[PATCH] kbuild: use objcopy to generate asm-offsets
From: Vegard Nossum <hidden>
Date: 2024-08-28 08:36:42
Also in:
bpf, kvm, kvmarm, linux-kbuild, linux-omap, linux-um, lkml, llvm
Subsystem:
arm port, arm/microchip (at91) soc support, arm64 port (aarch64 architecture), bpf [general] (safe dynamic programs and tools), kernel build + files below scripts/ (unless maintained elsewhere), kernel virtual machine for arm64 (kvm/arm64), kernel virtual machine for x86 (kvm/x86), memory controller drivers, omap2+ support, the rest, user-mode linux (uml), x86 architecture (32-bit and 64-bit) · Maintainers:
Russell King, Nicolas Ferre, Alexandre Belloni, Claudiu Beznea, Catalin Marinas, Will Deacon, Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Nathan Chancellor, Nicolas Schier, Marc Zyngier, Oliver Upton, Sean Christopherson, Paolo Bonzini, Krzysztof Kozlowski, Aaro Koskinen, Andreas Kemnade, Kevin Hilman, Roger Quadros, Tony Lindgren, Linus Torvalds, Richard Weinberger, Anton Ivanov, Johannes Berg, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
In order to give assembly code access to C structs without having to hardcore member offsets, the kernel compiles a C source file listing all the structs and offsets that are needed in assembly code. Using some C preprocessor trickery and a sed script, the compiled assembly code is turned back into C preprocessor code that in turn can be used by the asssembly code. This sed script is very hard to read and understand. Remove the sed script and compile the C source listing structs and offsets to an object file (instead of assembly code) that embeds C source directly. Then extract the C source using objcopy. The resulting code is more readable, less fragile, and sligthly shorter. Note to reviewers: The 'objcopy ... /dev/stdout | cat' bit is needed to force the correct ordering of the objcopy lines vs. the surrounding echo commands; without it, objcopy will open /dev/stdout (which refers to a temporary file created by kbuild) and reset the file offset to 0. In other words, the pipe ensures that objcopy doesn't overwrite the lines that already exist in /dev/stdout. Signed-off-by: Vegard Nossum <redacted> --- Kbuild | 10 +++++----- arch/arm/mach-at91/Makefile | 4 ++-- arch/arm/mach-omap2/Makefile | 4 ++-- arch/arm64/kvm/Makefile | 9 +++++---- arch/x86/kvm/Makefile | 4 ++-- arch/x86/um/Makefile | 6 +++--- drivers/memory/Makefile | 4 ++-- include/linux/kbuild.h | 15 +++++++++++---- samples/bpf/Makefile | 4 ++-- scripts/Makefile.lib | 13 +------------ scripts/mod/Makefile | 4 ++-- 11 files changed, 37 insertions(+), 40 deletions(-)
diff --git a/Kbuild b/Kbuild
index 464b34a08f51e..412b77007deb1 100644
--- a/Kbuild
+++ b/Kbuild@@ -9,9 +9,9 @@ bounds-file := include/generated/bounds.h -targets := kernel/bounds.s +targets := kernel/bounds.o -$(bounds-file): kernel/bounds.s FORCE +$(bounds-file): kernel/bounds.o FORCE $(call filechk,offsets,__LINUX_BOUNDS_H__) # Generate timeconst.h
@@ -27,11 +27,11 @@ $(timeconst-file): kernel/time/timeconst.bc FORCE offsets-file := include/generated/asm-offsets.h -targets += arch/$(SRCARCH)/kernel/asm-offsets.s +targets += arch/$(SRCARCH)/kernel/asm-offsets.o -arch/$(SRCARCH)/kernel/asm-offsets.s: $(timeconst-file) $(bounds-file) +arch/$(SRCARCH)/kernel/asm-offsets.o: $(timeconst-file) $(bounds-file) -$(offsets-file): arch/$(SRCARCH)/kernel/asm-offsets.s FORCE +$(offsets-file): arch/$(SRCARCH)/kernel/asm-offsets.o FORCE $(call filechk,offsets,__ASM_OFFSETS_H__) # Check for missing system calls
