breeze/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-01-25 15:03:52 +08:00
Code Issues Packages Projects Releases Wiki Activity

bpftool: __bpf_fastcall for kfuncs marked with special decl_tag

Browse Source 
Generate __attribute__((bpf_fastcall)) for kfuncs marked with
"bpf_fastcall" decl tag. E.g. for the following BTF:

    $ bpftool btf dump file vmlinux
    ...
    [A] FUNC 'bpf_rdonly_cast' type_id=...
    ...
    [B] DECL_TAG 'bpf_kfunc' type_id=A component_idx=-1
    [C] DECL_TAG 'bpf_fastcall' type_id=A component_idx=-1

Generate the following vmlinux.h:

    #ifndef __VMLINUX_H__
    #define __VMLINUX_H__
    ...
    #ifndef __bpf_fastcall
    #if __has_attribute(bpf_fastcall)
    #define __bpf_fastcall __attribute__((bpf_fastcall))
    #else
    #define __bpf_fastcall
    #endif
    #endif
    ...
    __bpf_fastcall extern void *bpf_rdonly_cast(...) ...;

The "bpf_fastcall" / "bpf_kfunc" tags pair would generated by pahole
when constructing vmlinux BTF.

While at it, sort printed kfuncs by name for better vmlinux.h
stability.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240916091712.2929279-5-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Eduard Zingerman
2024-09-16 02:17:12 -07:00
committed by Alexei Starovoitov
parent da7d71bcb0
commit bf7ce5416f
1 changed files with 88 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

98
tools/bpf/bpftool/btf.c
View File

@@ -1,11 +1,15 @@
// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
/* Copyright (C) 2019 Facebook */
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#include <errno.h>
#include <fcntl.h>
#include <linux/err.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <linux/btf.h>
@@ -21,6 +25,7 @@
#include "main.h"
#define KFUNC_DECL_TAG "bpf_kfunc"
#define FASTCALL_DECL_TAG "bpf_fastcall"
static const char * const btf_kind_str[NR_BTF_KINDS] = {
[BTF_KIND_UNKN] = "UNKNOWN",
@@ -464,19 +469,59 @@ static int dump_btf_raw(const struct btf *btf,
return 0;
}
struct ptr_array {
__u32 cnt;
__u32 cap;
const void **elems;
};
static int ptr_array_push(const void *ptr, struct ptr_array *arr)
{
__u32 new_cap;
void *tmp;
if (arr->cnt == arr->cap) {
new_cap = (arr->cap ?: 16) * 2;
tmp = realloc(arr->elems, sizeof(*arr->elems) * new_cap);
if (!tmp)
return -ENOMEM;
arr->elems = tmp;
arr->cap = new_cap;
}
arr->elems[arr->cnt++] = ptr;
return 0;
}
static void ptr_array_free(struct ptr_array *arr)
{
free(arr->elems);
}
static int cmp_kfuncs(const void *pa, const void *pb, void *ctx)
{
struct btf *btf = ctx;
const struct btf_type *a = *(void **)pa;
const struct btf_type *b = *(void **)pb;
return strcmp(btf__str_by_offset(btf, a->name_off),
btf__str_by_offset(btf, b->name_off));
}
static int dump_btf_kfuncs(struct btf_dump *d, const struct btf *btf)
{
LIBBPF_OPTS(btf_dump_emit_type_decl_opts, opts);
int cnt = btf__type_cnt(btf);
int i;
__u32 cnt = btf__type_cnt(btf), i, j;
struct ptr_array fastcalls = {};
struct ptr_array kfuncs = {};
int err = 0;
printf("\n/* BPF kfuncs */\n");
printf("#ifndef BPF_NO_KFUNC_PROTOTYPES\n");
for (i = 1; i < cnt; i++) {
const struct btf_type *t = btf__type_by_id(btf, i);
const struct btf_type *ft;
const char *name;
int err;
if (!btf_is_decl_tag(t))
continue;
@@ -484,27 +529,53 @@ static int dump_btf_kfuncs(struct btf_dump *d, const struct btf *btf)
if (btf_decl_tag(t)->component_idx != -1)
continue;
name = btf__name_by_offset(btf, t->name_off);
if (strncmp(name, KFUNC_DECL_TAG, sizeof(KFUNC_DECL_TAG)))
ft = btf__type_by_id(btf, t->type);
if (!btf_is_func(ft))
continue;
t = btf__type_by_id(btf, t->type);
if (!btf_is_func(t))
continue;
name = btf__name_by_offset(btf, t->name_off);
if (strncmp(name, KFUNC_DECL_TAG, sizeof(KFUNC_DECL_TAG)) == 0) {
err = ptr_array_push(ft, &kfuncs);
if (err)
goto out;
}
if (strncmp(name, FASTCALL_DECL_TAG, sizeof(FASTCALL_DECL_TAG)) == 0) {
err = ptr_array_push(ft, &fastcalls);
if (err)
goto out;
}
}
/* Sort kfuncs by name for improved vmlinux.h stability */
qsort_r(kfuncs.elems, kfuncs.cnt, sizeof(*kfuncs.elems), cmp_kfuncs, (void *)btf);
for (i = 0; i < kfuncs.cnt; i++) {
const struct btf_type *t = kfuncs.elems[i];
printf("extern ");
/* Assume small amount of fastcall kfuncs */
for (j = 0; j < fastcalls.cnt; j++) {
if (fastcalls.elems[j] == t) {
printf("__bpf_fastcall ");
break;
}
}
opts.field_name = btf__name_by_offset(btf, t->name_off);
err = btf_dump__emit_type_decl(d, t->type, &opts);
if (err)
return err;
goto out;
printf(" __weak __ksym;\n");
}
printf("#endif\n\n");
return 0;
out:
ptr_array_free(&fastcalls);
ptr_array_free(&kfuncs);
return err;
}
static void __printf(2, 0) btf_dump_printf(void *ctx,
@@ -718,6 +789,13 @@ static int dump_btf_c(const struct btf *btf,
printf("#ifndef __weak\n");
printf("#define __weak __attribute__((weak))\n");
printf("#endif\n\n");
printf("#ifndef __bpf_fastcall\n");
printf("#if __has_attribute(bpf_fastcall)\n");
printf("#define __bpf_fastcall __attribute__((bpf_fastcall))\n");
printf("#else\n");
printf("#define __bpf_fastcall\n");
printf("#endif\n");
printf("#endif\n\n");
if (root_type_cnt) {
for (i = 0; i < root_type_cnt; i++) {