From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7B32013957E; Thu, 28 Aug 2025 06:52:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756363924; cv=none; b=QIchLcpNkafHypHtqlG2o0bkIzofOa9PcRyrl7T9UOqC2muuyoCFdRak3WcVEb1/ro7S0SW0u1dnQ+ZOKdFia0D/FuJo7PFFUbsPwVCgu0/fSZ0vkWkNm8qZayW9U3D30r3iBkwfYKHZIXPNXxZ7R9r3DW8VuAoXPopQHee00YY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756363924; c=relaxed/simple; bh=fCVOV/aa9kx2YHBGI2L4+nLbGmu/QgZ/y4517/LJAMU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=e+YxYvawtnCpns+WGESwbfXlw4YLW1zrDnrgyBtBkMhWaaK9YrL+TAM4sl18gMNAueyCqj+R4TrJFtVSA9dxAAaD9BdAI4zvSMm3cUFWz83GLieff00YECMbxcLEUa8XAvsQxVuuAHfUkYTIEmPn1+yiJgwdpLXy3u6q9n8MOuU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Z0bgw7Qr; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Z0bgw7Qr" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 81CCFC4CEEB; Thu, 28 Aug 2025 06:52:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1756363924; bh=fCVOV/aa9kx2YHBGI2L4+nLbGmu/QgZ/y4517/LJAMU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Z0bgw7Qr3AD2hv+fsiJGK8Ys6ytPdZ7CMfQua6XlwiwoBuwGF0scXSJqL7UxqTSbS +lhEMGZojY5wQpppzYa9rkNolKrSZ5ikVGA5hhYSygWZSYiBD3ErGekt6ao27wELb8 oL7FNWkSj+SrI7gpEJ56hrqqHSR5JCVtWu3r0HE5gNCNqcgB74gyCNuB5IwjVH3ezL 3Q51xbTuMPb3c1rA/2d7W09u0R8mKU/3sMyWiVi6Ic5AxjpuEu0gzlX3Xuj/UlbyQu OQ/jcKSxHmC0NSS3CJn1+05V/S12KsKjS2s5tqDy58HqLUsUiBacUqCkVnC7W6/raN sHuFtgg2u0tsQ== Date: Wed, 27 Aug 2025 23:52:02 -0700 From: Namhyung Kim To: Zecheng Li Cc: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , "Liang, Kan" , Masami Hiramatsu , Xu Liu , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 01/10] perf dwarf-aux: Use signed variable types in match_var_offset Message-ID: References: <20250825195412.223077-1-zecheng@google.com> <20250825195412.223077-2-zecheng@google.com> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20250825195412.223077-2-zecheng@google.com> On Mon, Aug 25, 2025 at 07:54:03PM +0000, Zecheng Li wrote: > match_var_offset compares address offsets to determine if an access > falls within a variable's bounds. The offsets involved for those > relative to base registers from DW_OP_breg can be negative. > > The current implementation uses unsigned types (u64) for these offsets, > which rejects almost all negative values. Right, I thought it cannot get negative offsets except for stack access (e.g. fbreg). But it turns out that container_of() trick can generate them with optimizing compilers. > > Change the signature of match_var_offset to use signed types (s64). This > ensures correct behavior when addr_offset or addr_type are negative. > > Signed-off-by: Zecheng Li I've confirmed it produced slightly better results on my test sets. Reviewed-by: Namhyung Kim Thanks, Namhyung > --- > tools/perf/util/dwarf-aux.c | 11 ++++++----- > 1 file changed, 6 insertions(+), 5 deletions(-) > > diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c > index 559c953ca172..920054425578 100644 > --- a/tools/perf/util/dwarf-aux.c > +++ b/tools/perf/util/dwarf-aux.c > @@ -1388,18 +1388,19 @@ struct find_var_data { > #define DWARF_OP_DIRECT_REGS 32 > > static bool match_var_offset(Dwarf_Die *die_mem, struct find_var_data *data, > - u64 addr_offset, u64 addr_type, bool is_pointer) > + s64 addr_offset, s64 addr_type, bool is_pointer) > { > Dwarf_Die type_die; > Dwarf_Word size; > + s64 offset = addr_offset - addr_type; > > - if (addr_offset == addr_type) { > + if (offset == 0) { > /* Update offset relative to the start of the variable */ > data->offset = 0; > return true; > } > > - if (addr_offset < addr_type) > + if (offset < 0) > return false; > > if (die_get_real_type(die_mem, &type_die) == NULL) > @@ -1414,11 +1415,11 @@ static bool match_var_offset(Dwarf_Die *die_mem, struct find_var_data *data, > if (dwarf_aggregate_size(&type_die, &size) < 0) > return false; > > - if (addr_offset >= addr_type + size) > + if ((u64)offset >= size) > return false; > > /* Update offset relative to the start of the variable */ > - data->offset = addr_offset - addr_type; > + data->offset = offset; > return true; > } > > -- > 2.51.0.261.g7ce5a0a67e-goog >