atoi() doesn't detect errors. There is no way to know that a 0 return
is correct conversion or due to an error.

Introduce atoi_paranoid() to detect errors and provide correct
conversion. Replace all atoi() calls with atoi_paranoid().

Signed-off-by: Vipin Sharma <vipinsh@google.com>
Suggested-by: David Matlack <dmatlack@google.com>
Suggested-by: Sean Christopherson <seanjc@google.com>

---
 .../testing/selftests/kvm/aarch64/arch_timer.c |  8 ++++----
 tools/testing/selftests/kvm/aarch64/vgic_irq.c |  6 +++---
 .../selftests/kvm/access_tracking_perf_test.c  |  2 +-
 .../testing/selftests/kvm/demand_paging_test.c |  2 +-
 .../selftests/kvm/dirty_log_perf_test.c        |  8 ++++----
 .../testing/selftests/kvm/include/test_util.h  |  2 ++
 .../selftests/kvm/kvm_page_table_test.c        |  2 +-
 tools/testing/selftests/kvm/lib/test_util.c    | 18 ++++++++++++++++++
 .../selftests/kvm/max_guest_memory_test.c      |  6 +++---
 .../kvm/memslot_modification_stress_test.c     |  4 ++--
 .../testing/selftests/kvm/memslot_perf_test.c  | 10 +++++-----
 .../selftests/kvm/set_memory_region_test.c     |  2 +-
 .../selftests/kvm/x86_64/nx_huge_pages_test.c  |  4 ++--
 13 files changed, 47 insertions(+), 27 deletions(-)

