From 50ae81305c7a3ee802f0a1988503ce913c79cd6e Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Tue, 4 May 2021 11:25:22 -0500 Subject: signal: Verify the alignment and size of siginfo_t Update the static assertions about siginfo_t to also describe it's alignment and size. While investigating if it was possible to add a 64bit field into siginfo_t[1] it became apparent that the alignment of siginfo_t is as much a part of the ABI as the size of the structure. If the alignment changes siginfo_t when embedded in another structure can move to a different offset. Which is not acceptable from an ABI structure. So document that fact and add static assertions to notify developers if they change change the alignment by accident. [1] https://lkml.kernel.org/r/YJEZdhe6JGFNYlum@elver.google.com Acked-by: Marco Elver v1: https://lkml.kernel.org/r/20210505141101.11519-4-ebiederm@xmission.co Link: https://lkml.kernel.org/r/875yxaxmyl.fsf_-_@disp2133 Signed-off-by: "Eric W. Biederman" --- include/uapi/asm-generic/siginfo.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'include/uapi/asm-generic/siginfo.h') diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h index 5a3c221f4c9d..3ba180f550d7 100644 --- a/include/uapi/asm-generic/siginfo.h +++ b/include/uapi/asm-generic/siginfo.h @@ -29,6 +29,11 @@ typedef union sigval { #define __ARCH_SI_ATTRIBUTES #endif +/* + * Be careful when extending this union. On 32bit siginfo_t is 32bit + * aligned. Which means that a 64bit field or any other field that + * would increase the alignment of siginfo_t will break the ABI. + */ union __sifields { /* kill() */ struct { -- cgit v1.2.3