From: Alan Maguire <alan.maguire@oracle.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>, bpf@vger.kernel.org
Cc: daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com,
memxor@gmail.com
Subject: Re: [PATCH bpf-next 05/14] bpf: Allow names of Rust types and functions in BTF
Date: Thu, 1 Oct 2026 18:42:09 +0100 [thread overview]
Message-ID: <82f7ccc5-da2a-4b78-a10a-442acfac1855@oracle.com> (raw)
In-Reply-To: <20260930193127.2181684-6-alexei.starovoitov@gmail.com>
On 30/09/2026 20:31, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@kernel.org>
>
> Names of types and functions in BTF that LLVM makes for a Rust program
> are not C identifiers:
>
> [69] STRUCT 'NonNull<str>' size=16 vlen=1
> [147] FUNC 'write_fmt<scx_cosmos::BpfStream>' type_id=146
>
> and the kernel rejects such BTF with "Invalid name". scx_simple and
> scx_cosmos schedulers written in Rust have them in STRUCT, FWD and FUNC,
> made of letters, digits and " #&()*,:;<>[]{}", 430 characters at most.
>
> Allow any printable character in btf_name_valid_identifier(), like it's
> done for DATASEC. It checks names of types, functions, members,
> enumerators, variables and arguments, so all of them can have such
> characters now. The limit of KSYM_NAME_LEN stays.
>
> The name of FUNC is a part of the name of the program in kallsyms, where
> a space would break the parsers. Replace what is not a character of
> an identifier with '_' there.
One idea I've been experimenting with for pahole-generated BTF is to
retain a more friendly rust-centric name, while keeping the kallsyms name
(which is name-mangled) in a structured BTF decl tag pointing at it [1].
The idea is that for tracing rust functions you could specify the rust name
(from DWARF DW_AT_name) in the SEC(), but to map to the actual symbol
address in kallsyms the decl tag that referenced that function could use
the DW_AT_linkage name.
So the decl tag would have the form
<lang>:linkage:<linkage-symbol>
and it would reference the FUNC type id.
Could we do similar here for the name -> symbol mapping?
[1] https://github.com/acmel/dwarves/commit/a14b368960635b30b188a899a1245143df53e70b
>
> Tests in prog_tests/btf.c expect "Invalid name" for names with '!' and
> '*', which are valid now. Put a character that is not printable there.
> The type name '?foo' is expected to load.
>
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> ---
> kernel/bpf/btf.c | 15 ++----
> kernel/bpf/core.c | 5 ++
> tools/testing/selftests/bpf/prog_tests/btf.c | 52 ++++++++++----------
> 3 files changed, 33 insertions(+), 39 deletions(-)
>
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 8cc17a1cd25c..d27af5d8e495 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -901,16 +901,6 @@ static bool btf_name_offset_valid(const struct btf *btf, u32 offset)
> return offset < btf->hdr.str_len;
> }
>
> -static bool __btf_name_char_ok(char c, bool first)
> -{
> - if ((first ? !isalpha(c) :
> - !isalnum(c)) &&
> - c != '_' &&
> - c != '.')
> - return false;
> - return true;
> -}
> -
> const char *btf_str_by_offset(const struct btf *btf, u32 offset)
> {
> while (offset < btf->start_str_off)
> @@ -923,20 +913,21 @@ const char *btf_str_by_offset(const struct btf *btf, u32 offset)
> return NULL;
> }
>
> +/* Names in BTF of Rust are not C identifiers. Allow any printable character */
> static bool btf_name_valid_identifier(const struct btf *btf, u32 offset)
> {
> /* offset must be valid */
> const char *src = btf_str_by_offset(btf, offset);
> const char *src_limit;
>
> - if (!__btf_name_char_ok(*src, true))
> + if (!isprint(*src))
> return false;
>
> /* set a limit on identifier length */
> src_limit = src + KSYM_NAME_LEN;
> src++;
> while (*src && src < src_limit) {
> - if (!__btf_name_char_ok(*src, false))
> + if (!isprint(*src))
> return false;
> src++;
> }
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index a1721f9c0f52..36900b02d668 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -18,6 +18,7 @@
> */
>
> #include <uapi/linux/btf.h>
> +#include <linux/ctype.h>
> #include <linux/filter.h>
> #include <linux/sched/signal.h>
> #include <linux/skbuff.h>
> @@ -589,6 +590,10 @@ bpf_prog_ksym_set_name(struct bpf_prog *prog)
> prog->aux->func_info[prog->aux->func_idx].type_id);
> func_name = btf_name_by_offset(prog->aux->btf, type->name_off);
> snprintf(sym, (size_t)(end - sym), "_%s", func_name);
> + /* the name of a function of Rust is not an identifier */
> + for (; *sym; sym++)
> + if (!isalnum(*sym) && *sym != '_' && *sym != '.')
