On 4/3/21 2:42 PM, Sedat Dilek wrote:
On Sat, Apr 3, 2021 at 8:42 PM Yonghong Song <yhs@xxxxxx> wrote:
Currently, when DWARF5 is enabled in kernel, DEBUG_INFO_BTF
needs to be disabled. I hacked the kernel to enable DEBUG_INFO_BTF
like:
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -286,7 +286,6 @@ config DEBUG_INFO_DWARF5
bool "Generate DWARF Version 5 debuginfo"
depends on GCC_VERSION >= 50000 || CC_IS_CLANG
depends on CC_IS_GCC || $(success,$(srctree)/scripts/test_dwarf5_support.sh $(CC) $(CLANG_FLAGS))
- depends on !DEBUG_INFO_BTF
What Linux-kernel is your base?
For linus Git this is correct.
[ I have currently kbuild-next stuff in my custom patchset which has
for example CONFIG_AS_IS_XXX where XXX is "GNU" means GNU/binutils AS
or "LLVM" means LLVM/Clang Integrated ASsembler (IAS). ]
help
and tried DWARF5 with latest trunk clang, thin-lto and no lto.
In both cases, I got a few additional failures like:
$ ./test_progs -n 55/2
What do you mean with "trunk" clang - we have Git now no more SVN :-)?
From where is that "test_progs" ?
I tried to build:
LLVM_TOOLCHAIN_PATH="/opt/llvm-toolchain/bin"
if [ -d ${LLVM_TOOLCHAIN_PATH} ]; then
export PATH="${LLVM_TOOLCHAIN_PATH}:${PATH}"
fi
$ echo $PATH
/opt/llvm-toolchain/bin:/opt/proxychains-ng/bin:/home/dileks/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
$ clang --version
dileks clang version 12.0.0 (https://github.com/llvm/llvm-project.git
04ba60cfe598e41084fb848daae47e0ed910fa7d)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /opt/llvm-toolchain/bin
MAKE="make V=1"
MAKE_OPTS="HOSTCC=clang HOSTCXX=clang++ HOSTLD=ld.lld CC=clang
LD=ld.lld LLVM=1 LLVM_IAS=1"
MAKE_OPTS="$MAKE_OPTS PAHOLE=/opt/pahole/bin/pahole"
$ echo $MAKE $MAKE_OPTS
make V=1 HOSTCC=clang HOSTCXX=clang++ HOSTLD=ld.lld CC=clang LD=ld.lld
LLVM=1 LLVM_IAS=1 PAHOLE=/opt/pahole/bin/pahole
$ LC_ALL=C $MAKE $MAKE_OPTS -C tools/bpf/ 2&>1 | tee ../make-log_tools-bpf.txt
...is OK.
$ LC_ALL=C $MAKE $MAKE_OPTS -C tools/testing/selftests/bpf/ 2>&1 | tee
../make-log_tools-testing-selftests-bpf.txt
...is broken here.
NOTE: Both make-log_tools-bpf.txt and
make-log_tools-testing-selftests-bpf.txt are attached.
bpf selftest always tends to require latest clang.
For the error,
-idirafter /opt/llvm-toolchain/lib/clang/12.0.0/include -idirafter
/usr/include/x86_64-linux-gnu -idirafter /usr/include
-Wno-compare-distinct-pointer-types -DENABLE_ATOMICS_TESTS -O2 -target
bpf -c progs/local_storage.c -o
/home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/local_storage.o
-mcpu=v3
progs/local_storage.c:41:15: error: use of undeclared identifier
'BPF_MAP_TYPE_TASK_STORAGE'; did you mean 'BPF_MAP_TYPE_SK_STORAGE'?
__uint(type, BPF_MAP_TYPE_TASK_STORAGE);
^~~~~~~~~~~~~~~~~~~~~~~~~
BPF_MAP_TYPE_SK_STORAGE
/home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/tools/include/bpf/bpf_helpers.h:13:39:
note: expanded from macro '__uint'
#define __uint(name, val) int (*name)[val]
^
/home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/tools/include/vmlinux.h:10202:2:
note: 'BPF_MAP_TYPE_SK_STORAGE' declared here
BPF_MAP_TYPE_SK_STORAGE = 24,
^
1 error generated.
vmlinux.h does not contain BPF_MAP_TYPE_TASK_STORAGE.
vmlinux.h is generated from BTF of the vmlinux you just built,
but it looks like somehow it is generated from another vmlinux
it does not contain BPF_MAP_TYPE_TASK_STORAGE. There are some
build magic here to find correct vmlinux and maybe this just
does not work for you.
