On Thu, Jun 14, 2018 at 12:03:34PM -0300, Arnaldo Carvalho de Melo wrote:
> > > > > 1. The tools/testing/selftests/bpf/Makefile has the CLANG_FLAGS and
> > > > > LLC_FLAGS needed to compile the bpf prog. It requires a new
> > > > > "-mattr=dwarf" llc option which was added to the future
> > > > > llvm 7.0.
[ ... ]
> I tried it, but it didn't work, see:
>
> [root@jouet bpf]# cat hello.c
> #include "stdio.h"
>
> int syscall_enter(openat)(void *ctx)
> {
> puts("Hello, world\n");
> return 0;
> }
> [root@jouet bpf]# trace -e openat,hello.c touch /tmp/kafai
> clang-6.0: error: unknown argument: '-mattr=dwarf'
"-mattr=dwarf" is currently a llc only option.
tools/testing/selftests/bpf/Makefile has example on how to pipe clang to llc.
e.g.:
clang -g -O2 -target bpf -emit-llvm -c hello.c -o - | llc -march=bpf
-mcpu=generic -mattr=dwarfris -filetype=obj -o hello.o
> ERROR: unable to compile hello.c
> Hint: Check error message shown above.
> Hint: You can also pre-compile it into .o using:
> clang -target bpf -O2 -c hello.c
> with proper -I and -D options.
> event syntax error: 'hello.c'
> \___ Failed to load hello.c from source: Error when
> compiling BPF scriptlet
>
> (add -v to see detail)
> Run 'perf list' for a list of valid events
>
> Usage: perf trace [<options>] [<command>]
> or: perf trace [<options>] -- <command> [<options>]
> or: perf trace record [<options>] [<command>]
> or: perf trace record [<options>] -- <command> [<options>]
>
> -e, --event <event> event/syscall selector. use 'perf list' to list
> available events
> [root@jouet bpf]#
>
> The full command line with that is:
>
> [root@jouet bpf]# trace -v -e openat,hello.c touch /tmp/kafai |& grep mattr
> set env: CLANG_OPTIONS=-g -mattr=dwarf
> llvm compiling command : /usr/local/bin/clang -D__KERNEL__ -D__NR_CPUS__=4
> -DLINUX_VERSION_CODE=0x41100 -g -mattr=dwarf -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
> -I/home/acme/lib/include/perf/bpf -Wno-unused-value -Wno-pointer-sign
> -working-directory /lib/modules/4.17.0-rc5/build -c /home/acme/bpf/hello.c
> -target bpf -O2 -o -
> clang-6.0: error: unknown argument: '-mattr=dwarf'
> [root@jouet bpf]#
>
> This is with these llvm and clang trees:
>
> [root@jouet llvm]# git log --oneline -5
> 98c78e82f54 (HEAD -> master, origin/master, origin/HEAD) [asan] Instrument
> comdat globals on COFF targets
> 6ad988b5998 [DAGCombiner] clean up comments; NFC
> a735ba5b795 [X86][SSE] Support v8i16/v16i16 rotations
> 1503b9f6fe8 [x86] add tests for node-level FMF; NFC
> 4a49826736f [x86] regenerate test checks; NFC
> [root@jouet llvm]#
>
> [root@jouet llvm]# cd tools/clang/
> [root@jouet clang]# git log --oneline -5
> 8c873daccc (HEAD -> master, origin/master, origin/HEAD) [X86] Add builtins
> for vpermq/vpermpd instructions to enable target feature checking.
> a344be6ba4 [X86] Change immediate type for some builtins from char to int.
> dcdd53793e [CUDA] Fix emission of constant strings in sections
> a90c85acaf [X86] Add builtins for shufps and shufpd to enable target feature
> and immediate range checking.
> ff71c0eccc [X86] Add builtins for pshufd, pshuflw, and pshufhw to enable
> target feature and immediate range checking.
> [root@jouet clang]#
>
> [root@jouet clang]# git log | grep mattr=dwarf
> [root@jouet clang]# cd -
> /home/acme/git.tmp/git/llvm
> [root@jouet llvm]# git log | grep mattr=dwarf
> bpf: introduce -mattr=dwarfris to disable
> DwarfUsesRelocationsAcrossSections
> This patch introduces a new flag -mattr=dwarfris
> [root@jouet llvm]#
>
> Humm, so its -mattr=dwarfris and not -attr=dwarf?
>
> Didn't help :-\
>
> commit 0e0047f8c9ada2f0fe0c5f01579a80e2455b8df5
> Author: Yonghong Song <y...@fb.com>
> Date: Thu Mar 1 23:04:59 2018 +0000
>
> bpf: introduce -mattr=dwarfris to disable
> DwarfUsesRelocationsAcrossSections
>
> Commit e4507fb8c94b ("bpf: disable DwarfUsesRelocationsAcrossSections")
> disables MCAsmInfo DwarfUsesRelocationsAcrossSections unconditionally
> so that dwarf will not use cross section (between dwarf and symbol table)
> relocations. This new debug format enables pahole to dump structures
> correctly as libdwarves.so does not have BPF backend support yet.
>
> This new debug format, however, breaks bcc
> (https://github.com/iovisor/bcc)
> source debug output as llvm in-memory Dwarf support has some issues to
> handle it. More specifically, with DwarfUsesRelocationsAcrossSections
> disabled, JIT compiler does not generate .debug_abbrev and Dwarf
> DIE (debug info entry) processing is not happy about this.
>
> This patch introduces a new flag -mattr=dwarfris
> (dwarf relocation in section) to disable
> DwarfUsesRelocationsAcrossSections.
> DwarfUsesRelocationsAcrossSections is true by default.
>
> Signed-off-by: Yonghong Song <y...@fb.com>
>
> git-svn-id:
> https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_svn_llvm-2Dproject_llvm_trunk-40326505&d=DwIBAg&c=5VD0RTtNlTh3ycd41b3MUw&r=VQnoQ7LvghIj0gVEaiQSUw&m=LO28-RE-2ZJTXto_gff4BgnxXkbUq8d2CEz1jD_wDl4&s=VCR3pGVfY54-OsZ3BqRsOr3FF5JVyltwbnbzu30_4EY&e=
> 91177308-0d34-0410-b5e6-96231b3b80d8
>
>
