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| author | Masahiro Yamada <masahiroy@kernel.org> | 2022-05-27 19:01:49 +0900 |
|---|---|---|
| committer | Masahiro Yamada <masahiroy@kernel.org> | 2022-05-29 18:39:35 +0900 |
| commit | c25e1c55822f9b3b53ccbf88b85644317a525752 (patch) | |
| tree | 0a71732cc734866099013c08aafef8f7d4437619 /scripts/mod | |
| parent | 0cfd90060d714e3d1e0d1b30cfd1c46b71f4e721 (diff) | |
| download | linux-riscv-c25e1c55822f9b3b53ccbf88b85644317a525752.tar.gz linux-riscv-c25e1c55822f9b3b53ccbf88b85644317a525752.tar.bz2 linux-riscv-c25e1c55822f9b3b53ccbf88b85644317a525752.zip | |
kbuild: do not create *.prelink.o for Clang LTO or IBT
When CONFIG_LTO_CLANG=y, additional intermediate *.prelink.o is created
for each module. Also, objtool is postponed until LLVM IR is converted
to ELF.
CONFIG_X86_KERNEL_IBT works in a similar way to postpone objtool until
objects are merged together.
This commit stops generating *.prelink.o, so the build flow will look
similar with/without LTO.
The following figures show how the LTO build currently works, and
how this commit is changing it.
Current build flow
==================
[1] single-object module
$(LD)
$(CC) +objtool $(LD)
foo.c --------------------> foo.o -----> foo.prelink.o -----> foo.ko
(LLVM IR) (ELF) | (ELF)
|
foo.mod.o --/
(LLVM IR)
[2] multi-object module
$(LD)
$(CC) $(AR) +objtool $(LD)
foo1.c -----> foo1.o -----> foo.o -----> foo.prelink.o -----> foo.ko
| (archive) (ELF) | (ELF)
foo2.c -----> foo2.o --/ |
(LLVM IR) foo.mod.o --/
(LLVM IR)
One confusion is that foo.o in multi-object module is an archive
despite of its suffix.
New build flow
==============
[1] single-object module
Since there is only one object, there is no need to keep the LLVM IR.
Use $(CC)+$(LD) to generate an ELF object in one build rule. When LTO
is disabled, $(LD) is unneeded because $(CC) produces an ELF object.
$(CC)+$(LD)+objtool $(LD)
foo.c ----------------------------> foo.o ---------> foo.ko
(ELF) | (ELF)
|
foo.mod.o --/
(LLVM IR)
[2] multi-object module
Previously, $(AR) was used to combine LLVM IR files into an archive,
but there was no technical reason to do so. Use $(LD) to merge them
into a single ELF object.
$(LD)
$(CC) +objtool $(LD)
foo1.c ---------> foo1.o ---------> foo.o ---------> foo.ko
| (ELF) | (ELF)
foo2.c ---------> foo2.o ----/ |
(LLVM IR) foo.mod.o --/
(LLVM IR)
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM-14 (x86-64)
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Diffstat (limited to 'scripts/mod')
| -rw-r--r-- | scripts/mod/modpost.c | 7 |
1 files changed, 0 insertions, 7 deletions
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c index b70a31b4245a..e74224a6a8e8 100644 --- a/scripts/mod/modpost.c +++ b/scripts/mod/modpost.c @@ -1903,10 +1903,6 @@ static char *remove_dot(char *s) size_t m = strspn(s + n + 1, "0123456789"); if (m && (s[n + m + 1] == '.' || s[n + m + 1] == 0)) s[n] = 0; - - /* strip trailing .prelink */ - if (strends(s, ".prelink")) - s[strlen(s) - 8] = '\0'; } return s; } @@ -2028,9 +2024,6 @@ static void read_symbols(const char *modname) /* strip trailing .o */ tmp = NOFAIL(strdup(modname)); tmp[strlen(tmp) - 2] = '\0'; - /* strip trailing .prelink */ - if (strends(tmp, ".prelink")) - tmp[strlen(tmp) - 8] = '\0'; mod = new_module(tmp); free(tmp); } |