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[23.128.96.18]) by mx.google.com with ESMTP id j20si1235852ejt.403.2021.01.13.09.57.21; Wed, 13 Jan 2021 09:57:45 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=O5MT405b; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728236AbhAMRzr (ORCPT + 99 others); Wed, 13 Jan 2021 12:55:47 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53754 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727785AbhAMRzq (ORCPT ); Wed, 13 Jan 2021 12:55:46 -0500 Received: from mail-qk1-x72e.google.com (mail-qk1-x72e.google.com [IPv6:2607:f8b0:4864:20::72e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 08A1BC061786; Wed, 13 Jan 2021 09:55:06 -0800 (PST) Received: by mail-qk1-x72e.google.com with SMTP id 186so2989981qkj.3; Wed, 13 Jan 2021 09:55:05 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=+hfHoNO0I8KH/ocWW18bIfM/5TPtJSym5RVhTD/3ic4=; b=O5MT405bKjrTH7i3pchDFPTaWtmoF37VLhqyQWeF1I2s4knT4Q7H4qjAV29LVX+LOb ipTKy+j8dp/nErKfNOGKBJJ6id7b1GcJB/fMDTAbxfCJ6Uf4zqJa52vlZwghfEnTysrJ 8pItPKgLgj8qZRA6+VCv6zQUAt+f07+cPCno6FX3IqE+bz4Qi/uNIaKendURniZHRLNk clnJuG+cfKNFECa0H2OanZRxudh0FV2/aYKr8Ql04Gq7i+EZpe1OpPPTr3WlThEUxhrb XdbMlhoDsf9eOEvc0dYjk/JvWwb5e/yWakrNC/kyviUFTuPxzfqq1nt3qH3E50SigvHd 1KxQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=+hfHoNO0I8KH/ocWW18bIfM/5TPtJSym5RVhTD/3ic4=; b=cr1chDrLRGsDDcYZKi5JJJRqPtEdJBTI2F3ubyLkKDEFNFtzcLu1iCRxRjzyZfU73G PXzFV+02hPUaokgEx0O7H4KaDmugpFOd1H/Il6P/AqkGJ4qeuXv6cvq6wZ9Mvb1OMEnQ WV5IKUaYkwLMWJmyzWCxcLPb9oWfHczqBPsGHxpVSdf+vUkKi9Ot8aVz0EwAdPMITBwm Imp9mI+1yAntAC0WwId3nsrNRYUlSDmn1M7QnkkPoVKL7IPF74hK3Ffnt6lGfDrjwxYy 4ZjFEmSU5euD9TPt+OV0EO6ORJLOWDWMwKNBLJaj2bdm4bbi0mc/Pglu7smIuDJ2LQHi O35Q== X-Gm-Message-State: AOAM531dHh9/F0eKZ9hUBMdJnKk3wJnU3ymacEk6jy7NGDckEIHAb2jW EXroQe1/Ly1C242GkFIuJWc= X-Received: by 2002:a37:8d85:: with SMTP id p127mr3120897qkd.393.1610560505104; Wed, 13 Jan 2021 09:55:05 -0800 (PST) Received: from ubuntu-m3-large-x86 ([2604:1380:45f1:1d00::1]) by smtp.gmail.com with ESMTPSA id n14sm1385094qtr.9.2021.01.13.09.55.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 Jan 2021 09:55:04 -0800 (PST) Date: Wed, 13 Jan 2021 10:55:02 -0700 From: Nathan Chancellor To: Nick Desaulniers Cc: Masahiro Yamada , Andrew Morton , Sedat Dilek , linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com, linux-kbuild@vger.kernel.org, linux-arch@vger.kernel.org, Jakub Jelinek , Fangrui Song , Caroline Tice , Nick Clifton , Arvind Sankar Subject: Re: [PATCH v4 3/3] Kbuild: implement support for DWARF v5 Message-ID: <20210113175502.GC4158893@ubuntu-m3-large-x86> References: <20210113003235.716547-1-ndesaulniers@google.com> <20210113003235.716547-4-ndesaulniers@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210113003235.716547-4-ndesaulniers@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 12, 2021 at 04:32:35PM -0800, Nick Desaulniers wrote: > DWARF v5 is the latest standard of the DWARF debug info format. > > Feature detection of DWARF5 is onerous, especially given that we've > removed $(AS), so we must query $(CC) for DWARF5 assembler directive > support. GNU `as` only recently gained support for specifying > -gdwarf-5. > > The DWARF version of a binary can be validated with: > $ llvm-dwarfdump vmlinux | head -n 4 | grep version > or > $ readelf --debug-dump=info vmlinux 2>/dev/null | grep Version > > DWARF5 wins significantly in terms of size when mixed with compression > (CONFIG_DEBUG_INFO_COMPRESSED). > > 363M vmlinux.clang12.dwarf5.compressed > 434M vmlinux.clang12.dwarf4.compressed > 439M vmlinux.clang12.dwarf2.compressed > 457M vmlinux.clang12.dwarf5 > 536M vmlinux.clang12.dwarf4 > 548M vmlinux.clang12.dwarf2 > > 515M vmlinux.gcc10.2.dwarf5.compressed > 599M vmlinux.gcc10.2.dwarf4.compressed > 624M vmlinux.gcc10.2.dwarf2.compressed > 630M vmlinux.gcc10.2.dwarf5 > 765M vmlinux.gcc10.2.dwarf4 > 809M vmlinux.gcc10.2.dwarf2 > > Though the quality of debug info is harder to quantify; size is not a > proxy for quality. > > Jakub notes: > All [GCC] 5.1 - 6.x did was start accepting -gdwarf-5 as experimental > option that enabled