From: Yonghong Song <yhs@fb.com>
To: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: David Blaikie <dblaikie@gmail.com>, <dwarves@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Bill Wendling <morbo@google.com>, bpf <bpf@vger.kernel.org>,
<kernel-team@fb.com>, Nick Desaulniers <ndesaulniers@google.com>,
Jiri Olsa <jolsa@kernel.org>
Subject: Re: [PATCH dwarves] dwarf_loader: handle subprogram ret type with abstract_origin properly
Date: Fri, 2 Apr 2021 10:42:21 -0700 [thread overview]
Message-ID: <82dfd420-96f9-aedc-6cdc-bf20042455db@fb.com> (raw)
In-Reply-To: <2d55d22b-d136-82b9-6a0f-8b09eeef7047@fb.com>
On 4/2/21 10:23 AM, Yonghong Song wrote:
>
>
> On 4/2/21 7:57 AM, Arnaldo Carvalho de Melo wrote:
>> Em Fri, Apr 02, 2021 at 11:04:18AM -0300, Arnaldo Carvalho de Melo
>> escreveu:
>>> Em Thu, Apr 01, 2021 at 05:00:46PM -0700, David Blaikie escreveu:
>>>> On Thu, Apr 1, 2021 at 4:41 PM Yonghong Song <yhs@fb.com> wrote:
>>>>> On 4/1/21 3:27 PM, David Blaikie wrote:
>>>>>> Though people may come up with novel uses of DWARF features. What
>>>>>> would
>>>>>> happen if this constraint were violated/what's your motivation for
>>>>>> asking (I don't quite understand the connection between test_progs
>>>>>> failure description, and this question)
>>
>>>>> I have some codes to check the tag associated with abstract_origin
>>>>> for a subprogram must be a subprogram. Through experiment, I didn't
>>>>> see a violation, so I wonder that I can get confirmation from you
>>>>> and then I may delete that code.
>>
>>>>> The test_progs failure exposed the bug, that is all.
>>
>>>>> pahole cannot handle all weird usages of dwarf, so I think pahole
>>>>> is fine only to support well-formed dwarf.
>>
>>>> Sounds good. Thanks for the context!
>>
>>> David, since you took the time to go thru the changes and to agree that
>>> Yonghong's fix is good, can I add a:
>>
>>> Acked-by: David Blaikie <dblaikie@gmail.com>
>>
>>> to this patch?
>>
>>> Maybe even a:
>>
>>> Reviewed-by: David Blaikie <dblaikie@gmail.com>
>>
>> What I have is at tmp.master, please take a look and check that
>> everything is ok, the only think I wished to fix but I think can be left
>> for later is in the tmp.master branch at:
>>
>> git://git.kernel.org/pub/scm/devel/pahole/pahole.git tmp.master
>
> Thanks. I checked out the branch and did some testing with latest clang
> trunk (just pulled in).
>
> With kernel LTO note support, I tested gcc non-lto, and llvm-lto mode,
> it works fine.
>
> Without kernel LTO note support, I tested
> gcc non-lto <=== ok
> llvm non-lto <=== not ok
> llvm lto <=== ok
>
> Surprisingly llvm non-lto vmlinux had the same "tcp_slow_start" issue.
> Some previous version of clang does not have this issue.
> I double checked the dwarfdump and it is indeed has the same reason
> for lto vmlinux. I checked abbrev section and there is no cross-cu
> references.
>
> That means we need to adapt this patch
> dwarf_loader: Handle subprogram ret type with abstract_origin properly
> for non merging case as well.
> The previous patch fixed lto subprogram abstract_origin issue,
> I will submit a followup patch for this.
Actually, the change is pretty simple,
diff --git a/dwarf_loader.c b/dwarf_loader.c
index 5dea837..82d7131 100644
--- a/dwarf_loader.c
+++ b/dwarf_loader.c
@@ -2323,7 +2323,11 @@ static int die__process_and_recode(Dwarf_Die
*die, struct cu *cu)
int ret = die__process(die, cu);
if (ret != 0)
return ret;
- return cu__recode_dwarf_types(cu);
+ ret = cu__recode_dwarf_types(cu);
+ if (ret != 0)
+ return ret;
+
+ return cu__resolve_func_ret_types(cu);
}
Arnaldo, do you just want to fold into previous patches, or
you want me to submit a new one?
