Re: [PATCH RFC 1/6] bpf: Add BTF_KIND_FLOAT to uapi
From: Andrii Nakryiko <hidden>
Date: 2021-02-11 00:20:15
On Tue, Feb 9, 2021 at 7:03 PM Ilya Leoshkevich [off-list ref] wrote:
quoted hunk ↗ jump to hunk
Add a new kind value, expand the kind bitfield, add a macro for parsing the additional u32. Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> --- include/uapi/linux/btf.h | 10 ++++++++-- tools/include/uapi/linux/btf.h | 10 ++++++++-- 2 files changed, 16 insertions(+), 4 deletions(-)diff --git a/include/uapi/linux/btf.h b/include/uapi/linux/btf.h index 5a667107ad2c..e713430cb033 100644 --- a/include/uapi/linux/btf.h +++ b/include/uapi/linux/btf.h@@ -52,7 +52,7 @@ struct btf_type { }; }; -#define BTF_INFO_KIND(info) (((info) >> 24) & 0x0f) +#define BTF_INFO_KIND(info) (((info) >> 24) & 0x1f) #define BTF_INFO_VLEN(info) ((info) & 0xffff) #define BTF_INFO_KFLAG(info) ((info) >> 31)@@ -72,7 +72,8 @@ struct btf_type { #define BTF_KIND_FUNC_PROTO 13 /* Function Proto */ #define BTF_KIND_VAR 14 /* Variable */ #define BTF_KIND_DATASEC 15 /* Section */ -#define BTF_KIND_MAX BTF_KIND_DATASEC +#define BTF_KIND_FLOAT 16 /* Floating point */ +#define BTF_KIND_MAX BTF_KIND_FLOAT #define NR_BTF_KINDS (BTF_KIND_MAX + 1) /* For some specific BTF_KIND, "struct btf_type" is immediately@@ -169,4 +170,9 @@ struct btf_var_secinfo { __u32 size; }; +/* BTF_KIND_FLOAT is followed by a u32 and the following
what's the point of that u32, if BTF_FLOAT_BITS() is just t->size * 8? Why adding this complexity. BTF_KIND_INT has bits because we had an inconvenient bitfield encoding as a special BTF_KIND_INT types, which we since stopped using in favor of encoding bitfield sizes and offsets inside struct/union fields. I don't think there is any need for that with FLOAT, so why waste space and add complexity and possibility for inconsistencies? Disclaimer: I'm in a "just BTF_KIND_INT encoding bit for floating-point numbers" camp.
quoted hunk ↗ jump to hunk
+ * is the 32 bits arrangement: + */ +#define BTF_FLOAT_BITS(VAL) ((VAL) & 0x000000ff) + #endif /* _UAPI__LINUX_BTF_H__ */diff --git a/tools/include/uapi/linux/btf.h b/tools/include/uapi/linux/btf.h index 5a667107ad2c..e713430cb033 100644 --- a/tools/include/uapi/linux/btf.h +++ b/tools/include/uapi/linux/btf.h@@ -52,7 +52,7 @@ struct btf_type { }; }; -#define BTF_INFO_KIND(info) (((info) >> 24) & 0x0f) +#define BTF_INFO_KIND(info) (((info) >> 24) & 0x1f) #define BTF_INFO_VLEN(info) ((info) & 0xffff) #define BTF_INFO_KFLAG(info) ((info) >> 31)@@ -72,7 +72,8 @@ struct btf_type { #define BTF_KIND_FUNC_PROTO 13 /* Function Proto */ #define BTF_KIND_VAR 14 /* Variable */ #define BTF_KIND_DATASEC 15 /* Section */ -#define BTF_KIND_MAX BTF_KIND_DATASEC +#define BTF_KIND_FLOAT 16 /* Floating point */ +#define BTF_KIND_MAX BTF_KIND_FLOAT #define NR_BTF_KINDS (BTF_KIND_MAX + 1) /* For some specific BTF_KIND, "struct btf_type" is immediately@@ -169,4 +170,9 @@ struct btf_var_secinfo { __u32 size; }; +/* BTF_KIND_FLOAT is followed by a u32 and the following + * is the 32 bits arrangement: + */ +#define BTF_FLOAT_BITS(VAL) ((VAL) & 0x000000ff) + #endif /* _UAPI__LINUX_BTF_H__ */ --2.29.2