On 03. 05. 21, 12:08, Jiri Olsa wrote:
On Mon, May 03, 2021 at 10:59:44AM +0200, Jiri Slaby wrote:
CCing pahole people.
On 03. 05. 21, 9:59, Jiri Slaby wrote:
On 03. 05. 21, 8:11, Jiri Slaby wrote:
looks like vfs_truncate did not get into BTF data,
I'll try to reproduce
_None_ of the functions are generated by pahole -J from
debuginfo on ppc64. debuginfo appears to be correct. Neither
pahole -J fs/open.o works correctly. collect_functions in
dwarves seems to be defunct on ppc64... "functions" array is
bogus (so find_function -- the bsearch -- fails).
It's not that bogus. I forgot an asterisk:
#0 find_function (btfe=0x100269f80, name=0x10024631c
"stream_open") at
/usr/src/debug/dwarves-1.21-1.1.ppc64/btf_encoder.c:350
(gdb) p (*functions)@84
$5 = {{name = 0x7ffff68e0922 ".__se_compat_sys_ftruncate", addr
= 75232, size = 72, sh_addr = 65536, generated = false}, {
name = 0x7ffff68e019e ".__se_compat_sys_open", addr = 80592,
size = 216, sh_addr = 65536, generated = false}, {
name = 0x7ffff68e0076 ".__se_compat_sys_openat", addr =
80816, size = 232, sh_addr = 65536, generated = false}, {
name = 0x7ffff68e0908 ".__se_compat_sys_truncate", addr =
74304, size = 100, sh_addr = 65536, generated = false}, {
...
name = 0x7ffff68e0808 ".stream_open", addr = 65824, size =
72, sh_addr = 65536, generated = false}, {
...
name = 0x7ffff68e0751 ".vfs_truncate", addr = 73392, size =
544, sh_addr = 65536, generated = false}}
The dot makes the difference, of course. The question is why is it
there? I keep looking into it. Only if someone has an immediate
idea...
Well, .vfs_truncate is in .text (and contains an ._mcount call). And
vfs_truncate is in .opd (w/o an ._mcount call). Since setup_functions
excludes all functions without the ._mcount call, is_ftrace_func later
returns false for such functions and they are filtered before the BTF
processing.
Technically, get_vmlinux_addrs looks at a list of functions between
__start_mcount_loc and __stop_mcount_loc and considers only the listed.
I don't know what the correct fix is (exclude .opd functions from the
filter?). Neither why cross compiler doesn't fail, nor why ebi v2 avoids
this too.
Attaching a patch for pahole which fixes the issue, but I have no idea
whether it is the right fix at all.
hi,
we're considering to disable ftrace filter completely,
I guess that would solve this issue for ppc as well
https://lore.kernel.org/bpf/20210501001653.x3b4rk4vk4iqv3n7@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
Right, the attached patch fixes it for me too.
--
js
>From b0128f1ec6a234c5b40c40d73d55708d34f1a428 Mon Sep 17 00:00:00 2001
From: Jiri Slaby <jslaby@xxxxxxx>
Date: Tue, 4 May 2021 08:09:50 +0200
Subject: [PATCH] remove ftrace filter
Functions in the .opd section on ppc64 are currently ignored as they
don't contain mcount calls -- they are excluded by the ftrace filter.
Therefore, pahole cannot produce a .BTF section from vmlinux and kernel
build fails on ppc64.
Remove the ftrace filter completely as was discussed:
https://lore.kernel.org/bpf/20210501001653.x3b4rk4vk4iqv3n7@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
https://lore.kernel.org/bpf/YI%2FLgjLxo9VCN%2Fd+@krava/
---
btf_encoder.c | 272 +-------------------------------------------------
1 file changed, 5 insertions(+), 267 deletions(-)
diff --git a/btf_encoder.c b/btf_encoder.c
index 80e896961d4e..ba83bb088efa 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -27,17 +27,8 @@
*/
#define KSYM_NAME_LEN 128
-struct funcs_layout {
- unsigned long mcount_start;
- unsigned long mcount_stop;
- unsigned long mcount_sec_idx;
-};
-
struct elf_function {
const char *name;
- unsigned long addr;
- unsigned long size;
- unsigned long sh_addr;
bool generated;
};
@@ -98,250 +89,11 @@ static int collect_function(struct btf_elf *btfe, GElf_Sym *sym,
}
functions[functions_cnt].name = name;
- functions[functions_cnt].addr = elf_sym__value(sym);
- functions[functions_cnt].size = elf_sym__size(sym);
- functions[functions_cnt].sh_addr = sh.sh_addr;
functions[functions_cnt].generated = false;
functions_cnt++;
return 0;
}
-static int addrs_cmp(const void *_a, const void *_b)
-{
- const __u64 *a = _a;
- const __u64 *b = _b;
-
- if (*a == *b)
- return 0;
- return *a < *b ? -1 : 1;
-}
-
-static int get_vmlinux_addrs(struct btf_elf *btfe, struct funcs_layout *fl,
- __u64 **paddrs, __u64 *pcount)
-{
- __u64 *addrs, count, offset;
- unsigned int addr_size, i;
- Elf_Data *data;
- GElf_Shdr shdr;
- Elf_Scn *sec;
-
- /* Initialize for the sake of all error paths below. */
- *paddrs = NULL;
- *pcount = 0;
-
- if (!fl->mcount_start || !fl->mcount_stop)
- return 0;
-
- /*
- * Find mcount addressed marked by __start_mcount_loc
- * and __stop_mcount_loc symbols and load them into
- * sorted array.