diff --git a/arch/arm/mach-at91/Makefile b/arch/arm/mach-at91/Makefile
index 794bd12ab0a8e..4d4be0000fd98 100644
--- a/arch/arm/mach-at91/Makefile
+++ b/arch/arm/mach-at91/Makefile@@ -18,10 +18,10 @@ ifeq ($(CONFIG_PM_DEBUG),y) CFLAGS_pm.o += -DDEBUG endif -$(obj)/pm_data-offsets.h: $(obj)/pm_data-offsets.s FORCE +$(obj)/pm_data-offsets.h: $(obj)/pm_data-offsets.o FORCE $(call filechk,offsets,__PM_DATA_OFFSETS_H__) $(obj)/pm_suspend.o: $(obj)/pm_data-offsets.h -targets += pm_data-offsets.s +targets += pm_data-offsets.o clean-files += pm_data-offsets.h
diff --git a/arch/arm/mach-omap2/Makefile b/arch/arm/mach-omap2/Makefile
index daf21127c82f1..991ffe6871d1d 100644
--- a/arch/arm/mach-omap2/Makefile
+++ b/arch/arm/mach-omap2/Makefile@@ -217,12 +217,12 @@ obj-y += omap_phy_internal.o obj-$(CONFIG_MACH_OMAP2_TUSB6010) += usb-tusb6010.o -$(obj)/pm-asm-offsets.h: $(obj)/pm-asm-offsets.s FORCE +$(obj)/pm-asm-offsets.h: $(obj)/pm-asm-offsets.o FORCE $(call filechk,offsets,__TI_PM_ASM_OFFSETS_H__) $(obj)/sleep33xx.o $(obj)/sleep43xx.o: $(obj)/pm-asm-offsets.h -targets += pm-asm-offsets.s +targets += pm-asm-offsets.o clean-files += pm-asm-offsets.h obj-$(CONFIG_OMAP_IOMMU) += omap-iommu.o
diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
index 86a629aaf0a13..ee699a683d82c 100644
--- a/arch/arm64/kvm/Makefile
+++ b/arch/arm64/kvm/Makefile@@ -28,17 +28,18 @@ kvm-y += arm.o mmu.o mmio.o psci.o hypercalls.o pvtime.o \ kvm-$(CONFIG_HW_PERF_EVENTS) += pmu-emul.o pmu.o kvm-$(CONFIG_ARM64_PTR_AUTH) += pauth.o -always-y := hyp_constants.h hyp-constants.s +always-y := hyp_constants.h hyp-constants.o define rule_gen_hyp_constants $(call filechk,offsets,__HYP_CONSTANTS_H__) endef CFLAGS_hyp-constants.o = -I $(src)/hyp/include -$(obj)/hyp-constants.s: $(src)/hyp/hyp-constants.c FORCE - $(call if_changed_dep,cc_s_c) -$(obj)/hyp_constants.h: $(obj)/hyp-constants.s FORCE +$(obj)/hyp-constants.o: $(src)/hyp/hyp-constants.c FORCE + $(call if_changed_dep,cc_o_c) + +$(obj)/hyp_constants.h: $(obj)/hyp-constants.o FORCE $(call if_changed_rule,gen_hyp_constants) obj-kvm := $(addprefix $(obj)/, $(kvm-y))
diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
index 5494669a055a6..3b561c7e7c4f9 100644
--- a/arch/x86/kvm/Makefile
+++ b/arch/x86/kvm/Makefile@@ -42,8 +42,8 @@ $(obj)/svm/vmenter.o: $(obj)/kvm-asm-offsets.h AFLAGS_vmx/vmenter.o := -iquote $(obj) $(obj)/vmx/vmenter.o: $(obj)/kvm-asm-offsets.h -$(obj)/kvm-asm-offsets.h: $(obj)/kvm-asm-offsets.s FORCE +$(obj)/kvm-asm-offsets.h: $(obj)/kvm-asm-offsets.o FORCE $(call filechk,offsets,__KVM_ASM_OFFSETS_H__) -targets += kvm-asm-offsets.s +targets += kvm-asm-offsets.o clean-files += kvm-asm-offsets.h
diff --git a/arch/x86/um/Makefile b/arch/x86/um/Makefile
index 36e67fc97c22f..6563503d4b25d 100644
--- a/arch/x86/um/Makefile
+++ b/arch/x86/um/Makefile@@ -38,11 +38,11 @@ subarch-$(CONFIG_MODULES) += ../kernel/module.o USER_OBJS := bugs_$(BITS).o ptrace_user.o fault.o -$(obj)/user-offsets.s: c_flags = -Wp,-MD,$(depfile) $(USER_CFLAGS) \ +$(obj)/user-offsets.o: c_flags = -Wp,-MD,$(depfile) $(USER_CFLAGS) \ -Iarch/x86/include/generated -targets += user-offsets.s +targets += user-offsets.o -include/generated/user_constants.h: $(obj)/user-offsets.s FORCE +include/generated/user_constants.h: $(obj)/user-offsets.o FORCE $(call filechk,offsets,__USER_CONSTANT_H__) UNPROFILE_OBJS := stub_segv.o
diff --git a/drivers/memory/Makefile b/drivers/memory/Makefile
