Em Thu, Apr 01, 2021 at 12:35:45PM -0700, Bill Wendling escreveu:
> On Wed, Mar 31, 2021 at 7:58 PM Yonghong Song <yhs@xxxxxx> wrote:
> > Function cus__merging_cu() is introduced in Commit 39227909db3c
> > ("dwarf_loader: Permit merging all DWARF CU's for clang LTO built
> > binary") to test whether cross-cu references may happen.
> > The original implementation anticipates compilation flags
> > in dwarf, but later some concerns about binary size surfaced
> > and the decision is to scan .debug_abbrev as a faster way
> > to check cross-cu references. Also putting a note in vmlinux
> > to indicate whether lto is enabled for built or not can
> > provide a much faster way.
> > This patch set implemented this two approaches, first
> > checking the note (in Patch #2), if not found, then
> > check .debug_abbrev (in Patch #1).
> > Yonghong Song (2):
> > dwarf_loader: check .debug_abbrev for cross-cu references
> > dwarf_loader: check .notes section for lto build info
> > dwarf_loader.c | 76 ++++++++++++++++++++++++++++++++++++--------------
> > 1 file changed, 55 insertions(+), 21 deletions(-)
> With this series of patches, the compilation passes for me with
> ThinLTO. You may add this if you like:
> Tested-by: Bill Wendling <morbo@xxxxxxxxxx>
Thanks, added, and also this "Committer testing" section:
Committer testing:
Using a thin-LTO built vmlinux that doesn't have the
LINUX_ELFNOTE_BUILD_LTO note:
$ readelf --notes vmlinux.clang.thin.LTO
Displaying notes found in: .notes
Owner Data size Description
Xen 0x00000006 Unknown note type: (0x00000006)
description data: 6c 69 6e 75 78 00
Xen 0x00000004 Unknown note type: (0x00000007)
description data: 32 2e 36 00
Xen 0x00000008 Unknown note type: (0x00000005)
description data: 78 65 6e 2d 33 2e 30 00
Xen 0x00000008 Unknown note type: (0x00000003)
description data: 00 00 00 80 ff ff ff ff
Xen 0x00000008 Unknown note type: (0x0000000f)
description data: 00 00 00 00 80 00 00 00
Xen 0x00000008 NT_VERSION (version)
description data: c0 e1 33 83 ff ff ff ff
Xen 0x00000008 NT_ARCH (architecture)
description data: 00 20 00 81 ff ff ff ff
Xen 0x00000029 Unknown note type: (0x0000000a)
description data: 21 77 72 69 74 61 62 6c 65 5f 70 61 67 65 5f 74 61 62 6c 65 73 7c 70 61 65 5f 70 67 64 69 72 5f 61 62 6f 76 65 5f 34 67 62
Xen 0x00000004 Unknown note type: (0x00000011)
description data: 01 88 00 00
Xen 0x00000004 Unknown note type: (0x00000009)
description data: 79 65 73 00
Xen 0x00000008 Unknown note type: (0x00000008)
description data: 67 65 6e 65 72 69 63 00
Xen 0x00000010 Unknown note type: (0x0000000d)
description data: 01 00 00 00 00 00 00 00 01 00 00 00 00 00 00 00
Xen 0x00000004 Unknown note type: (0x0000000e)
description data: 01 00 00 00
Xen 0x00000004 Unknown note type: (0x00000010)
description data: 01 00 00 00
Xen 0x00000008 Unknown note type: (0x0000000c)
description data: 00 00 00 00 00 80 ff ff
Xen 0x00000008 Unknown note type: (0x00000004)
description data: 00 00 00 00 00 00 00 00
Xen 0x00000008 Unknown note type: (0x00000012)
description data: e0 02 00 01 00 00 00 00
Linux 0x00000017 OPEN
description data: 34 2e 31 39 2e 34 2d 33 30 30 2e 66 63 32 39 2e 78 38 36 5f 36 34 00
GNU 0x00000014 NT_GNU_BUILD_ID (unique build ID bitstring)
Build ID: 354f81317b1b3c35f3f81f8d9f04d0c8caccb09a