some small DWARF subset (initially only a few > DW_LANG_* codes newly added to DWARF5 drafts). Only GCC 7 (released > after DWARF 5 has been finalized) started emitting DWARF5 section > headers and got most of the DWARF5 changes in... > > Version check GCC so that we don't need to worry about the difference in > command line args between GNU readelf and llvm-readelf/llvm-dwarfdump to > validate the DWARF Version in the assembler feature detection script. > > Link: http://www.dwarfstd.org/doc/DWARF5.pdf > Suggested-by: Arvind Sankar > Suggested-by: Jakub Jelinek > Suggested-by: Masahiro Yamada > Suggested-by: Fangrui Song > Suggested-by: Caroline Tice > Signed-off-by: Nick Desaulniers One small nit below. Reviewed-by: Nathan Chancellor > --- > Makefile | 1 + > include/asm-generic/vmlinux.lds.h | 6 +++++- > lib/Kconfig.debug | 17 +++++++++++++++++ > scripts/test_dwarf5_support.sh | 9 +++++++++ > 4 files changed, 32 insertions(+), 1 deletion(-) > create mode 100755 scripts/test_dwarf5_support.sh > > diff --git a/Makefile b/Makefile > index 656fff17b331..1067cfd98249 100644 > --- a/Makefile > +++ b/Makefile > @@ -828,6 +828,7 @@ endif > > dwarf-version-$(CONFIG_DEBUG_INFO_DWARF2) := 2 > dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4 > +dwarf-version-$(CONFIG_DEBUG_INFO_DWARF5) := 5 > DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y) > ifneq ($(dwarf-version-y)$(LLVM_IAS),21) > # Binutils 2.35+ required for -gdwarf-4+ support. > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > index 49944f00d2b3..37dc4110875e 100644 > --- a/include/asm-generic/vmlinux.lds.h > +++ b/include/asm-generic/vmlinux.lds.h > @@ -843,7 +843,11 @@ > .debug_types 0 : { *(.debug_types) } \ > /* DWARF 5 */ \ > .debug_macro 0 : { *(.debug_macro) } \ > - .debug_addr 0 : { *(.debug_addr) } > + .debug_addr 0 : { *(.debug_addr) } \ > + .debug_line_str 0 : { *(.debug_line_str) } \ > + .debug_loclists 0 : { *(.debug_loclists) } \ > + .debug_rnglists 0 : { *(.debug_rnglists) } \ > + .debug_str_offsets 0 : { *(.debug_str_offsets) } > > /* Stabs debugging sections. */ > #define STABS_DEBUG \ > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index e80770fac4f0..60a4f5e27ada 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -273,6 +273,23 @@ config DEBUG_INFO_DWARF4 > It makes the debug information larger, but it significantly > improves the success of resolving variables in gdb on optimized code. > > +config DEBUG_INFO_DWARF5 > + bool "Generate DWARF Version 5 debuginfo" > + depends on GCC_VERSION >= 50000 || CC_IS_CLANG > + depends on CC_IS_GCC || $(success,$(srctree)/scripts/test_dwarf5_support.sh $(CC) $(CLANG_FLAGS)) > + help > + Generate DWARF v5 debug info. Requires binutils 2.35, gcc 5.0+ (gcc > + 5.0+ accepts the -gdwarf-5 flag but only had partial support for some > + draft features until 7.0), and gdb 8.0+. > + > + Changes to the structure of debug info in Version 5 allow for around > + 15-18% savings in resulting image and debug info section sizes as > + compared to DWARF Version 4. DWARF Version 5 standardizes previous > + extensions such as accelerators for symbol indexing and the format > + for fission (.dwo/.dwp) files. Users may not want to select this > + config if they rely on tooling that has not yet been updated to > + support DWARF Version 5. > + > endchoice # "DWARF version" > > config DEBUG_INFO_BTF > diff --git a/scripts/test_dwarf5_support.sh b/scripts/test_dwarf5_support.sh > new file mode 100755 > index 000000000000..142a1b5c7fa2 > --- /dev/null > +++ b/scripts/test_dwarf5_support.sh > @@ -0,0 +1,9 @@ > +#!/bin/sh > +# SPDX-License-Identifier: GPL-2.0 > + > +# Test that assembler accepts -gdwarf-5 and .file 0 directives, which were bugs > +# in binutils < 2.35. > +# https://sourceware.org/bugzilla/show_bug.cgi?id=25612 > +# https://sourceware.org/bugzilla/show_bug.cgi?id=25614 > +set -e This is unnecessary, clang will error without this and a script's exit code is the exit code of its last command. > +echo '.file 0 "filename"' | $* -gdwarf-5 -Wa,-gdwarf-5 -c -x assembler -o /dev/null - > -- > 2.30.0.284.gd98b1dd5eaa7-goog >