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Thu, 24 Sep 2026 09:20:12 -0700 (PDT) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Thu, 24 Sep 2026 16:20:08 +0000 Message-Id: Cc: "Alexei Starovoitov" , "Andrii Nakryiko" , , Subject: Re: [PATCH dwarves v2 0/3] pahole: Fix arm64 argument register allocation From: "Alexei Starovoitov" To: "Alan Maguire" , "Yonghong Song" , "Arnaldo Carvalho de Melo" , X-Mailer: aerc 0.20.1-349-gb940a4174a3e-dirty References: <20260917164038.1576763-1-yonghong.song@linux.dev> <09dbfeea-a4d1-4b7a-b92e-bcf8c4cdabb4@oracle.com> In-Reply-To: <09dbfeea-a4d1-4b7a-b92e-bcf8c4cdabb4@oracle.com> On Thu Sep 24, 2026 at 4:15 PM UTC, Alan Maguire wrote: > On 17/09/2026 17:40, Yonghong Song wrote: >>=20 >> The arm64 ABI starts an argument twice the register size on an even-numb= ered >> argument register, leaving a hole when the next free register is an odd = one: >>=20 >> u64 f(u64 a, __int128 v, u64 b); >>=20 >> passes a in x0, v in x2:x3 -- skipping x1 -- and b in x4. pahole did no= t >> model the hole, so b looked like it was in an unexpected register and th= e >> whole function was dropped from BTF. Patch 1 skips the register the ABI >> leaves behind, patch 3 adds a test for it. Only arm64 has this rule; th= e >> other architectures are unaffected. >>=20 >> Patch 2 is a small follow-up. Floating point and vector arguments are >> allocated from a register bank of their own -- v0-v7 on arm64, xmm0-xmm7= on >> x86-64 -- so a wide one never occupies a general purpose register pair a= nd >> must not trigger the even-register rule either. It does not change the = BTF >> emitted today, because such an argument still advances the general purpo= se >> register index by its own size, so it comes with no test of its own; it >> keeps the alignment rule scoped to the bank it applies to. >> > > one small issue here; we record alignment for structs from DW_AT_align > in associated tags; we should ensure that we utilize that alignment > where available. However it's a bit broken in that we don't appear > to record alignment for typedefs, just structs. > > I think we can tackle that with a followup though; unless anyone objects = I'll > land these patches later today. Pls go ahead. Also pls land LOC* things too, so you can post the rest of LOC* kernel bits= . So that everything lands and ready for the merge window in a couple weeks. People will be traveling soon, so the sooner the better.