From: Jonathan Rajotte Date: Mon, 6 Nov 2017 21:10:44 +0000 (-0500) Subject: ABI: refuse non-matching ABI minor version on event registration X-Git-Url: http://git.lttng.org/?p=lttng-ust.git;a=commitdiff_plain;h=refs%2Fheads%2Fstable-2.7 ABI: refuse non-matching ABI minor version on event registration In scenarios where a lttng-tools 2.8 (lttng-ust 2.8) stack is running and an application linked against a lttng-ust 2.7, event registration will fail on fields size validation [1]. This is not expected based on the ABI versioning exposed by lttng-ust 2.7 (6.0) and lttng-ust 2.8 (6.1). The same happen if the scenario is reversed. This is the result of a change in _ustctl_basic_type. 2.8 introduced enumeration to _ustctl_basic_type. The defined padding is of 296 while the new union member is 312 (310 of real data + 2 for alignment) pushing the structure size to 312 instead of the previous 296. This should have been an major ABI break but until now the problem did not surface. To prevent this, refuse non matching minor version. No need to check for particular major,minor version since only 6.0 (ust 2.7) and 6.1 (ust 2.8) exist until a major ABI break. Signed-off-by: Jonathan Rajotte Signed-off-by: Mathieu Desnoyers --- diff --git a/liblttng-ust-ctl/ustctl.c b/liblttng-ust-ctl/ustctl.c index 6b6f295b..5a7fa61f 100644 --- a/liblttng-ust-ctl/ustctl.c +++ b/liblttng-ust-ctl/ustctl.c @@ -1737,6 +1737,17 @@ int ustctl_recv_reg_msg(int sock, return -LTTNG_UST_ERR_UNSUP_MAJOR; } + /* + * Addition of enumeration inside _ustclt_basic_type should have been + * marked as a breaking ABI change since it blows past the included + * padding hence result in bigger than expected struct. Refuse + * registration for non-matching minor version since only two minor + * versions exist for ust-2.7(6.0) and 2.8(6.1). + */ + if (reg_msg.minor != LTTNG_UST_ABI_MINOR_VERSION) { + return -LTTNG_UST_ERR_UNSUP_MAJOR; + } + return 0; }