From 56a092c895054a6b423781d788339775bd2bda10 Mon Sep 17 00:00:00 2001 From: Quentin Monnet Date: Wed, 25 Apr 2018 18:16:52 +0100 Subject: bpf: add script and prepare bpf.h for new helpers documentation Remove previous "overview" of eBPF helpers from user bpf.h header. Replace it by a comment explaining how to process the new documentation (to come in following patches) with a Python script to produce RST, then man page documentation. Also add the aforementioned Python script under scripts/. It is used to process include/uapi/linux/bpf.h and to extract helper descriptions, to turn it into a RST document that can further be processed with rst2man to produce a man page. The script takes one "--filename " option. If the script is launched from scripts/ in the kernel root directory, it should be able to find the location of the header to parse, and "--filename " is then optional. If it cannot find the file, then the option becomes mandatory. RST-formatted documentation is printed to standard output. Typical workflow for producing the final man page would be: $ ./scripts/bpf_helpers_doc.py \ --filename include/uapi/linux/bpf.h > /tmp/bpf-helpers.rst $ rst2man /tmp/bpf-helpers.rst > /tmp/bpf-helpers.7 $ man /tmp/bpf-helpers.7 Note that the tool kernel-doc cannot be used to document eBPF helpers, whose signatures are not available directly in the header files (pre-processor directives are used to produce them at the beginning of the compilation process). v4: - Also remove overviews for newly added bpf_xdp_adjust_tail() and bpf_skb_get_xfrm_state(). - Remove vague statement about what helpers are restricted to GPL programs in "LICENSE" section for man page footer. - Replace license boilerplate with SPDX tag for Python script. v3: - Change license for man page. - Remove "for safety reasons" from man page header text. - Change "packets metadata" to "packets" in man page header text. - Move and fix comment on helpers introducing no overhead. - Remove "NOTES" section from man page footer. - Add "LICENSE" section to man page footer. - Edit description of file include/uapi/linux/bpf.h in man page footer. Signed-off-by: Quentin Monnet Signed-off-by: Daniel Borkmann --- scripts/bpf_helpers_doc.py | 421 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 421 insertions(+) create mode 100755 scripts/bpf_helpers_doc.py (limited to 'scripts') diff --git a/scripts/bpf_helpers_doc.py b/scripts/bpf_helpers_doc.py new file mode 100755 index 000000000000..30ba0fee36e4 --- /dev/null +++ b/scripts/bpf_helpers_doc.py @@ -0,0 +1,421 @@ +#!/usr/bin/python3 +# SPDX-License-Identifier: GPL-2.0-only +# +# Copyright (C) 2018 Netronome Systems, Inc. + +# In case user attempts to run with Python 2. +from __future__ import print_function + +import argparse +import re +import sys, os + +class NoHelperFound(BaseException): + pass + +class ParsingError(BaseException): + def __init__(self, line='', reader=None): + if reader: + BaseException.__init__(self, + 'Error at file offset %d, parsing line: %s' % + (reader.tell(), line)) + else: + BaseException.__init__(self, 'Error parsing line: %s' % line) + +class Helper(object): + """ + An object representing the description of an eBPF helper function. + @proto: function prototype of the helper function + @desc: textual description of the helper function + @ret: description of the return value of the helper function + """ + def __init__(self, proto='', desc='', ret=''): + self.proto = proto + self.desc = desc + self.ret = ret + + def proto_break_down(self): + """ + Break down helper function protocol into smaller chunks: return type, + name, distincts arguments. + """ + arg_re = re.compile('^((const )?(struct )?(\w+|...))( (\**)(\w+))?$') + res = {} + proto_re = re.compile('^(.