Modifies CONFIG_DEBUG_INFO_DWARF4 to be a member of a choice. Adds an
explicit CONFIG_DEBUG_INFO_DWARF2, which is the default. Does so in a
way that's forward compatible with existing configs, and makes adding
future versions more straightforward.
Suggested-by: Fangrui Song <[email protected]>
Suggested-by: Masahiro Yamada <[email protected]>
Signed-off-by: Nick Desaulniers <[email protected]>
---
Makefile | 14 ++++++++------
lib/Kconfig.debug | 21 ++++++++++++++++-----
2 files changed, 24 insertions(+), 11 deletions(-)
diff --git a/Makefile b/Makefile
index a2ded5029084..2430e1ee7c44 100644
--- a/Makefile
+++ b/Makefile
@@ -826,12 +826,14 @@ else
DEBUG_CFLAGS += -g
endif
-ifneq ($(LLVM_IAS),1)
-KBUILD_AFLAGS += -Wa,-gdwarf-2
-endif
-
-ifdef CONFIG_DEBUG_INFO_DWARF4
-DEBUG_CFLAGS += -gdwarf-4
+dwarf-version-$(CONFIG_DEBUG_INFO_DWARF2) := 2
+dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
+DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y)
+ifneq ($(dwarf-version-y)$(LLVM_IAS),21)
+# Binutils 2.35+ required for -gdwarf-4+ support.
+dwarf-aflag := $(call as-option,-Wa$(comma)-gdwarf-$(dwarf-version-y))
+DEBUG_CFLAGS += $(dwarf-aflag)
+KBUILD_AFLAGS += $(dwarf-aflag)
endif
ifdef CONFIG_DEBUG_INFO_REDUCED
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 0c7380e36370..04719294a7a3 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -256,14 +256,25 @@ config DEBUG_INFO_SPLIT
to know about the .dwo files and include them.
Incompatible with older versions of ccache.
+choice
+ prompt "DWARF version"
+ help
+ Which version of DWARF debug info to emit.
+
+config DEBUG_INFO_DWARF2
+ bool "Generate DWARF Version 2 debuginfo"
+ help
+ Generate DWARF v2 debug info.
+
config DEBUG_INFO_DWARF4
- bool "Generate dwarf4 debuginfo"
+ bool "Generate DWARF Version 4 debuginfo"
depends on $(cc-option,-gdwarf-4)
help
- Generate dwarf4 debug info. This requires recent versions
- of gcc and gdb. It makes the debug information larger.
- But it significantly improves the success of resolving
- variables in gdb on optimized code.
+ Generate DWARF v4 debug info. This requires gcc 4.5+ and gdb 7.0+.
+ It makes the debug information larger, but it significantly
+ improves the success of resolving variables in gdb on optimized code.
+
+endchoice # "DWARF version"
config DEBUG_INFO_BTF
bool "Generate BTF typeinfo"
--
2.29.2.576.ga3fc446d84-goog
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 <[email protected]>
Suggested-by: Jakub Jelinek <[email protected]>
Suggested-by: Masahiro Yamada <[email protected]>
Suggested-by: Fangrui Song <[email protected]>
Suggested-by: Caroline Tice <[email protected]>
Signed-off-by: Nick Desaulniers <[email protected]>
---
Makefile | 1 +
include/asm-generic/vmlinux.lds.h | 6 +++++-
lib/Kconfig.debug | 14 ++++++++++++++
scripts/test_dwarf5_support.sh | 9 +++++++++
4 files changed, 29 insertions(+), 1 deletion(-)
create mode 100755 scripts/test_dwarf5_support.sh
diff --git a/Makefile b/Makefile
index 2430e1ee7c44..45231f6c1935 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 b2b3d81b1535..76ce62c77029 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -829,7 +829,11 @@
.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 04719294a7a3..987815771ad6 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -274,6 +274,20 @@ 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 >= 70000 || CC_IS_CLANG
+ depends on $(success,$(srctree)/scripts/test_dwarf5_support.sh $(CC) $(CLANG_FLAGS))
+ help
+ Generate DWARF v5 debug info. Requires binutils 2.35, gcc 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..156ad5ec4274
--- /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
+echo '.file 0 "filename"' | $* -Wa,-gdwarf-5 -c -x assembler -o /dev/null -
--
2.29.2.576.ga3fc446d84-goog
(minus Chengbin due to bounces)
On Thu, Dec 3, 2020 at 5:11 PM Nick Desaulniers <[email protected]> wrote:
>
> Modifies CONFIG_DEBUG_INFO_DWARF4 to be a member of a choice. Adds an
> explicit CONFIG_DEBUG_INFO_DWARF2, which is the default. Does so in a
> way that's forward compatible with existing configs, and makes adding
> future versions more straightforward.
