[PATCH][gdb/symtab] Fix infinite recursion in dwarf2_cu::get_builder()

Tom de Vries
2021-05-06T12:04:06Z

Hi,

With the test-case attached in PR26327, gdb aborts:
...
$ gdb -q -batch 447.dealII -ex "b main"
Aborted (core dumped)
...
when running out of stack due to infinite recursion:
...
#8 0x00000000006aaba6 in dwarf2_cu::get_builder (this=0x35e4b40)
at src/gdb/dwarf2/read.c:700
#9 0x00000000006aaba6 in dwarf2_cu::get_builder (this=0x22ee2c0)
at src/gdb/dwarf2/read.c:700
#10 0x00000000006aaba6 in dwarf2_cu::get_builder (this=0x35e4b40)
at src/gdb/dwarf2/read.c:700
#11 0x00000000006aaba6 in dwarf2_cu::get_builder (this=0x22ee2c0)
at src/gdb/dwarf2/read.c:700
...

We're recursing in this code in dwarf2_cu::get_builder():
...
/* Otherwise, search ancestors for a valid builder. */
if (ancestor != nullptr)
return ancestor->get_builder ();
...
due to the fact that the ancestor chain is a cycle.

Higher up in the call stack, we find some code that is responsible for
triggering this, in new_symbol:
...
case DW_TAG_formal_parameter:
{
/* If we are inside a function, mark this as an argument. If
not, we might be looking at an argument to an inlined function
when we do not have enough information to show inlined frames;
pretend it's a local variable in that case so that the user can
still see it. */
struct context_stack *curr
= cu->get_builder ()->get_current_context_stack ();
if (curr != nullptr && curr->name != nullptr)
SYMBOL_IS_ARGUMENT (sym) = 1;
...

This is code that was added to support pre-4.1 gcc, to be able to show
arguments of inlined functions as locals, in the absense of sufficiently
correct debug information.

Removing this code (that is, doing SYMBOL_IS_ARGUMENT (sym) = 1
unconditially), fixes the crash. The ancestor variable also seems to have
been added specifically to deal with fallout from this code, so remove that as
well.

Tested on x86_64-linux:
- openSUSE Leap 15.2 with gcc 7.5.0, and
- openSUSE Tumbleweed with gcc 10.3.0.

Any comments?

Thanks,
- Tom

[gdb/symtab] Fix infinite recursion in dwarf2_cu::get_builder()

gdb/ChangeLog:

2021-05-06 Tom de Vries <tdevries@suse.de>

PR symtab/26327
* dwarf2/read.c (struct dwarf2_cu): Remove ancestor.
(dwarf2_cu::get_builder): Remove ancestor-related code.
(new_symbol): Remove code supporting pre-4.1 gcc that show arguments
of inlined functions as locals.
(follow_die_offset, follow_die_sig_1): Remove setting of ancestor.

---
gdb/doc/gdb.texinfo | 4 ++--
gdb/dwarf2/read.c | 25 ++-----------------------
2 files changed, 4 insertions(+), 25 deletions(-)

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 56f37eb2288..f4d7085da58 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -13842,8 +13842,8 @@ when using @sc{dwarf 2}. Versions of @value{NGCC} before 4.1
do not emit two required attributes (@samp{DW_AT_call_file} and
@samp{DW_AT_call_line}); @value{GDBN} does not display inlined
function calls with earlier versions of @value{NGCC}. It instead
-displays the arguments and local variables of inlined functions as
-local variables in the caller.
+displays local variables of inlined functions as local variables in
+the caller.

The body of an inlined function is directly included at its call site;
unlike a non-inlined function, there are no instructions devoted to
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 5796cf1730b..b2f48f1f395 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -684,10 +684,6 @@ struct dwarf2_cu

struct partial_die_info *find_partial_die (sect_offset sect_off);

- /* If this CU was inherited by another CU (via specification,
- abstract_origin, etc), this is the ancestor CU. */
- dwarf2_cu *ancestor;
-
/* Get the buildsym_compunit for this CU. */
buildsym_compunit *get_builder ()
{
@@ -695,10 +691,6 @@ struct dwarf2_cu
if (m_builder != nullptr)
return m_builder.get ();

- /* Otherwise, search ancestors for a valid builder. */
- if (ancestor != nullptr)
- return ancestor->get_builder ();
-
return nullptr;
}
};
@@ -22045,15 +22037,7 @@ new_symbol (struct die_info *die, struct type *type, struct dwarf2_cu *cu,
break;
case DW_TAG_formal_parameter:
{
- /* If we are inside a function, mark this as an argument. If
- not, we might be looking at an argument to an inlined function
- when we do not have enough information to show inlined frames;
- pretend it's a local variable in that case so that the user can
- still see it. */
- struct context_stack *curr
- = cu->get_builder ()->get_current_context_stack ();
- if (curr != nullptr && curr->name != nullptr)
- SYMBOL_IS_ARGUMENT (sym) = 1;
+ SYMBOL_IS_ARGUMENT (sym) = 1;
attr = dwarf2_attr (die, DW_AT_location, cu);
if (attr != nullptr)
{
@@ -23389,9 +23373,6 @@ follow_die_offset (sect_offset sect_off, int offset_in_dwz,
*ref_cu = target_cu;
temp_die.sect_off = sect_off;

- if (target_cu != cu)
- target_cu->ancestor = cu;
-
return (struct die_info *) htab_find_with_hash (target_cu->die_hash,
&temp_die,
to_underlying (sect_off));
@@ -23741,7 +23722,7 @@ follow_die_sig_1 (struct die_info *src_die, struct signatured_type *sig_type,
struct dwarf2_cu **ref_cu)
{
struct die_info temp_die;
- struct dwarf2_cu *sig_cu, *cu = *ref_cu;
+ struct dwarf2_cu *sig_cu;
struct die_info *die;
dwarf2_per_objfile *per_objfile = (*ref_cu)->per_objfile;

@@ -23777,8 +23758,6 @@ follow_die_sig_1 (struct die_info *src_die, struct signatured_type *sig_type,
}

*ref_cu = sig_cu;
- if (sig_cu != cu)
- sig_cu->ancestor = cu;

return die;
}