> + *sym = '_';
> return;
> }
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/btf.c b/tools/testing/selftests/bpf/prog_tests/btf.c
> index df6ad38d287d..87b554067071 100644
> --- a/tools/testing/selftests/bpf/prog_tests/btf.c
> +++ b/tools/testing/selftests/bpf/prog_tests/btf.c
> @@ -1987,14 +1987,14 @@ static struct btf_raw_test raw_tests[] = {
> },
>
> {
> - .descr = "typedef (invalid name, invalid identifier)",
> + .descr = "typedef (invalid name, not printable)",
> .raw_types = {
> BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4), /* [1] */
> BTF_TYPEDEF_ENC(NAME_TBD, 1), /* [2] */
> BTF_END_RAW,
> },
> - .str_sec = "\0__!int",
> - .str_sec_size = sizeof("\0__!int"),
> + .str_sec = "\0__\7int",
> + .str_sec_size = sizeof("\0__\7int"),
> .map_type = BPF_MAP_TYPE_ARRAY,
> .map_name = "typedef_check_btf",
> .key_size = sizeof(int),
> @@ -2112,15 +2112,15 @@ static struct btf_raw_test raw_tests[] = {
> },
>
> {
> - .descr = "fwd type (invalid name, invalid identifier)",
> + .descr = "fwd type (invalid name, not printable)",
> .raw_types = {
> BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4), /* [1] */
> BTF_TYPE_ENC(NAME_TBD,
> BTF_INFO_ENC(BTF_KIND_FWD, 0, 0), 0), /* [2] */
> BTF_END_RAW,
> },
> - .str_sec = "\0__!skb",
> - .str_sec_size = sizeof("\0__!skb"),
> + .str_sec = "\0__\7skb",
> + .str_sec_size = sizeof("\0__\7skb"),
> .map_type = BPF_MAP_TYPE_ARRAY,
> .map_name = "fwd_type_check_btf",
> .key_size = sizeof(int),
> @@ -2175,7 +2175,7 @@ static struct btf_raw_test raw_tests[] = {
> },
>
> {
> - .descr = "struct type (invalid name, invalid identifier)",
> + .descr = "struct type (invalid name, not printable)",
> .raw_types = {
> BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4), /* [1] */
> BTF_TYPE_ENC(NAME_TBD,
> @@ -2183,8 +2183,8 @@ static struct btf_raw_test raw_tests[] = {
> BTF_MEMBER_ENC(NAME_TBD, 1, 0),
> BTF_END_RAW,
> },
> - .str_sec = "\0A!\0B",
> - .str_sec_size = sizeof("\0A!\0B"),
> + .str_sec = "\0A\7\0B",
> + .str_sec_size = sizeof("\0A\7\0B"),
> .map_type = BPF_MAP_TYPE_ARRAY,
> .map_name = "struct_type_check_btf",
> .key_size = sizeof(int),
> @@ -2217,7 +2217,7 @@ static struct btf_raw_test raw_tests[] = {
> },
>
> {
> - .descr = "struct member (invalid name, invalid identifier)",
> + .descr = "struct member (invalid name, not printable)",
> .raw_types = {
> BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4), /* [1] */
> BTF_TYPE_ENC(NAME_TBD,
> @@ -2225,8 +2225,8 @@ static struct btf_raw_test raw_tests[] = {
> BTF_MEMBER_ENC(NAME_TBD, 1, 0),
> BTF_END_RAW,
> },
> - .str_sec = "\0A\0B*",
> - .str_sec_size = sizeof("\0A\0B*"),
> + .str_sec = "\0A\0B\7",
> + .str_sec_size = sizeof("\0A\0B\7"),