diff --git a/tools/testing/selftests/kvm/aarch64/arch_timer.c b/tools/testing/selftests/kvm/aarch64/arch_timer.c
index 574eb73f0e90..251e7ff04883 100644
--- a/tools/testing/selftests/kvm/aarch64/arch_timer.c
+++ b/tools/testing/selftests/kvm/aarch64/arch_timer.c
@@ -414,7 +414,7 @@ static bool parse_args(int argc, char *argv[])
 	while ((opt = getopt(argc, argv, "hn:i:p:m:")) != -1) {
 		switch (opt) {
 		case 'n':
-			test_args.nr_vcpus = atoi(optarg);
+			test_args.nr_vcpus = atoi_paranoid(optarg);
 			if (test_args.nr_vcpus <= 0) {
 				pr_info("Positive value needed for -n\n");
 				goto err;
@@ -425,21 +425,21 @@ static bool parse_args(int argc, char *argv[])
 			}
 			break;
 		case 'i':
-			test_args.nr_iter = atoi(optarg);
+			test_args.nr_iter = atoi_paranoid(optarg);
 			if (test_args.nr_iter <= 0) {
 				pr_info("Positive value needed for -i\n");
 				goto err;
 			}
 			break;
 		case 'p':
-			test_args.timer_period_ms = atoi(optarg);
+			test_args.timer_period_ms = atoi_paranoid(optarg);
 			if (test_args.timer_period_ms <= 0) {
 				pr_info("Positive value needed for -p\n");
 				goto err;
 			}
 			break;
 		case 'm':
-			test_args.migration_freq_ms = atoi(optarg);
+			test_args.migration_freq_ms = atoi_paranoid(optarg);
 			if (test_args.migration_freq_ms < 0) {
 				pr_info("0 or positive value needed for -m\n");
 				goto err;
diff --git a/tools/testing/selftests/kvm/aarch64/vgic_irq.c b/tools/testing/selftests/kvm/aarch64/vgic_irq.c
index 17417220a083..ae90b718070a 100644
--- a/tools/testing/selftests/kvm/aarch64/vgic_irq.c
+++ b/tools/testing/selftests/kvm/aarch64/vgic_irq.c
@@ -824,16 +824,16 @@ int main(int argc, char **argv)
 	while ((opt = getopt(argc, argv, "hn:e:l:")) != -1) {
 		switch (opt) {
 		case 'n':
-			nr_irqs = atoi(optarg);
+			nr_irqs = atoi_paranoid(optarg);
 			if (nr_irqs > 1024 || nr_irqs % 32)
 				help(argv[0]);
 			break;
 		case 'e':
-			eoi_split = (bool)atoi(optarg);
+			eoi_split = (bool)atoi_paranoid(optarg);
 			default_args = false;
 			break;
 		case 'l':
-			level_sensitive = (bool)atoi(optarg);
+			level_sensitive = (bool)atoi_paranoid(optarg);
 			default_args = false;
 			break;
 		case 'h':
diff --git a/tools/testing/selftests/kvm/access_tracking_perf_test.c b/tools/testing/selftests/kvm/access_tracking_perf_test.c
index 76c583a07ea2..c6bcc5301e2c 100644
--- a/tools/testing/selftests/kvm/access_tracking_perf_test.c
+++ b/tools/testing/selftests/kvm/access_tracking_perf_test.c
@@ -368,7 +368,7 @@ int main(int argc, char *argv[])
 			params.vcpu_memory_bytes = parse_size(optarg);
 			break;
 		case 'v':
-			params.nr_vcpus = atoi(optarg);
+			params.nr_vcpus = atoi_paranoid(optarg);
 			break;
 		case 'o':
 			overlap_memory_access = true;
diff --git a/tools/testing/selftests/kvm/demand_paging_test.c b/tools/testing/selftests/kvm/demand_paging_test.c
index 779ae54f89c4..82597fb04146 100644
--- a/tools/testing/selftests/kvm/demand_paging_test.c
+++ b/tools/testing/selftests/kvm/demand_paging_test.c
@@ -427,7 +427,7 @@ int main(int argc, char *argv[])
 			p.src_type = parse_backing_src_type(optarg);
 			break;
 		case 'v':
-			nr_vcpus = atoi(optarg);
+			nr_vcpus = atoi_paranoid(optarg);
 			TEST_ASSERT(nr_vcpus > 0 && nr_vcpus <= max_vcpus,
 				    "Invalid number of vcpus, must be between 1 and %d", max_vcpus);
 			break;
diff --git a/tools/testing/selftests/kvm/dirty_log_perf_test.c b/tools/testing/selftests/kvm/dirty_log_perf_test.c
index 5bb6954b2358..ecda802b78ff 100644
--- a/tools/testing/selftests/kvm/dirty_log_perf_test.c
+++ b/tools/testing/selftests/kvm/dirty_log_perf_test.c
@@ -416,7 +416,7 @@ int main(int argc, char *argv[])
 			run_vcpus_while_disabling_dirty_logging = true;
 			break;
 		case 'f':
-			p.wr_fract = atoi(optarg);
+			p.wr_fract = atoi_paranoid(optarg);
 			TEST_ASSERT(p.wr_fract >= 1,
 				    "Write fraction cannot be less than one");
 			break;
@@ -427,7 +427,7 @@ int main(int argc, char *argv[])
 			help(argv[0]);
 			break;
 		case 'i':
-			p.iterations = atoi(optarg);
+			p.iterations = atoi_paranoid(optarg);
 			break;
 		case 'm':
 			guest_modes_cmdline(optarg);
@@ -445,12 +445,12 @@ int main(int argc, char *argv[])
 			p.backing_src = parse_backing_src_type(optarg);
 			break;
 		case 'v':
-			nr_vcpus = atoi(optarg);
+			nr_vcpus = atoi_paranoid(optarg);
 			TEST_ASSERT(nr_vcpus > 0 && nr_vcpus <= max_vcpus,
 				    "Invalid number of vcpus, must be between 1 and %d", max_vcpus);
 			break;
 		case 'x':
-			p.slots = atoi(optarg);
+			p.slots = atoi_paranoid(optarg);
 			break;
 		default:
 			help(argv[0]);
diff --git a/tools/testing/selftests/kvm/include/test_util.h b/tools/testing/selftests/kvm/include/test_util.h
index befc754ce9b3..feae42863759 100644
--- a/tools/testing/selftests/kvm/include/test_util.h
+++ b/tools/testing/selftests/kvm/include/test_util.h
@@ -152,4 +152,6 @@ static inline void *align_ptr_up(void *x, size_t size)
 	return (void *)align_up((unsigned long)x, size);
 }
 
