091037fb77
With clang build kernel (adding LLVM=1 to kernel and selftests/bpf build
command line), I hit the following test failure:
$ ./test_progs -t btf_dump
...
btf_dump_data:PASS:ensure expected/actual match 0 nsec
btf_dump_data:FAIL:find type id unexpected find type id: actual -2 < expected 0
btf_dump_data:FAIL:find type id unexpected find type id: actual -2 < expected 0
test_btf_dump_int_data:FAIL:dump __int128 unexpected error: -2 (errno 2)
#15/9 btf_dump/btf_dump: int_data:FAIL
Further analysis showed gcc build kernel has type "__int128" in dwarf/BTF
and it doesn't exist in clang build kernel. Code searching for kernel code
found the following:
arch/s390/include/asm/types.h: unsigned __int128 pair;
crypto/ecc.c: unsigned __int128 m = (unsigned __int128)left * right;
include/linux/math64.h: return (u64)(((unsigned __int128)a * mul) >> shift);
include/linux/math64.h: return (u64)(((unsigned __int128)a * mul) >> shift);
lib/ubsan.h:typedef __int128 s_max;
lib/ubsan.h:typedef unsigned __int128 u_max;
In my case, CONFIG_UBSAN is not enabled. Even if we only have "unsigned __int128"
in the code, somehow gcc still put "__int128" in dwarf while clang didn't.
Hence current test works fine for gcc but not for clang.
Enabling CONFIG_UBSAN is an option to provide __int128 type into dwarf
reliably for both gcc and clang, but not everybody enables CONFIG_UBSAN
in their kernel build. So the best choice is to use "unsigned __int128" type
which is available in both clang and gcc build kernels. But clang and gcc
dwarf encoded names for "unsigned __int128" are different:
[$ ~] cat t.c
unsigned __int128 a;
[$ ~] gcc -g -c t.c && llvm-dwarfdump t.o | grep __int128
DW_AT_type (0x00000031 "__int128 unsigned")
DW_AT_name ("__int128 unsigned")
[$ ~] clang -g -c t.c && llvm-dwarfdump t.o | grep __int128
DW_AT_type (0x00000033 "unsigned __int128")
DW_AT_name ("unsigned __int128")
The test change in this patch tries to test type name before
doing actual test.
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Link: https://lore.kernel.org/bpf/20210924025856.2192476-1-yhs@fb.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.