| Message ID | 20220919174547.3730737-1-ndesaulniers@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v4] Makefile.debug: re-enable debug info for .S files | expand |
On Tue, Sep 20, 2022 at 2:45 AM Nick Desaulniers <ndesaulniers@google.com> wrote: > > Alexey reported that the fraction of unknown filename instances in > kallsyms grew from ~0.3% to ~10% recently; Bill and Greg tracked it down > to assembler defined symbols, which regressed as a result of: > > commit b8a9092330da ("Kbuild: do not emit debug info for assembly with LLVM_IAS=1") > > In that commit, I allude to restoring debug info for assembler defined > symbols in a follow up patch, but it seems I forgot to do so in > > commit a66049e2cf0e ("Kbuild: make DWARF version a choice") > > Link: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=31bf18645d98b4d3d7357353be840e320649a67d > Fixes: b8a9092330da ("Kbuild: do not emit debug info for assembly with LLVM_IAS=1") > Reported-by: Alexey Alexandrov <aalexand@google.com> > Reported-by: Bill Wendling <morbo@google.com> > Reported-by: Greg Thelen <gthelen@google.com> > Reviewed-by: Nathan Chancellor <nathan@kernel.org> > Suggested-by: Masahiro Yamada <masahiroy@kernel.org> > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > --- > Changes v3 -> v4: > * Break out into its own patch. > * Move addition of debug-flags-y to DEBUG_CFLAGS and KBUILD_AFLAGS up > grouping the -gdwarf-* handling together. > > lib/Kconfig.debug | 4 +++- > scripts/Makefile.debug | 18 +++++++++--------- > 2 files changed, 12 insertions(+), 10 deletions(-) > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index bcbe60d6c80c..d3e5f36bb01e 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -264,8 +264,10 @@ config DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT > config DEBUG_INFO_DWARF4 > bool "Generate DWARF Version 4 debuginfo" > select DEBUG_INFO > + depends on !CC_IS_CLANG || (CC_IS_CLANG && (AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502))) > help > - Generate DWARF v4 debug info. This requires gcc 4.5+ and gdb 7.0+. > + Generate DWARF v4 debug info. This requires gcc 4.5+, binutils 2.35.2 > + if using clang without clang's integrated assembler, and gdb 7.0+. > > If you have consumers of DWARF debug info that are not ready for > newer revisions of DWARF, you may wish to choose this or have your > diff --git a/scripts/Makefile.debug b/scripts/Makefile.debug > index 26d6a9d97a20..d6aecd78b942 100644 > --- a/scripts/Makefile.debug > +++ b/scripts/Makefile.debug > @@ -4,15 +4,15 @@ ifdef CONFIG_DEBUG_INFO_SPLIT > DEBUG_CFLAGS += -gsplit-dwarf > endif > > -ifndef CONFIG_AS_IS_LLVM > -KBUILD_AFLAGS += -Wa,-gdwarf-2 > -endif > - > -ifndef CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT > -dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4 > -dwarf-version-$(CONFIG_DEBUG_INFO_DWARF5) := 5 > -DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y) > +debug-flags-$(CONFIG_DEBUG_INFO_DWARF4) += -gdwarf-4 > +debug-flags-$(CONFIG_DEBUG_INFO_DWARF5) += -gdwarf-5 > +ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_AS_IS_GNU),yy) > +# Clang does not pass -g or -gdwarf-* option down to GAS. This patch still misses the debug info for *.S files for the combination of LLVM_IAS=0 and CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y because, as the comment says, Clang does not pass -g down to GAS. With "[v4] Makefile.debug: set -g unconditional on CONFIG_DEBUG_INFO_SPLIT" and this one applied, $ grep CONFIG_DEBUG_INFO_DWARF .config CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y # CONFIG_DEBUG_INFO_DWARF4 is not set # CONFIG_DEBUG_INFO_DWARF5 is not set $ make LLVM=1 LLVM_IAS=0 arch/x86/kernel/irqflags.o SYNC include/config/auto.conf.cmd SYSHDR arch/x86/include/generated/asm/unistd_32_ia32.h SYSHDR arch/x86/include/generated/asm/unistd_64_x32.h SYSTBL arch/x86/include/generated/asm/syscalls_64.h HOSTCC arch/x86/tools/relocs_32.o [snip] AS arch/x86/kernel/irqflags.o $ objdump -h arch/x86/kernel/irqflags.o | grep debug $ I think the following fix-up is needed on top. diff --git a/scripts/Makefile.debug b/scripts/Makefile.debug index d6aecd78b942..8cf1cb22dd93 100644 --- a/scripts/Makefile.debug +++ b/scripts/Makefile.debug @@ -1,4 +1,5 @@ -DEBUG_CFLAGS := -g +DEBUG_CFLAGS := +debug-flags-y := -g ifdef CONFIG_DEBUG_INFO_SPLIT DEBUG_CFLAGS += -gsplit-dwarf Then, I can see the debug sections. $ make LLVM=1 LLVM_IAS=0 arch/x86/kernel/irqflags.o CALL scripts/checksyscalls.sh DESCEND objtool AS arch/x86/kernel/irqflags.o $ objdump -h arch/x86/kernel/irqflags.o | grep debug 6 .debug_line 00000050 0000000000000000 0000000000000000 0000008f 2**0 7 .debug_info 0000002e 0000000000000000 0000000000000000 000000f8 2**0 8 .debug_abbrev 00000014 0000000000000000 0000000000000000 000001d0 2**0 9 .debug_aranges 00000030 0000000000000000 0000000000000000 000001f0 2**4 10 .debug_str 0000004d 0000000000000000 0000000000000000 00000250 2**0 If you agree, I can locally fix it up as such. -- Best Regards Masahiro Yamada