>
> Suggested-by: Fangrui Song <[email protected]>
> Suggested-by: Masahiro Yamada <[email protected]>
> Signed-off-by: Nick Desaulniers <[email protected]>
> ---
> Makefile | 14 ++++++++------
> lib/Kconfig.debug | 21 ++++++++++++++++-----
> 2 files changed, 24 insertions(+), 11 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index a2ded5029084..2430e1ee7c44 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -826,12 +826,14 @@ else
> DEBUG_CFLAGS += -g
> endif
>
> -ifneq ($(LLVM_IAS),1)
> -KBUILD_AFLAGS += -Wa,-gdwarf-2
> -endif
> -
> -ifdef CONFIG_DEBUG_INFO_DWARF4
> -DEBUG_CFLAGS += -gdwarf-4
> +dwarf-version-$(CONFIG_DEBUG_INFO_DWARF2) := 2
> +dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
> +DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y)
> +ifneq ($(dwarf-version-y)$(LLVM_IAS),21)
> +# Binutils 2.35+ required for -gdwarf-4+ support.
> +dwarf-aflag := $(call as-option,-Wa$(comma)-gdwarf-$(dwarf-version-y))
> +DEBUG_CFLAGS += $(dwarf-aflag)
> +KBUILD_AFLAGS += $(dwarf-aflag)
> endif
>
> ifdef CONFIG_DEBUG_INFO_REDUCED
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 0c7380e36370..04719294a7a3 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -256,14 +256,25 @@ config DEBUG_INFO_SPLIT
> to know about the .dwo files and include them.
> Incompatible with older versions of ccache.
>
> +choice
> + prompt "DWARF version"
> + help
> + Which version of DWARF debug info to emit.
> +
> +config DEBUG_INFO_DWARF2
> + bool "Generate DWARF Version 2 debuginfo"
> + help
> + Generate DWARF v2 debug info.
> +
> config DEBUG_INFO_DWARF4
> - bool "Generate dwarf4 debuginfo"
> + bool "Generate DWARF Version 4 debuginfo"
> depends on $(cc-option,-gdwarf-4)
> help
> - Generate dwarf4 debug info. This requires recent versions
> - of gcc and gdb. It makes the debug information larger.
> - But it significantly improves the success of resolving
> - variables in gdb on optimized code.
> + Generate DWARF v4 debug info. This requires gcc 4.5+ and gdb 7.0+.
> + It makes the debug information larger, but it significantly
> + improves the success of resolving variables in gdb on optimized code.
^ I kept the previous help text, but while this may have been the case
when DWARF v4 support was first introduced in GCC, by my (lone)
measure of x86_64 defconfig with gcc 10.2, this doesn't or no longer
seems to be the case. See patch 2 for measurements:
https://lore.kernel.org/lkml/[email protected]/.
(also, missed the cover letter, here it is:
https://lore.kernel.org/lkml/CAKwvOdkZEiHK01OD420USb0j=F0LcrnRbauv9Yw26tu-GRbYkg@mail.gmail.com/)
> +
> +endchoice # "DWARF version"
>
> config DEBUG_INFO_BTF
> bool "Generate BTF typeinfo"
> --
> 2.29.2.576.ga3fc446d84-goog
>
--
Thanks,
~Nick Desaulniers
On Thu, Dec 03, 2020 at 05:11:26PM -0800, 'Nick Desaulniers' via Clang Built Linux wrote:
> Modifies CONFIG_DEBUG_INFO_DWARF4 to be a member of a choice. Adds an
> explicit CONFIG_DEBUG_INFO_DWARF2, which is the default. Does so in a
> way that's forward compatible with existing configs, and makes adding
> future versions more straightforward.
