GDB reports duplicate local vars with "<optimized out>" values for
inlined functions that are compiled with Clang.
Suppose we have
__attribute__((always_inline))
static void aFunction() {
int a = 42;
if(a > 2) {
int value = a;
value += 10; /* break here */
}
}
The "info locals" command at the "break here" line gives the following
output:
...
Breakpoint 1, aFunction () at test.c:6
6 value += 10; /* break here */
(gdb) info locals
value = 42
a = 42
value = <optimized out>
(gdb)
The reason is, inlined functions that are compiled by Clang do not
contain DW_AT_abstract_origin attributes in the DW_TAG_lexical_block
entries. See
https://bugs.llvm.org/show_bug.cgi?id=49953
E.g. the DIE of the inlined function above is
0x00000087: DW_TAG_inlined_subroutine
DW_AT_abstract_origin (0x0000002a "aFunction")
DW_AT_low_pc (0x00000000004004b2)
DW_AT_high_pc (0x00000000004004d2)
DW_AT_call_file ("/tmp/test.c")
DW_AT_call_line (11)
DW_AT_call_column (0x03)
0x0000009b: DW_TAG_variable
DW_AT_location (DW_OP_fbreg -4)
DW_AT_abstract_origin (0x00000032 "a")
0x000000a3: DW_TAG_lexical_block
DW_AT_low_pc (0x00000000004004c3)
DW_AT_high_pc (0x00000000004004d2)
0x000000b0: DW_TAG_variable
DW_AT_location (DW_OP_fbreg -8)
DW_AT_abstract_origin (0x0000003e "value")
This causes GDB to fail matching the concrete lexical scope with the
corresponding abstract entry. Hence, the local vars of the abstract
function that are contained in the lexical scope are read separately
(and thus, in addition to) the local vars of the concrete scope.
Because the abstract definitions of the vars do not contain location
information, we see the extra 'value = <optimized out>' above.
This bug is highly related to PR gdb/25695, but the root cause is not
exactly the same. In PR gdb/25695, GCC emits an extra
DW_TAG_lexical_block without an DW_AT_abstract_origin that wraps the
body of the inlined function. That is, the trees of the abstract DIE
for the function and its concrete instance are structurally not the
same. In the case of using Clang, the trees have the same structure.
To tackle the Clang case, when traversing the children of the concrete
instance root, keep a reference to the child of the abstract DIE that
corresponds to the concrete child, so that we can match the two DIEs
heuristically in case of missing DW_AT_abstract_origin attributes.
The updated gdb.opt/inline-locals.exp test has been checked with GCC
5-10 and Clang 5-11.
gdb/ChangeLog:
2021-04-14 Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
* dwarf2/read.c (inherit_abstract_dies): Keep a reference to the
corresponding child of the abstract DIE when iterating the
children of the concrete DIE.
gdb/testsuite/ChangeLog:
2021-04-14 Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
* gdb.opt/inline-locals.c (scoped): New function.
(main): Call 'scoped'.
* gdb.opt/inline-locals.exp: Update with "info locals" tests
for scoped variables.
* gdb.dwarf2/dw2-inline-with-lexical-scope.c: New file.
* gdb.dwarf2/dw2-inline-with-lexical-scope.exp: New file.
This commits the result of running gdb/copyright.py as per our Start
of New Year procedure...
gdb/ChangeLog
Update copyright year range in copyright header of all GDB files.
When running testcase gdb.opt/inline-locals.exp on openSUSE Tumbleweed, I get:
...
(gdb) info locals^M
array = {0 <repeats 48 times>, 15775231, 0, 194, 0, -11497, 32767, 4199061, \
0, 0, 0, 0, 0, 4198992, 0, 4198432, 0}^M
(gdb) FAIL: gdb.opt/inline-locals.exp: info locals above bar 2
...
Fix this by:
- completely initializing array before printing any value
- updating the pattern to match "array = {0 <repeats 64 times>}"
Tested on x86_64-linux.
gdb/testsuite/ChangeLog:
2020-07-21 Tom de Vries <tdevries@suse.de>
* gdb.opt/inline-locals.c (init_array): New func.
(func1): Use init_array.
* gdb.opt/inline-locals.exp: Update pattern.
This commit applies all changes made after running the gdb/copyright.py
script.
Note that one file was flagged by the script, due to an invalid
copyright header
(gdb/unittests/basic_string_view/element_access/char/empty.cc).
As the file was copied from GCC's libstdc++-v3 testsuite, this commit
leaves this file untouched for the time being; a patch to fix the header
was sent to gcc-patches first.
gdb/ChangeLog:
Update copyright year range in all GDB files.
This applies the second part of GDB's End of Year Procedure, which
updates the copyright year range in all of GDB's files.
gdb/ChangeLog:
Update copyright year range in all GDB files.
While doing some powerpc Linux tests on a ppc 476 board using GCC 5.2, i
noticed inline-bt.exp, inline-cmds.exp and inline-locals.exp failing.
