[DTrace-devel] [PATCH v2] btf: support compilation in older environments
Alan Maguire
alan.maguire at oracle.com
Fri Dec 1 14:15:12 UTC 2023
On 29/11/2023 21:07, Kris Van Hees via DTrace-devel wrote:
> Include a btf.h from a recent enough kernel to support all the type
> kinds that the BTF-to-CTF convertor provides code for.
>
> Note that the BTF-to-CTF convertor requires libctf. This patch also
> ensures that the BTF-to-CTF convertor is not used when CTF is provided
> by libdtrace-ctf (which is deprecated).
>
> Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
Reviewed-by: Alan Maguire <alan.maguire at oracle.com>
> ---
> include/linux/btf.h | 200 ++++++++++++++++++++++++++++++++++++++++++
> libdtrace/Build | 5 +-
> libdtrace/dt_btf.c | 6 +-
> libdtrace/dt_btf.h | 1 -
> libdtrace/dt_module.c | 15 +++-
> 5 files changed, 221 insertions(+), 6 deletions(-)
> create mode 100644 include/linux/btf.h
>
> diff --git a/include/linux/btf.h b/include/linux/btf.h
> new file mode 100644
> index 00000000..ec1798b6
> --- /dev/null
> +++ b/include/linux/btf.h
> @@ -0,0 +1,200 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +/* Copyright (c) 2018 Facebook */
> +#ifndef _UAPI__LINUX_BTF_H__
> +#define _UAPI__LINUX_BTF_H__
> +
> +#include <linux/types.h>
> +
> +#define BTF_MAGIC 0xeB9F
> +#define BTF_VERSION 1
> +
> +struct btf_header {
> + __u16 magic;
> + __u8 version;
> + __u8 flags;
> + __u32 hdr_len;
> +
> + /* All offsets are in bytes relative to the end of this header */
> + __u32 type_off; /* offset of type section */
> + __u32 type_len; /* length of type section */
> + __u32 str_off; /* offset of string section */
> + __u32 str_len; /* length of string section */
> +};
> +
> +/* Max # of type identifier */
> +#define BTF_MAX_TYPE 0x000fffff
> +/* Max offset into the string section */
> +#define BTF_MAX_NAME_OFFSET 0x00ffffff
> +/* Max # of struct/union/enum members or func args */
> +#define BTF_MAX_VLEN 0xffff
> +
> +struct btf_type {
> + __u32 name_off;
> + /* "info" bits arrangement
> + * bits 0-15: vlen (e.g. # of struct's members)
> + * bits 16-23: unused
> + * bits 24-28: kind (e.g. int, ptr, array...etc)
> + * bits 29-30: unused
> + * bit 31: kind_flag, currently used by
> + * struct, union, enum, fwd and enum64
> + */
> + __u32 info;
> + /* "size" is used by INT, ENUM, STRUCT, UNION, DATASEC and ENUM64.
> + * "size" tells the size of the type it is describing.
> + *
> + * "type" is used by PTR, TYPEDEF, VOLATILE, CONST, RESTRICT,
> + * FUNC, FUNC_PROTO, VAR, DECL_TAG and TYPE_TAG.
> + * "type" is a type_id referring to another type.