+) (\**)(\w+)\(((([^,]+)(, )?){1,5})\)$') + + capture = proto_re.match(self.proto) + res['ret_type'] = capture.group(1) + res['ret_star'] = capture.group(2) + res['name'] = capture.group(3) + res['args'] = [] + + args = capture.group(4).split(', ') + for a in args: + capture = arg_re.match(a) + res['args'].append({ + 'type' : capture.group(1), + 'star' : capture.group(6), + 'name' : capture.group(7) + }) + + return res + +class HeaderParser(object): + """ + An object used to parse a file in order to extract the documentation of a + list of eBPF helper functions. All the helpers that can be retrieved are + stored as Helper object, in the self.helpers() array. + @filename: name of file to parse, usually include/uapi/linux/bpf.h in the + kernel tree + """ + def __init__(self, filename): + self.reader = open(filename, 'r') + self.line = '' + self.helpers = [] + + def parse_helper(self): + proto = self.parse_proto() + desc = self.parse_desc() + ret = self.parse_ret() + return Helper(proto=proto, desc=desc, ret=ret) + + def parse_proto(self): + # Argument can be of shape: + # - "void" + # - "type name" + # - "type *name" + # - Same as above, with "const" and/or "struct" in front of type + # - "..." (undefined number of arguments, for bpf_trace_printk()) + # There is at least one term ("void"), and at most five arguments. + p = re.compile('^ \* ((.+) \**\w+\((((const )?(struct )?(\w+|\.\.\.)( \**\w+)?)(, )?){1,5}\))$') + capture = p.match(self.line) + if not capture: + raise NoHelperFound + self.line = self.reader.readline() + return capture.group(1) + + def parse_desc(self): + p = re.compile('^ \* \tDescription$') + capture = p.match(self.line) + if not capture: + # Helper can have empty description and we might be parsing another + # attribute: return but do not consume. + return '' + # Description can be several lines, some of them possibly empty, and it + # stops when another subsection title is met. + desc = '' + while True: + self.line = self.reader.readline() + if self.line == ' *\n': + desc += '\n' + else: + p = re.compile('^ \* \t\t(.*)') + capture = p.match(self.line) + if capture: + desc += capture.group(1) + '\n' + else: + break + return desc + + def parse_ret(self): + p = re.compile('^ \* \tReturn$') + capture = p.match(self.line) + if not capture: + # Helper can have empty retval and we might be parsing another + # attribute: return but do not consume. + return '' + # Return value description can be several lines, some of them possibly + # empty, and it stops when another subsection title is met. + ret = '' + while True: + self.line = self.reader.readline() + if self.line == ' *\n': + ret += '\n' + else: + p = re.compile('^ \* \t\t(.*)') + capture = p.match(self.line) + if capture: + ret += capture.group(1) + '\n' + else: + break + return ret + + def run(self): + # Advance to start of helper function descriptions. + offset = self.reader.read().find('* Start of BPF helper function descriptions:') + if offset == -1: + raise Exception('Could not find start of eBPF helper descriptions list') + self.reader.seek(offset) + self.reader.readline() + self.reader.readline() + self.line = self.reader.readline() + + while True: + try: + helper = self.parse_helper() + self.helpers.append(helper) + except NoHelperFound: + break + + self.reader.close() + print('Parsed description of %d helper function(s)' % len(self.helpers), + file=sys.stderr) + +############################################################################### + +class Printer(object): + """ + A generic class for printers. Printers should be created with an array of + Helper objects, and implement a way to print them in the desired fashion. + @helpers: array of Helper objects to print to standard output + """ + def __init__(self, helpers): + self.helpers = helpers + + def print_header(self): + pass + + def print_footer(self): + pass + + def print_one(self, helper): + pass + + def print_all(self): + self.print_header() + for helper in self.helpers: + self.print_one(helper) + self.print_footer() + +class PrinterRST(Printer): + """ + A printer for dumping collected information about helpers as a ReStructured + Text page compatible with the rst2man program, which can be used to + generate a manual page for the helpers. + @helpers: array of Helper objects to print to standard output + """ + def print_header(self): + header = '''\ +.. Copyright (C) All BPF authors and contributors from 2014 to present. +.. See git log include/uapi/linux/bpf.h in kernel tree for details. +.. +.. %%%LICENSE_START(VERBATIM) +.. Permission is granted to make and distribute verbatim copies of this +.. manual provided the copyright notice and this permission notice are +.. preserved on all copies. +.. +.. Permission is granted to copy and distribute modified versions of this +.. manual under the conditions for verbatim copying, provided that the +.. entire resulting derived work is distributed under the terms of a +.. permission notice identical to this one. +.. +.. Since