Due to libdw does not have proper BPF relocation support, the pahole cannot display filenames correctly for objects with default llvm options. So we have to invent a special option "llc -march=bpf -mattr=dwarfris" to prevent llvm from generating cross-section dwarf relocation records (https://reviews.llvm.org/rL326505). The pahole related discussion is in linux netdev mailing list (http://lists.openwall.net/netdev/2018/06/15/38, etc.)
We would like to add proper BPF relocation support to libdw so eventually we could retire the special llc bpf flag "-mattr=dwarfris". The bpf relocations are defined in llvm_repo:include/llvm/BinaryFormat/ELFRelocs/BPF.def: ELF_RELOC(R_BPF_NONE, 0) ELF_RELOC(R_BPF_64_64, 1) ELF_RELOC(R_BPF_64_32, 10) Removed the relocation type R_BPF_MAP_FD whoes name does not confirm to llvm definition and replaced it with R_BPF_64_64. The BPF object is just a relocatible object, not an executable or a shared library, so assign ELF type to REL only in bpf_reloc.def. Tested locally with building pahole with this patch and pahole is able to display structures in bpf object file properly. Signed-off-by: Yonghong Song <y...@fb.com> --- backends/Makefile.am | 2 +- backends/bpf_init.c | 1 + backends/bpf_reloc.def | 3 ++- backends/bpf_symbol.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++ libelf/elf.h | 3 ++- 5 files changed, 60 insertions(+), 3 deletions(-) create mode 100644 backends/bpf_symbol.c diff --git a/backends/Makefile.am b/backends/Makefile.am index 80aa00e7..b5e721d8 100644 --- a/backends/Makefile.am +++ b/backends/Makefile.am @@ -126,7 +126,7 @@ am_libebl_m68k_pic_a_OBJECTS = $(m68k_SRCS:.c=.os) # an issue. m68k_corenote_no_Wpacked_not_aligned = yes -bpf_SRCS = bpf_init.c bpf_regs.c +bpf_SRCS = bpf_init.c bpf_regs.c bpf_symbol.c cpu_bpf = ../libcpu/libcpu_bpf.a libebl_bpf_pic_a_SOURCES = $(bpf_SRCS) am_libebl_bpf_pic_a_OBJECTS = $(bpf_SRCS:.c=.os) diff --git a/backends/bpf_init.c b/backends/bpf_init.c index 8ea1bc1a..a046e069 100644 --- a/backends/bpf_init.c +++ b/backends/bpf_init.c @@ -53,6 +53,7 @@ bpf_init (Elf *elf __attribute__ ((unused)), bpf_init_reloc (eh); HOOK (eh, register_info); HOOK (eh, disasm); + HOOK (eh, reloc_simple_type); return MODVERSION; } diff --git a/backends/bpf_reloc.def b/backends/bpf_reloc.def index a410da97..59f519b5 100644 --- a/backends/bpf_reloc.def +++ b/backends/bpf_reloc.def @@ -28,4 +28,5 @@ /* NAME, REL|EXEC|DYN */ RELOC_TYPE (NONE, EXEC|DYN) -RELOC_TYPE (MAP_FD, REL|EXEC|DYN) +RELOC_TYPE (64_64, REL) +RELOC_TYPE (64_32, REL) diff --git a/backends/bpf_symbol.c b/backends/bpf_symbol.c new file mode 100644 index 00000000..c9856f26 --- /dev/null +++ b/backends/bpf_symbol.c @@ -0,0 +1,54 @@ +/* BPF specific symbolic name handling. + This file is part of elfutils. + + This file is free software; you can redistribute it and/or modify + it under the terms of either + + * the GNU Lesser General Public License as published by the Free + Software Foundation; either version 3 of the License, or (at + your option) any later version + + or + + * the GNU General Public License as published by the Free + Software Foundation; either version 2 of the License, or (at + your option) any later version + + or both in parallel, as here. + + elfutils is distributed in the hope that it will be useful, but + WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + General Public License for more details. + + You should have received copies of the GNU General Public License and + the GNU Lesser General Public License along with this program. If + not, see <http://www.gnu.org/licenses/>. */ + +#ifdef HAVE_CONFIG_H +# include <config.h> +#endif + +#include <assert.h> +#include <elf.h> +#include <stddef.h> +#include <string.h> + +#define BACKEND bpf_ +#include "libebl_CPU.h" + + +/* Check for the simple reloc types. */ +Elf_Type +bpf_reloc_simple_type (Ebl *ebl __attribute__ ((unused)), int type) +{ + switch (type) + { + case R_BPF_64_64: + return ELF_T_XWORD; + case R_BPF_64_32: + return ELF_T_WORD; + default: + return ELF_T_NUM; + } +} diff --git a/libelf/elf.h b/libelf/elf.h index f7748983..940e88dd 100644 --- a/libelf/elf.h +++ b/libelf/elf.h @@ -3848,7 +3848,8 @@ enum /* BPF specific declarations. */ #define R_BPF_NONE 0 /* No reloc */ -#define R_BPF_MAP_FD 1 /* Map fd to pointer */ +#define R_BPF_64_64 1 +#define R_BPF_64_32 10 /* Imagination Meta specific relocations. */ -- 2.14.3