> + */
> + union {
> + __u32 size;
> + __u32 type;
> + };
> +};
> +
> +#define BTF_INFO_KIND(info) (((info) >> 24) & 0x1f)
> +#define BTF_INFO_VLEN(info) ((info) & 0xffff)
> +#define BTF_INFO_KFLAG(info) ((info) >> 31)
> +
> +enum {
> + BTF_KIND_UNKN = 0, /* Unknown */
> + BTF_KIND_INT = 1, /* Integer */
> + BTF_KIND_PTR = 2, /* Pointer */
> + BTF_KIND_ARRAY = 3, /* Array */
> + BTF_KIND_STRUCT = 4, /* Struct */
> + BTF_KIND_UNION = 5, /* Union */
> + BTF_KIND_ENUM = 6, /* Enumeration up to 32-bit values */
> + BTF_KIND_FWD = 7, /* Forward */
> + BTF_KIND_TYPEDEF = 8, /* Typedef */
> + BTF_KIND_VOLATILE = 9, /* Volatile */
> + BTF_KIND_CONST = 10, /* Const */
> + BTF_KIND_RESTRICT = 11, /* Restrict */
> + BTF_KIND_FUNC = 12, /* Function */
> + BTF_KIND_FUNC_PROTO = 13, /* Function Proto */
> + BTF_KIND_VAR = 14, /* Variable */
> + BTF_KIND_DATASEC = 15, /* Section */
> + BTF_KIND_FLOAT = 16, /* Floating point */
> + BTF_KIND_DECL_TAG = 17, /* Decl Tag */
> + BTF_KIND_TYPE_TAG = 18, /* Type Tag */
> + BTF_KIND_ENUM64 = 19, /* Enumeration up to 64-bit values */
> +
> + NR_BTF_KINDS,
> + BTF_KIND_MAX = NR_BTF_KINDS - 1,
> +};
> +
> +/* For some specific BTF_KIND, "struct btf_type" is immediately
> + * followed by extra data.
> + */
> +
> +/* BTF_KIND_INT is followed by a u32 and the following
> + * is the 32 bits arrangement:
> + */
> +#define BTF_INT_ENCODING(VAL) (((VAL) & 0x0f000000) >> 24)
> +#define BTF_INT_OFFSET(VAL) (((VAL) & 0x00ff0000) >> 16)
> +#define BTF_INT_BITS(VAL) ((VAL) & 0x000000ff)
> +
> +/* Attributes stored in the BTF_INT_ENCODING */
> +#define BTF_INT_SIGNED (1 << 0)
> +#define BTF_INT_CHAR (1 << 1)
> +#define BTF_INT_BOOL (1 << 2)
> +
> +/* BTF_KIND_ENUM is followed by multiple "struct btf_enum".
> + * The exact number of btf_enum is stored in the vlen (of the
> + * info in "struct btf_type").
> + */
> +struct btf_enum {
> + __u32 name_off;
> + __s32 val;
> +};
> +
> +/* BTF_KIND_ARRAY is followed by one "struct btf_array" */
> +struct btf_array {
> + __u32 type;
> + __u32 index_type;
> + __u32 nelems;
> +};
> +
> +/* BTF_KIND_STRUCT and BTF_KIND_UNION are followed
> + * by multiple "struct btf_member". The exact number
> + * of btf_member is stored in the vlen (of the info in
> + * "struct btf_type").
> + */
> +struct btf_member {
> + __u32 name_off;
> + __u32 type;
> + /* If the type info kind_flag is set, the btf_member offset
> + * contains both member bitfield size and bit offset. The
> + * bitfield size is set for bitfield members. If the type
> + * info kind_flag is not set, the offset contains only bit
> + * offset.
> + */
> + __u32 offset;
> +};
> +
> +/* If the struct/union type info kind_flag is set, the
> + * following two macros are used to access bitfield_size
> + * and bit_offset from btf_member.offset.
> + */
> +#define BTF_MEMBER_BITFIELD_SIZE(val) ((val) >> 24)
> +#define BTF_MEMBER_BIT_OFFSET(val) ((val) & 0xffffff)
> +
> +/* BTF_KIND_FUNC_PROTO is followed by multiple "struct btf_param".
> + * The exact number of btf_param is stored in the vlen (of the
> + * info in "struct btf_type").
> + */
> +struct btf_param {
> + __u32 name_off;
> + __u32 type;
> +};
> +
> +enum {
> + BTF_VAR_STATIC = 0,
> + BTF_VAR_GLOBAL_ALLOCATED = 1,
> + BTF_VAR_GLOBAL_EXTERN = 2,
> +};
> +
> +enum btf_func_linkage {
> + BTF_FUNC_STATIC = 0,
> + BTF_FUNC_GLOBAL = 1,
> + BTF_FUNC_EXTERN = 2,
> +};
> +
> +/* BTF_KIND_VAR is followed by a single "struct btf_var" to describe
> + * additional information related to the variable such as its linkage.