On Fri, Sep 23, 2022 at 7:12 PM Masahiro Yamada <masahiroy@kernel.org> wrote: > > This patch still misses the debug info for *.S files > for the combination of LLVM_IAS=0 and > CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y > because, as the comment says, Clang does not pass -g down to GAS. > > > With "[v4] Makefile.debug: set -g unconditional on CONFIG_DEBUG_INFO_SPLIT" > and this one applied, > > > > $ grep CONFIG_DEBUG_INFO_DWARF .config > CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y > # CONFIG_DEBUG_INFO_DWARF4 is not set > # CONFIG_DEBUG_INFO_DWARF5 is not set > $ make LLVM=1 LLVM_IAS=0 arch/x86/kernel/irqflags.o > SYNC include/config/auto.conf.cmd > SYSHDR arch/x86/include/generated/asm/unistd_32_ia32.h > SYSHDR arch/x86/include/generated/asm/unistd_64_x32.h > SYSTBL arch/x86/include/generated/asm/syscalls_64.h > HOSTCC arch/x86/tools/relocs_32.o > [snip] > AS arch/x86/kernel/irqflags.o > $ objdump -h arch/x86/kernel/irqflags.o | grep debug > $ > > > > > > > > > I think the following fix-up is needed on top. > > > > > diff --git a/scripts/Makefile.debug b/scripts/Makefile.debug > index d6aecd78b942..8cf1cb22dd93 100644 > --- a/scripts/Makefile.debug > +++ b/scripts/Makefile.debug > @@ -1,4 +1,5 @@ > -DEBUG_CFLAGS := -g > +DEBUG_CFLAGS := > +debug-flags-y := -g > > ifdef CONFIG_DEBUG_INFO_SPLIT > DEBUG_CFLAGS += -gsplit-dwarf > > > > > Then, I can see the debug sections. > > > > $ make LLVM=1 LLVM_IAS=0 arch/x86/kernel/irqflags.o > CALL scripts/checksyscalls.sh > DESCEND objtool > AS arch/x86/kernel/irqflags.o > $ objdump -h arch/x86/kernel/irqflags.o | grep debug > 6 .debug_line 00000050 0000000000000000 0000000000000000 0000008f 2**0 > 7 .debug_info 0000002e 0000000000000000 0000000000000000 000000f8 2**0 > 8 .debug_abbrev 00000014 0000000000000000 0000000000000000 000001d0 2**0 > 9 .debug_aranges 00000030 0000000000000000 0000000000000000 000001f0 2**4 > 10 .debug_str 0000004d 0000000000000000 0000000000000000 00000250 2**0 > > > > > > If you agree, I can locally fix it up as such. Ah, sorry I missed testing that combination. Thanks for your thoroughness. Yes please apply that diff on top.
On Sat, Sep 24, 2022 at 11:20 AM Nick Desaulniers <ndesaulniers@google.com> wrote: > > On Fri, Sep 23, 2022 at 7:12 PM Masahiro Yamada <masahiroy@kernel.org> wrote: > > > > This patch still misses the debug info for *.S files > > for the combination of LLVM_IAS=0 and > > CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y > > because, as the comment says, Clang does not pass -g down to GAS. > > > > > > With "[v4] Makefile.debug: set -g unconditional on CONFIG_DEBUG_INFO_SPLIT" > > and this one applied, > > > > > > > > $ grep CONFIG_DEBUG_INFO_DWARF .config > > CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y > > # CONFIG_DEBUG_INFO_DWARF4 is not set > > # CONFIG_DEBUG_INFO_DWARF5 is not set > > $ make LLVM=1 LLVM_IAS=0 arch/x86/kernel/irqflags.o > > SYNC include/config/auto.conf.cmd > > SYSHDR arch/x86/include/generated/asm/unistd_32_ia32.h > > SYSHDR arch/x86/include/generated/asm/unistd_64_x32.h > > SYSTBL arch/x86/include/generated/asm/syscalls_64.h > > HOSTCC arch/x86/tools/relocs_32.o > > [snip] > > AS arch/x86/kernel/irqflags.o > > $ objdump -h arch/x86/kernel/irqflags.o | grep debug > > $ > > > > > > > > > > > > > > > > > > I think the following fix-up is needed on top. > > > > > > > > > > diff --git a/scripts/Makefile.debug b/scripts/Makefile.debug > > index d6aecd78b942..8cf1cb22dd93 100644 > > --- a/scripts/Makefile.debug > > +++ b/scripts/Makefile.debug > > @@ -1,4 +1,5 @@ > > -DEBUG_CFLAGS := -g > > +DEBUG_CFLAGS := > > +debug-flags-y := -g > > > > ifdef CONFIG_DEBUG_INFO_SPLIT > > DEBUG_CFLAGS += -gsplit-dwarf > > > > > > > > > > Then, I can see the debug sections. > > > > > > > > $ make LLVM=1 LLVM_IAS=0 arch/x86/kernel/irqflags.o > > CALL scripts/checksyscalls.sh > > DESCEND objtool > > AS arch/x86/kernel/irqflags.o > > $ objdump -h arch/x86/kernel/irqflags.o | grep debug > > 6 .debug_line 00000050 0000000000000000 0000000000000000 0000008f 2**0 > > 7 .debug_info 0000002e 0000000000000000 0000000000000000 000000f8 2**0 > > 8 .debug_abbrev 00000014 0000000000000000 0000000000000000 000001d0 2**0 > > 9 .debug_aranges 00000030 0000000000000000 0000000000000000 000001f0 2**4 > > 10 .debug_str 0000004d 0000000000000000 0000000000000000 00000250 2**0 > > > > > > > > > > > > If you agree, I can locally fix it up as such. > > Ah, sorry I missed testing that combination. Thanks for your > thoroughness. Yes please apply that diff on top. > -- > Thanks, > ~Nick Desaulniers Applied to linux-kbuild with the fixup.
