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* [binutils-gdb] [gdb/exp] Redo cast handling for indirection
@ 2024-05-06 12:22 Tom de Vries
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From: Tom de Vries @ 2024-05-06 12:22 UTC (permalink / raw)
To: gdb-cvs
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=5edbb6ed920057df4cca423e3fc54f27f7685def
commit 5edbb6ed920057df4cca423e3fc54f27f7685def
Author: Tom de Vries <tdevries@suse.de>
Date: Mon May 6 14:23:25 2024 +0200
[gdb/exp] Redo cast handling for indirection
In commit ed8fd0a342f ("[gdb/exp] Fix cast handling for indirection"), I
introduced the behaviour that even though we have:
...
(gdb) p *a_loc ()
'a_loc' has unknown return type; cast the call to its declared return type
...
we get:
...
(gdb) p (char)*a_loc ()
$1 = 97 'a'
...
In other words, the unknown return type of a_loc is inferred from the cast,
effectually evaluating:
...
(gdb) p (char)*(char *)a_loc ()
...
This is convient for the case that errno is defined as:
...
#define errno (*__errno_location ())
...
and the return type of __errno_location is unknown but the macro definition is
known, such that we can use:
...
(gdb) p (int)errno
...
instead of
...
(gdb) p *(int *)__errno_location ()
...
However, as Pedro has pointed out in post-commit review [1], this makes it
harder to reason about the semantics of an expression.
For instance, this:
...
(gdb) p (long long)*a_loc ()"
...
would be evaluated without debug info as:
...
(gdb) p (long long)*(long long *)a_loc ()"
...
but with debug info as:
...
(gdb) p (long long)*(char *)a_loc ()"
...
Fix this by instead simply erroring out for this case:
...
(gdb) p (char)*a_loc ()
'a_loc' has unknown return type; cast the call to its declared return type
...
Tested on x86_64-linux.
Approved-By: Pedro Alves <pedro@palves.net>
[1] https://sourceware.org/pipermail/gdb-patches/2024-May/208821.html
Diff:
---
gdb/expop.h | 5 +----
gdb/testsuite/gdb.base/cast-indirection.exp | 5 +++--
2 files changed, 4 insertions(+), 6 deletions(-)
diff --git a/gdb/expop.h b/gdb/expop.h
index 1967d9779b7..2d46a9dad6a 100644
--- a/gdb/expop.h
+++ b/gdb/expop.h
@@ -1513,11 +1513,8 @@ public:
struct expression *exp,
enum noside noside) override
{
- struct type *pointer_to_expect_type = (expect_type != nullptr
- ? lookup_pointer_type (expect_type)
- : nullptr);
value *val
- = std::get<0> (m_storage)->evaluate (pointer_to_expect_type, exp, noside);
+ = std::get<0> (m_storage)->evaluate (nullptr, exp, noside);
return eval_op_ind (expect_type, exp, noside, val);
}
diff --git a/gdb/testsuite/gdb.base/cast-indirection.exp b/gdb/testsuite/gdb.base/cast-indirection.exp
index d2c6d58e3ca..7b9b5a5d677 100644
--- a/gdb/testsuite/gdb.base/cast-indirection.exp
+++ b/gdb/testsuite/gdb.base/cast-indirection.exp
@@ -13,7 +13,7 @@
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
-# Check that "p (char)*a_loc ()" is handled as "p (char)*(char *)a_loc ()".
+# Check that "p (char)*a_loc ()" is handled correctly.
standard_testfile
@@ -37,4 +37,5 @@ gdb_test "p *(char *)a_loc ()" " = 97 'a'"
gdb_test "p (char)*(char *)a_loc ()" " = 97 'a'"
# Regression test for PR31693.
-gdb_test "p (char)*a_loc ()" " = 97 'a'"
+gdb_test "p (char)*a_loc ()" \
+ "'a_loc' has unknown return type; cast the call to its declared return type"
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