Skip to content

Commit 58a98f7

Browse files
iamkafaiacmel
iamkafai
authored and
acmel
committed
btf: Remove ftrace filter
BTF is currently generated for functions that are in ftrace list or extern. A recent use case also needs BTF generated for functions included in allowlist. In particular, the kernel commit: e78aea8b2170 ("bpf: tcp: Put some tcp cong functions in allowlist for bpf-tcp-cc") allows bpf program to directly call a few tcp cc kernel functions. Those kernel functions are currently allowed only if CONFIG_DYNAMIC_FTRACE is set to ensure they are in the ftrace list but this kconfig dependency is unnecessary. Those kernel functions are specified under an ELF section .BTF_ids. There was an earlier attempt [0] to add another filter for the functions in the .BTF_ids section. That discussion concluded that the ftrace filter should be removed instead. This patch is to remove the ftrace filter and its related functions. Number of BTF FUNC with and without is_ftrace_func(): My kconfig in x86: 40643 vs 46225 Jiri reported on arm: 25022 vs 55812 [0]: https://lore.kernel.org/dwarves/20210423213728.3538141-1-kafai@fb.com/ Signed-off-by: Martin KaFai Lau <kafai@fb.com> Tested-by: Nathan Chancellor <nathan@kernel.org> # build Acked-by: Jiri Olsa <jolsa@kernel.org> Acked-by: Jiri Slaby <jirislaby@kernel.org> Cc: Andrii Nakryiko <andrii@kernel.org> Cc: Jiri Olsa <jolsa@kernel.org> Cc: kernel-team@fb.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
1 parent 7c60b04 commit 58a98f7

File tree

1 file changed

+7
-278
lines changed

1 file changed

+7
-278
lines changed

‎btf_encoder.c‎

Lines changed: 7 additions & 278 deletions
Original file line numberDiff line numberDiff line change
@@ -27,17 +27,8 @@
2727
*/
2828
#define KSYM_NAME_LEN 128
2929

30-
struct funcs_layout {
31-
unsigned long mcount_start;
32-
unsigned long mcount_stop;
33-
unsigned long mcount_sec_idx;
34-
};
35-
3630
struct elf_function {
3731
const char *name;
38-
unsigned long addr;
39-
unsigned long size;
40-
unsigned long sh_addr;
4132
bool generated;
4233
};
4334

@@ -64,12 +55,9 @@ static void delete_functions(void)
6455
#define max(x, y) ((x) < (y) ? (y) : (x))
6556
#endif
6657

67-
static int collect_function(struct btf_elf *btfe, GElf_Sym *sym,
68-
size_t sym_sec_idx)
58+
static int collect_function(struct btf_elf *btfe, GElf_Sym *sym)
6959
{
7060
struct elf_function *new;
71-
static GElf_Shdr sh;
72-
static size_t last_idx;
7361
const char *name;
7462

7563
if (elf_sym__type(sym) != STT_FUNC)
@@ -91,257 +79,12 @@ static int collect_function(struct btf_elf *btfe, GElf_Sym *sym,
9179
functions = new;
9280
}
9381

94-
if (sym_sec_idx != last_idx) {
95-
if (!elf_section_by_idx(btfe->elf, &sh, sym_sec_idx))
96-
return 0;
97-
last_idx = sym_sec_idx;
98-
}
99-
10082
functions[functions_cnt].name = name;
101-
functions[functions_cnt].addr = elf_sym__value(sym);
102-
functions[functions_cnt].size = elf_sym__size(sym);
103-
functions[functions_cnt].sh_addr = sh.sh_addr;
10483
functions[functions_cnt].generated = false;
10584
functions_cnt++;
10685
return 0;
10786
}
10887