> + */
> +struct btf_var {
> + __u32 linkage;
> +};
> +
> +/* BTF_KIND_DATASEC is followed by multiple "struct btf_var_secinfo"
> + * to describe all BTF_KIND_VAR types it contains along with it's
> + * in-section offset as well as size.
> + */
> +struct btf_var_secinfo {
> + __u32 type;
> + __u32 offset;
> + __u32 size;
> +};
> +
> +/* BTF_KIND_DECL_TAG is followed by a single "struct btf_decl_tag" to describe
> + * additional information related to the tag applied location.
> + * If component_idx == -1, the tag is applied to a struct, union,
> + * variable or function. Otherwise, it is applied to a struct/union
> + * member or a func argument, and component_idx indicates which member
> + * or argument (0 ... vlen-1).
> + */
> +struct btf_decl_tag {
> + __s32 component_idx;
> +};
> +
> +/* BTF_KIND_ENUM64 is followed by multiple "struct btf_enum64".
> + * The exact number of btf_enum64 is stored in the vlen (of the
> + * info in "struct btf_type").
> + */
> +struct btf_enum64 {
> + __u32 name_off;
> + __u32 val_lo32;
> + __u32 val_hi32;
> +};
> +
> +#endif /* _UAPI__LINUX_BTF_H__ */
> diff --git a/libdtrace/Build b/libdtrace/Build
> index 76fd32e4..cbeefe44 100644
> --- a/libdtrace/Build
> +++ b/libdtrace/Build
> @@ -13,7 +13,6 @@ libdtrace-build_DIR := $(current-dir)
> libdtrace-build_SOURCES = dt_aggregate.c \
> dt_as.c \
> dt_bpf.c \
> - dt_btf.c \
> dt_buf.c \
> dt_cc.c \
> dt_cg.c \
> @@ -71,6 +70,10 @@ libdtrace-build_SOURCES = dt_aggregate.c \
> dt_work.c \
> dt_xlator.c
>
> +ifdef HAVE_LIBCTF
> +libdtrace-build_SOURCES += dt_btf.c
> +endif
> +
> libdtrace-build_SRCDEPS := dt_grammar.h $(objdir)/dt_git_version.h
>
> SHLIBS += libdtrace
> diff --git a/libdtrace/dt_btf.c b/libdtrace/dt_btf.c
> index 2cb26aa5..01630b9c 100644
> --- a/libdtrace/dt_btf.c
> +++ b/libdtrace/dt_btf.c
> @@ -7,7 +7,6 @@
>
> #include <assert.h>
> #include <byteswap.h>
> -#include <ctf.h>
> #include <errno.h>
> #include <stdio.h>
> #include <sys/mman.h>
> @@ -147,6 +146,8 @@ dt_btf_type_size(const char *ptr)
> return size + vlen * sizeof(btf_var_secinfo_t);
> case BTF_KIND_DECL_TAG:
> return size + sizeof(btf_decl_tag_t);
> + case BTF_KIND_TYPE_TAG:
> + return size;
> case BTF_KIND_ENUM64:
> return size + vlen * sizeof(btf_enum64_t);
> case BTF_KIND_PTR:
> @@ -157,7 +158,6 @@ dt_btf_type_size(const char *ptr)
> case BTF_KIND_RESTRICT:
> case BTF_KIND_FUNC:
> case BTF_KIND_FLOAT:
> - case BTF_KIND_TYPE_TAG:
> return size;
> default:
> return -EINVAL;
> @@ -658,8 +658,8 @@ dt_btf_add_to_ctf(dtrace_hdl_t *dtp, dt_btf_t *btf, ctf_dict_t *ctf,
