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1fdd7433a9
Currently, clang LTO built vmlinux won't work with pahole.
LTO introduced cross-cu dwarf tag references and broke
current pahole model which handles one cu as a time.
The solution is to merge all cu's as one pahole cu as in [1].
We would like to do this merging only if cross-cu dwarf
references happens. The LTO build mode is a pretty good
indication for that.
In earlier version of this patch ([2]), clang flag
-grecord-gcc-switches is proposed to add to compilation flags
so pahole could detect "-flto" and then merging cu's.
This will increate the binary size of 1% without LTO though.
Arnaldo suggested to use a note to indicate the vmlinux
is built with LTO. Such a cheap way to get whether the vmlinux
is built with LTO or not helps pahole but is also useful
for tracing as LTO may inline/delete/demote global functions,
promote static functions, etc.
So this patch added an elfnote with a new type LINUX_ELFNOTE_LTO_INFO.
The owner of the note is "Linux".
With gcc 8.4.1 and clang trunk, without LTO, I got
$ readelf -n vmlinux
Displaying notes found in: .notes
Owner Data size Description
...
Linux 0x00000004 func
description data: 00 00 00 00
...
With "readelf -x ".notes" vmlinux", I can verify the above "func"
with type code 0x101.
With clang thin-LTO, I got the same as above except the following:
description data: 01 00 00 00
which indicates the vmlinux is built with LTO.
[1] https://lore.kernel.org/bpf/20210325065316.3121287-1-yhs@fb.com/
[2] https://lore.kernel.org/bpf/20210331001623.2778934-1-yhs@fb.com/
Suggested-by: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM/Clang v12.0.0-rc4 (x86-64)
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
50 lines
1.1 KiB
C
50 lines
1.1 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* linux/init/version.c
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*
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* Copyright (C) 1992 Theodore Ts'o
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*
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* May be freely distributed as part of Linux.
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*/
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#include <generated/compile.h>
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#include <linux/build-salt.h>
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#include <linux/elfnote-lto.h>
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#include <linux/export.h>
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#include <linux/uts.h>
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#include <linux/utsname.h>
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#include <generated/utsrelease.h>
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#include <linux/version.h>
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#include <linux/proc_ns.h>
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struct uts_namespace init_uts_ns = {
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.ns.count = REFCOUNT_INIT(2),
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.name = {
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.sysname = UTS_SYSNAME,
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.nodename = UTS_NODENAME,
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.release = UTS_RELEASE,
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.version = UTS_VERSION,
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.machine = UTS_MACHINE,
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.domainname = UTS_DOMAINNAME,
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},
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.user_ns = &init_user_ns,
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.ns.inum = PROC_UTS_INIT_INO,
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#ifdef CONFIG_UTS_NS
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.ns.ops = &utsns_operations,
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#endif
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};
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EXPORT_SYMBOL_GPL(init_uts_ns);
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/* FIXED STRINGS! Don't touch! */
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const char linux_banner[] =
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"Linux version " UTS_RELEASE " (" LINUX_COMPILE_BY "@"
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LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION "\n";
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const char linux_proc_banner[] =
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"%s version %s"
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" (" LINUX_COMPILE_BY "@" LINUX_COMPILE_HOST ")"
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" (" LINUX_COMPILER ") %s\n";
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BUILD_SALT;
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BUILD_LTO_INFO;
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