the Linux kernel and libraries are constantly changing, this +.. manual page may be incorrect or out-of-date. The author(s) assume no +.. responsibility for errors or omissions, or for damages resulting from +.. the use of the information contained herein. The author(s) may not +.. have taken the same level of care in the production of this manual, +.. which is licensed free of charge, as they might when working +.. professionally. +.. +.. Formatted or processed versions of this manual, if unaccompanied by +.. the source, must acknowledge the copyright and authors of this work. +.. %%%LICENSE_END +.. +.. Please do not edit this file. It was generated from the documentation +.. located in file include/uapi/linux/bpf.h of the Linux kernel sources +.. (helpers description), and from scripts/bpf_helpers_doc.py in the same +.. repository (header and footer). + +=========== +BPF-HELPERS +=========== +------------------------------------------------------------------------------- +list of eBPF helper functions +------------------------------------------------------------------------------- + +:Manual section: 7 + +DESCRIPTION +=========== + +The extended Berkeley Packet Filter (eBPF) subsystem consists in programs +written in a pseudo-assembly language, then attached to one of the several +kernel hooks and run in reaction of specific events. This framework differs +from the older, "classic" BPF (or "cBPF") in several aspects, one of them being +the ability to call special functions (or "helpers") from within a program. +These functions are restricted to a white-list of helpers defined in the +kernel. + +These helpers are used by eBPF programs to interact with the system, or with +the context in which they work. For instance, they can be used to print +debugging messages, to get the time since the system was booted, to interact +with eBPF maps, or to manipulate network packets. Since there are several eBPF +program types, and that they do not run in the same context, each program type +can only call a subset of those helpers. + +Due to eBPF conventions, a helper can not have more than five arguments. + +Internally, eBPF programs call directly into the compiled helper functions +without requiring any foreign-function interface. As a result, calling helpers +introduces no overhead, thus offering excellent performance. + +This document is an attempt to list and document the helpers available to eBPF +developers. They are sorted by chronological order (the oldest helpers in the +kernel at the top). + +HELPERS +======= +''' + print(header) + + def print_footer(self): + footer = ''' +EXAMPLES +======== + +Example usage for most of the eBPF helpers listed in this manual page are +available within the Linux kernel sources, at the following locations: + +* *samples/bpf/* +* *tools/testing/selftests/bpf/* + +LICENSE +======= + +eBPF programs can have an associated license, passed along with the bytecode +instructions to the kernel when the programs are loaded. The format for that +string is identical to the one in use for kernel modules (Dual licenses, such +as "Dual BSD/GPL", may be used). Some helper functions are only accessible to +programs that are compatible with the GNU Privacy License (GPL). + +In order to use such helpers, the eBPF program must be loaded with the correct +license string passed (via **attr**) to the **bpf**\ () system call, and this +generally translates into the C source code of the program containing a line +similar to the following: + +:: + + char ____license[] __attribute__((section("license"), used)) = "GPL"; + +IMPLEMENTATION +============== + +This manual page is an effort to document the existing eBPF helper functions. +But as of this writing, the BPF sub-system is under heavy development. New eBPF +program or map types are added, along with new helper functions. Some helpers +are occasionally made available for additional program types. So in spite of +the efforts of the community, this page might not be up-to-date. If you want to +check by yourself what helper functions exist in your kernel, or what types of +programs they can support, here are some files among the kernel tree that you +may be interested in: + +* *include/uapi/linux/bpf.h* is the main BPF header. It contains the full list + of all helper functions, as well as many other BPF definitions including most + of