> case BTF_KIND_DATASEC:
> case BTF_KIND_DECL_TAG:
> case BTF_KIND_TYPE_TAG:
> - case BTF_KIND_FUNC:
> case BTF_KIND_ENUM64:
> + case BTF_KIND_FUNC:
> return btf->ctfids[0]; /* Ignored for CTF */
> default:
> return dt_ctf_error(dtp, ctf);
> diff --git a/libdtrace/dt_btf.h b/libdtrace/dt_btf.h
> index 3db4203a..863fa470 100644
> --- a/libdtrace/dt_btf.h
> +++ b/libdtrace/dt_btf.h
> @@ -8,7 +8,6 @@
> #ifndef _DT_BTF_H
> #define _DT_BTF_H
>
> -#include <ctf.h>
> #include <dt_impl.h>
>
> #ifdef __cplusplus
> diff --git a/libdtrace/dt_module.c b/libdtrace/dt_module.c
> index 41c5083e..1e730426 100644
> --- a/libdtrace/dt_module.c
> +++ b/libdtrace/dt_module.c
> @@ -26,9 +26,12 @@
> #include <dt_kernel_module.h>
> #include <dt_module.h>
> #include <dt_impl.h>
> -#include <dt_btf.h>
> #include <dt_string.h>
>
> +#ifdef HAVE_LIBCTF
> +# include <dt_btf.h>
> +#endif
> +
> #define KSYM_NAME_MAX 128 /* from kernel/scripts/kallsyms.c */
> #define GZCHUNKSIZE (1024*512) /* gzip uncompression chunk size */
>
> @@ -827,6 +830,7 @@ dt_kern_module_init(dtrace_hdl_t *dtp, dt_module_t *dmp)
> return 0;
> }
>
> +#ifdef HAVE_LIBCTF
> static void
> dt_kern_module_ctf_from_btf(dtrace_hdl_t *dtp, dt_module_t *dmp)
> {
> @@ -848,6 +852,7 @@ dt_kern_module_ctf_from_btf(dtrace_hdl_t *dtp, dt_module_t *dmp)
> else
> dmp->dm_flags |= DT_DM_CTF_ARCHIVED;
> }
> +#endif
>
> /*
> * Determine the location of a kernel module's CTF data.
> @@ -867,6 +872,7 @@ dt_kern_module_find_ctf(dtrace_hdl_t *dtp, dt_module_t *dmp)
> dt_kern_module_init(dtp, dmp);
> }
>
> +#ifdef HAVE_LIBCTF
> /*
> * If we already know that our CTF data is derived from BTF data (i.e.
> * there is no CTF archive for the runtime kernel), there is no point
> @@ -876,6 +882,7 @@ dt_kern_module_find_ctf(dtrace_hdl_t *dtp, dt_module_t *dmp)
> dt_kern_module_ctf_from_btf(dtp, dmp);
> return;
> }
> +#endif
>
> /*
> * Kernel modules' CTF can be in one of two places: the CTF archive or
> @@ -923,6 +930,7 @@ dt_kern_module_find_ctf(dtrace_hdl_t *dtp, dt_module_t *dmp)
> ctfa_name);
> }
> } else {
> +#ifdef HAVE_LIBCTF
> dt_dprintf("Cannot open CTF archive %s: %s; "
> "trying BTF.\n",
> ctfa_name, ctf_errmsg(dtp->dt_ctferr));
> @@ -933,6 +941,11 @@ dt_kern_module_find_ctf(dtrace_hdl_t *dtp, dt_module_t *dmp)
> */
> dt_kern_module_ctf_from_btf(dtp,
> dt_module_lookup_by_name(dtp, "vmlinux"));
> +#else
> + dt_dprintf("Cannot open CTF archive %s: %s; "
> + "looking for in-module CTF instead.\n",
> + ctfa_name, ctf_errmsg(dtp->dt_ctferr));
> +#endif
> return;
> }
>
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