109-
static int addrs_cmp(const void *_a, const void *_b)
110-
{
111-
const __u64 *a = _a;
112-
const __u64 *b = _b;
113-
114-
if (*a == *b)
115-
return 0;
116-
return *a < *b ? -1 : 1;
117-
}
118-
119-
static int get_vmlinux_addrs(struct btf_elf *btfe, struct funcs_layout *fl,
120-
__u64 **paddrs, __u64 *pcount)
121-
{
122-
__u64 *addrs, count, offset;
123-
unsigned int addr_size, i;
124-
Elf_Data *data;
125-
GElf_Shdr shdr;
126-
Elf_Scn *sec;
127-
128-
/* Initialize for the sake of all error paths below. */
129-
*paddrs = NULL;
130-
*pcount = 0;
131-
132-
if (!fl->mcount_start || !fl->mcount_stop)
133-
return 0;
134-
135-
/*
136-
* Find mcount addressed marked by __start_mcount_loc
137-
* and __stop_mcount_loc symbols and load them into
138-
* sorted array.
139-
*/
140-
sec = elf_getscn(btfe->elf, fl->mcount_sec_idx);
141-
if (!sec || !gelf_getshdr(sec, &shdr)) {
142-
fprintf(stderr, "Failed to get section(%lu) header.\n",
143-
fl->mcount_sec_idx);
144-
return -1;
145-
}
146-
147-
/* Get address size from processed file's ELF class. */
148-
addr_size = gelf_getclass(btfe->elf) == ELFCLASS32 ? 4 : 8;
149-
150-
offset = fl->mcount_start - shdr.sh_addr;
151-
count = (fl->mcount_stop - fl->mcount_start) / addr_size;
152-
153-
data = elf_getdata(sec, 0);
154-
if (!data) {
155-
fprintf(stderr, "Failed to get section(%lu) data.\n",
156-
fl->mcount_sec_idx);
157-
return -1;
158-
}
159-
160-
addrs = malloc(count * sizeof(addrs[0]));
161-
if (!addrs) {
162-
fprintf(stderr, "Failed to allocate memory for ftrace addresses.\n");
163-
return -1;
164-
}
165-
166-
if (addr_size == sizeof(__u64)) {
167-
memcpy(addrs, data->d_buf + offset, count * addr_size);
168-
} else {
169-
for (i = 0; i < count; i++)
170-
addrs[i] = (__u64) *((__u32 *) (data->d_buf + offset + i * addr_size));
171-
}
172-
173-
*paddrs = addrs;
174-
*pcount = count;
175-
return 0;
176-
}
177-
178-
static int
179-
get_kmod_addrs(struct btf_elf *btfe, __u64 **paddrs, __u64 *pcount)
180-
{
181-
__u64 *addrs, count;
182-
unsigned int addr_size, i;
183-
GElf_Shdr shdr_mcount;
184-
Elf_Data *data;
185-
Elf_Scn *sec;
186-
187-
/* Initialize for the sake of all error paths below. */
188-
*paddrs = NULL;
189-
*pcount = 0;
190-
191-
/* get __mcount_loc */
192-
sec = elf_section_by_name(btfe->elf, &btfe->ehdr, &shdr_mcount,
193-
"__mcount_loc", NULL);
194-
if (!sec) {
195-
if (btf_elf__verbose) {
196-
printf("%s: '%s' doesn't have __mcount_loc section\n", __func__,
197-
btfe->filename);
198-
}
199-
return 0;
200-
}
201-
202-
data = elf_getdata(sec, NULL);
203-
if (!data) {
204-
fprintf(stderr, "Failed to data for __mcount_loc section.\n");
205-
return -1;
206-
}
207-
208-
/* Get address size from processed file's ELF class. */
209-
addr_size = gelf_getclass(btfe->elf) == ELFCLASS32 ? 4 : 8;
210-
211-
count = data->d_size / addr_size;
212-
213-
addrs = malloc(count * sizeof(addrs[0]));
214-
if (!addrs) {
215-
fprintf(stderr, "Failed to allocate memory for ftrace addresses.\n");
216-
return -1;
217-
}
218-
219-
if (addr_size == sizeof(__u64)) {
220-
memcpy(addrs, data->d_buf, count * addr_size);
221-
} else {
222-
for (i = 0; i < count; i++)
223-
addrs[i] = (__u64) *((__u32 *) (data->d_buf + i * addr_size));
224-
}
225-
226-
/*
227-
* We get Elf object from dwfl_module_getelf function,
228-
* which performs all possible relocations, including
229-
* __mcount_loc section.
230-
*
231-
* So addrs array now contains relocated values, which
232-
* we need take into account when we compare them to
233-
* functions values, see comment in setup_functions
234-
* function.
235-
*/
236-
*paddrs = addrs;
237-
*pcount = count;
238-
return 0;
239-
}
240-
241-
static int is_ftrace_func(struct elf_function *func, __u64 *addrs, __u64 count)
242-
{
243-
__u64 start = func->addr;
244-
__u64 addr, end = func->addr + func->size;
245-
246-
/*
247-
* The invariant here is addr[r] that is the smallest address
248-
* that is >= than function start addr. Except the corner case
249-
* where there is no such r, but for that we have a final check
250-
* in the return.
251-
*/
252-
size_t l = 0, r = count - 1, m;
253-
254-
/* make sure we don't use invalid r */
255-
if (count == 0)
256-
return false;
257-
258-
while (l < r) {
259-
m = l + (r - l) / 2;
260-
addr = addrs[m];
261-
262-
if (addr >= start) {
263-
/* we satisfy invariant, so tighten r */
264-
r = m;
265-
} else {
266-
/* m is not good enough as l, maybe m + 1 will be */
267-
l = m + 1;
268-
}
269-
}
270-
271-
return start <= addrs[r] && addrs[r] < end;
272-
}
273-
274-
static int setup_functions(struct btf_elf *btfe, struct funcs_layout *fl)
275-
{
276-
__u64 *addrs, count, i;
277-
int functions_valid = 0;
278-
bool kmod = false;
279-
280-
/*
281-
* Check if we are processing vmlinux image and
282-
* get mcount data if it's detected.
283-
*/
284-
if (get_vmlinux_addrs(btfe, fl, &addrs, &count))
285-
return -1;
286-
287-
/*
288-
* Check if we are processing kernel module and
289-
* get mcount data if it's detected.
290-
*/
291-
if (!addrs) {
292-
if (get_kmod_addrs(btfe, &addrs, &count))
293-
return -1;
294-
kmod = true;
295-
}
296-
297-
if (!addrs) {
298-
if (btf_elf__verbose)
299-
printf("ftrace symbols not detected, falling back to DWARF data\n");
300-
delete_functions();
301-
return 0;
302-
}
303-
304-
qsort(addrs, count, sizeof(addrs[0]), addrs_cmp);
305-
qsort(functions, functions_cnt, sizeof(functions[0]), functions_cmp);
306-
307-
/*
308-
* Let's got through all collected functions and filter
309-
* out those that are not in ftrace.
310-
*/
311-
for (i = 0; i < functions_cnt; i++) {
312-
struct elf_function *func = &functions[i];
313-
/*
314-
* For vmlinux image both addrs[x] and functions[x]::addr
315-
* values are final address and are comparable.
316-
*
317-
* For kernel module addrs[x] is final address, but
318-
* functions[x]::addr is relative address within section
319-
* and needs to be relocated by adding sh_addr.
320-
*/
321-
if (kmod)
322-
func->addr += func->sh_addr;
323-
324-
/* Make sure function is within ftrace addresses. */
325-
if (is_ftrace_func(func, addrs, count)) {
326-
/*
327-
* We iterate over sorted array, so we can easily skip
328-
* not valid item and move following valid field into
329-
* its place, and still keep the 'new' array sorted.
330-
*/
331-
if (i != functions_valid)
332-
functions[functions_valid] = functions[i];
333-
functions_valid++;
334-
}
335-
}
336-
337-
functions_cnt = functions_valid;
338-
free(addrs);
339-
340-
if (btf_elf__verbose)
341-
printf("Found %d functions!\n", functions_cnt);
342-
return 0;
343-
}
344-
34588
static struct elf_function *find_function(const struct btf_elf *btfe,
34689
const char *name)
34790
{
@@ -620,23 +363,8 @@ static int collect_percpu_var(struct btf_elf *btfe, GElf_Sym *sym,
620363
return 0;
621364
}
622365

