binutils-gdb/gdb/buildsym.h
Andrew Burgess 8c95582da8 gdb: Add support for tracking the DWARF line table is-stmt field
This commit brings support for the DWARF line table is_stmt field to
GDB.  The is_stmt field is used by the compiler when a single source
line is split into multiple assembler instructions, especially if the
assembler instructions are interleaved with instruction from other
source lines.

The compiler will set the is_stmt flag false from some instructions
from the source lines, these instructions are not a good place to
insert a breakpoint in order to stop at the source line.
Instructions which are marked with the is_stmt flag true are a good
place to insert a breakpoint for that source line.

Currently GDB ignores all instructions for which is_stmt is false.
This is fine in a lot of cases, however, there are some cases where
this means the debug experience is not as good as it could be.

Consider stopping at a random instruction, currently this instruction
will be attributed to the last line table entry before this point for
which is_stmt was true - as these are the only line table entries that
GDB tracks.  This can easily be incorrect in code with even a low
level of optimisation.

With is_stmt tracking in place, when stopping at a random instruction
we now attribute the instruction back to the real source line, even
when is_stmt is false for that instruction in the line table.

When inserting breakpoints we still select line table entries for
which is_stmt is true, so the breakpoint placing behaviour should not
change.

When stepping though code (at the line level, not the instruction
level) we will still stop at instruction where is_stmt is true, I
think this is more likely to be the desired behaviour.

Instruction stepping is, of course, unchanged, stepping one
instruction at a time, but we should now report more accurate line
table information with each instruction step.

The original motivation for this work was a patch posted by Bernd
here:
  https://sourceware.org/ml/gdb-patches/2019-11/msg00792.html

As part of that thread it was suggested that many issues would be
resolved if GDB supported line table views, this isn't something I've
attempted in this patch, though reading the spec, it seems like this
would be a useful feature to support in GDB in the future.  The spec
is here:
  http://dwarfstd.org/ShowIssue.php?issue=170427.1

And Bernd gives a brief description of the benefits here:
  https://sourceware.org/ml/gdb-patches/2020-01/msg00147.html

With that all said, I think that there is benefit to having proper
is_stmt support regardless of whether we have views support, so I
think we should consider getting this in first, and then building view
support on top of this.

The gdb.cp/step-and-next-inline.exp test is based off a test proposed
by Bernd Edlinger in this message:
  https://sourceware.org/ml/gdb-patches/2019-12/msg00842.html

gdb/ChangeLog:

	* buildsym-legacy.c (record_line): Pass extra parameter to
	record_line.
	* buildsym.c (buildsym_compunit::record_line): Take an extra
	parameter, reduce duplication in the line table, and record the
	is_stmt flag in the line table.
	* buildsym.h (buildsym_compunit::record_line): Add extra
	parameter.
	* disasm.c (do_mixed_source_and_assembly_deprecated): Ignore
	non-statement lines.
	* dwarf2/read.c (dwarf_record_line_1): Add extra parameter, pass
	this to the symtab builder.
	(dwarf_finish_line): Pass extra parameter to dwarf_record_line_1.
	(lnp_state_machine::record_line): Pass a suitable is_stmt flag
	through to dwarf_record_line_1.
	* infrun.c (process_event_stop_test): When stepping, don't stop at
	a non-statement instruction, and only refresh the step info when
	we land in the middle of a line's range.  Also add an extra
	comment.
	* jit.c (jit_symtab_line_mapping_add_impl): Initialise is_stmt
	field.
	* record-btrace.c (btrace_find_line_range): Only record lines
	marked as is-statement.
	* stack.c (frame_show_address): Show the frame address if we are
	in a non-statement sal.
	* symmisc.c (dump_symtab_1): Print the is_stmt flag.
	(maintenance_print_one_line_table): Print a header for the is_stmt
	column, and include is_stmt information in the output.
	* symtab.c (find_pc_sect_line): Find lines marked as statements in
	preference to non-statements.
	(find_pcs_for_symtab_line): Prefer is-statement entries.
	(find_line_common): Likewise.
	* symtab.h (struct linetable_entry): Add is_stmt field.
	(struct symtab_and_line): Likewise.
	* xcoffread.c (arrange_linetable): Initialise is_stmt field when
	arranging the line table.

gdb/testsuite/ChangeLog:

	* gdb.cp/step-and-next-inline.cc: New file.
	* gdb.cp/step-and-next-inline.exp: New file.
	* gdb.cp/step-and-next-inline.h: New file.
	* gdb.dwarf2/dw2-is-stmt.c: New file.
	* gdb.dwarf2/dw2-is-stmt.exp: New file.
	* gdb.dwarf2/dw2-is-stmt-2.c: New file.
	* gdb.dwarf2/dw2-is-stmt-2.exp: New file.
	* gdb.dwarf2/dw2-ranges-base.exp: Update line table pattern.
2020-03-10 22:32:07 +00:00

