optimized_out_pieced_value, indirect_pieced_value, coerce_pieced_ref, check_pieced_synthetic_pointer, diff --git a/gdb/dwarf2/loc.c b/gdb/dwarf2/loc.c index 16e0be73d02..0e5599353c4 100644 --- a/gdb/dwarf2/loc.c +++ b/gdb/dwarf2/loc.c @@ -1282,6 +1282,7 @@ static const struct lval_funcs entry_data_value_funcs = { NULL, /* read */ NULL, /* write */ + nullptr, NULL, /* indirect */ entry_data_value_coerce_ref, NULL, /* check_synthetic_pointer */ diff --git a/gdb/opencl-lang.c b/gdb/opencl-lang.c index b877de400d7..b279674da98 100644 --- a/gdb/opencl-lang.c +++ b/gdb/opencl-lang.c @@ -254,6 +254,7 @@ static const struct lval_funcs opencl_value_funcs = { lval_func_read, lval_func_write, + nullptr, NULL, /* indirect */ NULL, /* coerce_ref */ lval_func_check_synthetic_pointer, diff --git a/gdb/value.c b/gdb/value.c index b9d3112387f..3aa5fac2306 100644 --- a/gdb/value.c +++ b/gdb/value.c @@ -1407,10 +1407,21 @@ value_contents_writeable (struct value *value) int value_optimized_out (struct value *value) { - /* We can only know if a value is optimized out once we have tried to - fetch it. */ - if (value->optimized_out.empty () && value->lazy) + if (value->lazy) { + /* See if we can compute the result without fetching the + value. */ + if (VALUE_LVAL (value) == lval_memory) + return false; + else if (VALUE_LVAL (value) == lval_computed) + { + const struct lval_funcs *funcs = value->location.computed.funcs; + + if (funcs->is_optimized_out != nullptr) + return funcs->is_optimized_out (value); + } + + /* Fall back to fetching. */ try { value_fetch_lazy (value); diff --git a/gdb/value.h b/gdb/value.h index 3f00444e7e3..45012372dbf 100644 --- a/gdb/value.h +++ b/gdb/value.h @@ -264,6 +264,12 @@ struct lval_funcs TOVAL is not considered as an lvalue. */ void (*write) (struct value *toval, struct value *fromval); + /* Return true if any part of V is optimized out, false otherwise. + This will only be called for lazy values -- if the value has been + fetched, then the value's optimized-out bits are consulted + instead. */ + bool (*is_optimized_out) (struct value *v); + /* If non-NULL, this is used to implement pointer indirection for this value. This method may return NULL, in which case value_ind will fall back to ordinary indirection. */ -- 2.30.2