+int atoi_paranoid(const char *num_str);
+
 #endif /* SELFTEST_KVM_TEST_UTIL_H */
diff --git a/tools/testing/selftests/kvm/kvm_page_table_test.c b/tools/testing/selftests/kvm/kvm_page_table_test.c
index f42c6ac6d71d..ea7feb69bb88 100644
--- a/tools/testing/selftests/kvm/kvm_page_table_test.c
+++ b/tools/testing/selftests/kvm/kvm_page_table_test.c
@@ -461,7 +461,7 @@ int main(int argc, char *argv[])
 			p.test_mem_size = parse_size(optarg);
 			break;
 		case 'v':
-			nr_vcpus = atoi(optarg);
+			nr_vcpus = atoi_paranoid(optarg);
 			TEST_ASSERT(nr_vcpus > 0 && nr_vcpus <= max_vcpus,
 				    "Invalid number of vcpus, must be between 1 and %d", max_vcpus);
 			break;
diff --git a/tools/testing/selftests/kvm/lib/test_util.c b/tools/testing/selftests/kvm/lib/test_util.c
index 6d23878bbfe1..8cce52ee139f 100644
--- a/tools/testing/selftests/kvm/lib/test_util.c
+++ b/tools/testing/selftests/kvm/lib/test_util.c
@@ -334,3 +334,21 @@ long get_run_delay(void)
 
 	return val[1];
 }
+
+int atoi_paranoid(const char *num_str)
+{
+	int num;
+	char *end_ptr;
+
+	errno = 0;
+	num = (int)strtol(num_str, &end_ptr, 10);
+	TEST_ASSERT(!errno, "strtol(\"%s\") failed", num_str);
+	TEST_ASSERT(num_str != end_ptr,
+		    "strtol(\"%s\") didn't find any valid number.\n", num_str);
+	TEST_ASSERT(
+		*end_ptr == '\0',
+		"strtol(\"%s\") failed to parse trailing characters \"%s\".\n",
+		num_str, end_ptr);
+
+	return num;
+}
diff --git a/tools/testing/selftests/kvm/max_guest_memory_test.c b/tools/testing/selftests/kvm/max_guest_memory_test.c
index 9a6e4f3ad6b5..1595b73dc09a 100644
--- a/tools/testing/selftests/kvm/max_guest_memory_test.c
+++ b/tools/testing/selftests/kvm/max_guest_memory_test.c
@@ -193,15 +193,15 @@ int main(int argc, char *argv[])
 	while ((opt = getopt(argc, argv, "c:h:m:s:H")) != -1) {
 		switch (opt) {
 		case 'c':
-			nr_vcpus = atoi(optarg);
+			nr_vcpus = atoi_paranoid(optarg);
 			TEST_ASSERT(nr_vcpus > 0, "number of vcpus must be >0");
 			break;
 		case 'm':
-			max_mem = atoi(optarg) * size_1gb;
+			max_mem = atoi_paranoid(optarg) * size_1gb;
 			TEST_ASSERT(max_mem > 0, "memory size must be >0");
 			break;
 		case 's':
-			slot_size = atoi(optarg) * size_1gb;
+			slot_size = atoi_paranoid(optarg) * size_1gb;
 			TEST_ASSERT(slot_size > 0, "slot size must be >0");
 			break;
 		case 'H':
diff --git a/tools/testing/selftests/kvm/memslot_modification_stress_test.c b/tools/testing/selftests/kvm/memslot_modification_stress_test.c
index 6ee7e1dde404..865276993ffb 100644
--- a/tools/testing/selftests/kvm/memslot_modification_stress_test.c
+++ b/tools/testing/selftests/kvm/memslot_modification_stress_test.c
@@ -166,7 +166,7 @@ int main(int argc, char *argv[])
 			guest_percpu_mem_size = parse_size(optarg);
 			break;
 		case 'v':
-			nr_vcpus = atoi(optarg);
+			nr_vcpus = atoi_paranoid(optarg);
 			TEST_ASSERT(nr_vcpus > 0 && nr_vcpus <= max_vcpus,
 				    "Invalid number of vcpus, must be between 1 and %d",
 				    max_vcpus);
@@ -175,7 +175,7 @@ int main(int argc, char *argv[])
 			p.partition_vcpu_memory_access = false;
 			break;
 		case 'i':
-			p.nr_memslot_modifications = atoi(optarg);
+			p.nr_memslot_modifications = atoi_paranoid(optarg);
 			break;
 		case 'h':
 		default:
diff --git a/tools/testing/selftests/kvm/memslot_perf_test.c b/tools/testing/selftests/kvm/memslot_perf_test.c
index 44995446d942..4bae9e3f5ca1 100644
--- a/tools/testing/selftests/kvm/memslot_perf_test.c
+++ b/tools/testing/selftests/kvm/memslot_perf_test.c
@@ -885,21 +885,21 @@ static bool parse_args(int argc, char *argv[],
 			map_unmap_verify = true;
 			break;
 		case 's':
-			targs->nslots = atoi(optarg);
+			targs->nslots = atoi_paranoid(optarg);
 			if (targs->nslots <= 0 && targs->nslots != -1) {
 				pr_info("Slot count cap has to be positive or -1 for no cap\n");
 				return false;
 			}
 			break;
 		case 'f':
-			targs->tfirst = atoi(optarg);
+			targs->tfirst = atoi_paranoid(optarg);
 			if (targs->tfirst < 0) {
 				pr_info("First test to run has to be non-negative\n");
 				return false;
 			}
 			break;
 		case 'e':
-			targs->tlast = atoi(optarg);
+			targs->tlast = atoi_paranoid(optarg);
 			if (targs->tlast < 0 || targs->tlast >= NTESTS) {
 				pr_info("Last test to run has to be non-negative and less than %zu\n",
 					NTESTS);
@@ -907,14 +907,14 @@ static bool parse_args(int argc, char *argv[],
 			}
 			break;
 		case 'l':
-			targs->seconds = atoi(optarg);
+			targs->seconds = atoi_paranoid(optarg);
 			if (targs->seconds < 0) {
 				pr_info("Test length in seconds has to be non-negative\n");
 				return false;
 			}
 			break;
 		case 'r':
-			targs->runs = atoi(optarg);
+			targs->runs = atoi_paranoid(optarg);
 			if (targs->runs <= 0) {
 				pr_info("Runs per test has to be positive\n");
 				return false;
diff --git a/tools/testing/selftests/kvm/set_memory_region_test.c b/tools/testing/selftests/kvm/set_memory_region_test.c
index 0d55f508d595..c366949c8362 100644
--- a/tools/testing/selftests/kvm/set_memory_region_test.c
+++ b/tools/testing/selftests/kvm/set_memory_region_test.c
@@ -407,7 +407,7 @@ int main(int argc, char *argv[])
 
