From: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
To: linux-sparse@vger.kernel.org
Cc: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Subject: [PATCH] force to 0 expressions which are erroneously non-constant
Date: Mon, 10 Aug 2020 07:51:03 +0200 [thread overview]
Message-ID: <20200810055103.67977-1-luc.vanoostenryck@gmail.com> (raw)
When an expression that needs to be constant but is, in fact,
not constant, sparse throws an error and leaves it as-is.
But some code makes the assumption that the expression is
constant and uses its value, with some random result.
One situation where this happens is in code like:
switch (x) {
case <some non-const expression>: ...
In this case, the linearization of the switch/case statement
will unconditionally use the value of the case expression
but the expression has no value.
One way to avoid this would be to add defensive checks each
time a value is retrieved but this is a lot of work and time
for no benefits.
So, change this by forcing the expression to be a constant
value of 0 just after the error message has been issued.
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
---
expand.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/expand.c b/expand.c
index 623b180025ad..c4f806dee1ba 100644
--- a/expand.c
+++ b/expand.c
@@ -1177,8 +1177,12 @@ static void expand_const_expression(struct expression *expr, const char *where)
{
if (expr) {
expand_expression(expr);
- if (expr->type != EXPR_VALUE)
+ if (expr->type != EXPR_VALUE) {
expression_error(expr, "Expected constant expression in %s", where);
+ expr->ctype = &int_ctype;
+ expr->type = EXPR_VALUE;
+ expr->value = 0;
+ }
}
}
--
2.28.0
next reply other threads:[~2020-08-10 5:51 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-10 5:51 Luc Van Oostenryck [this message]
-- strict thread matches above, loose matches on Subject: below --
2020-08-09 16:41 [PATCH] force to 0 expressions which are erroneously non-constant Luc Van Oostenryck
2017-05-31 13:31 Luc Van Oostenryck
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200810055103.67977-1-luc.vanoostenryck@gmail.com \
--to=luc.vanoostenryck@gmail.com \
--cc=linux-sparse@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).