From c25e1c55822f9b3b53ccbf88b85644317a525752 Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Fri, 27 May 2022 19:01:49 +0900 Subject: 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 Reviewed-by: Nicolas Schier Tested-by: Nathan Chancellor Reviewed-by: Sami Tolvanen Tested-by: Sedat Dilek # LLVM-14 (x86-64) Acked-by: Josh Poimboeuf --- scripts/mod/modpost.c | 7 ------- 1 file changed, 7 deletions(-) (limited to 'scripts/mod/modpost.c') 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); } -- cgit v1.2.3