Re: perf test LLVM & clang 6 failing

[Yonghong Song <yhs@fb.com>]

On 11/27/17 9:04 AM, Arnaldo Carvalho de Melo wrote:
> Em Fri, Nov 24, 2017 at 04:16:52PM +0100, Daniel Borkmann escreveu:
>> [ +Yonghong ]
> 
> + Josh
>   
>> On 11/24/2017 03:47 PM, Arnaldo Carvalho de Melo wrote:
>>> FYI, just noticed, recently updated clang to version 6, from its
>>> upstream git repo.
>>
>> Do you recall what was your LLVM version prior to this where it was
>> working fine? (Wild guess from below would be the BPF inline asm
>> support that was added recently to LLVM (2865ab6996) vs asm() used
>> in headers included in the stdin header causing trouble due to arch
>> mixup?)
> 
> So, if I go to the cset just before:
> 
> commit f5caf621ee357279e759c0911daf6d55c7d36f03
> Author: Josh Poimboeuf <jpoimboe@redhat.com>
> Date:   Wed Sep 20 16:24:33 2017 -0500
> 
>      x86/asm: Fix inline asm call constraints for Clang
> ---
> 
> 'perf test LLVM' works again:
> 
> [root@jouet ~]# perf test LLVM
> 37: LLVM search and compile                               :
> 37.1: Basic BPF llvm compile                              : Ok
> 37.2: kbuild searching                                    : Ok
> 37.3: Compile source for BPF prologue generation          : Ok
> 37.4: Compile source for BPF relocation                   : Ok
> [root@jouet ~]#
> 
> I.e. 'perf test LLVM' built from what is in my acme/perf/urgent branch,
> targetted to v4.15, uses kernel headers and if I go to just before
> f5caf621ee, it works again, both with clang from fedora26 (4.0.1) and
> with 6.0, built from sources.

This patch introduced a module level inline assembly.

...
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -132,4 +132,15 @@
  /* For C file, we already have NOKPROBE_SYMBOL macro */
  #endif

+#ifndef __ASSEMBLY__
+/*
+ * This output constraint should be used for any inline asm which has a 
"call"
+ * instruction.  Otherwise the asm may be inserted before the frame pointer
+ * gets set up by the containing function.  If you forget to do this, 
objtool
+ * may print a "call without frame pointer save/setup" warning.
+ */
+register unsigned int __asm_call_sp asm("esp");
+#define ASM_CALL_CONSTRAINT "+r" (__asm_call_sp)
+#endif
...

This will cause "clang ... -target bpf ..." failure since 4.0 does not 
have bpf inline asm support and 6.0 does not recognize the register 'esp'.

> 
> 'perf test BPF' breaks for another reason, needs another investigation,
> maybe you guys can spot something changed recently in that area:
> 
> libbpf: failed to create map (name: 'flip_table'): Invalid argument
> libbpf: failed to load object '[basic_bpf_test]'

Not sure whether this is the root cause or not, but the below section name
    SEC("func=SyS_epoll_wait")
is not a good one.
If it is used to represent the program name in the kernel, the kernel 
will reject it with invalid argument since it contains "=".