623-
static void collect_symbol(GElf_Sym *sym, struct funcs_layout *fl,
624-
size_t sym_sec_idx)
625-
{
626-
if (!fl->mcount_start &&
627-
!strcmp("__start_mcount_loc", elf_sym__name(sym, btfe->symtab))) {
628-
fl->mcount_start = sym->st_value;
629-
fl->mcount_sec_idx = sym_sec_idx;
630-
}
631-
632-
if (!fl->mcount_stop &&
633-
!strcmp("__stop_mcount_loc", elf_sym__name(sym, btfe->symtab)))
634-
fl->mcount_stop = sym->st_value;
635-
}
636-
637366
static int collect_symbols(struct btf_elf *btfe, bool collect_percpu_vars)
638367
{
639-
struct funcs_layout fl = { };
640368
Elf32_Word sym_sec_idx;
641369
uint32_t core_id;
642370
GElf_Sym sym;
@@ -648,9 +376,8 @@ static int collect_symbols(struct btf_elf *btfe, bool collect_percpu_vars)
648376
elf_symtab__for_each_symbol_index(btfe->symtab, core_id, sym, sym_sec_idx) {
649377
if (collect_percpu_vars && collect_percpu_var(btfe, &sym, sym_sec_idx))
650378
return -1;
651-
if (collect_function(btfe, &sym, sym_sec_idx))
379+
if (collect_function(btfe, &sym))
652380
return -1;
653-
collect_symbol(&sym, &fl, sym_sec_idx);
654381
}
655382

656383
if (collect_percpu_vars) {
@@ -661,9 +388,11 @@ static int collect_symbols(struct btf_elf *btfe, bool collect_percpu_vars)
661388
printf("Found %d per-CPU variables!\n", percpu_var_cnt);
662389
}
663390

664-
if (functions_cnt && setup_functions(btfe, &fl)) {
665-
fprintf(stderr, "Failed to filter DWARF functions\n");
666-
return -1;
391+
if (functions_cnt) {
392+
qsort(functions, functions_cnt, sizeof(functions[0]),
393+
functions_cmp);
394+
if (btf_elf__verbose)
395+
printf("Found %d functions!\n", functions_cnt);
667396
}
668397

669398
return 0;

0 commit comments

Comments
 (0)