the flags, structs or constants used by the helpers. +* *net/core/filter.c* contains the definition of most network-related helper + functions, and the list of program types from which they can be used. +* *kernel/trace/bpf_trace.c* is the equivalent for most tracing program-related + helpers. +* *kernel/bpf/verifier.c* contains the functions used to check that valid types + of eBPF maps are used with a given helper function. +* *kernel/bpf/* directory contains other files in which additional helpers are + defined (for cgroups, sockmaps, etc.). + +Compatibility between helper functions and program types can generally be found +in the files where helper functions are defined. Look for the **struct +bpf_func_proto** objects and for functions returning them: these functions +contain a list of helpers that a given program type can call. Note that the +**default:** label of the **switch ... case** used to filter helpers can call +other functions, themselves allowing access to additional helpers. The +requirement for GPL license is also in those **struct bpf_func_proto**. + +Compatibility between helper functions and map types can be found in the +**check_map_func_compatibility**\ () function in file *kernel/bpf/verifier.c*. + +Helper functions that invalidate the checks on **data** and **data_end** +pointers for network processing are listed in function +**bpf_helper_changes_pkt_data**\ () in file *net/core/filter.c*. + +SEE ALSO +======== + +**bpf**\ (2), +**cgroups**\ (7), +**ip**\ (8), +**perf_event_open**\ (2), +**sendmsg**\ (2), +**socket**\ (7), +**tc-bpf**\ (8)''' + print(footer) + + def print_proto(self, helper): + """ + Format function protocol with bold and italics markers. This makes RST + file less readable, but gives nice results in the manual page. + """ + proto = helper.proto_break_down() + + print('**%s %s%s(' % (proto['ret_type'], + proto['ret_star'].replace('*', '\\*'), + proto['name']), + end='') + + comma = '' + for a in proto['args']: + one_arg = '{}{}'.format(comma, a['type']) + if a['name']: + if a['star']: + one_arg += ' {}**\ '.format(a['star'].replace('*', '\\*')) + else: + one_arg += '** ' + one_arg += '*{}*\\ **'.format(a['name']) + comma = ', ' + print(one_arg, end='') + + print(')**') + + def print_one(self, helper): + self.print_proto(helper) + + if (helper.desc): + print('\tDescription') + # Do not strip all newline characters: formatted code at the end of + # a section must be followed by a blank line. + for line in re.sub('\n$', '', helper.desc, count=1).split('\n'): + print('{}{}'.format('\t\t' if line else '', line)) + + if (helper.ret): + print('\tReturn') + for line in helper.ret.rstrip().split('\n'): + print('{}{}'.format('\t\t' if line else '', line)) + + print('') + +############################################################################### + +# If script is launched from scripts/ from kernel tree and can access +# ../include/uapi/linux/bpf.h, use it as a default name for the file to parse, +# otherwise the --filename argument will be required from the command line. +script = os.path.abspath(sys.argv[0]) +linuxRoot = os.path.dirname(os.path.dirname(script)) +bpfh = os.path.join(linuxRoot, 'include/uapi/linux/bpf.h') + +argParser = argparse.ArgumentParser(description=""" +Parse eBPF header file and generate documentation for eBPF helper functions. +The RST-formatted output produced can be turned into a manual page with the +rst2man utility. +""") +if (os.path.isfile(bpfh)): + argParser.add_argument('--filename', help='path to include/uapi/linux/bpf.h', + default=bpfh) +else: + argParser.add_argument('--filename', help='path to include/uapi/linux/bpf.h') +args = argParser.parse_args() + +# Parse file. +headerParser = HeaderParser(args.filename) +headerParser.run() + +# Print formatted output to standard output. +printer = PrinterRST(headerParser.helpers) +printer.print_all() -- cgit v1.2.3 From 6f96674dbd8ca659769f1c65ca15638e50b69341 Mon Sep 17 00:00:00 2001 From: Quentin Monnet Date: Wed, 2 May 2018 14:20:24 +0100 Subject: bpf: relax constraints on formatting for eBPF helper documentation The Python script used to parse and extract eBPF helpers documentation from include/uapi/linux/bpf.h expects a very specific formatting for the descriptions (single dot represents a space, '>' stands for a tab): /* ... *.int bpf_helper(list of arguments) *.> Description *.