>
> Suggested-by: Fangrui Song <[email protected]>
> Suggested-by: Masahiro Yamada <[email protected]>
> Signed-off-by: Nick Desaulniers <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
> ---
> Makefile | 14 ++++++++------
> lib/Kconfig.debug | 21 ++++++++++++++++-----
> 2 files changed, 24 insertions(+), 11 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index a2ded5029084..2430e1ee7c44 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -826,12 +826,14 @@ else
> DEBUG_CFLAGS += -g
> endif
>
> -ifneq ($(LLVM_IAS),1)
> -KBUILD_AFLAGS += -Wa,-gdwarf-2
> -endif
> -
> -ifdef CONFIG_DEBUG_INFO_DWARF4
> -DEBUG_CFLAGS += -gdwarf-4
> +dwarf-version-$(CONFIG_DEBUG_INFO_DWARF2) := 2
> +dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
> +DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y)
> +ifneq ($(dwarf-version-y)$(LLVM_IAS),21)
> +# Binutils 2.35+ required for -gdwarf-4+ support.
> +dwarf-aflag := $(call as-option,-Wa$(comma)-gdwarf-$(dwarf-version-y))
> +DEBUG_CFLAGS += $(dwarf-aflag)
> +KBUILD_AFLAGS += $(dwarf-aflag)
> endif
>
> ifdef CONFIG_DEBUG_INFO_REDUCED
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 0c7380e36370..04719294a7a3 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -256,14 +256,25 @@ config DEBUG_INFO_SPLIT
> to know about the .dwo files and include them.
> Incompatible with older versions of ccache.
>
> +choice
> + prompt "DWARF version"
> + help
> + Which version of DWARF debug info to emit.
> +
> +config DEBUG_INFO_DWARF2
> + bool "Generate DWARF Version 2 debuginfo"
> + help
> + Generate DWARF v2 debug info.
> +
> config DEBUG_INFO_DWARF4
> - bool "Generate dwarf4 debuginfo"
> + bool "Generate DWARF Version 4 debuginfo"
> depends on $(cc-option,-gdwarf-4)
> help
> - Generate dwarf4 debug info. This requires recent versions
> - of gcc and gdb. It makes the debug information larger.
> - But it significantly improves the success of resolving
> - variables in gdb on optimized code.
> + Generate DWARF v4 debug info. This requires gcc 4.5+ and gdb 7.0+.
> + It makes the debug information larger, but it significantly
> + improves the success of resolving variables in gdb on optimized code.
> +
> +endchoice # "DWARF version"
>
> config DEBUG_INFO_BTF
> bool "Generate BTF typeinfo"
> --
> 2.29.2.576.ga3fc446d84-goog
>
On Thu, Dec 03, 2020 at 05:11:27PM -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 <[email protected]>
> Suggested-by: Jakub Jelinek <[email protected]>
> Suggested-by: Masahiro Yamada <[email protected]>
> Suggested-by: Fangrui Song <[email protected]>
> Suggested-by: Caroline Tice <[email protected]>
> Signed-off-by: Nick Desaulniers <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
> ---
> Makefile | 1 +
> include/asm-generic/vmlinux.lds.h | 6 +++++-
> lib/Kconfig.debug | 14 ++++++++++++++
> scripts/test_dwarf5_support.sh | 9 +++++++++
> 4 files changed, 29 insertions(+), 1 deletion(-)
> create mode 100755 scripts/test_dwarf5_support.sh
>
> diff --git a/Makefile b/Makefile
> index 2430e1ee7c44..45231f6c1935 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 b2b3d81b1535..76ce62c77029 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -829,7 +829,11 @@
> .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 04719294a7a3..987815771ad6 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -274,6 +274,20 @@ 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 >= 70000 || CC_IS_CLANG
> + depends on $(success,$(srctree)/scripts/test_dwarf5_support.sh $(CC) $(CLANG_FLAGS))
> + help
> + Generate DWARF v5 debug info. Requires binutils 2.35, gcc 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..156ad5ec4274
> --- /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
> +echo '.file 0 "filename"' | $* -Wa,-gdwarf-5 -c -x assembler -o /dev/null -
> --
> 2.29.2.576.ga3fc446d84-goog
>