But you can use the pahole output comparison of BTF VAR encoding
between dwarf4 and dwarf5, this will have even more coverage.
...
libbpf: extern (var ksym) 'bpf_prog_active': failed to find BTF ID in kernel BTF(s).
libbpf: failed to load object 'kfunc_call_test_subprog'
libbpf: failed to load BPF skeleton 'kfunc_call_test_subprog': -22
test_subprog:FAIL:skel unexpected error: 0
#55/2 subprog:FAIL
Here, bpf_prog_active is a percpu global variable and pahole is supposed to
put into BTF, but it is not there.
Further analysis shows this is due to encoding difference between
DWARF4 and DWARF5. In DWARF5, a new section .debug_addr
and several new ops, e.g. DW_OP_addrx, are introduced.
DW_OP_addrx is actually an index into .debug_addr section starting
from an offset encoded with DW_AT_addr_base in DW_TAG_compile_unit.
With LLVM toolchain v12.0.0-rc4 I see "DW_OP_addrx".
I need a test-case to hit the issue(s) and test this or any other
(pahole) patches.
Thanks.
- Sedat -
For the above 'bpf_prog_active' example, with DWARF4, we have
0x02281a96: DW_TAG_variable
DW_AT_name ("bpf_prog_active")
DW_AT_decl_file ("/home/yhs/work/bpf-next/include/linux/bpf.h")
DW_AT_decl_line (1170)
DW_AT_decl_column (0x01)
DW_AT_type (0x0226d171 "int")
DW_AT_external (true)
DW_AT_declaration (true)
0x02292f04: DW_TAG_variable
DW_AT_specification (0x02281a96 "bpf_prog_active")
DW_AT_decl_file ("/home/yhs/work/bpf-next/kernel/bpf/syscall.c")
DW_AT_decl_line (45)
DW_AT_location (DW_OP_addr 0x28940)
For DWARF5, we have
0x0138b0a1: DW_TAG_variable
DW_AT_name ("bpf_prog_active")
DW_AT_type (0x013760b9 "int")
DW_AT_external (true)
DW_AT_decl_file ("/home/yhs/work/bpf-next/kernel/bpf/syscall.c")
DW_AT_decl_line (45)
DW_AT_location (DW_OP_addrx 0x16)
This patch added support for DW_OP_addrx. With the patch, the above
failing bpf selftest and other similar failed selftests succeeded.
---
dwarf_loader.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
NOTE: with this patch, at least for clang trunk, all bpf selftests
are fine for DWARF5 w.r.t. compiler and pahole. Hopefully
after pahole 1.21 release, we can remove DWARF5 dependence
with !DEBUG_INFO_BTF.
diff --git a/dwarf_loader.c b/dwarf_loader.c
index 82d7131..49336ac 100644
--- a/dwarf_loader.c
+++ b/dwarf_loader.c
@@ -401,8 +401,19 @@ static int attr_location(Dwarf_Die *die, Dwarf_Op **expr, size_t *exprlen)
{
Dwarf_Attribute attr;
if (dwarf_attr(die, DW_AT_location, &attr) != NULL) {
- if (dwarf_getlocation(&attr, expr, exprlen) == 0)
+ if (dwarf_getlocation(&attr, expr, exprlen) == 0) {
+ /* DW_OP_addrx needs additional lookup for real addr. */
+ if (*exprlen != 0 && expr[0]->atom == DW_OP_addrx) {
+ Dwarf_Attribute addr_attr;
+ dwarf_getlocation_attr(&attr, expr[0], &addr_attr);
+
+ Dwarf_Addr address;
+ dwarf_formaddr (&addr_attr, &address);
+
+ expr[0]->number = address;
+ }
return 0;
+ }
}
return 1;
@@ -626,6 +637,7 @@ static enum vscope dwarf__location(Dwarf_Die *die, uint64_t *addr, struct locati
Dwarf_Op *expr = location->expr;
switch (expr->atom) {
case DW_OP_addr:
+ case DW_OP_addrx:
scope = VSCOPE_GLOBAL;
*addr = expr[0].number;
break;
--
2.30.2