FAIL: gdb.opt/inline-bt.exp: continue to bar (1)
FAIL: gdb.opt/inline-bt.exp: backtrace from bar (1)
FAIL: gdb.opt/inline-bt.exp: continue to bar (2)
FAIL: gdb.opt/inline-bt.exp: backtrace from bar (2)
FAIL: gdb.opt/inline-bt.exp: continue to bar (3)
FAIL: gdb.opt/inline-bt.exp: backtrace from bar (3)
FAIL: gdb.opt/inline-cmds.exp: continue to bar (1)
FAIL: gdb.opt/inline-cmds.exp: backtrace from bar (1)
FAIL: gdb.opt/inline-cmds.exp: continue to bar (2)
FAIL: gdb.opt/inline-cmds.exp: backtrace from bar (2)
FAIL: gdb.opt/inline-cmds.exp: continue to marker
FAIL: gdb.opt/inline-cmds.exp: backtrace from marker
FAIL: gdb.opt/inline-cmds.exp: step into finish marker
FAIL: gdb.opt/inline-locals.exp: continue to bar (1)
FAIL: gdb.opt/inline-locals.exp: continue to bar (2)
FAIL: gdb.opt/inline-locals.exp: backtrace from bar (2)
FAIL: gdb.opt/inline-locals.exp: continue to bar (3)
FAIL: gdb.opt/inline-locals.exp: backtrace from bar (3)
They failed because the breakpoint supposedly inserted at bar was actually
inserted at noinline.
(gdb) break inline-markers.c:20^M
Breakpoint 2 at 0x1000079c: file gdb/testsuite/gdb.opt/inline-markers.c, line 20.^M
(gdb) continue^M
Continuing.^M
^M
Breakpoint 2, noinline () at gdb/testsuite/gdb.opt/inline-markers.c:35^M
35 inlined_fn (); /* inlined */^M
As we can see, line 20 is really inside bar, not noinline:
18 void bar(void)
19 {
20 x += y; /* set breakpoint 1 here */
21 }
Further investigation shows that this is really due to GCC 5's new
ICF pass (-fipa-icf), now enabled by default at -O2, which folds bar
and marker into noinline, where the call to inlined_fn was inlined.
This breaks the testcase since it expects to stop at specific spots.
I thought about two possible fixes for this issue.
- Disable the ICF pass manually when building the binary (-fno-ipa-icf).
This has the advantage of not having to touch the testcase sources themselves,
but the disadvantage of having to add conditional blocks to test the GCC
version. If we ever change GCC's default, we will have to adjust the
conditional block again to match GCC's behavior.
- Modify the testcase sources to make the identical functions unique.
This solution doesn't touch the testcase itself, but changes the source
code slightly in order to make bar, marker and inlined_fn unique. This
causes GCC's ICF pass to ignore these functions and not fold them into
a common identical function.
I'm good with either of them, but i'm more inclined to go with the second
one.
The attached patch implements this by adding the new global variable z, set
to 0, that gets added in different ways to marker and inlined_fn. Since it
is 0, it doesn't affect any possible value checks that we may wish to do
in the future (we currently only check for values changed by bar).
Ok?
ps: I also noticed GDB doesn't do a great job at stating that the breakpoint
was actually inserted at a different source line than previously requested,
so this sounds like a bug that should be fixed, if it is not just wrong
DWARF information (did not investigate it further).
gdb/testsuite/ChangeLog:
2015-08-24 Luis Machado <lgustavo@codesourcery.com>
* gdb.opt/inline-bt.c: New volatile global z.
* gdb.opt/inline-cmds.c: Likewise.
* gdb.opt/inline-locals.c: Likewise.
* gdb.opt/inline-markers.c: New extern global z.
(marker): Use z.
(inline_fn): Likewise.
Two modifications:
1. The addition of 2013 to the copyright year range for every file;
2. The use of a single year range, instead of potentially multiple
year ranges, as approved by the FSF.
(func1): Use it.
(func2): Likewise.
(func3): Likewise.
(outer_inline1): Likewise.
(outer_inline2): Likewise.
* gdb.opt/inline-bt.c (ATTR): New define.
(func1): Use it.
(func2): Likewise.
* gdb.opt/inline-locals.c (ATTR): New define.
(func1): Use it.
(func2): Likewise.
* NEWS: Document inlined function support.
* Makefile.in (SFILES): Add inline-frame.c.
(COMMON_OBS): Add inline-frame.o.
* block.c (contained_in): Rewrite to use lexical nesting.
(block_linkage_function): Skip inlined function blocks.
(block_inlined_p): New.
* block.h (struct block): Update comment.
(block_inlined_p): New prototype.
* blockframe.c (get_frame_block): Handle inlined functions.
(get_frame_function): Do not use block_linkage_function.
(block_innermost_frame): Use get_frame_block and contained_in.
* breakpoint.c (watchpoint_check): Remove extra reinit_frame_cache.
Skip over inlined functions. Simplify epilogue check.
(bpstat_check_breakpoint_conditions): Use get_stack_frame_id.
Update comments.
(set_momentary_breakpoint): Only accept non-inlined frames.
(watch_command_1): Use frame_unwind_caller_pc and
frame_unwind_caller_id instead of get_prev_frame.
(until_break_command): Likewise. Use get_stack_frame_id.