> .map_type = BPF_MAP_TYPE_ARRAY,
> .map_name = "struct_type_check_btf",
> .key_size = sizeof(int),
> @@ -2260,7 +2260,7 @@ static struct btf_raw_test raw_tests[] = {
> },
>
> {
> - .descr = "enum type (invalid name, invalid identifier)",
> + .descr = "enum type (invalid name, not printable)",
> .raw_types = {
> BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4), /* [1] */
> BTF_TYPE_ENC(NAME_TBD,
> @@ -2269,8 +2269,8 @@ static struct btf_raw_test raw_tests[] = {
> BTF_ENUM_ENC(NAME_TBD, 0),
> BTF_END_RAW,
> },
> - .str_sec = "\0A!\0B",
> - .str_sec_size = sizeof("\0A!\0B"),
> + .str_sec = "\0A\7\0B",
> + .str_sec_size = sizeof("\0A\7\0B"),
> .map_type = BPF_MAP_TYPE_ARRAY,
> .map_name = "enum_type_check_btf",
> .key_size = sizeof(int),
> @@ -2306,7 +2306,7 @@ static struct btf_raw_test raw_tests[] = {
> },
>
> {
> - .descr = "enum member (invalid name, invalid identifier)",
> + .descr = "enum member (invalid name, not printable)",
> .raw_types = {
> BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4), /* [1] */
> BTF_TYPE_ENC(0,
> @@ -2315,8 +2315,8 @@ static struct btf_raw_test raw_tests[] = {
> BTF_ENUM_ENC(NAME_TBD, 0),
> BTF_END_RAW,
> },
> - .str_sec = "\0A!",
> - .str_sec_size = sizeof("\0A!"),
> + .str_sec = "\0A\7",
> + .str_sec_size = sizeof("\0A\7"),
> .map_type = BPF_MAP_TYPE_ARRAY,
> .map_name = "enum_type_check_btf",
> .key_size = sizeof(int),
> @@ -2625,14 +2625,14 @@ static struct btf_raw_test raw_tests[] = {
> .raw_types = {
> BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4), /* [1] */
> BTF_TYPE_INT_ENC(0, 0, 0, 32, 4), /* [2] */
> - /* void (*)(int a, unsigned int !!!) */
> + /* void (*)(int a, unsigned int \7) */
> BTF_FUNC_PROTO_ENC(0, 2), /* [3] */
> BTF_FUNC_PROTO_ARG_ENC(NAME_TBD, 1),
> BTF_FUNC_PROTO_ARG_ENC(NAME_TBD, 2),
> BTF_END_RAW,
> },
> - .str_sec = "\0a\0!!!",
> - .str_sec_size = sizeof("\0a\0!!!"),
> + .str_sec = "\0a\0\7",
> + .str_sec_size = sizeof("\0a\0\7"),
> .map_type = BPF_MAP_TYPE_ARRAY,
> .map_name = "func_proto_type_check_btf",
> .key_size = sizeof(int),
> @@ -2775,12 +2775,12 @@ static struct btf_raw_test raw_tests[] = {
> BTF_FUNC_PROTO_ENC(0, 2), /* [3] */
> BTF_FUNC_PROTO_ARG_ENC(NAME_TBD, 1),
> BTF_FUNC_PROTO_ARG_ENC(NAME_TBD, 2),
> - /* void !!!(int a, unsigned int b) */
> + /* void \7(int a, unsigned int b) */
> BTF_FUNC_ENC(NAME_TBD, 3), /* [4] */
> BTF_END_RAW,
> },
> - .str_sec = "\0a\0b\0!!!",
> - .str_sec_size = sizeof("\0a\0b\0!!!"),
> + .str_sec = "\0a\0b\0\7",
> + .str_sec_size = sizeof("\0a\0b\0\7"),
> .map_type = BPF_MAP_TYPE_ARRAY,
> .map_name = "func_type_check_btf",
> .key_size = sizeof(int),
> @@ -3585,15 +3585,13 @@ static struct btf_raw_test raw_tests[] = {
> .btf_load_err = true,
