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SubjectRe: [PATCH] x86: use enum instead of literals for trap values

* Kees Cook <keescook@chromium.org> wrote:

> The traps are referred to by their numbers and it can be difficult to
> understand them while reading the code without context. This patch adds
> enumeration of the trap numbers and replaces the numbers with the correct
> enum for x86.
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
>
> ---
> I've updated Aditya Kali's earlier patch:
> https://lkml.org/lkml/2011/4/22/328
> ---
> arch/x86/include/asm/traps.h | 25 +++++++++
> arch/x86/kernel/irqinit.c | 2 +-
> arch/x86/kernel/traps.c | 117 ++++++++++++++++++++++--------------------
> 3 files changed, 88 insertions(+), 56 deletions(-)
>
> diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
> index 0012d09..768afb2 100644
> --- a/arch/x86/include/asm/traps.h
> +++ b/arch/x86/include/asm/traps.h
> @@ -89,4 +89,29 @@ asmlinkage void smp_thermal_interrupt(void);
> asmlinkage void mce_threshold_interrupt(void);
> #endif
>
> +/* Interrupts/Exceptions */
> +enum {
> + INTR_DIV_BY_ZERO = 0, /* 0 */
> + INTR_DEBUG, /* 1 */
> + INTR_NMI, /* 2 */
> + INTR_BREAKPOINT, /* 3 */
> + INTR_OVERFLOW, /* 4 */
> + INTR_BOUNDS_CHECK, /* 5 */
> + INTR_INVALID_OP, /* 6 */
> + INTR_NO_DEV, /* 7 */
> + INTR_DBL_FAULT, /* 8 */
> + INTR_SEG_OVERRUN, /* 9 */
> + INTR_INVALID_TSS, /* 10 */
> + INTR_NO_SEG, /* 11 */
> + INTR_STACK_FAULT, /* 12 */
> + INTR_GPF, /* 13 */
> + INTR_PAGE_FAULT, /* 14 */
> + INTR_SPURIOUS, /* 15 */
> + INTR_COPROCESSOR, /* 16 */
> + INTR_ALIGNMENT, /* 17 */
> + INTR_MCE, /* 18 */
> + INTR_SIMD_COPROCESSOR, /* 19 */
> + INTR_IRET = 32, /* 32 */
> +};

> @@ -453,14 +458,15 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
> /*
> * Note that we play around with the 'TS' bit in an attempt to get
> * the correct behaviour even in the presence of the asynchronous
> - * IRQ13 behaviour
> + * INTR_GPF behaviour
> */

> @@ -529,8 +535,9 @@ void math_error(struct pt_regs *regs, int error_code, int trapnr)
> info.si_code = FPE_FLTRES;
> } else {
> /*
> - * If we're using IRQ 13, or supposedly even some trap 16
> - * implementations, it's possible we get a spurious trap...
> + * If we're using INTR_GPF, or supposedly even some trap
> + * INTR_COPROCESSOR implementations, it's possible we get a
> + * spurious trap...

There's confusion in this patch between legacy IRQ #13 [vector
0x20 + 13 ] and #GPF general protection fault [vector 13] - they
are not the same.

Furthermore, the INTR_ naming is not ideal either for (most of)
these entries: for example we don't think of a page fault as an
asynchronous interrupt entity - we think of it as a more or less
synchronous fault/exception.

Thus a X86_*_FAULT_VEC naming pattern might be better:

X86_PAGE_FAULT_VEC
X86_DOUBLE_FAULT_VEC

(With X86_*_EXCEPTION_VEC applied where appropriate.)

I don't disagree with the general principle of the cleanup
otherwise, the numeric literals are often ambiguous and
confusing - as the trap 13 - irq 13 mixup above shows.

Thanks,

Ingo


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