[PATCH v3 23/28] Add support for any location description in CFI
Zoran Zaric
zoran.zaric@amd.com
Thu Nov 4 15:09:31 GMT 2021
On 10/31/21 10:58 PM, Lancelot SIX wrote:
> [CAUTION: External Email]
>
> Hi,
>
> I have included minor nits below
>
> On Thu, Oct 14, 2021 at 10:32:30AM +0100, Zoran Zaric via Gdb-patches wrote:
>> From: Zoran Zaric <Zoran.Zaric@amd.com>
>>
>> One of the main benefits of allowing location description to be on the
>> DWARF stack is that now CFI expression based register rules can be
>> defined using a location description operations. This allows a register
>> of one frame to be saved in any location, including any composite
>> location.
>>
>> To fully support this feature, the execute_stack_op function in
>> dwarf2/frame.c needs to return a single struct value object instead of
>> just an address.
>>
>> Function put_frame_register_bytes also needs to change to support any
>> location description.
>>
>> This support is a one of the key features to truly support optimized
>> code.
>>
>> gdb/ChangeLog:
>>
>> * dwarf2/frame.c (execute_stack_op): Change to return a struct
>> value object.
>> (dwarf2_frame_cache): Change to call new execute_stack_op
>> definition.
>> (dwarf2_frame_prev_register): Change to call new execute_stack_op
>> definition.
>> * frame.c (put_frame_register_bytes): Add support for writing to
>> composite location description.
>> ---
>> gdb/dwarf2/frame.c | 54 ++++++++++++++++++++++++++--------------------
>> gdb/frame.c | 36 +++++++++++++++++++++++++------
>> 2 files changed, 61 insertions(+), 29 deletions(-)
>>
>> diff --git a/gdb/dwarf2/frame.c b/gdb/dwarf2/frame.c
>> index e17b36e243b..e70dcd5a86e 100644
>> --- a/gdb/dwarf2/frame.c
>> +++ b/gdb/dwarf2/frame.c
>> @@ -236,16 +236,17 @@ register %s (#%d) at %s"),
>> }
>> }
>>
>> -static CORE_ADDR
>> +static value *
>> execute_stack_op (const gdb_byte *exp, ULONGEST len, int addr_size,
>> struct frame_info *this_frame, CORE_ADDR initial,
>> - int initial_in_stack_memory, dwarf2_per_objfile *per_objfile)
>> + int initial_in_stack_memory, dwarf2_per_objfile *per_objfile,
>> + struct type* type = nullptr, bool as_lval = true)
>> {
>> scoped_value_mark free_values;
>> - struct type *type = address_type (per_objfile->objfile->arch (),
>> - addr_size);
>> + struct type *init_type = address_type (per_objfile->objfile->arch (),
>> + addr_size);
>>
>> - value *init_value = value_at_lazy (type, initial);
>> + value *init_value = value_at_lazy (init_type, initial);
>> std::vector<value *> init_values;
>>
>> set_value_stack (init_value, initial_in_stack_memory);
>> @@ -255,10 +256,15 @@ execute_stack_op (const gdb_byte *exp, ULONGEST len, int addr_size,
>> = dwarf2_evaluate (exp, len, true, per_objfile, nullptr,
>> this_frame, addr_size, &init_values, nullptr);
>>
>> - if (VALUE_LVAL (result_val) == lval_memory)
>> - return value_address (result_val);
>> - else
>> - return value_as_address (result_val);
>> + /* We need to clean up all the values that are not needed any more.
>> + The problem with a value_ref_ptr class is that it disconnects the
>> + RETVAL from the value garbage collection, so we need to make
>> + a copy of that value on the stack to keep everything consistent.