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index bcbe60d6c80c..d3e5f36bb01e 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -264,8 +264,10 @@ config DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT config DEBUG_INFO_DWARF4 bool "Generate DWARF Version 4 debuginfo" select DEBUG_INFO + depends on !CC_IS_CLANG || (CC_IS_CLANG && (AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502))) help - Generate DWARF v4 debug info. This requires gcc 4.5+ and gdb 7.0+. + Generate DWARF v4 debug info. This requires gcc 4.5+, binutils 2.35.2 + if using clang without clang's integrated assembler, and gdb 7.0+. If you have consumers of DWARF debug info that are not ready for newer revisions of DWARF, you may wish to choose this or have your diff --git a/scripts/Makefile.debug b/scripts/Makefile.debug index 26d6a9d97a20..d6aecd78b942 100644 --- a/scripts/Makefile.debug +++ b/scripts/Makefile.debug @@ -4,15 +4,15 @@ ifdef CONFIG_DEBUG_INFO_SPLIT DEBUG_CFLAGS += -gsplit-dwarf endif -ifndef CONFIG_AS_IS_LLVM -KBUILD_AFLAGS += -Wa,-gdwarf-2 -endif - -ifndef CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT -dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4 -dwarf-version-$(CONFIG_DEBUG_INFO_DWARF5) := 5 -DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y) +debug-flags-$(CONFIG_DEBUG_INFO_DWARF4) += -gdwarf-4 +debug-flags-$(CONFIG_DEBUG_INFO_DWARF5) += -gdwarf-5 +ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_AS_IS_GNU),yy) +# Clang does not pass -g or -gdwarf-* option down to GAS. +# Add -Wa, prefix to explicitly specify the flags. +KBUILD_AFLAGS += $(addprefix -Wa$(comma), $(debug-flags-y)) endif +DEBUG_CFLAGS += $(debug-flags-y) +KBUILD_AFLAGS += $(debug-flags-y) ifdef CONFIG_DEBUG_INFO_REDUCED DEBUG_CFLAGS += -fno-var-tracking @@ -27,5 +27,5 @@ KBUILD_AFLAGS += -gz=zlib KBUILD_LDFLAGS += --compress-debug-sections=zlib endif -KBUILD_CFLAGS += $(DEBUG_CFLAGS) +KBUILD_CFLAGS += $(DEBUG_CFLAGS) export DEBUG_CFLAGS
Alexey reported that the fraction of unknown filename instances in kallsyms grew from ~0.3% to ~10% recently; Bill and Greg tracked it down to assembler defined symbols, which regressed as a result of: commit b8a9092330da ("Kbuild: do not emit debug info for assembly with LLVM_IAS=1") In that commit, I allude to restoring debug info for assembler defined symbols in a follow up patch, but it seems I forgot to do so in commit a66049e2cf0e ("Kbuild: make DWARF version a choice") Link: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=31bf18645d98b4d3d7357353be840e320649a67d Fixes: b8a9092330da ("Kbuild: do not emit debug info for assembly with LLVM_IAS=1") Reported-by: Alexey Alexandrov <aalexand@google.com> Reported-by: Bill Wendling <morbo@google.com> Reported-by: Greg Thelen <gthelen@google.com> Reviewed-by: Nathan Chancellor <nathan@kernel.org> Suggested-by: Masahiro Yamada <masahiroy@kernel.org> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> --- Changes v3 -> v4: * Break out into its own patch. * Move addition of debug-flags-y to DEBUG_CFLAGS and KBUILD_AFLAGS up grouping the -gdwarf-* handling together. lib/Kconfig.debug | 4 +++- scripts/Makefile.debug | 18 +++++++++--------- 2 files changed, 12 insertions(+), 10 deletions(-)