 #ifdef __x86_64__
 	if (argc > 1)
-		loops = atoi(argv[1]);
+		loops = atoi_paranoid(argv[1]);
 	else
 		loops = 10;
 
diff --git a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
index 59ffe7fd354f..354b6902849c 100644
--- a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
+++ b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
@@ -241,10 +241,10 @@ int main(int argc, char **argv)
 	while ((opt = getopt(argc, argv, "hp:t:r")) != -1) {
 		switch (opt) {
 		case 'p':
-			reclaim_period_ms = atoi(optarg);
+			reclaim_period_ms = atoi_paranoid(optarg);
 			break;
 		case 't':
-			token = atoi(optarg);
+			token = atoi_paranoid(optarg);
 			break;
 		case 'r':
 			reboot_permissions = true;
-- 
2.38.0.rc1.362.ged0d419d3c-goog

On Thu, Oct 06, 2022, Vipin Sharma wrote:
> +int atoi_paranoid(const char *num_str)
> +{
> +	int num;
> +	char *end_ptr;

Reverse fir-tree when it's convention:

	char *end_ptr;

> +
> +	errno = 0;
> +	num = (int)strtol(num_str, &end_ptr, 10);
> +	TEST_ASSERT(!errno, "strtol(\"%s\") failed", num_str);
> +	TEST_ASSERT(num_str != end_ptr,
> +		    "strtol(\"%s\") didn't find any valid number.\n", num_str);

s/number/integer ?  And should that be "a valid intenger", not "any valid integer"?
"any" implies that this helper will be happy if there's at least one integer,
whereas I believe the intent is to find _exactly_ one integer.

