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Diffstat (limited to '')
| -rw-r--r-- | Documentation/kbuild/makefiles.rst | 108 |
1 files changed, 71 insertions, 37 deletions
diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst index b008b90b92c9..6b7368d1f516 100644 --- a/Documentation/kbuild/makefiles.rst +++ b/Documentation/kbuild/makefiles.rst @@ -29,8 +29,9 @@ This document describes the Linux kernel Makefiles. --- 4.1 Simple Host Program --- 4.2 Composite Host Programs --- 4.3 Using C++ for host programs - --- 4.4 Controlling compiler options for host programs - --- 4.5 When host programs are actually built + --- 4.4 Using Rust for host programs + --- 4.5 Controlling compiler options for host programs + --- 4.6 When host programs are actually built === 5 Userspace Program support --- 5.1 Simple Userspace Program @@ -340,19 +341,7 @@ more details, with real examples. Examples are: - 1) head objects - - Some objects must be placed at the head of vmlinux. They are - directly linked to vmlinux without going through built-in.a - A typical use-case is an object that contains the entry point. - - arch/$(SRCARCH)/Makefile should specify such objects as head-y. - - Discussion: - Given that we can control the section order in the linker script, - why do we need head-y? - - 2) vmlinux linker script + 1) vmlinux linker script The linker script for vmlinux is located at arch/$(SRCARCH)/kernel/vmlinux.lds @@ -360,10 +349,6 @@ more details, with real examples. Example:: # arch/x86/kernel/Makefile - extra-y := head_$(BITS).o - extra-y += head$(BITS).o - extra-y += ebda.o - extra-y += platform-quirks.o extra-y += vmlinux.lds $(extra-y) should only contain targets needed for vmlinux. @@ -682,22 +667,27 @@ more details, with real examples. In the above example, -Wno-unused-but-set-variable will be added to KBUILD_CFLAGS only if gcc really accepts it. - cc-ifversion - cc-ifversion tests the version of $(CC) and equals the fourth parameter - if version expression is true, or the fifth (if given) if the version - expression is false. + gcc-min-version + gcc-min-version tests if the value of $(CONFIG_GCC_VERSION) is greater than + or equal to the provided value and evaluates to y if so. + + Example:: + + cflags-$(call gcc-min-version, 70100) := -foo + + In this example, cflags-y will be assigned the value -foo if $(CC) is gcc and + $(CONFIG_GCC_VERSION) is >= 7.1. + + clang-min-version + clang-min-version tests if the value of $(CONFIG_CLANG_VERSION) is greater + than or equal to the provided value and evaluates to y if so. Example:: - #fs/reiserfs/Makefile - ccflags-y := $(call cc-ifversion, -lt, 0402, -O1) + cflags-$(call clang-min-version, 110000) := -foo - In this example, ccflags-y will be assigned the value -O1 if the - $(CC) version is less than 4.2. - cc-ifversion takes all the shell operators: - -eq, -ne, -lt, -le, -gt, and -ge - The third parameter may be a text as in this example, but it may also - be an expanded variable or a macro. + In this example, cflags-y will be assigned the value -foo if $(CC) is clang + and $(CONFIG_CLANG_VERSION) is >= 11.0.0. cc-cross-prefix cc-cross-prefix is used to check if there exists a $(CC) in path with @@ -835,7 +825,24 @@ Both possibilities are described in the following. qconf-cxxobjs := qconf.o qconf-objs := check.o -4.4 Controlling compiler options for host programs +4.4 Using Rust for host programs +-------------------------------- + + Kbuild offers support for host programs written in Rust. However, + since a Rust toolchain is not mandatory for kernel compilation, + it may only be used in scenarios where Rust is required to be + available (e.g. when ``CONFIG_RUST`` is enabled). + + Example:: + + hostprogs := target + target-rust := y + + Kbuild will compile ``target`` using ``target.rs`` as the crate root, + located in the same directory as the ``Makefile``. The crate may + consist of several source files (see ``samples/rust/hostprogs``). + +4.5 Controlling compiler options for host programs -------------------------------------------------- When compiling host programs, it is possible to set specific flags. @@ -867,7 +874,7 @@ Both possibilities are described in the following. When linking qconf, it will be passed the extra option "-L$(QTDIR)/lib". -4.5 When host programs are actually built +4.6 When host programs are actually built ----------------------------------------- Kbuild will only build host-programs when they are referenced @@ -982,6 +989,8 @@ The syntax is quite similar. The difference is to use "userprogs" instead of When linking bpfilter_umh, it will be passed the extra option -static. + From command line, :ref:`USERCFLAGS and USERLDFLAGS <userkbuildflags>` will also be used. + 5.4 When userspace programs are actually built ---------------------------------------------- @@ -1079,8 +1088,7 @@ When kbuild executes, the following steps are followed (roughly): - The values of the above variables are expanded in arch/$(SRCARCH)/Makefile. 5) All object files are then linked and the resulting file vmlinux is located at the root of the obj tree. - The very first objects linked are listed in head-y, assigned by - arch/$(SRCARCH)/Makefile. + The very first objects linked are listed in scripts/head-object-list.txt. 6) Finally, the architecture-specific part does any required post processing and builds the final bootimage. - This includes building boot records @@ -1179,6 +1187,17 @@ When kbuild executes, the following steps are followed (roughly): The first example utilises the trick that a config option expands to 'y' when selected. + KBUILD_RUSTFLAGS + $(RUSTC) compiler flags + + Default value - see top level Makefile + Append or modify as required per architecture. + + Often, the KBUILD_RUSTFLAGS variable depends on the configuration. + + Note that target specification file generation (for ``--target``) + is handled in ``scripts/generate_rust_target.rs``. + KBUILD_AFLAGS_KERNEL Assembler options specific for built-in @@ -1206,6 +1225,19 @@ When kbuild executes, the following steps are followed (roughly): are used for $(CC). From commandline CFLAGS_MODULE shall be used (see kbuild.rst). + KBUILD_RUSTFLAGS_KERNEL + $(RUSTC) options specific for built-in + + $(KBUILD_RUSTFLAGS_KERNEL) contains extra Rust compiler flags used to + compile resident kernel code. + + KBUILD_RUSTFLAGS_MODULE + Options for $(RUSTC) when building modules + + $(KBUILD_RUSTFLAGS_MODULE) is used to add arch-specific options that + are used for $(RUSTC). + From commandline RUSTFLAGS_MODULE shall be used (see kbuild.rst). + KBUILD_LDFLAGS_MODULE Options for $(LD) when linking modules @@ -1228,6 +1260,9 @@ When kbuild executes, the following steps are followed (roughly): All object files for vmlinux. They are linked to vmlinux in the same order as listed in KBUILD_VMLINUX_OBJS. + The objects listed in scripts/head-object-list.txt are exceptions; + they are placed before the other objects. + KBUILD_VMLINUX_LIBS All .a "lib" files for vmlinux. KBUILD_VMLINUX_OBJS and @@ -1271,8 +1306,7 @@ When kbuild executes, the following steps are followed (roughly): machinery is all architecture-independent. - head-y, core-y, libs-y, drivers-y - $(head-y) lists objects to be linked first in vmlinux. + core-y, libs-y, drivers-y $(libs-y) lists directories where a lib.a archive can be located. |