[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [XEN PATCH v2 2/3] xen/arm: add SAF deviation for debugging and logging effects
On 27/11/23 11:46, Jan Beulich wrote: On 24.11.2023 18:29, Simone Ballarin wrote:Rule 13.1: Initializer lists shall not contain persistent side effects Effects caused by debug/logging macros and functions (like ASSERT, __bad_atomic_size, LOG, etc ...) that crash execution or produce logs are not dangerous in initializer lists. The evaluation order in abnormal conditions is not relevant. Evaluation order of logging effects is always safe. This patch deviates violations using SAF commits caused by debug/logging macros and functions. Asm volatile statements in initializer lists that do not perform any persistent side effect are safe: this patch deviates violations caused by uses of the current macro (that contains an asm volatile) in initializer lists. No functional changes. Signed-off-by: Simone Ballarin <simone.ballarin@xxxxxxxxxxx> --- Changes in v2: New patch based on the discussion for "xen/arm: address violations of MISRA C:2012 Rule 13.1". --- docs/misra/safe.json | 16 ++++++++++++++++ xen/arch/arm/device.c | 1 + xen/arch/arm/guestcopy.c | 4 ++++ xen/arch/x86/hvm/hvm.c | 1 + xen/common/sched/core.c | 3 +++The latter two don't really fit the title prefix.--- a/docs/misra/safe.json +++ b/docs/misra/safe.json @@ -28,6 +28,22 @@ }, { "id": "SAF-3-safe", + "analyser": { + "eclair": "MC3R1.R13.1" + }, + "name": "MC3R1.R13.1: effects for debugging and logging", + "text": "Effects for debugging and loggings reasons that crash execution or produce logs are allowed in initializer lists. The evaluation order in abnormal conditions is not relevant." + },I'm wary of this statement. Order may not matter much anymore _after_ an abnormal condition was encountered, but in the course of determining whether an abnormal condition might have been reached it may very well still matter. Do you object to the deviation in general? Or just to the wording? + { + "id": "SAF-4-safe", + "analyser": { + "eclair": "MC3R1.R13.1" + }, + "name": "MC3R1.R13.1: volatile asm statements that do not perform any persistent side effect", + "text": "Volatile asm statements in an initializer list if do not perform persistent side effects are safe."Since each respective comment ought to affect just a single asm(), I think this wants writing in singular. I further don't think it is useful for "text" to largely restate what "name" already says. Ok. --- a/xen/arch/arm/device.c +++ b/xen/arch/arm/device.c @@ -331,6 +331,7 @@ int handle_device(struct domain *d, struct dt_device_node *dev, p2m_type_t p2mt, .p2mt = p2mt, .skip_mapping = !own_device || (is_pci_passthrough_enabled() && + /* SAF-3-safe effects for debugging/logging reasons are safe */ (device_get_class(dev) == DEVICE_PCI_HOSTBRIDGE)),What's the debugging / logging reason on the commented line? The "ASSERT(dev != NULL)" in its body. --- a/xen/arch/arm/guestcopy.c +++ b/xen/arch/arm/guestcopy.c @@ -110,18 +110,21 @@ static unsigned long copy_guest(void *buf, uint64_t addr, unsigned int len, unsigned long raw_copy_to_guest(void *to, const void *from, unsigned int len) { return copy_guest((void *)from, (vaddr_t)to, len, + /* SAF-4-safe No persistent side effects */ GVA_INFO(current), COPY_to_guest | COPY_linear); }unsigned long raw_copy_to_guest_flush_dcache(void *to, const void *from,unsigned int len) { + /* SAF-4-safe No persistent side effects */ return copy_guest((void *)from, (vaddr_t)to, len, GVA_INFO(current), COPY_to_guest | COPY_flush_dcache | COPY_linear); }unsigned long raw_clear_guest(void *to, unsigned int len){ + /* SAF-4-safe No persistent side effects */ return copy_guest(NULL, (vaddr_t)to, len, GVA_INFO(current), COPY_to_guest | COPY_linear); } @@ -129,6 +132,7 @@ unsigned long raw_clear_guest(void *to, unsigned int len) unsigned long raw_copy_from_guest(void *to, const void __user *from, unsigned int len) { + /* SAF-4-safe No persistent side effects */ return copy_guest(to, (vaddr_t)from, len, GVA_INFO(current), COPY_from_guest | COPY_linear); }I can only guess that in all four of these it's the use of "current" which requires the comment. Yet imo that either needs making explicit, or such a comment shouldn't go on use sites of "current", but on its definition site. "current" does not contain any violation of R13.1. Its expansion produces a side-effect, but this is not a problem in itself. The real problem is that GVA_INFO expands it in an initializer list: #define GVA_INFO(vcpu) ((copy_info_t) { .gva = { vcpu } }) GVA_INFO(current) is the real piece of code that requires to be deviated. --- a/xen/common/sched/core.c +++ b/xen/common/sched/core.c @@ -1517,6 +1517,7 @@ long vcpu_yield(void)SCHED_STAT_CRANK(vcpu_yield); + /* SAF-4-safe No persistent side effects */TRACE_2D(TRC_SCHED_YIELD, current->domain->domain_id, current->vcpu_id); raise_softirq(SCHEDULE_SOFTIRQ); return 0; @@ -1895,6 +1896,7 @@ ret_t do_sched_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg) if ( copy_from_guest(&sched_shutdown, arg, 1) ) break;+ /* SAF-4-safe No persistent side effects */TRACE_3D(TRC_SCHED_SHUTDOWN, current->domain->domain_id, current->vcpu_id, sched_shutdown.reason); @@ -1912,6 +1914,7 @@ ret_t do_sched_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg) if ( copy_from_guest(&sched_shutdown, arg, 1) ) break;+ /* SAF-4-safe No persistent side effects */TRACE_3D(TRC_SCHED_SHUTDOWN_CODE, d->domain_id, current->vcpu_id, sched_shutdown.reason);In at least the former two of these cases pulling out "current" into a local variable "curr" would likely eliminate the violation and at the same time improve code a little. Yes, I agree. Jan -- Simone Ballarin, M.Sc. Field Application Engineer, BUGSENG (https://bugseng.com)
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