> > Start of description *.> > Another line of description *.> > And yet another line of description *.> Return *.> > 0 on success, or a negative error in case of failure ... */ This is too strict, and painful for developers who wants to add documentation for new helpers. Worse, it is extremely difficult to check that the formatting is correct during reviews. Change the format expected by the script and make it more flexible. The script now works whether or not the initial space (right after the star) is present, and accepts both tabs and white spaces (or a combination of both) for indenting description sections and contents. Concretely, something like the following would now be supported: /* ... *int bpf_helper(list of arguments) *......Description *.> > Start of description... *> > Another line of description *..............And yet another line of description *> Return *.> ........0 on success, or a negative error in case of failure ... */ While at it, remove unnecessary carets from each regex used with match() in the script. They are redundant, as match() tries to match from the beginning of the string by default. v2: Remove unnecessary caret when a regex is used with match(). Signed-off-by: Quentin Monnet Signed-off-by: Daniel Borkmann --- scripts/bpf_helpers_doc.py | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) (limited to 'scripts') diff --git a/scripts/bpf_helpers_doc.py b/scripts/bpf_helpers_doc.py index 30ba0fee36e4..8f59897fbda1 100755 --- a/scripts/bpf_helpers_doc.py +++ b/scripts/bpf_helpers_doc.py @@ -39,9 +39,9 @@ class Helper(object): Break down helper function protocol into smaller chunks: return type, name, distincts arguments. """ - arg_re = re.compile('^((const )?(struct )?(\w+|...))( (\**)(\w+))?$') + arg_re = re.compile('((const )?(struct )?(\w+|...))( (\**)(\w+))?$') res = {} - proto_re = re.compile('^(.+) (\**)(\w+)\(((([^,]+)(, )?){1,5})\)$') + proto_re = re.compile('(.+) (\**)(\w+)\(((([^,]+)(, )?){1,5})\)$') capture = proto_re.match(self.proto) res['ret_type'] = capture.group(1) @@ -87,7 +87,7 @@ class HeaderParser(object): # - Same as above, with "const" and/or "struct" in front of type # - "..." (undefined number of arguments, for bpf_trace_printk()) # There is at least one term ("void"), and at most five arguments. - p = re.compile('^ \* ((.+) \**\w+\((((const )?(struct )?(\w+|\.\.\.)( \**\w+)?)(, )?){1,5}\))$') + p = re.compile(' \* ?((.+) \**\w+\((((const )?(struct )?(\w+|\.\.\.)( \**\w+)?)(, )?){1,5}\))$') capture = p.match(self.line) if not capture: raise NoHelperFound @@ -95,7 +95,7 @@ class HeaderParser(object): return capture.group(1) def parse_desc(self): - p = re.compile('^ \* \tDescription$') + p = re.compile(' \* ?(?:\t| {6,8})Description$') capture = p.match(self.line) if not capture: # Helper can have empty description and we might be parsing another @@ -109,7 +109,7 @@ class HeaderParser(object): if self.line == ' *\n': desc += '\n' else: - p = re.compile('^ \* \t\t(.*)') + p = re.compile(' \* ?(?:\t| {6,8})(?:\t| {8})(.*)') capture = p.match(self.line) if capture: desc += capture.group(1) + '\n' @@ -118,7 +118,7 @@ class HeaderParser(object): return desc def parse_ret(self): - p = re.compile('^ \* \tReturn$') + p = re.compile(' \* ?(?:\t| {6,8})Return$') capture = p.match(self.line) if not capture: # Helper can have empty retval and we might be parsing another @@ -132,7 +132,7 @@ class HeaderParser(object): if self.line == ' *\n': ret += '\n' else: - p = re.compile('^ \* \t\t(.*)') + p = re.compile(' \* ?(?:\t| {6,8})(?:\t| {8})(.*)') capture = p.match(self.line) if capture: ret += capture.group(1) + '\n' -- cgit v1.2.3 From eeacb7166df6ed1cffa923ea04c70043285783b8 Mon Sep 17 00:00:00 2001 From: Quentin Monnet Date: Thu, 17 May 2018 13:43:56 +0100 Subject: bpf: change eBPF helper doc parsing script to allow for smaller indent Documentation for eBPF helpers can be parsed from bpf.h and eventually turned into a man page. Commit 6f96674dbd8c ("bpf: relax constraints on formatting for eBPF helper documentation") changed the script used to parse it, in order to allow for different indent style and to ease the work for writing documentation for future helpers. The script currently considers that the first tab can be replaced by 6 to 8 spaces. But the documentation for bpf_fib_lookup() uses a mix of tabs (for the "Description" part) and of