On Thu, 2021-02-18 at 20:22 -0800, Yonghong Song wrote:
>
>
> On 2/18/21 6:25 PM, Ilya Leoshkevich wrote:
> > The logic follows that of BTF_KIND_INT most of the time.
> > Sanitization
> > replaces BTF_KIND_FLOATs with BTF_KIND_TYPEDEFs pointing to
> > equally-sized BTF_KIND_ARRAYs on older kernels.
> >
> > Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
> > ---
> > tools/lib/bpf/btf.c | 44
> > ++++++++++++++++++++++++++++++++
> > tools/lib/bpf/btf.h | 8 ++++++
> > tools/lib/bpf/btf_dump.c | 4 +++
> > tools/lib/bpf/libbpf.c | 45
> > ++++++++++++++++++++++++++++++++-
> > tools/lib/bpf/libbpf.map | 5 ++++
> > tools/lib/bpf/libbpf_internal.h | 2 ++
> > 6 files changed, 107 insertions(+), 1 deletion(-)
> >
> [...]
> > diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
> > index 2f9d685bd522..5e957fcceee6 100644
> > --- a/tools/lib/bpf/btf_dump.c
> > +++ b/tools/lib/bpf/btf_dump.c
> > @@ -279,6 +279,7 @@ static int btf_dump_mark_referenced(struct
> > btf_dump *d)
> > case BTF_KIND_INT:
> > case BTF_KIND_ENUM:
> > case BTF_KIND_FWD:
> > + case BTF_KIND_FLOAT:
> > break;
> >
> > case BTF_KIND_VOLATILE:
> > @@ -453,6 +454,7 @@ static int btf_dump_order_type(struct btf_dump
> > *d, __u32 id, bool through_ptr)
> >
> > switch (btf_kind(t)) {
> > case BTF_KIND_INT:
> > + case BTF_KIND_FLOAT:
> > tstate->order_state = ORDERED;
> > return 0;
> >
> > @@ -1133,6 +1135,7 @@ static void btf_dump_emit_type_decl(struct
> > btf_dump *d, __u32 id,
> > case BTF_KIND_STRUCT:
> > case BTF_KIND_UNION:
> > case BTF_KIND_TYPEDEF:
> > + case BTF_KIND_FLOAT:
> > goto done;
> > default:
> > pr_warn("unexpected type in decl chain,
> > kind:%u, id:[%u]\n",
> > @@ -1247,6 +1250,7 @@ static void btf_dump_emit_type_chain(struct
> > btf_dump *d,
> >
> > switch (kind) {
> > case BTF_KIND_INT:
> > + case BTF_KIND_FLOAT:
> > btf_dump_emit_mods(d, decls);
> > name = btf_name_of(d, t->name_off);
> > btf_dump_printf(d, "%s", name);
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index d43cc3f29dae..3b170066d613 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -178,6 +178,8 @@ enum kern_feature_id {
> > FEAT_PROG_BIND_MAP,
> > /* Kernel support for module BTFs */
> > FEAT_MODULE_BTF,
> > + /* BTF_KIND_FLOAT support */
> > + FEAT_BTF_FLOAT,
> > __FEAT_CNT,
> > };
> >
> > @@ -1935,6 +1937,7 @@ static const char *btf_kind_str(const struct
> > btf_type *t)
> > case BTF_KIND_FUNC_PROTO: return "func_proto";
> > case BTF_KIND_VAR: return "var";
> > case BTF_KIND_DATASEC: return "datasec";
> > + case BTF_KIND_FLOAT: return "float";
> > default: return "unknown";
> > }
> > }
> > @@ -2384,18 +2387,22 @@ static bool btf_needs_sanitization(struct
> > bpf_object *obj)
> > {
> > bool has_func_global =
> > kernel_supports(FEAT_BTF_GLOBAL_FUNC);
> > bool has_datasec = kernel_supports(FEAT_BTF_DATASEC);
> > + bool has_float = kernel_supports(FEAT_BTF_FLOAT);
> > bool has_func = kernel_supports(FEAT_BTF_FUNC);
> >
> > - return !has_func || !has_datasec || !has_func_global;
> > + return !has_func || !has_datasec || !has_func_global ||
> > !has_float;
> > }
> >
> > static void bpf_object__sanitize_btf(struct bpf_object *obj,
> > struct btf *btf)
> > {
> > bool has_func_global =
> > kernel_supports(FEAT_BTF_GLOBAL_FUNC);
> > bool has_datasec = kernel_supports(FEAT_BTF_DATASEC);
> > + bool has_float = kernel_supports(FEAT_BTF_FLOAT);
> > bool has_func = kernel_supports(FEAT_BTF_FUNC);
> > struct btf_type *t;
> > int i, j, vlen;
> > + int t_u32 = 0;
> > + int t_u8 = 0;
> >
> > for (i = 1; i <= btf__get_nr_types(btf); i++) {
> > t = (struct btf_type *)btf__type_by_id(btf, i);
> > @@ -2445,6 +2452,23 @@ static void bpf_object__sanitize_btf(struct
> > bpf_object *obj, struct btf *btf)
> > } else if (!has_func_global && btf_is_func(t)) {
> > /* replace BTF_FUNC_GLOBAL with
> > BTF_FUNC_STATIC */
> > t->info = BTF_INFO_ENC(BTF_KIND_FUNC, 0,
> > 0);
> > + } else if (!has_float && btf_is_float(t)) {
> > + /* replace FLOAT with TYPEDEF(u8[]) */
> > + int t_array;
> > + __u32 size;
> > +
> > + size = t->size;
> > + if (!t_u8)
> > + t_u8 = btf__add_int(btf, "u8", 1,
> > 0);
> > + if (!t_u32)
> > + t_u32 = btf__add_int(btf, "u32", 4,
> > 0);
> > + t_array = btf__add_array(btf, t_u32, t_u8,
> > size);
> > +
> > + /* adding new types may have invalidated t
> > */
> > + t = (struct btf_type *)btf__type_by_id(btf,
> > i);
> > +
> > + t->info = BTF_INFO_ENC(BTF_KIND_TYPEDEF, 0,
> > 0);
>
> This won't work. The typedef must have a valid name. Otherwise,
> kernel
> will reject it. A const char array should be okay here.
Wouldn't it reuse the old t->name? At least in my testing with v5.7
kernel this was the case, and BTF wasn't rejected. And the original
BTF_KIND_FLOAT always has a valid name, this is enforced in libbpf and
in the verifier. For example:
[1] PTR '(anon)' type_id=2
[2] STRUCT 'foo' size=4 vlen=1
'bar' type_id=3 bits_offset=0
[3] FLOAT 'float' size=4
[4] FUNC_PROTO '(anon)' ret_type_id=5 vlen=1
'f' type_id=1
[5] PTR '(anon)' type_id=0
[6] FUNC 'func' type_id=4 linkage=global
becomes
[1] PTR '(anon)' type_id=2
[2] STRUCT 'foo' size=4 vlen=1
'bar' type_id=3 bits_offset=0
[3] TYPEDEF 'float' type_id=9
[4] FUNC_PROTO '(anon)' ret_type_id=5 vlen=1
'f' type_id=1
[5] PTR '(anon)' type_id=0
[6] FUNC 'func' type_id=4 linkage=global
[7] INT 'u8' size=1 bits_offset=0 nr_bits=8 encoding=(none)
[8] INT 'u32' size=4 bits_offset=0 nr_bits=32 encoding=(none)
[9] ARRAY '(anon)' type_id=7 index_type_id=8 nr_elems=4