> },
> {
> - .descr = "type name '?foo' is not ok",
> + .descr = "type name '?foo' is ok",
> .raw_types = {
> /* union ?foo; */
> BTF_TYPE_ENC(1, BTF_INFO_ENC(BTF_KIND_FWD, 1, 0), 0), /* [1] */
> BTF_END_RAW,
> },
> BTF_STR_SEC("\0?foo"),
> - .err_str = "Invalid name",
> - .btf_load_err = true,
> },
>
> {
next prev parent reply other threads:[~2026-10-01 17:42 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-30 19:31 [PATCH bpf-next 00/14] bpf: Support programs compiled by rust-bpf Alexei Starovoitov
2026-09-30 19:31 ` [PATCH bpf-next 01/14] bpf: Allow bitwise ops, shifts and mul/div on pointers with CAP_PERFMON Alexei Starovoitov
2026-09-30 19:31 ` [PATCH bpf-next 02/14] selftests/bpf: Add tests for ALU " Alexei Starovoitov
2026-09-30 19:31 ` [PATCH bpf-next 03/14] bpf: Treat load and store through a number as arena access Alexei Starovoitov
2026-09-30 19:31 ` [PATCH bpf-next 04/14] selftests/bpf: Add tests for arena access through numbers Alexei Starovoitov
2026-09-30 19:48 ` sashiko-bot
2026-09-30 20:22 ` bot+bpf-ci
2026-09-30 19:31 ` [PATCH bpf-next 05/14] bpf: Allow names of Rust types and functions in BTF Alexei Starovoitov
2026-09-30 20:22 ` bot+bpf-ci
2026-10-01 17:42 ` Alan Maguire [this message]
2026-10-02 12:24 ` Alexei Starovoitov
2026-10-02 13:38 ` Alan Maguire
2026-09-30 19:31 ` [PATCH bpf-next 06/14] selftests/bpf: Add tests for " Alexei Starovoitov
2026-09-30 20:22 ` bot+bpf-ci
2026-09-30 19:31 ` [PATCH bpf-next 07/14] bpf: Allow arguments without names in static " Alexei Starovoitov
2026-10-01 21:14 ` Alan Maguire
2026-09-30 19:31 ` [PATCH bpf-next 08/14] selftests/bpf: Add test for arguments without names in static functions Alexei Starovoitov
2026-10-01 21:22 ` Alan Maguire
2026-09-30 19:31 ` [PATCH bpf-next 09/14] bpf: Allow a variable in DATASEC that is smaller than its type Alexei Starovoitov
2026-09-30 19:47 ` sashiko-bot
2026-09-30 19:31 ` [PATCH bpf-next 10/14] selftests/bpf: Add tests for a variable " Alexei Starovoitov
2026-09-30 19:31 ` [PATCH bpf-next 11/14] libbpf: Keep global data in arena when the object has .arena.data Alexei Starovoitov
2026-09-30 19:46 ` sashiko-bot
2026-09-30 20:22 ` bot+bpf-ci
2026-09-30 19:31 ` [PATCH bpf-next 12/14] libbpf: Keep format strings of bpf_printk() in .rodata.str Alexei Starovoitov
2026-09-30 20:22 ` bot+bpf-ci
2026-09-30 19:31 ` [PATCH bpf-next 13/14] selftests/bpf: Add test for global data in arena Alexei Starovoitov
2026-09-30 20:22 ` bot+bpf-ci
2026-09-30 19:31 ` [PATCH bpf-next 14/14] selftests/bpf: Add test for global data of a program in Rust Alexei Starovoitov
2026-09-30 19:53 ` sashiko-bot
2026-09-30 20:22 ` bot+bpf-ci
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