[PATCH bpf-next v2 25/31] bpf: btf: Add BTF_FMODEL_SIGNED_ARG flag

Ilya Leoshkevich
2023-01-28T00:08:02Z

s390x eBPF JIT needs to know whether a function return value is signed
and which function arguments are signed, in order to generate code
compliant with the s390x ABI.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
include/linux/bpf.h | 4 ++++
include/linux/btf.h | 15 ++++++++++-----
kernel/bpf/btf.c | 16 +++++++++++++++-
3 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 6415b54fea4e..8aafbe6af21c 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -899,8 +899,12 @@ enum bpf_cgroup_storage_type {
/* The argument is a structure. */
#define BTF_FMODEL_STRUCT_ARG BIT(0)

+/* The argument is signed. */
+#define BTF_FMODEL_SIGNED_ARG BIT(1)
+
struct btf_func_model {
u8 ret_size;
+ u8 ret_flags;
u8 nr_args;
u8 arg_size[MAX_BPF_FUNC_ARGS];
u8 arg_flags[MAX_BPF_FUNC_ARGS];
diff --git a/include/linux/btf.h b/include/linux/btf.h
index 5f628f323442..e9b90d9c3569 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -236,6 +236,16 @@ static inline bool btf_type_is_small_int(const struct btf_type *t)
return btf_type_is_int(t) && t->size <= sizeof(u64);
}

+static inline u8 btf_int_encoding(const struct btf_type *t)
+{
+ return BTF_INT_ENCODING(*(u32 *)(t + 1));
+}
+
+static inline bool btf_type_is_signed_int(const struct btf_type *t)
+{
+ return btf_type_is_int(t) && (btf_int_encoding(t) & BTF_INT_SIGNED);
+}
+
static inline bool btf_type_is_enum(const struct btf_type *t)
{
return BTF_INFO_KIND(t->info) == BTF_KIND_ENUM;
@@ -306,11 +316,6 @@ static inline u8 btf_int_offset(const struct btf_type *t)
return BTF_INT_OFFSET(*(u32 *)(t + 1));
}

-static inline u8 btf_int_encoding(const struct btf_type *t)
-{
- return BTF_INT_ENCODING(*(u32 *)(t + 1));
-}
-
static inline bool btf_type_is_scalar(const struct btf_type *t)
{
return btf_type_is_int(t) || btf_type_is_enum(t);
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 47b8cb96f2c2..1622a3b15d6f 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6453,6 +6453,18 @@ static int __get_type_size(struct btf *btf, u32 btf_id,
return -EINVAL;
}

+static u8 __get_type_fmodel_flags(const struct btf_type *t)
+{
+ u8 flags = 0;
+
+ if (__btf_type_is_struct(t))
+ flags |= BTF_FMODEL_STRUCT_ARG;
+ if (btf_type_is_signed_int(t))
+ flags |= BTF_FMODEL_SIGNED_ARG;
+
+ return flags;
+}
+
int btf_distill_func_proto(struct bpf_verifier_log *log,
struct btf *btf,
const struct btf_type *func,
@@ -6473,6 +6485,7 @@ int btf_distill_func_proto(struct bpf_verifier_log *log,
m->arg_flags[i] = 0;
}
m->ret_size = 8;
+ m->ret_flags = 0;
m->nr_args = MAX_BPF_FUNC_REG_ARGS;
return 0;
}
@@ -6492,6 +6505,7 @@ int btf_distill_func_proto(struct bpf_verifier_log *log,
return -EINVAL;
}
m->ret_size = ret;
+ m->ret_flags = __get_type_fmodel_flags(t);

for (i = 0; i < nargs; i++) {
if (i == nargs - 1 && args[i].type == 0) {
@@ -6516,7 +6530,7 @@ int btf_distill_func_proto(struct bpf_verifier_log *log,
return -EINVAL;
}
m->arg_size[i] = ret;
- m->arg_flags[i] = __btf_type_is_struct(t) ? BTF_FMODEL_STRUCT_ARG : 0;
+ m->arg_flags[i] = __get_type_fmodel_flags(t);
}
m->nr_args = nargs;
return 0;
--
2.39.1