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/* Build symbol tables in GDB's internal format.
Copyright (C) 1986-2020 Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#if !defined (BUILDSYM_H)
#define BUILDSYM_H 1
#include "gdb_obstack.h"
struct objfile;
struct symbol;
struct addrmap;
struct compunit_symtab;
enum language;
/* This module provides definitions used for creating and adding to
the symbol table. These routines are called from various symbol-
file-reading routines.
They originated in dbxread.c of gdb-4.2, and were split out to
make xcoffread.c more maintainable by sharing code. */
struct block;
struct pending_block;
struct dynamic_prop;
/* The list of sub-source-files within the current individual
compilation. Each file gets its own symtab with its own linetable
and associated info, but they all share one blockvector. */
struct subfile
{
struct subfile *next;
/* Space for this is malloc'd. */
char *name;
/* Space for this is malloc'd. */
struct linetable *line_vector;
int line_vector_length;
/* The "containing" compunit. */
struct buildsym_compunit *buildsym_compunit;
enum language language;
struct symtab *symtab;
};
/* Record the symbols defined for each context in a list. We don't
create a struct block for the context until we know how long to
make it. */
#define PENDINGSIZE 100
struct pending
{
struct pending *next;
int nsyms;
struct symbol *symbol[PENDINGSIZE];
};
/* Stack representing unclosed lexical contexts (that will become
blocks, eventually). */
struct context_stack
{
/* Outer locals at the time we entered */
struct pending *locals;
/* Pending using directives at the time we entered. */
struct using_direct *local_using_directives;
/* Pointer into blocklist as of entry */
struct pending_block *old_blocks;
/* Name of function, if any, defining context */
struct symbol *name;
/* Expression that computes the frame base of the lexically enclosing
function, if any. NULL otherwise. */
struct dynamic_prop *static_link;
/* PC where this context starts */
CORE_ADDR start_addr;
/* Temp slot for exception handling. */
CORE_ADDR end_addr;
/* For error-checking matching push/pop */
int depth;
};
/* Buildsym's counterpart to struct compunit_symtab. */
struct buildsym_compunit
{
/* Start recording information about a primary source file (IOW, not an
included source file).
COMP_DIR is the directory in which the compilation unit was compiled
(or NULL if not known). */
buildsym_compunit (struct objfile *objfile_, const char *name,
const char *comp_dir_, enum language language_,
CORE_ADDR last_addr);
/* Reopen an existing compunit_symtab so that additional symbols can
be added to it. Arguments are as for the main constructor. CUST
is the expandable compunit_symtab to be reopened. */
buildsym_compunit (struct objfile *objfile_, const char *name,
const char *comp_dir_, enum language language_,
CORE_ADDR last_addr, struct compunit_symtab *cust)
: m_objfile (objfile_),
m_last_source_file (name == nullptr ? nullptr : xstrdup (name)),
m_comp_dir (comp_dir_ == nullptr ? nullptr : xstrdup (comp_dir_)),
m_compunit_symtab (cust),
m_language (language_),
m_last_source_start_addr (last_addr)
{
}
~buildsym_compunit ();
DISABLE_COPY_AND_ASSIGN (buildsym_compunit);
void set_last_source_file (const char *name)
{
char *new_name = name == NULL ? NULL : xstrdup (name);
m_last_source_file.reset (new_name);
}
const char *get_last_source_file ()
{
return m_last_source_file.get ();
}
struct macro_table *get_macro_table ();
struct macro_table *release_macros ()
{
struct macro_table *result = m_pending_macros;
m_pending_macros = nullptr;
return result;
}
/* This function is called to discard any pending blocks. */
void free_pending_blocks ()
{
m_pending_block_obstack.clear ();
m_pending_blocks = nullptr;
}
struct block *finish_block (struct symbol *symbol,
struct pending_block *old_blocks,
const struct dynamic_prop *static_link,
CORE_ADDR start, CORE_ADDR end);
void record_block_range (struct block *block,
CORE_ADDR start, CORE_ADDR end_inclusive);
void start_subfile (const char *name);
void patch_subfile_names (struct subfile *subfile, const char *name);
void push_subfile ();
const char *pop_subfile ();
void record_line (struct subfile *subfile, int line, CORE_ADDR pc,
bool is_stmt);
struct compunit_symtab *get_compunit_symtab ()
{
return m_compunit_symtab;
}
void set_last_source_start_addr (CORE_ADDR addr)
{
m_last_source_start_addr = addr;
}
CORE_ADDR get_last_source_start_addr ()
{
return m_last_source_start_addr;
}
struct using_direct **get_local_using_directives ()
{
return &m_local_using_directives;
}
void set_local_using_directives (struct using_direct *new_local)
{
m_local_using_directives = new_local;
}
struct using_direct **get_global_using_directives ()
{
return &m_global_using_directives;
}
bool outermost_context_p () const
{
return m_context_stack.empty ();
}
struct context_stack *get_current_context_stack ()
{
if (m_context_stack.empty ())
return nullptr;
return &m_context_stack.back ();
}
int get_context_stack_depth () const
{
return m_context_stack.size ();
}
