[PATCH v2] backends,bpf: add proper relocation support
Yonghong Song
yhs@fb.com
Sat Jun 16 20:02:00 GMT 2018
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.
Signed-off-by: Yonghong Song <yhs@fb.com>
---
backends/ChangeLog | 7 +++++
backends/Makefile.am | 2 +-
backends/bpf_init.c | 1 +
backends/bpf_reloc.def | 3 +-
backends/bpf_symbol.c | 54 ++++++++++++++++++++++++++++++++++++
libelf/elf.h | 3 +-
tests/ChangeLog | 9 ++++++
tests/Makefile.am | 5 +++-
tests/run-reloc-bpf.sh | 33 ++++++++++++++++++++++
tests/testfile-bpf-reloc.expect.bz2 | Bin 0 -> 300 bytes
tests/testfile-bpf-reloc.o.bz2 | Bin 0 -> 933 bytes
11 files changed, 113 insertions(+), 4 deletions(-)
create mode 100644 backends/bpf_symbol.c
create mode 100755 tests/run-reloc-bpf.sh
create mode 100644 tests/testfile-bpf-reloc.expect.bz2
create mode 100644 tests/testfile-bpf-reloc.o.bz2
Note:
I didn't add the Changelog to libelf/elf.h as I anticipate the
change will come from sync'ing with glibc.
If this patch version looks good, I can send another revision
once the libelf/elf.h is synced.
diff --git a/backends/ChangeLog b/backends/ChangeLog
index 0dde0ff3..1ffe5ba4 100644
--- a/backends/ChangeLog
+++ b/backends/ChangeLog
@@ -1,3 +1,10 @@
+2018-06-16 Yonghong Song <yhs@fb.com>
+
+ * Makefile.am (bpf_SRCS): Add bpf_symbol.c.
+ * bpf_init.c (bpf_init): Add reloc_simple_type HOOK.
+ * bpf_reloc.def: Add RELOC_TYPE 64_64 and 64_32.
+ * bpf_symbol.c: New file.
+
2018-05-15 Andreas Schwab <schwab@suse.de>
* riscv_init.c (riscv_init): Hook check_special_symbol.
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. */
diff --git a/tests/ChangeLog b/tests/ChangeLog
index 4abbd125..c4942860 100644
--- a/tests/ChangeLog
+++ b/tests/ChangeLog
@@ -1,3 +1,12 @@
+2018-06-16 Yonghong Song <yhs@fb.com>
+
+ * run-reloc-bpf.sh: New test.
+ * testfile-bpf-reloc.o.bz2: New test file.
+ * testfile-bpf-reloc.expect.bz2: New test file.
+ * Makefile.am (TESTS): Add run-reloc-bpf.sh.
+ (EXTRA_DIST): Add run-reloc-bpf.sh, testfile-bpf-reloc.o.bz2 and
+ testfile-bpf-reloc.expect.bz2.
+
2018-06-13 Mark Wielaard <mark@klomp.org>
* run-readelf-const-values.sh: New test.
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 2d63da6a..bdb82fc0 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -146,7 +146,8 @@ TESTS = run-arextract.sh run-arsymtest.sh run-ar.sh newfile test-nlist \
run-dwarf-die-addr-die.sh \
run-get-units-invalid.sh run-get-units-split.sh \
run-attr-integrate-skel.sh \
- run-all-dwarf-ranges.sh run-unit-info.sh
+ run-all-dwarf-ranges.sh run-unit-info.sh \
+ run-reloc-bpf.sh
if !BIARCH
export ELFUTILS_DISABLE_BIARCH = 1
@@ -376,6 +377,8 @@ EXTRA_DIST = run-arextract.sh run-arsymtest.sh run-ar.sh \
run-zstrptr.sh run-compress-test.sh \
run-disasm-bpf.sh \
testfile-bpf-dis1.expect.bz2 testfile-bpf-dis1.o.bz2 \
+ run-reloc-bpf.sh \
+ testfile-bpf-reloc.expect.bz2 testfile-bpf-reloc.o.bz2 \
testfile-m68k-core.bz2 testfile-m68k.bz2 testfile-m68k-s.bz2 \
run-dwarf-die-addr-die.sh \
run-get-units-invalid.sh run-get-units-split.sh \
diff --git a/tests/run-reloc-bpf.sh b/tests/run-reloc-bpf.sh
new file mode 100755
index 00000000..feb75575
--- /dev/null
+++ b/tests/run-reloc-bpf.sh
@@ -0,0 +1,33 @@
+#! /bin/sh
+# Copyright (C) 2018 Facebook, Inc.
+# This file is part of elfutils.
+#
+# This file is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# 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 a copy of the GNU General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+. $srcdir/test-subr.sh
+
+# This test file is created with
+# $ cat t.c
+# struct tt {
+# int a;
+# char b;
+# };
+# int test(struct tt *t) {
+# return t->a;
+# }
+# $ clang -O2 -g -emit-llvm -c t.c -o - | llc -march=bpf -filetype=obj -o t.o
+# $ mv t.o testfile-bpf-reloc.o
+
+testfiles testfile-bpf-reloc.o testfile-bpf-reloc.expect
+testrun_compare ${abs_top_builddir}/src/objdump -r testfile-bpf-reloc.o < testfile-bpf-reloc.expect
diff --git a/tests/testfile-bpf-reloc.expect.bz2 b/tests/testfile-bpf-reloc.expect.bz2
new file mode 100644
index 0000000000000000000000000000000000000000..0ff8cc4cce9180c8dc17c52d9dd417c04cf0628e
GIT binary patch
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HcmV?d00001
diff --git a/tests/testfile-bpf-reloc.o.bz2 b/tests/testfile-bpf-reloc.o.bz2
new file mode 100644
index 0000000000000000000000000000000000000000..295634f909b2b58f6a3e3ffc729507cd7e7e1fce
GIT binary patch
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--
2.14.3
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