On Thu, Jan 14, 2021 at 8:27 AM Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote: > > Sedat, > Thanks for testing, and congrats on https://lwn.net/Articles/839772/. > I always appreciate you taking the time to help test my work, and > other Clang+Linux kernel patches! > > On Wed, Jan 13, 2021 at 1:24 PM Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote: > > > > On Wed, Jan 13, 2021 at 1:32 AM Nick Desaulniers > > <ndesaulniers@xxxxxxxxxx> wrote: > > > > > > --- a/Makefile > > > +++ b/Makefile > > > @@ -826,12 +826,16 @@ else > > > DEBUG_CFLAGS += -g > > > endif > > > > > > -ifneq ($(LLVM_IAS),1) > > > -KBUILD_AFLAGS += -Wa,-gdwarf-2 > > > +dwarf-version-$(CONFIG_DEBUG_INFO_DWARF2) := 2 > > > +dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4 > > > +DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y) > > ^ DEBUG_CFLAGS are set for everyone (all toolchains) if > CONFIG_DEBUG_INFO is defined. > > > > +ifneq ($(dwarf-version-y)$(LLVM_IAS),21) > > ^ "If not using dwarf 2 and LLVM_IAS=1", ie. CONFIG_DEBUG_INFO_DWARF5 > && CONFIG_CC_IS_GCC > > > > +# Binutils 2.35+ required for -gdwarf-4+ support. > > > +dwarf-aflag := $(call as-option,-Wa$(comma)-gdwarf-$(dwarf-version-y)) > > > +ifdef CONFIG_CC_IS_CLANG > > ^ "if clang" > > > > +DEBUG_CFLAGS += $(dwarf-aflag) > > > endif > > > > Why is that "ifdef CONFIG_CC_IS_CLANG"? > > That's what Arvind requested on v2, IIUC: > https://lore.kernel.org/lkml/X8psgMuL4jMjP%2FOy@xxxxxxxxxxxxxxxxxx/ If CONFIG_CC_IS_CLANG is set, both -gdwarf and -Wa,-gdwarf-4 are passed to DEBUG_CFLAGS. Is it necessary? IIUC, -Wa,-gdwarf is meaningless when you build *.c files. I passed -v option to see how gas is invoked behind the scene. See the following results for [1] GCC + GAS and [2] Clang + GAS cases [1] GCC + GAS masahiro@grover:~$ cat test.c int main(void) { return 0; } masahiro@grover:~$ gcc -v -gdwarf-4 -c -o test.o test.c Using built-in specs. COLLECT_GCC=gcc OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa:hsa OFFLOAD_TARGET_DEFAULT=1 Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu 10.2.0-13ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-10/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix=/usr --with-gcc-major-version-only --program-suffix=-10 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib --enable-libphobos-checking=release --with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none=/build/gcc-10-JvwpWM/gcc-10-10.2.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-10-JvwpWM/gcc-10-10.2.0/debian/tmp-gcn/usr,hsa --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix Supported LTO compression algorithms: zlib zstd gcc version 10.2.0 (Ubuntu 10.2.0-13ubuntu1) COLLECT_GCC_OPTIONS='-v' '-gdwarf-4' '-c' '-o' 'test.o' '-mtune=generic' '-march=x86-64' /usr/lib/gcc/x86_64-linux-gnu/10/cc1 -quiet -v -imultiarch x86_64-linux-gnu test.c -quiet -dumpbase test.c -mtune=generic -march=x86-64 -auxbase-strip test.o -gdwarf-4 -version -fasynchronous-unwind-tables -fstack-protector-strong -Wformat -Wformat-security -fstack-clash-protection -fcf-protection -o /tmp/cc4hKJeo.s GNU C17 (Ubuntu 10.2.0-13ubuntu1) version 10.2.0 (x86_64-linux-gnu) compiled by GNU C version 10.2.0, GMP version 6.2.0, MPFR version 4.1.0, MPC version 1.2.0-rc1, isl version isl-0.22.1-GMP GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu" ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/10/include-fixed" ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/10/../../../../x86_64-linux-gnu/include" #include "..." search starts here: #include <...