* [PATCH] x86/fpu: use _Alignof to avoid UB in TYPE_ALIGN
@ 2022-09-26 13:51 YingChi Long
0 siblings, 0 replies; 2+ messages in thread
From: YingChi Long @ 2022-09-26 13:51 UTC (permalink / raw)
To: peterz
Cc: me, ndesaulniers, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Nathan Chancellor, Tom Rix,
Paolo Bonzini, Chang S. Bae, linux-kernel, llvm
WG14 N2350 made very clear that it is an UB having type definitions
within "offsetof". This patch changes the implementation of macro
"TYPE_ALIGN" to builtin "_Alignof" to avoid undefined behavior.
I've grepped all source files to find any type definitions within
"offsetof".
offsetof\(struct .*\{ .*,
This implementation of macro "TYPE_ALIGN" seemes to be the only case of
type definitions within offsetof in the kernel codebase.
GCC builtin __alignof__ has different semantics here. __alignof__() will
in fact return the 'sane' result while structure alignment and
_Alignof() return the ABI required minimum alignment.
Signed-off-by: YingChi Long <me@inclyc.cn>
Link: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm
Link: https://godbolt.org/z/T749MfM9o
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=10360
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69560
Link: https://reviews.llvm.org/D133574
---
arch/x86/kernel/fpu/init.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 621f4b6cac4a..de96c11e1fe9 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -133,9 +133,6 @@ static void __init fpu__init_system_generic(void)
fpu__init_system_mxcsr();
}
-/* Get alignment of the TYPE. */
-#define TYPE_ALIGN(TYPE) offsetof(struct { char x; TYPE test; }, test)
-
/*
* Enforce that 'MEMBER' is the last field of 'TYPE'.
*
@@ -143,8 +140,8 @@ static void __init fpu__init_system_generic(void)
* because that's how C aligns structs.
*/
#define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
- BUILD_BUG_ON(sizeof(TYPE) != ALIGN(offsetofend(TYPE, MEMBER), \
- TYPE_ALIGN(TYPE)))
+ BUILD_BUG_ON(sizeof(TYPE) != \
+ ALIGN(offsetofend(TYPE, MEMBER), _Alignof(TYPE)))
/*
* We append the 'struct fpu' to the task_struct:
--
2.35.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* [PATCH] x86/fpu: use _Alignof to avoid UB in TYPE_ALIGN
[not found] <Peter Zijlstra <peterz@infradead.org>
@ 2022-09-26 13:48 ` YingChi Long
0 siblings, 0 replies; 2+ messages in thread
From: YingChi Long @ 2022-09-26 13:48 UTC (permalink / raw)
Cc: me, ndesaulniers, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Nathan Chancellor, Tom Rix,
Paolo Bonzini, Chang S. Bae, linux-kernel, llvm
WG14 N2350 made very clear that it is an UB having type definitions
within "offsetof". This patch changes the implementation of macro
"TYPE_ALIGN" to builtin "_Alignof" to avoid undefined behavior.
I've grepped all source files to find any type definitions within
"offsetof".
offsetof\(struct .*\{ .*,
This implementation of macro "TYPE_ALIGN" seemes to be the only case of
type definitions within offsetof in the kernel codebase.
GCC builtin __alignof__ has different semantics here. __alignof__() will
in fact return the 'sane' result while structure alignment and
_Alignof() return the ABI required minimum alignment.
Signed-off-by: YingChi Long <me@inclyc.cn>
Link: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm
Link: https://godbolt.org/z/T749MfM9o
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=10360
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69560
Link: https://reviews.llvm.org/D133574
---
arch/x86/kernel/fpu/init.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 621f4b6cac4a..de96c11e1fe9 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -133,9 +133,6 @@ static void __init fpu__init_system_generic(void)
fpu__init_system_mxcsr();
}
-/* Get alignment of the TYPE. */
-#define TYPE_ALIGN(TYPE) offsetof(struct { char x; TYPE test; }, test)
-
/*
* Enforce that 'MEMBER' is the last field of 'TYPE'.
*
@@ -143,8 +140,8 @@ static void __init fpu__init_system_generic(void)
* because that's how C aligns structs.
*/
#define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
- BUILD_BUG_ON(sizeof(TYPE) != ALIGN(offsetofend(TYPE, MEMBER), \
- TYPE_ALIGN(TYPE)))
+ BUILD_BUG_ON(sizeof(TYPE) != \
+ ALIGN(offsetofend(TYPE, MEMBER), _Alignof(TYPE)))
/*
* We append the 'struct fpu' to the task_struct:
--
2.35.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
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2022-09-26 13:51 [PATCH] x86/fpu: use _Alignof to avoid UB in TYPE_ALIGN YingChi Long
[not found] <Peter Zijlstra <peterz@infradead.org>
2022-09-26 13:48 ` YingChi Long
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