> 
> Complete logs up to this error are below, I'll go read Yonghong message
> to see if I can get the 'perf test LLVM' case fixed.
> 
> - Arnaldo
> 
> [root@jouet ~]# perf test BPF
> 39: BPF filter                                            :
> 39.1: Basic BPF filtering                                 : FAILED!
> 39.2: BPF pinning                                         : Skip
> 39.3: BPF prologue generation                             : Skip
> 39.4: BPF relocation checker                              : Skip
> [root@jouet ~]# perf test -v BPF
> 39: BPF filter                                            :
> 39.1: Basic BPF filtering                                 :
> --- start ---
> test child forked, pid 3541
> Kernel build dir is set to /lib/modules/4.14.0+/build
> set env: KBUILD_DIR=/lib/modules/4.14.0+/build
> unset env: KBUILD_OPTS
> include option is set to  -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/7/include -I/home/acme/git/linux/arch/x86/include -I./arch/x86/include/generated  -I/home/acme/git/linux/include -I./include -I/home/acme/git/linux/arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I/home/acme/git/linux/include/uapi -I./include/generated/uapi -include /home/acme/git/linux/include/linux/kconfig.h
> set env: NR_CPUS=4
> set env: LINUX_VERSION_CODE=0x40e00
> set env: CLANG_EXEC=/usr/lib64/ccache/clang
> set env: CLANG_OPTIONS=-xc
> set env: KERNEL_INC_OPTIONS= -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/7/include -I/home/acme/git/linux/arch/x86/include -I./arch/x86/include/generated  -I/home/acme/git/linux/include -I./include -I/home/acme/git/linux/arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I/home/acme/git/linux/include/uapi -I./include/generated/uapi -include /home/acme/git/linux/include/linux/kconfig.h
> set env: WORKING_DIR=/lib/modules/4.14.0+/build
> set env: CLANG_SOURCE=-
> llvm compiling command template: echo '/*
>   * bpf-script-example.c
>   * Test basic LLVM building
>   */
> #ifndef LINUX_VERSION_CODE
> # error Need LINUX_VERSION_CODE
> # error Example: for 4.2 kernel, put 'clang-opt="-DLINUX_VERSION_CODE=0x40200" into llvm section of ~/.perfconfig'
> #endif
> #define BPF_ANY 0
> #define BPF_MAP_TYPE_ARRAY 2
> #define BPF_FUNC_map_lookup_elem 1
> #define BPF_FUNC_map_update_elem 2
> 
> static void *(*bpf_map_lookup_elem)(void *map, void *key) =
> 	(void *) BPF_FUNC_map_lookup_elem;
> static void *(*bpf_map_update_elem)(void *map, void *key, void *value, int flags) =
> 	(void *) BPF_FUNC_map_update_elem;
> 
> struct bpf_map_def {
> 	unsigned int type;
> 	unsigned int key_size;
> 	unsigned int value_size;
> 	unsigned int max_entries;
> };
> 
> #define SEC(NAME) __attribute__((section(NAME), used))
> struct bpf_map_def SEC("maps") flip_table = {
> 	.type = BPF_MAP_TYPE_ARRAY,
> 	.key_size = sizeof(int),
> 	.value_size = sizeof(int),
> 	.max_entries = 1,
> };
> 
> SEC("func=SyS_epoll_wait")
> int bpf_func__SyS_epoll_wait(void *ctx)
> {
> 	int ind =0;
> 	int *flag = bpf_map_lookup_elem(&flip_table, &ind);
> 	int new_flag;
> 	if (!flag)
> 		return 0;
> 	/* flip flag and store back */
> 	new_flag = !*flag;
> 	bpf_map_update_elem(&flip_table, &ind, &new_flag, BPF_ANY);
> 	return new_flag;
> }
> char _license[] SEC("license") = "GPL";
> int _version SEC("version") = LINUX_VERSION_CODE;
> ' | $CLANG_EXEC -D__KERNEL__ -D__NR_CPUS__=$NR_CPUS -DLINUX_VERSION_CODE=$LINUX_VERSION_CODE $CLANG_OPTIONS $KERNEL_INC_OPTIONS -Wno-unused-value -Wno-pointer-sign -working-directory $WORKING_DIR -c "$CLANG_SOURCE" -target bpf -O2 -o -
> libbpf: loading object '[basic_bpf_test]' from buffer
> libbpf: section .strtab, size 120, link 0, flags 0, type=3
> libbpf: section .text, size 0, link 0, flags 6, type=1
> libbpf: section func=SyS_epoll_wait, size 200, link 0, flags 6, type=1
> libbpf: found program func=SyS_epoll_wait
> libbpf: section .relfunc=SyS_epoll_wait, size 32, link 8, flags 0, type=9
> libbpf: section maps, size 16, link 0, flags 3, type=1
> libbpf: section license, size 4, link 0, flags 3, type=1
> libbpf: license of [basic_bpf_test] is GPL
> libbpf: section version, size 4, link 0, flags 3, type=1
> libbpf: kernel version of [basic_bpf_test] is 40e00
> libbpf: section .symtab, size 168, link 1, flags 0, type=2
> libbpf: maps in [basic_bpf_test]: 1 maps in 16 bytes
> libbpf: map 0 is "flip_table"
> libbpf: collecting relocating info for: 'func=SyS_epoll_wait'
> libbpf: relocation: insn_idx=4
> libbpf: relocation: find map 0 (flip_table) for insn 4
> libbpf: relocation: insn_idx=18
> libbpf: relocation: find map 0 (flip_table) for insn 18
> bpf: config program 'func=SyS_epoll_wait'
> symbol:SyS_epoll_wait file:(null) line:0 offset:0 return:0 lazy:(null)
> bpf: config 'func=SyS_epoll_wait' is ok
> Looking at the vmlinux_path (8 entries long)
> Using /lib/modules/4.14.0+/build/vmlinux for symbols
> Open Debuginfo file: /lib/modules/4.14.0+/build/vmlinux
> Try to find probe point from debuginfo.
> Matched function: SyS_epoll_wait [2e5a9be]
> found inline addr: 0xffffffff812af256
> Probe point found: compat_SyS_epoll_pwait+150
> found inline addr: 0xffffffff812af037
> Probe point found: SyS_epoll_pwait+135
> found inline addr: 0xffffffff812aeed0
> Probe point found: SyS_epoll_wait+0
> Found 3 probe_trace_events.
> Opening /sys/kernel/debug/tracing//kprobe_events write=1
> Writing event: p:perf_bpf_probe/func _text+2814550
> Writing event: p:perf_bpf_probe/func_1 _text+2814007
> Writing event: p:perf_bpf_probe/func_2 _text+2813648
> libbpf: failed to create map (name: 'flip_table'): Invalid argument
> libbpf: failed to load object '[basic_bpf_test]'
> bpf: load objects failed
> Failed to add events selected by BPF
>