From: Jiri Slaby <jirislaby@kernel.org>
To: "Michal Suchánek" <msuchanek@suse.de>, "Jiri Olsa" <jolsa@redhat.com>
Cc: Yonghong Song <yhs@fb.com>,
linux-kernel@vger.kernel.org, Martin KaFai Lau <kafai@fb.com>,
"David S. Miller" <davem@davemloft.net>,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
David Ahern <dsahern@kernel.org>,
Jakub Kicinski <kuba@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Song Liu <songliubraving@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
netdev@vger.kernel.org, bpf@vger.kernel.org,
Jiri Olsa <jolsa@kernel.org>,
Jesper Dangaard Brouer <brouer@redhat.com>,
dwarves@vger.kernel.org,
Arnaldo Carvalho de Melo <acme@redhat.com>
Subject: Re: linux-next failing build due to missing cubictcp_state symbol
Date: Mon, 3 May 2021 10:59:44 +0200 [thread overview]
Message-ID: <cbaf50c3-c85d-9239-0b37-c88e8cbed8c8@kernel.org> (raw)
In-Reply-To: <4e051459-8532-7b61-c815-f3435767f8a0@kernel.org>
[-- Attachment #1: Type: text/plain, Size: 2383 bytes --]
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.
> regards,--
js
suse labs
[-- Attachment #2: ppc64-opd-fix.patch --]
[-- Type: text/x-patch, Size: 1686 bytes --]
From: Jiri Slaby <jslaby@suse.cz>
Subject: ppc64: .opd section fix
Patch-mainline: submitted 2021/05/03
Functions in the .opd section should be considered valid too. Otherwise,
pahole cannot produce a .BTF section from vmlinux and kernel build
fails on ppc64.
---
btf_encoder.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -31,6 +31,8 @@ struct funcs_layout {
unsigned long mcount_start;
unsigned long mcount_stop;
unsigned long mcount_sec_idx;
+ unsigned long opd_start;
+ unsigned long opd_stop;
};
struct elf_function {
@@ -271,11 +273,24 @@ static int is_ftrace_func(struct elf_fun
return start <= addrs[r] && addrs[r] < end;
}
+static int is_opd_func(struct elf_function *func, struct funcs_layout *fl)
+{
+ return fl->opd_start <= func->addr && func->addr < fl->opd_stop;
+}
+
static int setup_functions(struct btf_elf *btfe, struct funcs_layout *fl)
{
__u64 *addrs, count, i;
int functions_valid = 0;
bool kmod = false;
+ GElf_Shdr shdr;
+ Elf_Scn *sec;
+
+ sec = elf_section_by_name(btfe->elf, &btfe->ehdr, &shdr, ".opd", NULL);
+ if (sec) {
+ fl->opd_start = shdr.sh_addr;
+ fl->opd_stop = shdr.sh_addr + shdr.sh_size;
+ }
/*
* Check if we are processing vmlinux image and
@@ -322,7 +337,8 @@ static int setup_functions(struct btf_el
func->addr += func->sh_addr;
/* Make sure function is within ftrace addresses. */
- if (is_ftrace_func(func, addrs, count)) {
+ if (is_opd_func(func, fl) ||
+ 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
next parent reply other threads:[~2021-05-03 8:59 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
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[not found] ` <20210425111545.GL15381@kitsune.suse.cz>
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[not found] ` <6c14f3c8-7474-9f3f-b4a6-2966cb19e1ed@kernel.org>
[not found] ` <4e051459-8532-7b61-c815-f3435767f8a0@kernel.org>
2021-05-03 8:59 ` Jiri Slaby [this message]
2021-05-03 10:08 ` linux-next failing build due to missing cubictcp_state symbol Jiri Olsa
2021-05-03 16:46 ` Michal Suchánek
2021-05-03 16:58 ` Michal Suchánek
2021-05-04 6:41 ` Jiri Slaby
2021-05-06 5:31 ` Martin KaFai Lau
2021-05-06 13:16 ` Jiri Olsa
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