>> + The value_ref_ptr will clean up after itself at the end of this block. */
>> + value_ref_ptr value_holder = value_ref_ptr::new_reference (result_val);
>> + free_values.free_to_mark ();
>> +
>> + return value_copy (result_val);
>> }
>>
>>
>> @@ -989,10 +995,14 @@ dwarf2_frame_cache (struct frame_info *this_frame, void **this_cache)
>> break;
>>
>> case CFA_EXP:
>> - cache->cfa =
>> - execute_stack_op (fs.regs.cfa_exp, fs.regs.cfa_exp_len,
>> - cache->addr_size, this_frame, 0, 0,
>> - cache->per_objfile);
>> + {
>> + struct value *value
>> + = execute_stack_op (fs.regs.cfa_exp, fs.regs.cfa_exp_len,
>> + cache->addr_size, this_frame, 0, 0,
>> + cache->per_objfile);
>> + cache->cfa = value_address (value);
>> + }
>> +
>> break;
>>
>> default:
>> @@ -1190,24 +1200,22 @@ dwarf2_frame_prev_register (struct frame_info *this_frame, void **this_cache,
>> return frame_unwind_got_register (this_frame, regnum, realnum);
>>
>> case DWARF2_FRAME_REG_SAVED_EXP:
>> - addr = execute_stack_op (cache->reg[regnum].loc.exp.start,
>> + return execute_stack_op (cache->reg[regnum].loc.exp.start,
>> cache->reg[regnum].loc.exp.len,
>> - cache->addr_size,
>> - this_frame, cache->cfa, 1,
>> - cache->per_objfile);
>> - return frame_unwind_got_memory (this_frame, regnum, addr);
>> + cache->addr_size, this_frame,
>> + cache->cfa, 1, cache->per_objfile,
>> + register_type (gdbarch, regnum));
>>
>> case DWARF2_FRAME_REG_SAVED_VAL_OFFSET:
>> addr = cache->cfa + cache->reg[regnum].loc.offset;
>> return frame_unwind_got_constant (this_frame, regnum, addr);
>>
>> case DWARF2_FRAME_REG_SAVED_VAL_EXP:
>> - addr = execute_stack_op (cache->reg[regnum].loc.exp.start,
>> + return execute_stack_op (cache->reg[regnum].loc.exp.start,
>> cache->reg[regnum].loc.exp.len,
>> - cache->addr_size,
>> - this_frame, cache->cfa, 1,
>> - cache->per_objfile);
>> - return frame_unwind_got_constant (this_frame, regnum, addr);
>> + cache->addr_size, this_frame,
>> + cache->cfa, 1, cache->per_objfile,
>> + register_type (gdbarch, regnum), false);
>>
>> case DWARF2_FRAME_REG_UNSPECIFIED:
>> /* GCC, in its infinite wisdom decided to not provide unwind
>> diff --git a/gdb/frame.c b/gdb/frame.c
>> index 16673258373..3d85d2c7b59 100644
>> --- a/gdb/frame.c
>> +++ b/gdb/frame.c
>> @@ -1532,26 +1532,50 @@ put_frame_register_bytes (struct frame_info *frame, int regnum,
>> {
>> int curr_len = register_size (gdbarch, regnum) - offset;
>>
>> + struct value *value = frame_unwind_register_value (frame->next,
>> + regnum);
>> +
>> if (curr_len > len)
>> curr_len = len;
>>
>> const gdb_byte *myaddr = buffer.data ();
>> - if (curr_len == register_size (gdbarch, regnum))
>> +
>> + /* Compute value is a special new case. The problem is that
> ^^
> There is one extra space at the start of the comment (and in the
> subsequent lines I guess).
>
> Also the comment related to a 'new case'. From the perspective of
> someone reading the comment in frame.c (not in a patch), this just like
> a special case. Maybe rephrase with something like:
>
> Computed value is a special case. The computed callback
> mechanism requires a strut value argument, so we need to make
> one.
>
>> + the computed callback mechanism only supports a struct
>> + value arguments, so we need to make one. */
>> + if (value != NULL && VALUE_LVAL (value) == lval_computed)
>
> Prefer nullptr over NULL.
>
>> + {
>> + const lval_funcs *funcs = value_computed_funcs (value);
>> + type * reg_type = register_type (gdbarch, regnum);
>
> I guess funcs->write could be checked to be non nullptr before
> retrieving regtype. If 'error' is called, reg_type has no use.
>
>> +
>> + if (funcs->write == NULL)
>
> NULL -> nullptr
>
>> + error (_("Attempt to assign to an unmodifiable value."));
>> +
>> + struct value *from_value = allocate_value (reg_type);
>> + memcpy (value_contents_raw (from_value), myaddr,
>> + TYPE_LENGTH (reg_type));
>> +
>> + set_value_offset (value, offset);
>> +
>> + funcs->write (value, from_value);
>> + release_value (from_value);
>> + }
>> + else if (curr_len == register_size (gdbarch, regnum))
>> {
>> put_frame_register (frame, regnum, myaddr);
>> }
>> else
>> {
>> - struct value *value = frame_unwind_register_value (frame->next,
>> - regnum);
>> gdb_assert (value != NULL);
>>
>> - memcpy ((char *) value_contents_writeable (value) + offset, myaddr,
>> - curr_len);
>> + memcpy ((char *) value_contents_writeable (value) + offset,
>> + myaddr, curr_len);
>> put_frame_register (frame, regnum, value_contents_raw (value));
>> - release_value (value);
>> }
>>
>> + if (value != NULL)
>
> NULL -> nullptr
>
> Best,
> Lancelot.
>
All valid points.
Thank you,
Zoran
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