Re: [PATCH dwarves] dwarf_loader: handle subprogram ret type with abstract_origin properly

From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Yonghong Song <yhs@fb.com>
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 11:57:38 -0300	[thread overview]
Message-ID: <YGcw4iq9QNkFFfyt@kernel.org> (raw)
In-Reply-To: <YGckYjyfxfNLzc34@kernel.org>

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

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