$
Then with one with the new ELF note stating that this binary was built
with LTO:
[acme@five pahole]$ readelf --notes vmlinux.clang.thin.LTO+ELF_note
Displaying notes found in: .notes
Owner Data size Description
Xen 0x00000006 Unknown note type: (0x00000006)
description data: 6c 69 6e 75 78 00
Xen 0x00000004 Unknown note type: (0x00000007)
description data: 32 2e 36 00
Xen 0x00000008 Unknown note type: (0x00000005)
description data: 78 65 6e 2d 33 2e 30 00
Xen 0x00000008 Unknown note type: (0x00000003)
description data: 00 00 00 80 ff ff ff ff
Xen 0x00000008 Unknown note type: (0x0000000f)
description data: 00 00 00 00 80 00 00 00
Xen 0x00000008 NT_VERSION (version)
description data: c0 e1 33 83 ff ff ff ff
Xen 0x00000008 NT_ARCH (architecture)
description data: 00 20 00 81 ff ff ff ff
Xen 0x00000029 Unknown note type: (0x0000000a)
description data: 21 77 72 69 74 61 62 6c 65 5f 70 61 67 65 5f 74 61 62 6c 65 73 7c 70 61 65 5f 70 67 64 69 72 5f 61 62 6f 76 65 5f 34 67 62
Xen 0x00000004 Unknown note type: (0x00000011)
description data: 01 88 00 00
Xen 0x00000004 Unknown note type: (0x00000009)
description data: 79 65 73 00
Xen 0x00000008 Unknown note type: (0x00000008)
description data: 67 65 6e 65 72 69 63 00
Xen 0x00000010 Unknown note type: (0x0000000d)
description data: 01 00 00 00 00 00 00 00 01 00 00 00 00 00 00 00
Xen 0x00000004 Unknown note type: (0x0000000e)
description data: 01 00 00 00
Xen 0x00000004 Unknown note type: (0x00000010)
description data: 01 00 00 00
Xen 0x00000008 Unknown note type: (0x0000000c)
description data: 00 00 00 00 00 80 ff ff
Xen 0x00000008 Unknown note type: (0x00000004)
description data: 00 00 00 00 00 00 00 00
Xen 0x00000008 Unknown note type: (0x00000012)
description data: e0 02 00 01 00 00 00 00
Linux 0x00000017 OPEN
description data: 34 2e 31 39 2e 34 2d 33 30 30 2e 66 63 32 39 2e 78 38 36 5f 36 34 00
Linux 0x00000004 func
description data: 01 00 00 00
GNU 0x00000014 NT_GNU_BUILD_ID (unique build ID bitstring)
Build ID: aeba9ffc929acd3cd573b4d1afc8df9af4f3694d
$
Now to see the diff:
$ readelf --notes vmlinux.clang.thin.LTO+ELF_note > with-note
$ readelf --notes vmlinux.clang.thin.LTO > without-note
$ diff -u without-note with-note
--- without-note 2021-04-02 10:23:57.545349084 -0300
+++ with-note 2021-04-02 10:23:50.690196102 -0300
@@ -37,5 +37,7 @@
description data: e0 02 00 01 00 00 00 00
Linux 0x00000017 OPEN
description data: 34 2e 31 39 2e 34 2d 33 30 30 2e 66 63 32 39 2e 78 38 36 5f 36 34 00
+ Linux 0x00000004 func
+ description data: 01 00 00 00
GNU 0x00000014 NT_GNU_BUILD_ID (unique build ID bitstring)
- Build ID: 354f81317b1b3c35f3f81f8d9f04d0c8caccb09a
+ Build ID: aeba9ffc929acd3cd573b4d1afc8df9af4f3694d
$
Signed-off-by: Yonghong Song <yhs@xxxxxx>
Suggested-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Tested-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Tested-by: Bill Wendling <morbo@xxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Andrii Nakryiko <andrii@xxxxxxxxxx>
Cc: David Blaikie <dblaikie@xxxxxxxxx>
Cc: Fāng-ruì Sòng <maskray@xxxxxxxxxx>
Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Cc: bpf@xxxxxxxxxxxxxxx
Cc: dwarves@xxxxxxxxxxxxxxx
Cc: kernel-team@xxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