struct subfile *get_current_subfile ()
{
return m_current_subfile;
}
struct pending **get_local_symbols ()
{
return &m_local_symbols;
}
struct pending **get_file_symbols ()
{
return &m_file_symbols;
}
struct pending **get_global_symbols ()
{
return &m_global_symbols;
}
void record_debugformat (const char *format)
{
m_debugformat = format;
}
void record_producer (const char *producer)
{
m_producer = producer;
}
struct context_stack *push_context (int desc, CORE_ADDR valu);
struct context_stack pop_context ();
struct block *end_symtab_get_static_block (CORE_ADDR end_addr,
int expandable, int required);
struct compunit_symtab *end_symtab_from_static_block
(struct block *static_block, int section, int expandable);
struct compunit_symtab *end_symtab (CORE_ADDR end_addr, int section);
struct compunit_symtab *end_expandable_symtab (CORE_ADDR end_addr,
int section);
void augment_type_symtab ();
private:
void record_pending_block (struct block *block, struct pending_block *opblock);
struct block *finish_block_internal (struct symbol *symbol,
struct pending **listhead,
struct pending_block *old_blocks,
const struct dynamic_prop *static_link,
CORE_ADDR start, CORE_ADDR end,
int is_global, int expandable);
struct blockvector *make_blockvector ();
void watch_main_source_file_lossage ();
struct compunit_symtab *end_symtab_with_blockvector
(struct block *static_block, int section, int expandable);
/* The objfile we're reading debug info from. */
struct objfile *m_objfile;
/* List of subfiles (source files).
Files are added to the front of the list.
This is important mostly for the language determination hacks we use,
which iterate over previously added files. */
struct subfile *m_subfiles = nullptr;
/* The subfile of the main source file. */
struct subfile *m_main_subfile = nullptr;
/* Name of source file whose symbol data we are now processing. This
comes from a symbol of type N_SO for stabs. For DWARF it comes
from the DW_AT_name attribute of a DW_TAG_compile_unit DIE. */
gdb::unique_xmalloc_ptr<char> m_last_source_file;
/* E.g., DW_AT_comp_dir if DWARF. Space for this is malloc'd. */
gdb::unique_xmalloc_ptr<char> m_comp_dir;
/* Space for this is not malloc'd, and is assumed to have at least
the same lifetime as objfile. */
const char *m_producer = nullptr;
/* Space for this is not malloc'd, and is assumed to have at least
the same lifetime as objfile. */
const char *m_debugformat = nullptr;
/* The compunit we are building. */
struct compunit_symtab *m_compunit_symtab = nullptr;
/* Language of this compunit_symtab. */
enum language m_language;
/* The macro table for the compilation unit whose symbols we're
currently reading. */
struct macro_table *m_pending_macros = nullptr;
/* True if symtab has line number info. This prevents an otherwise
empty symtab from being tossed. */
bool m_have_line_numbers = false;
/* Core address of start of text of current source file. This too
comes from the N_SO symbol. For Dwarf it typically comes from the
DW_AT_low_pc attribute of a DW_TAG_compile_unit DIE. */
CORE_ADDR m_last_source_start_addr;
/* Stack of subfile names. */
std::vector<const char *> m_subfile_stack;
/* The "using" directives local to lexical context. */
struct using_direct *m_local_using_directives = nullptr;
/* Global "using" directives. */
struct using_direct *m_global_using_directives = nullptr;
/* The stack of contexts that are pushed by push_context and popped
by pop_context. */
std::vector<struct context_stack> m_context_stack;
struct subfile *m_current_subfile = nullptr;
/* The mutable address map for the compilation unit whose symbols
we're currently reading. The symtabs' shared blockvector will
point to a fixed copy of this. */
struct addrmap *m_pending_addrmap = nullptr;
/* The obstack on which we allocate pending_addrmap.
If pending_addrmap is NULL, this is uninitialized; otherwise, it is
initialized (and holds pending_addrmap). */
auto_obstack m_pending_addrmap_obstack;
/* True if we recorded any ranges in the addrmap that are different
from those in the blockvector already. We set this to false when
we start processing a symfile, and if it's still false at the
end, then we just toss the addrmap. */
bool m_pending_addrmap_interesting = false;
/* An obstack used for allocating pending blocks. */
auto_obstack m_pending_block_obstack;
/* Pointer to the head of a linked list of symbol blocks which have
already been finalized (lexical contexts already closed) and which
are just waiting to be built into a blockvector when finalizing the
associated symtab. */
struct pending_block *m_pending_blocks = nullptr;
/* Pending static symbols and types at the top level. */
struct pending *m_file_symbols = nullptr;
/* Pending global functions and variables. */
struct pending *m_global_symbols = nullptr;
/* Pending symbols that are local to the lexical context. */
struct pending *m_local_symbols = nullptr;
};
extern void add_symbol_to_list (struct symbol *symbol,
struct pending **listhead);
extern struct symbol *find_symbol_in_list (struct pending *list,
char *name, int length);
#endif /* defined (BUILDSYM_H) */