* buildsym.c (end_symtab): Set SYMBOL_SYMTAB for block functions.
* dwarf2loc.c (dwarf_expr_frame_base): Use block_linkage_function.
* dwarf2read.c (process_die): Handle DW_TAG_inlined_subroutine.
(read_func_scope, new_symbol): Likewise. Handle arguments specially
for inlined functions without call site information.
(inherit_abstract_dies): Allow tag mismatch for inlined subroutines.
(die_specification): Treat DW_AT_abstract_origin as a specification.
(read_type_die): Handle DW_TAG_inlined_subroutine.
* frame-unwind.c (frame_unwind_init): Add inline_frame_unwind.
* frame.c (fprint_frame_id): Print inline depth.
(fprint_frame_type): Handle INLINE_FRAME and SENTINEL_FRAME.
(skip_inlined_frames, get_stack_frame_id): New.
(frame_unwind_caller_id): Use skip_inlined_frames.
(frame_id_inlined_p): New.
(frame_id_eq): Make the logic match the comments. Add inline_depth
check.
(frame_id_inner): Handle inlined functions.
(frame_unwind_pc): New function, copied from frame_unwind_caller_pc.
(frame_unwind_caller_pc): Use skip_inlined_frames and frame_unwind_pc.
(get_prev_frame_1): Check for inline frames. Split out frame
allocation to get_prev_frame_raw.
(get_prev_frame_raw): New function.
(get_prev_frame): Handle inline frames.
(get_frame_pc): Use frame_unwind_pc.
(get_frame_address_in_block): Skip inlined frames on both sides.
(pc_notcurrent): Delete.
(find_frame_sal): Rewrite to handle inline call sites. Use
get_frame_address_in_block.
(deprecated_update_frame_pc_hack): Make static.
* frame.h: Update comments.
(struct frame_id): Add inline_depth.
(enum frame_type): Add INLINE_FRAME.
(frame_id_inlined_p, get_stack_frame_id): New prototypes.
* gdbthread.h (struct thread_info): Add step_stack_frame_id field.
* infcmd.c (set_step_frame): New function.
(step_once): Use set_step_frame. Handle inlined functions.
(until_next_command): Use set_step_frame.
(finish_backward), finish_forward): Use get_stack_frame_id.
(finish_command): Support inlined functions.
* inferior.h (set_step_info): New prototype.
* infrun.c (RESUME_ALL): Use minus_one_ptid.
(clear_proceed_status): Clear step_stack_frame_id.
(init_wait_for_inferior): Call clear_inline_frame_state.
(init_execution_control_state): Make static.
(set_step_info): New function.
(init_thread_stepping_state): Do not set the symtab or line here.
(stepped_in_from): New function.
(handle_inferior_event): Handle inlined functions. Use set_step_info.
(insert_step_resume_breakpoint_at_frame): Use get_stack_frame_id.
(struct inferior_status): Add step_stack_frame_id.
(save_inferior_status, restore_inferior_status): Save and restore
step_stack_frame_id.
* inline-frame.c, inline-frame.h: New files.
* minsyms.c (prim_record_minimal_symbol_and_info): Use XCALLOC.
* regcache.c (regcache_write_pc): Call reinit_frame_cache.
* s390-tdep.c (s390_prologue_frame_unwind_cache): Handle INLINE_FRAME.
* stack.c (frame_show_address): New.
(print_frame_info, print_frame): Use it.
(find_frame_funname): Use get_frame_function. Handle inlined blocks.
(frame_info): Mark inlined functions.
(backtrace_command_1): Use get_current_user_frame.
(print_frame_local_vars, print_frame_label_vars): Update comments.
(return_command): Refuse inlined functions.
* symtab.c (lookup_symbol_aux_local): Stop at inlined function
boundaries.
(find_function_start_sal): Avoid inlined functions.
(completion_list_add_fields): New function.
(default_make_symbol_completion_list): Use it. Use block_static_block
and block_global_block. Check for inlined functions.
(skip_prologue_using_sal): Avoid line number comparison across
inlining.
* symtab.h (struct symbol): Add is_inlined.
(SYMBOL_INLINED): New.
* target.c (target_resume): Call clear_inline_frame_state.
* valops.c (value_of_variable): Check block_inlined_p.
gdb/doc/
* gdb.texinfo (Debugging Optimized Code): New chapter.
(Compiling for Debugging): Reference it. Move some
text to the new section.
gdb/testsuite/
* gdb.base/break.exp: Add an XFAIL for gcc/36748.
* gdb.cp/annota2.exp: Accept frames-invalid in more places.
* gdb.opt/Makefile.in (EXECUTABLES): Update.
* gdb.opt/clobbered-registers-O2.exp: Update to GPL v3.
* gdb.opt/inline-bt.c, gdb.opt/inline-bt.exp,
gdb.opt/inline-cmds.c, gdb.opt/inline-cmds.exp,
gdb.opt/inline-locals.c, gdb.opt/inline-locals.exp,
gdb.opt/inline-markers.c: New files.
* lib/gdb.exp (skip_inline_frame_tests): New function.
(skip_inline_var_tests): New function.