>
>>
>> I did some testing for this ret type fix:
>>
>> https://git.kernel.org/pub/scm/devel/pahole/pahole.git/commit/?h=tmp.master
>>
>>
>> And for the LTO ELF notes:
>>
>> https://git.kernel.org/pub/scm/devel/pahole/pahole.git/commit/?h=tmp.master&id=7a79d2d7a573a863aa36fd06f540fe9fa824db4e
>>
>>
>> The only remaining thing, which I think can be left for 1.22 is:
>>
>> [acme@five pahole]$ btfdiff vmlinux.clang.thin.LTO
>> vmlinux.clang.thin.LTO vmlinux.clang.thin.LTO+ELF_note
>> [acme@five pahole]$ btfdiff vmlinux.clang.thin.LTO+ELF_note
>> --- /tmp/btfdiff.dwarf.CtLJpQ 2021-04-02 11:55:09.658433186 -0300
>> +++ /tmp/btfdiff.btf.d3L3vy 2021-04-02 11:55:09.925439277 -0300
>> @@ -67255,7 +67255,7 @@ struct cpu_rmap {
>> struct {
>> u16 index; /* 16 2 */
>> u16 dist; /* 18 2 */
>> - } near[0]; /* 16 0 */
>> + } near[]; /* 16 0 */
>>
>> /* size: 16, cachelines: 1, members: 5 */
>> /* last cacheline: 16 bytes */
>> @@ -101181,7 +101181,7 @@ struct linux_efi_memreserve {
>> struct {
>> phys_addr_t base; /* 16 8 */
>> phys_addr_t size; /* 24 8 */
>> - } entry[0]; /* 16 0 */
>> + } entry[]; /* 16 0 */
>>
>> /* size: 16, cachelines: 1, members: 4 */
>> /* last cacheline: 16 bytes */
>> @@ -113516,7 +113516,7 @@ struct netlink_policy_dump_state {
>> struct {
>> const struct nla_policy * policy; /* 16 8 */
>> unsigned int maxtype; /* 24 4 */
>> - } policies[0]; /* 16 0 */
>> + } policies[]; /* 16 0 */
>>
>> /* size: 16, cachelines: 1, members: 4 */
>> /* sum members: 12, holes: 1, sum holes: 4 */
>> [acme@five pahole]$
>>
>> - Arnaldo
>>
next prev parent reply other threads:[~2021-04-02 17:42 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-01 21:36 [PATCH dwarves] dwarf_loader: handle subprogram ret type with abstract_origin properly Yonghong Song
2021-04-01 21:41 ` Yonghong Song
2021-04-01 22:30 ` David Blaikie
[not found] ` <CAENS6EsZ5OX9o=Cn5L1jmx8ucR9siEWbGYiYHCUWuZjLyP3E7Q@mail.gmail.com>
2021-04-01 23:40 ` Yonghong Song
2021-04-02 0:00 ` David Blaikie
2021-04-02 14:04 ` Arnaldo Carvalho de Melo
2021-04-02 14:57 ` Arnaldo Carvalho de Melo
2021-04-02 17:23 ` Yonghong Song
2021-04-02 17:42 ` Yonghong Song [this message]
2021-04-02 18:08 ` Arnaldo
2021-04-02 19:01 ` Jiri Olsa
2021-04-02 19:41 ` Yonghong Song
2021-04-03 17:08 ` Arnaldo Carvalho de Melo
2021-04-04 17:22 ` Jiri Olsa
2021-04-07 14:54 ` Yonghong Song
2021-04-07 15:37 ` Arnaldo Carvalho de Melo
2021-04-07 15:40 ` [RFT] prepping up pahole 1.21, wanna test it? was " Arnaldo Carvalho de Melo
2021-04-07 22:53 ` Yonghong Song
2021-04-09 13:52 ` Arnaldo Carvalho de Melo
2021-04-08 21:23 ` Jiri Olsa
2021-04-09 13:51 ` Arnaldo Carvalho de Melo
2021-04-07 22:51 ` Yonghong Song
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