- */
- sec = elf_getscn(btfe->elf, fl->mcount_sec_idx);
- if (!sec || !gelf_getshdr(sec, &shdr)) {
- fprintf(stderr, "Failed to get section(%lu) header.\n",
- fl->mcount_sec_idx);
- return -1;
- }
-
- /* Get address size from processed file's ELF class. */
- addr_size = gelf_getclass(btfe->elf) == ELFCLASS32 ? 4 : 8;
-
- offset = fl->mcount_start - shdr.sh_addr;
- count = (fl->mcount_stop - fl->mcount_start) / addr_size;
-
- data = elf_getdata(sec, 0);
- if (!data) {
- fprintf(stderr, "Failed to get section(%lu) data.\n",
- fl->mcount_sec_idx);
- return -1;
- }
-
- addrs = malloc(count * sizeof(addrs[0]));
- if (!addrs) {
- fprintf(stderr, "Failed to allocate memory for ftrace addresses.\n");
- return -1;
- }
-
- if (addr_size == sizeof(__u64)) {
- memcpy(addrs, data->d_buf + offset, count * addr_size);
- } else {
- for (i = 0; i < count; i++)
- addrs[i] = (__u64) *((__u32 *) (data->d_buf + offset + i * addr_size));
- }
-
- *paddrs = addrs;
- *pcount = count;
- return 0;
-}
-
-static int
-get_kmod_addrs(struct btf_elf *btfe, __u64 **paddrs, __u64 *pcount)
-{
- __u64 *addrs, count;
- unsigned int addr_size, i;
- GElf_Shdr shdr_mcount;
- Elf_Data *data;
- Elf_Scn *sec;
-
- /* Initialize for the sake of all error paths below. */
- *paddrs = NULL;
- *pcount = 0;
-
- /* get __mcount_loc */
- sec = elf_section_by_name(btfe->elf, &btfe->ehdr, &shdr_mcount,
- "__mcount_loc", NULL);
- if (!sec) {
- if (btf_elf__verbose) {
- printf("%s: '%s' doesn't have __mcount_loc section\n", __func__,
- btfe->filename);
- }
- return 0;
- }
-
- data = elf_getdata(sec, NULL);
- if (!data) {
- fprintf(stderr, "Failed to data for __mcount_loc section.\n");
- return -1;
- }
-
- /* Get address size from processed file's ELF class. */
- addr_size = gelf_getclass(btfe->elf) == ELFCLASS32 ? 4 : 8;
-
- count = data->d_size / addr_size;
-
- addrs = malloc(count * sizeof(addrs[0]));
- if (!addrs) {
- fprintf(stderr, "Failed to allocate memory for ftrace addresses.\n");
- return -1;
- }
-
- if (addr_size == sizeof(__u64)) {
- memcpy(addrs, data->d_buf, count * addr_size);
- } else {
- for (i = 0; i < count; i++)
- addrs[i] = (__u64) *((__u32 *) (data->d_buf + i * addr_size));
- }
-
- /*
- * We get Elf object from dwfl_module_getelf function,
- * which performs all possible relocations, including
- * __mcount_loc section.
- *
- * So addrs array now contains relocated values, which
- * we need take into account when we compare them to
- * functions values, see comment in setup_functions
- * function.
- */
- *paddrs = addrs;
- *pcount = count;
- return 0;
-}
-
-static int is_ftrace_func(struct elf_function *func, __u64 *addrs, __u64 count)
-{
- __u64 start = func->addr;
- __u64 addr, end = func->addr + func->size;
-
- /*
- * The invariant here is addr[r] that is the smallest address
- * that is >= than function start addr. Except the corner case
- * where there is no such r, but for that we have a final check
- * in the return.