> +	TEST_ASSERT(
> +		*end_ptr == '\0',

Weird and unnecessary wrap+indentation.

> +		"strtol(\"%s\") failed to parse trailing characters \"%s\".\n",
> +		num_str, end_ptr);
> +
> +	return num;
> +}
> diff --git a/tools/testing/selftests/kvm/max_guest_memory_test.c b/tools/testing/selftests/kvm/max_guest_memory_test.c
> index 9a6e4f3ad6b5..1595b73dc09a 100644
> --- a/tools/testing/selftests/kvm/max_guest_memory_test.c
> +++ b/tools/testing/selftests/kvm/max_guest_memory_test.c
> @@ -193,15 +193,15 @@ int main(int argc, char *argv[])
>  	while ((opt = getopt(argc, argv, "c:h:m:s:H")) != -1) {
>  		switch (opt) {
>  		case 'c':
> -			nr_vcpus = atoi(optarg);
> +			nr_vcpus = atoi_paranoid(optarg);
>  			TEST_ASSERT(nr_vcpus > 0, "number of vcpus must be >0");

Many users require a positive and or non-negative value, maybe add wrappers in
a follow-up?

			nr_vcpus = atoi_positive(optarg);

and later down

			targs->tfirst = atoi_non_negative(optarg);

We'll lose custom error messages, but I don't think that's a big deal.  Definitely
not required, just a thought.

> diff --git a/tools/testing/selftests/kvm/set_memory_region_test.c b/tools/testing/selftests/kvm/set_memory_region_test.c
> index 0d55f508d595..c366949c8362 100644
> --- a/tools/testing/selftests/kvm/set_memory_region_test.c
> +++ b/tools/testing/selftests/kvm/set_memory_region_test.c
> @@ -407,7 +407,7 @@ int main(int argc, char *argv[])
>  
>  #ifdef __x86_64__
>  	if (argc > 1)
> -		loops = atoi(argv[1]);
> +		loops = atoi_paranoid(argv[1]);

This is a good candidate for atoi_positive().

>  	else
>  		loops = 10;
>  
> diff --git a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
> index 59ffe7fd354f..354b6902849c 100644
> --- a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
> +++ b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
> @@ -241,10 +241,10 @@ int main(int argc, char **argv)
>  	while ((opt = getopt(argc, argv, "hp:t:r")) != -1) {
>  		switch (opt) {
>  		case 'p':
> -			reclaim_period_ms = atoi(optarg);
> +			reclaim_period_ms = atoi_paranoid(optarg);
>  			break;
>  		case 't':
> -			token = atoi(optarg);
> +			token = atoi_paranoid(optarg);
>  			break;
>  		case 'r':
>  			reboot_permissions = true;
> -- 
> 2.38.0.rc1.362.ged0d419d3c-goog
>

On Thu, Oct 6, 2022 at 12:58 PM Sean Christopherson <seanjc@google.com> wrote:
>
> On Thu, Oct 06, 2022, Vipin Sharma wrote:
> > +int atoi_paranoid(const char *num_str)
> > +{
> > +     int num;
> > +     char *end_ptr;
>
> Reverse fir-tree when it's convention:
>
>         char *end_ptr;
>

Okay, I will do:
        char *end_ptr;
        int num;

I was not aware of reverse christmas tree convention in KVM subsystem.

> > +
> > +     errno = 0;
> > +     num = (int)strtol(num_str, &end_ptr, 10);
> > +     TEST_ASSERT(!errno, "strtol(\"%s\") failed", num_str);
> > +     TEST_ASSERT(num_str != end_ptr,
> > +                 "strtol(\"%s\") didn't find any valid number.\n", num_str);
>
> s/number/integer ?  And should that be "a valid intenger", not "any valid integer"?
> "any" implies that this helper will be happy if there's at least one integer,
> whereas I believe the intent is to find _exactly_ one integer.
>

I will change it to "a valid integer".

> > +     TEST_ASSERT(
> > +             *end_ptr == '\0',
>
> Weird and unnecessary wrap+indentation.

