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[v3,for-4.7,14/16] oxenstored: fix error when shifting negative value

Message ID 1461755514-23754-15-git-send-email-roger.pau@citrix.com (mailing list archive)
State New, archived
Headers show

Commit Message

Roger Pau Monné April 27, 2016, 11:11 a.m. UTC 
By explicitly casting it to unsigned.

Reasoning on why this is needed, provided by Andrew Cooper:

"Ocaml stores integers shifted left by one, and with the bottom bit set.

Values with the bottom bit clear are pointers into the GC'd heap. Values
with the bottom bit set are integers, and need to be shifted by 1 bit to
have calculations performed."

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
---
Changes since v2:
 - Expand commit message with Andrew's reasoning.
---
 tools/ocaml/xenstored/systemd_stubs.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Wei Liu April 27, 2016, 11:26 a.m. UTC | #1 
On Wed, Apr 27, 2016 at 01:11:52PM +0200, Roger Pau Monne wrote:
> By explicitly casting it to unsigned.
> 
> Reasoning on why this is needed, provided by Andrew Cooper:
> 
> "Ocaml stores integers shifted left by one, and with the bottom bit set.
> 
> Values with the bottom bit clear are pointers into the GC'd heap. Values
> with the bottom bit set are integers, and need to be shifted by 1 bit to
> have calculations performed."
> 
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

Acked-by: Wei Liu <wei.liu2@citrix.com>
diff mbox

Patch

diff --git a/tools/ocaml/xenstored/systemd_stubs.c b/tools/ocaml/xenstored/systemd_stubs.c
index 1bd5dea..a78a72b 100644
--- a/tools/ocaml/xenstored/systemd_stubs.c
+++ b/tools/ocaml/xenstored/systemd_stubs.c
@@ -124,7 +124,7 @@  CAMLprim value ocaml_sd_listen_fds(value connect_to)
 	CAMLparam1(connect_to);
 	CAMLlocal1(sock_ret);
 
-	sock_ret = Val_int(-1);
+	sock_ret = Val_int(-1U);
 
 	CAMLreturn(sock_ret);
 }
@@ -144,7 +144,7 @@  CAMLprim value ocaml_sd_notify_ready(value ignore)
 	CAMLparam1(ignore);
 	CAMLlocal1(ret);
 
-	ret = Val_int(-1);
+	ret = Val_int(-1U);
 
 	CAMLreturn(ret);
 }