On Fri, Mar 31, 2023 at 7:29 AM Nathan Chancellor <nathan@xxxxxxxxxx> wrote:
>
> On Thu, Mar 30, 2023 at 06:22:24PM +0000, Alyssa Ross wrote:
> > Since 32ef9e5054ec, -Wa,-gdwarf-2 is no longer used in KBUILD_AFLAGS.
> > Instead, it includes -g, the appropriate -gdwarf-* flag, and also the
> > -Wa versions of both of those if building with Clang and GNU as. As a
> > result, debug info was being generated for the purgatory objects, even
> > though the intention was that it not be.
> >
> > Fixes: 32ef9e5054ec ("Makefile.debug: re-enable debug info for .S files")
> > Signed-off-by: Alyssa Ross <hi@xxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > Acked-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
>
> This is definitely more future proof.
>
> Reviewed-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx>
I prefer v3 since it is cleaner, but unfortunately
it does not work for Clang+GAS.
With v3 applied, I still see the debug info.
$ make LLVM=1 LLVM_IAS=0 arch/x86/purgatory/setup-x86_64.o
UPD include/config/kernel.release
UPD include/generated/utsrelease.h
CALL scripts/checksyscalls.sh
DESCEND objtool
INSTALL libsubcmd_headers
AS arch/x86/purgatory/setup-x86_64.o
$ readelf -S arch/x86/purgatory/setup-x86_64.o
There are 18 section headers, starting at offset 0x14d8:
Section Headers:
[Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
[ 0] NULL 0000000000000000 00000000
0000000000000000 0000000000000000 0 0 0
[ 1] .text PROGBITS 0000000000000000 00000040
0000000000000027 0000000000000000 AX 0 0 16
[ 2] .rela.text RELA 0000000000000000 000012f8
0000000000000060 0000000000000018 I 15 1 8
[ 3] .data PROGBITS 0000000000000000 00000067
0000000000000000 0000000000000000 WA 0 0 1
[ 4] .bss NOBITS 0000000000000000 00001000
0000000000001000 0000000000000000 WA 0 0 4096
[ 5] .rodata PROGBITS 0000000000000000 00001000
0000000000000020 0000000000000000 A 0 0 16
[ 6] .rela.rodata RELA 0000000000000000 00001358
0000000000000018 0000000000000018 I 15 5 8
[ 7] .debug_line PROGBITS 0000000000000000 00001020
000000000000005f 0000000000000000 0 0 1
[ 8] .rela.debug_line RELA 0000000000000000 00001370
0000000000000018 0000000000000018 I 15 7 8
[ 9] .debug_info PROGBITS 0000000000000000 0000107f
0000000000000027 0000000000000000 0 0 1
[10] .rela.debug_info RELA 0000000000000000 00001388
0000000000000090 0000000000000018 I 15 9 8
[11] .debug_abbrev PROGBITS 0000000000000000 000010a6
0000000000000014 0000000000000000 0 0 1
[12] .debug_aranges PROGBITS 0000000000000000 000010c0
0000000000000030 0000000000000000 0 0 16
[13] .rela.debug_[...] RELA 0000000000000000 00001418
0000000000000030 0000000000000018 I 15 12 8
[14] .debug_str PROGBITS 0000000000000000 000010f0
0000000000000054 0000000000000001 MS 0 0 1
[15] .symtab SYMTAB 0000000000000000 00001148
0000000000000168 0000000000000018 16 12 8
[16] .strtab STRTAB 0000000000000000 000012b0
0000000000000041 0000000000000000 0 0 1
[17] .shstrtab STRTAB 0000000000000000 00001448
000000000000008d 0000000000000000 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
L (link order), O (extra OS processing required), G (group), T (TLS),
C (compressed), x (unknown), o (OS specific), E (exclude),
D (mbind), l (large), p (processor specific)
With -g0 given, GCC stops passing -g -gdwarf-4 down to GAS.
Clang does not do anything about -g0 for the external assembler.
I was thinking of dropping LLVM_IAS=0 support.
When we decide to give up -fno-integrated-as,
we can clean up the code in various places.
Anyway, v3 does not work in the current situation.
V2 works for all usecases.
--
Best Regards
Masahiro Yamada
