linux-kernel - Re: [PATCH RFC 09/10] unwind: Introduce SFrame user space unwinding

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Date:   Thu, 9 Nov 2023 11:53:04 -0800
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Indu Bhagat <indu.bhagat@...cle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-perf-users@...r.kernel.org, Mark Brown <broonie@...nel.org>,
        linux-toolchains@...r.kernel.org
Subject: Re: [PATCH RFC 09/10] unwind: Introduce SFrame user space unwinding

On Thu, Nov 09, 2023 at 02:49:56PM -0500, Steven Rostedt wrote:
> On Thu, 9 Nov 2023 11:37:59 -0800
> Josh Poimboeuf <jpoimboe@...nel.org> wrote:
> 
> > > The structure SFrame FDE in SFRAME_VERSION_1 was unaligned on-disk.  We
> > > fixed that in SFRAME_VERSION_2 (Binutils 2.41) by adding some padding as you
> > > have already noted. For x86_64, its not an issue though, yes.  
> > 
> > Agreed.  I actually had v2 implemented but then realized my binutils was
> > older so I changed to v1 for testing.  But yeah, we can make v2 the
> > minimum.
> 
> Cool, my test box has binutils 2.41, so it should be good to go ;-)

You'll need something like this (untested!)

diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index b167c19497e5..f8b2a520a689 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -142,10 +142,8 @@ static int find_fre(struct sframe_section *sec, struct sframe_fde *fde,
 				break;
 		} else {
 			/* SFRAME_FDE_TYPE_PCMASK */
-#if 0 /* sframe v2 */
 			if (ip_off % fde->rep_size < fre_ip_off)
 				break;
-#endif
 		}
 
 		SFRAME_GET_USER_UNSIGNED(fre_info, f, 1);
@@ -304,7 +302,7 @@ int __sframe_add_section(struct sframe_file *file)
 		return -EFAULT;
 
 	if (shdr.preamble.magic != SFRAME_MAGIC ||
-	    shdr.preamble.version != SFRAME_VERSION_1 ||
+	    shdr.preamble.version != SFRAME_VERSION_2 ||
 	    (!shdr.preamble.flags & SFRAME_F_FDE_SORTED) ||
 	    shdr.auxhdr_len || !shdr.num_fdes || !shdr.num_fres ||
 	    shdr.fdes_off > shdr.fres_off) {
diff --git a/kernel/unwind/sframe.h b/kernel/unwind/sframe.h
index 1f91b696daf5..1adfc88b784d 100644
--- a/kernel/unwind/sframe.h
+++ b/kernel/unwind/sframe.h
@@ -125,10 +125,8 @@ struct sframe_fde {
 	u32 fres_off;
 	u32 fres_num;
 	u8  info;
-#if 0 /* TODO sframe v2 */
 	u8  rep_size;
 	u16 padding;
-#endif
 } __packed;
 
 /*