File gdb-exp-redo-cast-handling-for-indirection.patch of Package gdb

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File gdb-exp-redo-cast-handling-for-indirection.patch of Package gdb

From a6800d9c8145f25001dd39afc3571e3350573e81 Mon Sep 17 00:00:00 2001
From: Tom de Vries <tdevries@suse.de>
Date: Mon, 6 May 2024 14:23:25 +0200
Subject: [PATCH] [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
---
 gdb/testsuite/gdb.base/cast-indirection.exp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gdb/testsuite/gdb.base/cast-indirection.exp b/gdb/testsuite/gdb.base/cast-indirection.exp
index f1fe4302d27..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

base-commit: fc73000faa1798573090994167b7e2d451c211db
-- 
2.35.3

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File gdb-exp-redo-cast-handling-for-indirection.patch of Package gdb

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