On Tue, Jan 5, 2021 at 9:10 PM Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: > > On Tue, Jan 5, 2021 at 6:45 AM Sean Young <sean@xxxxxxxx> wrote: > > > > clang supports arbitrary length ints using the _ExtInt extension. This > > can be useful to hold very large values, e.g. 256 bit or 512 bit types. > > > > Larger types (e.g. 1024 bits) are possible but I am unaware of a use > > case for these. > > > > This requires the _ExtInt extension enabled in clang, which is under > > review. > > > > Link: https://clang.llvm.org/docs/LanguageExtensions.html#extended-integer-types > > Link: https://reviews.llvm.org/D93103 > > > > Signed-off-by: Sean Young <sean@xxxxxxxx> > > --- > > Documentation/bpf/btf.rst | 4 +-- > > include/uapi/linux/btf.h | 2 +- > > kernel/bpf/btf.c | 54 ++++++++++++++++++++++++++++------ > > tools/include/uapi/linux/btf.h | 2 +- > > 4 files changed, 49 insertions(+), 13 deletions(-) > > > > diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst > > index 44dc789de2b4..784f1743dbc7 100644 > > --- a/Documentation/bpf/btf.rst > > +++ b/Documentation/bpf/btf.rst > > @@ -132,7 +132,7 @@ The following sections detail encoding of each kind. > > > > #define BTF_INT_ENCODING(VAL) (((VAL) & 0x0f000000) >> 24) > > #define BTF_INT_OFFSET(VAL) (((VAL) & 0x00ff0000) >> 16) > > - #define BTF_INT_BITS(VAL) ((VAL) & 0x000000ff) > > + #define BTF_INT_BITS(VAL) ((VAL) & 0x000003ff) > > > > The ``BTF_INT_ENCODING`` has the following attributes:: > > > > @@ -147,7 +147,7 @@ pretty print. At most one encoding can be specified for the int type. > > The ``BTF_INT_BITS()`` specifies the number of actual bits held by this int > > type. For example, a 4-bit bitfield encodes ``BTF_INT_BITS()`` equals to 4. > > The ``btf_type.size * 8`` must be equal to or greater than ``BTF_INT_BITS()`` > > -for the type. The maximum value of ``BTF_INT_BITS()`` is 128. > > +for the type. The maximum value of ``BTF_INT_BITS()`` is 512. > > > > The ``BTF_INT_OFFSET()`` specifies the starting bit offset to calculate values > > for this int. For example, a bitfield struct member has: > > diff --git a/include/uapi/linux/btf.h b/include/uapi/linux/btf.h > > index 5a667107ad2c..1696fd02b302 100644 > > --- a/include/uapi/linux/btf.h > > +++ b/include/uapi/linux/btf.h > > @@ -84,7 +84,7 @@ struct btf_type { > > */ > > #define BTF_INT_ENCODING(VAL) (((VAL) & 0x0f000000) >> 24) > > #define BTF_INT_OFFSET(VAL) (((VAL) & 0x00ff0000) >> 16) > > -#define BTF_INT_BITS(VAL) ((VAL) & 0x000000ff) > > +#define BTF_INT_BITS(VAL) ((VAL) & 0x000003ff) > > > > /* Attributes stored in the BTF_INT_ENCODING */ > > #define BTF_INT_SIGNED (1 << 0) > > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c > > index 8d6bdb4f4d61..44bc17207e9b 100644 > > --- a/kernel/bpf/btf.c > > +++ b/kernel/bpf/btf.c > > @@ -166,7 +166,8 @@ > > * > > */ > > > > -#define BITS_PER_U128 (sizeof(u64) * BITS_PER_BYTE * 2) > > +#define BITS_PER_U128 128 > > +#define BITS_PER_U512 512 > > #define BITS_PER_BYTE_MASK (BITS_PER_BYTE - 1) > > #define BITS_PER_BYTE_MASKED(bits) ((bits) & BITS_PER_BYTE_MASK) > > #define BITS_ROUNDDOWN_BYTES(bits) ((bits) >> 3) > > @@ -1907,9 +1908,9 @@ static int btf_int_check_member(struct btf_verifier_env *env, > > nr_copy_bits = BTF_INT_BITS(int_data) + > > BITS_PER_BYTE_MASKED(struct_bits_off); > > > > - if (nr_copy_bits > BITS_PER_U128) { > > + if (nr_copy_bits > BITS_PER_U512) { > > btf_verifier_log_member(env, struct_type, member, > > - "nr_copy_bits exceeds 128"); > > + "nr_copy_bits exceeds 512"); > > return -EINVAL; > > } > > > > @@ -1963,9 +1964,9 @@ static int btf_int_check_kflag_member(struct btf_verifier_env *env, > > > > bytes_offset = BITS_ROUNDDOWN_BYTES(struct_bits_off); > > nr_copy_bits = nr_bits + BITS_PER_BYTE_MASKED(struct_bits_off); > > - if (nr_copy_bits > BITS_PER_U128) { > > + if (nr_copy_bits > BITS_PER_U512) { > > btf_verifier_log_member(env, struct_type, member, > > - "nr_copy_bits exceeds 128"); > > + "nr_copy_bits exceeds 512"); > > return -EINVAL; > > } > > > > @@ -2012,9 +2013,9 @@ static s32 btf_int_check_meta(struct btf_verifier_env *env, > > > > nr_bits = BTF_INT_BITS(int_data) + BTF_INT_OFFSET(int_data); > > > > - if (nr_bits > BITS_PER_U128) { > > - btf_verifier_log_type(env, t, "nr_bits exceeds %zu", > > - BITS_PER_U128); > > + if (nr_bits > BITS_PER_U512) { > > + btf_verifier_log_type(env, t, "nr_bits exceeds %u", > > + BITS_PER_U512); > > return -EINVAL; > > } > > > > @@ -2080,6 +2081,37 @@ static void btf_int128_print(struct btf_show *show, void *data) > > lower_num); > > } > > > > +static void btf_bigint_print(struct btf_show *show, void *data, u16 nr_bits) > > +{ > > + /* data points to 256 or 512 bit int type */ > > + char buf[129]; > > + int last_u64 = nr_bits / 64 - 1; > > + bool seen_nonzero = false; > > + int i; > > + > > + for (i = 0; i <= last_u64; i++) { > > +#ifdef __BIG_ENDIAN_BITFIELD > > + u64 v = ((u64 *)data)[i]; > > +#else > > + u64 v = ((u64 *)data)[last_u64 - i]; > > +#endif to avoid duplicating this #ifdef with my suggestion, you can do something like #ifdef __BIG_ENDIAN_BITFIELD u64 *v = (u64 *)data; int step = 1; #else u64 *v = (u64 *)data + last_u64; int step = -1; #endif and then just `v += step;` everywhere > > + if (!seen_nonzero) { > > + if (!v && i != last_u64) > > + continue; > > + > > + snprintf(buf, sizeof(buf), "%llx", v); > > + > > + seen_nonzero = true; > > + } else { > > + size_t off = strlen(buf); > > this is wasteful, snprintf() returns number of characters printed, so > you can maintain offset properly > > > + > > + snprintf(buf + off, sizeof(buf) - off, "%016llx", v); > > + } > > + } > > + > > + btf_show_type_value(show, "0x%s", buf); > > +} > > seen_nonzero is a bit convoluted, two simple loops might be more > straightforward: > > u64 v; > int off; > > /* find first non-zero u64 (or stop on the last one regardless) */ > for (i = 0; i < last_u64; i++) { > v = ...; > if (!v) > continue; > } > /* print non-zero or zero, but last u64 */ > off = snprintf(buf, sizeof(buf), "%llx", v); > /* print the rest with zero padding */ > for (i++; i <= last_u64; i++) { > v = ...; > off += snprintf(buf + off, sizeof(buf) - off, "%016llx", v); > } > > > + > > static void btf_int128_shift(u64 *print_num, u16 left_shift_bits, > > u16 right_shift_bits) > > { > > @@ -2172,7 +2204,7 @@ static void btf_int_show(const struct btf *btf, const struct btf_type *t, > > u32 int_data = btf_type_int(t); > > u8 encoding = BTF_INT_ENCODING(int_data); > > bool sign = encoding & BTF_INT_SIGNED; > > - u8 nr_bits = BTF_INT_BITS(int_data); > > + u16 nr_bits = BTF_INT_BITS(int_data); > > void *safe_data; > > > > safe_data = btf_show_start_type(show, t, type_id, data); > > @@ -2186,6 +2218,10 @@ static void btf_int_show(const struct btf *btf, const struct btf_type *t, > > } > > > > switch (nr_bits) { > > + case 512: > > + case 256: > > + btf_bigint_print(show, safe_data, nr_bits); > > + break; > > case 128: > > btf_int128_print(show, safe_data); > > btf_bigint_print() supersedes btf_int128_print(), why maintain both? > > > break; > > diff --git a/tools/include/uapi/linux/btf.h b/tools/include/uapi/linux/btf.h > > index 5a667107ad2c..1696fd02b302 100644 > > --- a/tools/include/uapi/linux/btf.h > > +++ b/tools/include/uapi/linux/btf.h > > @@ -84,7 +84,7 @@ struct btf_type { > > */ > > #define BTF_INT_ENCODING(VAL) (((VAL) & 0x0f000000) >> 24) > > #define BTF_INT_OFFSET(VAL) (((VAL) & 0x00ff0000) >> 16) > > -#define BTF_INT_BITS(VAL) ((VAL) & 0x000000ff) > > +#define BTF_INT_BITS(VAL) ((VAL) & 0x000003ff) > > > > /* Attributes stored in the BTF_INT_ENCODING */ > > #define BTF_INT_SIGNED (1 << 0) > > -- > > 2.29.2 > >
