Commit 50ae8130 authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

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: default avatarMarco Elver <elver@google.com>
v1: https://lkml.kernel.org/r/20210505141101.11519-4-ebiederm@xmission.co
Link: https://lkml.kernel.org/r/875yxaxmyl.fsf_-_@disp2133


Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent c7fff928

arch/arm/kernel/signal.c

+2 −0
Original line number Diff line number Diff line
@@ -737,6 +737,8 @@ static_assert(NSIGBUS == 5); 
static_assert(NSIGTRAP	== 6);

static_assert(NSIGCHLD	== 6);

static_assert(NSIGSYS	== 2);

static_assert(sizeof(siginfo_t) == 128);

static_assert(__alignof__(siginfo_t) == 4);

static_assert(offsetof(siginfo_t, si_signo)	== 0x00);

static_assert(offsetof(siginfo_t, si_errno)	== 0x04);

static_assert(offsetof(siginfo_t, si_code)	== 0x08);

arch/arm64/kernel/signal.c

+2 −0
Original line number Diff line number Diff line
@@ -1011,6 +1011,8 @@ static_assert(NSIGBUS == 5); 
static_assert(NSIGTRAP	== 6);

static_assert(NSIGCHLD	== 6);

static_assert(NSIGSYS	== 2);

static_assert(sizeof(siginfo_t) == 128);

static_assert(__alignof__(siginfo_t) == 8);

static_assert(offsetof(siginfo_t, si_signo)	== 0x00);

static_assert(offsetof(siginfo_t, si_errno)	== 0x04);

static_assert(offsetof(siginfo_t, si_code)	== 0x08);

arch/arm64/kernel/signal32.c

+2 −0
Original line number Diff line number Diff line
@@ -469,6 +469,8 @@ static_assert(NSIGBUS == 5); 
static_assert(NSIGTRAP	== 6);

static_assert(NSIGCHLD	== 6);

static_assert(NSIGSYS	== 2);

static_assert(sizeof(compat_siginfo_t) == 128);

static_assert(__alignof__(compat_siginfo_t) == 4);

static_assert(offsetof(compat_siginfo_t, si_signo)	== 0x00);

static_assert(offsetof(compat_siginfo_t, si_errno)	== 0x04);

static_assert(offsetof(compat_siginfo_t, si_code)	== 0x08);

arch/sparc/kernel/signal32.c

+2 −0
Original line number Diff line number Diff line
@@ -757,6 +757,8 @@ static_assert(NSIGBUS == 5); 
static_assert(NSIGTRAP	== 6);

static_assert(NSIGCHLD	== 6);

static_assert(NSIGSYS	== 2);

static_assert(sizeof(compat_siginfo_t) == 128);

static_assert(__alignof__(compat_siginfo_t) == 4);

static_assert(offsetof(compat_siginfo_t, si_signo)	== 0x00);

static_assert(offsetof(compat_siginfo_t, si_errno)	== 0x04);

static_assert(offsetof(compat_siginfo_t, si_code)	== 0x08);

arch/sparc/kernel/signal_64.c

+2 −0
Original line number Diff line number Diff line
@@ -567,6 +567,8 @@ static_assert(NSIGBUS == 5); 
static_assert(NSIGTRAP	== 6);

static_assert(NSIGCHLD	== 6);

static_assert(NSIGSYS	== 2);

static_assert(sizeof(siginfo_t) == 128);

static_assert(__alignof__(siginfo_t) == 8);

static_assert(offsetof(siginfo_t, si_signo)	== 0x00);

static_assert(offsetof(siginfo_t, si_errno)	== 0x04);

static_assert(offsetof(siginfo_t, si_code)	== 0x08);