This fixes the UBSAN build for GCC 8 and later.  The sanitiser checks for
passing 0 to the ctz()/clz() builtins.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wl@xen.org>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Julien Grall <julien.grall@arm.com>
---
 xen/common/ubsan/ubsan.c | 21 +++++++++++++++++++++
 xen/common/ubsan/ubsan.h |  9 +++++++++
 2 files changed, 30 insertions(+)

diff --git a/xen/common/ubsan/ubsan.c b/xen/common/ubsan/ubsan.c
index 50a4e14fac..e75f614fa7 100644
--- a/xen/common/ubsan/ubsan.c
+++ b/xen/common/ubsan/ubsan.c
@@ -518,3 +518,24 @@ void __ubsan_handle_pointer_overflow(struct pointer_overflow_data *data,
 
 	ubsan_epilogue(&flags);
 }
+
+void __ubsan_handle_invalid_builtin(struct invalid_builtin_data *data)
+{
+	unsigned long flags;
+	const char *fn;
+
+	if (suppress_report(&data->location))
+		return;
+
+	ubsan_prologue(&data->location, &flags);
+
+	switch (data->kind) {
+	case kind_ctz: fn = "ctz"; break;
+	case kind_clz: fn = "clz"; break;
+	default: fn = "<UNKNOWN>"; break;
+	}
+
+	pr_err("passing zero to %s(), which is not a valid argument\n", fn);
+
+	ubsan_epilogue(&flags);
+}
diff --git a/xen/common/ubsan/ubsan.h b/xen/common/ubsan/ubsan.h
index 2710cd423e..a3159040fe 100644
--- a/xen/common/ubsan/ubsan.h
+++ b/xen/common/ubsan/ubsan.h
@@ -84,6 +84,15 @@ struct pointer_overflow_data {
 	struct source_location location;
 };
 
+struct invalid_builtin_data {
+	struct source_location location;
+	unsigned char kind;
+};
+enum {
+	kind_ctz,
+	kind_clz,
+};
+
 #if defined(CONFIG_ARCH_SUPPORTS_INT128) && defined(__SIZEOF_INT128__)
 typedef __int128 s_max;
 typedef unsigned __int128 u_max;
-- 
2.11.0


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>>> On 24.06.19 at 12:17, <andrew.cooper3@citrix.com> wrote:
> This fixes the UBSAN build for GCC 8 and later.  The sanitiser checks for
> passing 0 to the ctz()/clz() builtins.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Fundamentally
Acked-by: Jan Beulich <jbeulich@suse.com>

However,

> --- a/xen/common/ubsan/ubsan.c
> +++ b/xen/common/ubsan/ubsan.c
> @@ -518,3 +518,24 @@ void __ubsan_handle_pointer_overflow(struct pointer_overflow_data *data,
>  
>  	ubsan_epilogue(&flags);
>  }
> +
> +void __ubsan_handle_invalid_builtin(struct invalid_builtin_data *data)
> +{
> +	unsigned long flags;
> +	const char *fn;
> +
> +	if (suppress_report(&data->location))
> +		return;
> +
> +	ubsan_prologue(&data->location, &flags);
> +
> +	switch (data->kind) {
> +	case kind_ctz: fn = "ctz"; break;
> +	case kind_clz: fn = "clz"; break;
> +	default: fn = "<UNKNOWN>"; break;
> +	}
> +
> +	pr_err("passing zero to %s(), which is not a valid argument\n", fn);

... logging the unknown enumerator value might turn out helpful
down the road.

Jan



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