spaces ("Return" part), and only has 5 space long indent for the latter. We probably do not want to change the values accepted by the script each time a new helper gets a new indent style. However, it is worth noting that with those 5 spaces, the "Description" and "Return" part *look* aligned in the generated patch and in `git show`, so it is likely other helper authors will use the same length. Therefore, allow for helper documentation to use 5 spaces only for the first indent level. Signed-off-by: Quentin Monnet Signed-off-by: Daniel Borkmann --- scripts/bpf_helpers_doc.py | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'scripts') diff --git a/scripts/bpf_helpers_doc.py b/scripts/bpf_helpers_doc.py index 8f59897fbda1..5010a4d5bfba 100755 --- a/scripts/bpf_helpers_doc.py +++ b/scripts/bpf_helpers_doc.py @@ -95,7 +95,7 @@ class HeaderParser(object): return capture.group(1) def parse_desc(self): - p = re.compile(' \* ?(?:\t| {6,8})Description$') + p = re.compile(' \* ?(?:\t| {5,8})Description$') capture = p.match(self.line) if not capture: # Helper can have empty description and we might be parsing another @@ -109,7 +109,7 @@ class HeaderParser(object): if self.line == ' *\n': desc += '\n' else: - p = re.compile(' \* ?(?:\t| {6,8})(?:\t| {8})(.*)') + p = re.compile(' \* ?(?:\t| {5,8})(?:\t| {8})(.*)') capture = p.match(self.line) if capture: desc += capture.group(1) + '\n' @@ -118,7 +118,7 @@ class HeaderParser(object): return desc def parse_ret(self): - p = re.compile(' \* ?(?:\t| {6,8})Return$') + p = re.compile(' \* ?(?:\t| {5,8})Return$') capture = p.match(self.line) if not capture: # Helper can have empty retval and we might be parsing another @@ -132,7 +132,7 @@ class HeaderParser(object): if self.line == ' *\n': ret += '\n' else: - p = re.compile(' \* ?(?:\t| {6,8})(?:\t| {8})(.*)') + p = re.compile(' \* ?(?:\t| {5,8})(?:\t| {8})(.*)') capture = p.match(self.line) if capture: ret += capture.group(1) + '\n' -- cgit v1.2.3 From 819dd92b9c0bc7bce9097d8c1f14240f471bb386 Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Mon, 4 Jun 2018 19:53:41 -0700 Subject: bpfilter: switch to CC from HOSTCC check that CC can build executables and use that compiler instead of HOSTCC Suggested-by: Arnd Bergmann Signed-off-by: Alexei Starovoitov Signed-off-by: David S. Miller --- Makefile | 5 +++++ net/Makefile | 4 ++++ net/bpfilter/Makefile | 2 ++ scripts/cc-can-link.sh | 11 +++++++++++ 4 files changed, 22 insertions(+) create mode 100755 scripts/cc-can-link.sh (limited to 'scripts') diff --git a/Makefile b/Makefile index 56ba070dfa09..62c110084fae 100644 --- a/Makefile +++ b/Makefile @@ -510,6 +510,11 @@ ifeq ($(call shell-cached,$(CONFIG_SHELL) $(srctree)/scripts/gcc-goto.sh $(CC) $ KBUILD_AFLAGS += -DCC_HAVE_ASM_GOTO endif +ifeq ($(call shell-cached,$(CONFIG_SHELL) $(srctree)/scripts/cc-can-link.sh $(CC)), y) + CC_CAN_LINK := y + export CC_CAN_LINK +endif + ifeq ($(config-targets),1) # =========================================================================== # *config targets only - make sure prerequisites are updated, and descend diff --git a/net/Makefile b/net/Makefile index bdaf53925acd..13ec0d5415c7 100644 --- a/net/Makefile +++ b/net/Makefile @@ -20,7 +20,11 @@ obj-$(CONFIG_TLS) += tls/ obj-$(CONFIG_XFRM) += xfrm/ obj-$(CONFIG_UNIX) += unix/ obj-$(CONFIG_NET) += ipv6/ +ifneq ($(CC_CAN_LINK),y) +$(warning CC cannot link executables. Skipping bpfilter.) +else obj-$(CONFIG_BPFILTER) += bpfilter/ +endif obj-$(CONFIG_PACKET) += packet/ obj-$(CONFIG_NET_KEY) += key/ obj-$(CONFIG_BRIDGE) += bridge/ diff --git a/net/bpfilter/Makefile b/net/bpfilter/Makefile index 3f3cb87c668f..aafa72001fcd 100644 --- a/net/bpfilter/Makefile +++ b/net/bpfilter/Makefile @@ -6,6 +6,8 @@ hostprogs-y := bpfilter_umh bpfilter_umh-objs := main.o HOSTCFLAGS += -I. -Itools/include/ -Itools/include/uapi +HOSTCC := $(CC) + ifeq ($(CONFIG_BPFILTER_UMH), y) # builtin bpfilter_umh should be compiled with -static # since rootfs isn't mounted at the time of __init diff --git a/scripts/cc-can-link.sh b/scripts/cc-can-link.sh new file mode 100755 index 000000000000..208eb2825dab --- /dev/null +++ b/scripts/cc-can-link.sh @@ -0,0 +1,11 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 + +cat << "END" | $@ -x c - -o /dev/null >/dev/null 2>&1 && echo "y" +#include +int main(void) +{ + printf(""); + return 0; +} +END -- cgit v1.2.3