- */
- size_t l = 0, r = count - 1, m;
-
- /* make sure we don't use invalid r */
- if (count == 0)
- return false;
-
- while (l < r) {
- m = l + (r - l) / 2;
- addr = addrs[m];
-
- if (addr >= start) {
- /* we satisfy invariant, so tighten r */
- r = m;
- } else {
- /* m is not good enough as l, maybe m + 1 will be */
- l = m + 1;
- }
- }
-
- return start <= addrs[r] && addrs[r] < end;
-}
-
-static int setup_functions(struct btf_elf *btfe, struct funcs_layout *fl)
-{
- __u64 *addrs, count, i;
- int functions_valid = 0;
- bool kmod = false;
-
- /*
- * Check if we are processing vmlinux image and
- * get mcount data if it's detected.
- */
- if (get_vmlinux_addrs(btfe, fl, &addrs, &count))
- return -1;
-
- /*
- * Check if we are processing kernel module and
- * get mcount data if it's detected.
- */
- if (!addrs) {
- if (get_kmod_addrs(btfe, &addrs, &count))
- return -1;
- kmod = true;
- }
-
- if (!addrs) {
- if (btf_elf__verbose)
- printf("ftrace symbols not detected, falling back to DWARF data\n");
- delete_functions();
- return 0;
- }
-
- qsort(addrs, count, sizeof(addrs[0]), addrs_cmp);
- qsort(functions, functions_cnt, sizeof(functions[0]), functions_cmp);
-
- /*
- * Let's got through all collected functions and filter
- * out those that are not in ftrace.
- */
- for (i = 0; i < functions_cnt; i++) {
- struct elf_function *func = &functions[i];
- /*
- * For vmlinux image both addrs[x] and functions[x]::addr
- * values are final address and are comparable.
- *
- * For kernel module addrs[x] is final address, but
- * functions[x]::addr is relative address within section
- * and needs to be relocated by adding sh_addr.
- */
- if (kmod)
- func->addr += func->sh_addr;
-
- /* Make sure function is within ftrace addresses. */
- if (is_ftrace_func(func, addrs, count)) {
- /*
- * We iterate over sorted array, so we can easily skip
- * not valid item and move following valid field into
- * its place, and still keep the 'new' array sorted.
- */
- if (i != functions_valid)
- functions[functions_valid] = functions[i];
- functions_valid++;
- }
- }
-
- functions_cnt = functions_valid;
- free(addrs);
-
- if (btf_elf__verbose)
- printf("Found %d functions!\n", functions_cnt);
- return 0;
-}
-
static struct elf_function *find_function(const struct btf_elf *btfe,
const char *name)
{
@@ -620,23 +372,8 @@ static int collect_percpu_var(struct btf_elf *btfe, GElf_Sym *sym,
return 0;
}
-static void collect_symbol(GElf_Sym *sym, struct funcs_layout *fl,
- size_t sym_sec_idx)
-{
- if (!fl->mcount_start &&
- !strcmp("__start_mcount_loc", elf_sym__name(sym, btfe->symtab))) {
- fl->mcount_start = sym->st_value;
- fl->mcount_sec_idx = sym_sec_idx;
- }
-
- if (!fl->mcount_stop &&
- !strcmp("__stop_mcount_loc", elf_sym__name(sym, btfe->symtab)))
- fl->mcount_stop = sym->st_value;
-}
-
static int collect_symbols(struct btf_elf *btfe, bool collect_percpu_vars)
{
- struct funcs_layout fl = { };
Elf32_Word sym_sec_idx;
uint32_t core_id;
GElf_Sym sym;
@@ -650,7 +387,6 @@ static int collect_symbols(struct btf_elf *btfe, bool collect_percpu_vars)
return -1;
if (collect_function(btfe, &sym, sym_sec_idx))
return -1;
- collect_symbol(&sym, &fl, sym_sec_idx);
}
if (collect_percpu_vars) {
@@ -661,9 +397,11 @@ static int collect_symbols(struct btf_elf *btfe, bool collect_percpu_vars)
printf("Found %d per-CPU variables!\n", percpu_var_cnt);
}
- if (functions_cnt && setup_functions(btfe, &fl)) {
- fprintf(stderr, "Failed to filter DWARF functions\n");
- return -1;
+ if (functions_cnt) {
+ qsort(functions, functions_cnt, sizeof(functions[0]), functions_cmp);
+
+ if (btf_elf__verbose)
+ printf("Found %d functions!\n", functions_cnt);
}
return 0;
--
2.31.1