Clang-format script did it. I think it is because the script is
considering 80 characters limit and the next line "strtol..."
overshoots that 80 character limit.
I will manually change it to:

       TEST_ASSERT(*end_ptr == '\0',

and align "strtol..." to * above.

>
> > +             "strtol(\"%s\") failed to parse trailing characters \"%s\".\n",
> > +             num_str, end_ptr);
> > +
> > +     return num;
> > +}
> > diff --git a/tools/testing/selftests/kvm/max_guest_memory_test.c b/tools/testing/selftests/kvm/max_guest_memory_test.c
> > index 9a6e4f3ad6b5..1595b73dc09a 100644
> > --- a/tools/testing/selftests/kvm/max_guest_memory_test.c
> > +++ b/tools/testing/selftests/kvm/max_guest_memory_test.c
> > @@ -193,15 +193,15 @@ int main(int argc, char *argv[])
> >       while ((opt = getopt(argc, argv, "c:h:m:s:H")) != -1) {
> >               switch (opt) {
> >               case 'c':
> > -                     nr_vcpus = atoi(optarg);
> > +                     nr_vcpus = atoi_paranoid(optarg);
> >                       TEST_ASSERT(nr_vcpus > 0, "number of vcpus must be >0");
>
> Many users require a positive and or non-negative value, maybe add wrappers in
> a follow-up?
>
>                         nr_vcpus = atoi_positive(optarg);
>
> and later down
>
>                         targs->tfirst = atoi_non_negative(optarg);
>
> We'll lose custom error messages, but I don't think that's a big deal.  Definitely
> not required, just a thought.
>

I think atoi_positive() and atoi_non_negative() will be useful
additions. I will add one more patch in v5, which replaces
atoi_paranoid() and update/remove TEST_ASSERT() condition from all
test cases.

> > diff --git a/tools/testing/selftests/kvm/set_memory_region_test.c b/tools/testing/selftests/kvm/set_memory_region_test.c
> > index 0d55f508d595..c366949c8362 100644
> > --- a/tools/testing/selftests/kvm/set_memory_region_test.c
> > +++ b/tools/testing/selftests/kvm/set_memory_region_test.c
> > @@ -407,7 +407,7 @@ int main(int argc, char *argv[])
> >
> >  #ifdef __x86_64__
> >       if (argc > 1)
> > -             loops = atoi(argv[1]);
> > +             loops = atoi_paranoid(argv[1]);
>
> This is a good candidate for atoi_positive().
>
> >       else
> >               loops = 10;
> >
> > diff --git a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
> > index 59ffe7fd354f..354b6902849c 100644
> > --- a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
> > +++ b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
> > @@ -241,10 +241,10 @@ int main(int argc, char **argv)
> >       while ((opt = getopt(argc, argv, "hp:t:r")) != -1) {
> >               switch (opt) {
> >               case 'p':
> > -                     reclaim_period_ms = atoi(optarg);
> > +                     reclaim_period_ms = atoi_paranoid(optarg);
> >                       break;
> >               case 't':
> > -                     token = atoi(optarg);
> > +                     token = atoi_paranoid(optarg);
> >                       break;
> >               case 'r':
> >                       reboot_permissions = true;
> > --
> > 2.38.0.rc1.362.ged0d419d3c-goog
> >

On Thu, Oct 06, 2022, Vipin Sharma wrote:
> On Thu, Oct 6, 2022 at 12:58 PM Sean Christopherson <seanjc@google.com> wrote:
> >
> > On Thu, Oct 06, 2022, Vipin Sharma wrote:
> > > +int atoi_paranoid(const char *num_str)
> > > +{
> > > +     int num;
> > > +     char *end_ptr;
> >
> > Reverse fir-tree when it's convention:
> >
> >         char *end_ptr;
> >
> 
> Okay, I will do:
>         char *end_ptr;
>         int num;
> 
> I was not aware of reverse christmas tree convention in KVM subsystem.

Oh, the above was a typo.  It was supposed to be "convenient".  KVM doesn't strictly
follow the almighty fir tree, but I try to use it and encourage others to do so as
it helps with continuity when switching between x86/kvm and the rest of x86/ (the
tip tree maintainers and thus most of the x86 code are devout believers).