index d2e6ca9abbe02..efae95f315a12 100644
--- a/drivers/memory/Makefile
+++ b/drivers/memory/Makefile@@ -34,8 +34,8 @@ ti-emif-sram-objs := ti-emif-pm.o ti-emif-sram-pm.o $(obj)/ti-emif-sram-pm.o: $(obj)/ti-emif-asm-offsets.h -$(obj)/ti-emif-asm-offsets.h: $(obj)/emif-asm-offsets.s FORCE +$(obj)/ti-emif-asm-offsets.h: $(obj)/emif-asm-offsets.o FORCE $(call filechk,offsets,__TI_EMIF_ASM_OFFSETS_H__) -targets += emif-asm-offsets.s +targets += emif-asm-offsets.o clean-files += ti-emif-asm-offsets.h
diff --git a/include/linux/kbuild.h b/include/linux/kbuild.h
index e7be517aaaf68..d253ae4dfd1c1 100644
--- a/include/linux/kbuild.h
+++ b/include/linux/kbuild.h@@ -2,15 +2,22 @@ #ifndef __LINUX_KBUILD_H #define __LINUX_KBUILD_H -#define DEFINE(sym, val) \ - asm volatile("\n.ascii \"->" #sym " %0 " #val "\"" : : "i" (val)) +#define _LINE(x, ...) \ + asm volatile( \ + ".pushsection \".data.kbuild\"; "\ + ".ascii \"" x "\\n\"; "\ + ".popsection" : : __VA_ARGS__) -#define BLANK() asm volatile("\n.ascii \"->\"" : : ) +#define DEFINE(sym, val) \ + _LINE("#define " #sym " %c0 /* " #val " */", "i" (val)) #define OFFSET(sym, str, mem) \ DEFINE(sym, offsetof(struct str, mem)) +#define BLANK() \ + _LINE("") + #define COMMENT(x) \ - asm volatile("\n.ascii \"->#" x "\"") + _LINE("/* " #x " */") #endif
diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 3e003dd6bea09..a5d86ac8f5f57 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile@@ -270,10 +270,10 @@ $(LIBBPF_OUTPUT) $(BPFTOOL_OUTPUT): $(call msg,MKDIR,$@) $(Q)mkdir -p $@ -$(obj)/syscall_nrs.h: $(obj)/syscall_nrs.s FORCE +$(obj)/syscall_nrs.h: $(obj)/syscall_nrs.o FORCE $(call filechk,offsets,__SYSCALL_NRS_H__) -targets += syscall_nrs.s +targets += syscall_nrs.o clean-files += syscall_nrs.h FORCE:
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 207325eaf1d1c..f78b0b12ace26 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib@@ -583,17 +583,6 @@ quiet_cmd_zstd22_with_size = ZSTD22 $@ # ASM offsets # --------------------------------------------------------------------------- -# Default sed regexp - multiline due to syntax constraints -# -# Use [:space:] because LLVM's integrated assembler inserts <tab> around -# the .ascii directive whereas GCC keeps the <space> as-is. -define sed-offsets - 's:^[[:space:]]*\.ascii[[:space:]]*"\(.*\)".*:\1:; \ - /^->/{s:->#\(.*\):/* \1 */:; \ - s:^->\([^ ]*\) [\$$#]*\([^ ]*\) \(.*\):#define \1 \2 /* \3 */:; \ - s:->::; p;}' -endef - # Use filechk to avoid rebuilds when a header changes, but the resulting file # does not define filechk_offsets
@@ -605,7 +594,7 @@ define filechk_offsets echo " * This file was generated by Kbuild"; \ echo " */"; \ echo ""; \ - sed -ne $(sed-offsets) < $<; \ + $(OBJCOPY) -j .data.kbuild -O binary $< /dev/stdout | cat; \ echo ""; \ echo "#endif" endef
diff --git a/scripts/mod/Makefile b/scripts/mod/Makefile
index c729bc936bae1..3c3f5e16a30a2 100644
--- a/scripts/mod/Makefile
+++ b/scripts/mod/Makefile@@ -8,10 +8,10 @@ modpost-objs := modpost.o file2alias.o sumversion.o symsearch.o devicetable-offsets-file := devicetable-offsets.h -$(obj)/$(devicetable-offsets-file): $(obj)/devicetable-offsets.s FORCE +$(obj)/$(devicetable-offsets-file): $(obj)/devicetable-offsets.o FORCE $(call filechk,offsets,__DEVICETABLE_OFFSETS_H__) -targets += $(devicetable-offsets-file) devicetable-offsets.s +targets += $(devicetable-offsets-file) devicetable-offsets.o # dependencies on generated files need to be listed explicitly
--
2.34.1