> search starts here: /usr/lib/gcc/x86_64-linux-gnu/10/include /usr/local/include /usr/include/x86_64-linux-gnu /usr/include End of search list. GNU C17 (Ubuntu 10.2.0-13ubuntu1) version 10.2.0 (x86_64-linux-gnu) compiled by GNU C version 10.2.0, GMP version 6.2.0, MPFR version 4.1.0, MPC version 1.2.0-rc1, isl version isl-0.22.1-GMP GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 Compiler executable checksum: 4831429547eb0be4fec215fca56ed5cf COLLECT_GCC_OPTIONS='-v' '-gdwarf-4' '-c' '-o' 'test.o' '-mtune=generic' '-march=x86-64' as -v --64 -o test.o /tmp/cc4hKJeo.s GNU assembler version 2.35.1 (x86_64-linux-gnu) using BFD version (GNU Binutils for Ubuntu) 2.35.1 COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/ LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/10/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/10/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/10/../../../:/lib/:/usr/lib/ COLLECT_GCC_OPTIONS='-v' '-gdwarf-4' '-c' '-o' 'test.o' '-mtune=generic' '-march=x86-64' masahiro@grover:~$ readelf --debug-dump=info test.o Contents of the .debug_info section: Compilation Unit @ offset 0x0: Length: 0x4f (32-bit) Version: 4 Abbrev Offset: 0x0 Pointer Size: 8 <0><b>: Abbrev Number: 1 (DW_TAG_compile_unit) <c> DW_AT_producer : (indirect string, offset: 0x16): GNU C17 10.2.0 -mtune=generic -march=x86-64 -gdwarf-4 -fasynchronous-unwind-tables -fstack-protector-strong -fstack-clash-protection -fcf-protection <10> DW_AT_language : 12 (ANSI C99) <11> DW_AT_name : (indirect string, offset: 0xf): test.c <15> DW_AT_comp_dir : (indirect string, offset: 0x0): /home/masahiro <19> DW_AT_low_pc : 0x0 <21> DW_AT_high_pc : 0xf <29> DW_AT_stmt_list : 0x0 <1><2d>: Abbrev Number: 2 (DW_TAG_subprogram) <2e> DW_AT_external : 1 <2e> DW_AT_name : (indirect string, offset: 0xab): main <32> DW_AT_decl_file : 1 <33> DW_AT_decl_line : 1 <34> DW_AT_decl_column : 5 <35> DW_AT_prototyped : 1 <35> DW_AT_type : <0x4b> <39> DW_AT_low_pc : 0x0 <41> DW_AT_high_pc : 0xf <49> DW_AT_frame_base : 1 byte block: 9c (DW_OP_call_frame_cfa) <4b> DW_AT_GNU_all_call_sites: 1 <1><4b>: Abbrev Number: 3 (DW_TAG_base_type) <4c> DW_AT_byte_size : 4 <4d> DW_AT_encoding : 5 (signed) <4e> DW_AT_name : int <1><52>: Abbrev Number: 0 [2] Clang + GAS masahiro@grover:~$ clang -v -fno-integrated-as -gdwarf-4 -c -o test.o test.c Ubuntu clang version 11.0.0-2 Target: x86_64-pc-linux-gnu Thread model: posix InstalledDir: /usr/bin Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/10 Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/8 Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/9 Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10 Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8 Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/9 Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/10 Candidate multilib: .;@m64 Selected multilib: .;@m64 "/usr/lib/llvm-11/bin/clang" -cc1 -triple x86_64-pc-linux-gnu -S -disable-free -disable-llvm-verifier -discard-value-names -main-file-name test.c -mrelocation-model static -mframe-pointer=all -fmath-errno -fno-rounding-math -no-integrated-as -mconstructor-aliases -munwind-tables -target-cpu x86-64 -fno-split-dwarf-inlining -debug-info-kind=limited -dwarf-version=4 -debugger-tuning=gdb -v -resource-dir /usr/lib/llvm-11/lib/clang/11.0.0 -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm-11/lib/clang/11.0.0/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -fno-dwarf-directory-asm -fdebug-compilation-dir /home/masahiro -ferror-limit 19 -fgnuc-version=4.2.1 -fcolor-diagnostics -o /tmp/test-f43580.s -x c test.c clang -cc1 version 11.0.0 based upon LLVM 11.0.0 default target x86_64-pc-linux-gnu ignoring nonexistent directory "/include" #include "..." search starts here: #include <...> search starts here: /usr/local/include /usr/lib/llvm-11/lib/clang/11.0.0/include /usr/include/x86_64-linux-gnu /usr/include End of search list. "/usr/bin/as" --64 -o test.o /tmp/test-f43580.s masahiro@grover:~$ readelf --debug-dump=info test.o Contents of the .debug_info section: Compilation Unit @ offset 0x0: Length: 0x47 (32-bit) Version: 4 Abbrev Offset: 0x0 Pointer Size: 8 <0><b>: Abbrev Number: 1 (DW_TAG_compile_unit) <c> DW_AT_producer : (indirect string, offset: 0x0): Ubuntu clang version 11.0.0-2 <10> DW_AT_language : 12 (ANSI C99) <12> DW_AT_name : (indirect string, offset: 0x1e): test.c <16> DW_AT_stmt_list : 0x0 <1a> DW_AT_comp_dir : (indirect string, offset: 0x25): /home/masahiro <1e> DW_AT_low_pc : 0x0 <26> DW_AT_high_pc : 0xf <1><2a>: Abbrev Number: 2 (DW_TAG_subprogram) <2b> DW_AT_low_pc : 0x0 <33> DW_AT_high_pc : 0xf <37> DW_AT_frame_base : 1 byte block: 56 (DW_OP_reg6 (rbp)) <39> DW_AT_name : (indirect string, offset: 0x34): main <3d> DW_AT_decl_file : 1 <3e> DW_AT_decl_line : 1 <3f> DW_AT_prototyped : 1 <3f> DW_AT_type : <0x43> <43> DW_AT_external : 1 <1><43>: Abbrev Number: 3 (DW_TAG_base_type) <44> DW_AT_name : (indirect string, offset: 0x39): int <48> DW_AT_encoding : 5 (signed) <49> DW_AT_byte_size : 4 <1><4a>: Abbrev Number: 0 In [1], "as -v --64 -o test.o /tmp/cc4hKJeo.s" is the command that invoked gas. There is no -gdwarf-4 option passed to gas here, but the produced object has the correct dwarf4 info. In [2], "/usr/bin/as" --64 -o test.o /tmp/test-f43580.s is the command that invoked gas. Again, no -gdwarf-4 option here, but the produced object has the correct dwarf4 info. So, when you build *.c -> *.o, passing -gdwarf-* is enough. The debug info is generated in the compile stage (i.e. by cc1) and included in the intermediate /tmp/*.s file. All gas needs to do is to transform the debug sections in the intermediate /tmp/*.s file into the binary stream in the .o file. GAS does it without being instructed by the explicit -Wa,-gdwarf-* option. In my understanding, passing -Wa,-gdwarf makes sense only when you build *.S -> *.o This is why I think DEBUG_CFLAGS += -gdwarf-4 (for source debug of .c files) and KBUILD_AFLAGS += -Wa,gdwarf-4 (for source debug of .S files) are basically orthogonal (and they can be even controlled by separate CONFIG options). As stated above, DEBUG_CFLAGS += -Wa,gdward-4 does not make sense. I am not a compiler expert, but that is what I understood from some experiments. Please correct me if I am wrong. > > When I use GCC v10.2.1 DEBUG_CFLAGS are not set. > > You should have -gdwarf-4 (and not -Wa,-gwarf-4) set for DEBUG_CFLAGS > when compiling with GCC and enabling CONFIG_DEBUG_INFO_DWARF4. Can you > please confirm? (Perhaps you may have accidentally disabled > CONFIG_DEBUG_INFO by rerunning `make defconfig`?) > -- > Thanks, > ~Nick Desaulniers -- Best Regards Masahiro Yamada
