linux/tools
Andrii Nakryiko 3e6fe5ce4d libbpf: Fix internal USDT address translation logic for shared libraries
Perform the same virtual address to file offset translation that libbpf
is doing for executable ELF binaries also for shared libraries.
Currently libbpf is making a simplifying and sometimes wrong assumption
that for shared libraries relative virtual addresses inside ELF are
always equal to file offsets.

Unfortunately, this is not always the case with LLVM's lld linker, which
now by default generates quite more complicated ELF segments layout.
E.g., for liburandom_read.so from selftests/bpf, here's an excerpt from
readelf output listing ELF segments (a.k.a. program headers):

  Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
  PHDR           0x000040 0x0000000000000040 0x0000000000000040 0x0001f8 0x0001f8 R   0x8
  LOAD           0x000000 0x0000000000000000 0x0000000000000000 0x0005e4 0x0005e4 R   0x1000
  LOAD           0x0005f0 0x00000000000015f0 0x00000000000015f0 0x000160 0x000160 R E 0x1000
  LOAD           0x000750 0x0000000000002750 0x0000000000002750 0x000210 0x000210 RW  0x1000
  LOAD           0x000960 0x0000000000003960 0x0000000000003960 0x000028 0x000029 RW  0x1000

Compare that to what is generated by GNU ld (or LLVM lld's with extra
-znoseparate-code argument which disables this cleverness in the name of
file size reduction):

  Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
  LOAD           0x000000 0x0000000000000000 0x0000000000000000 0x000550 0x000550 R   0x1000
  LOAD           0x001000 0x0000000000001000 0x0000000000001000 0x000131 0x000131 R E 0x1000
  LOAD           0x002000 0x0000000000002000 0x0000000000002000 0x0000ac 0x0000ac R   0x1000
  LOAD           0x002dc0 0x0000000000003dc0 0x0000000000003dc0 0x000262 0x000268 RW  0x1000

You can see from the first example above that for executable (Flg == "R E")
PT_LOAD segment (LOAD #2), Offset doesn't match VirtAddr columns.
And it does in the second case (GNU ld output).

This is important because all the addresses, including USDT specs,
operate in a virtual address space, while kernel is expecting file
offsets when performing uprobe attach. So such mismatches have to be
properly taken care of and compensated by libbpf, which is what this
patch is fixing.

Also patch clarifies few function and variable names, as well as updates
comments to reflect this important distinction (virtaddr vs file offset)
and to ephasize that shared libraries are not all that different from
executables in this regard.

This patch also changes selftests/bpf Makefile to force urand_read and
liburand_read.so to be built with Clang and LLVM's lld (and explicitly
request this ELF file size optimization through -znoseparate-code linker
parameter) to validate libbpf logic and ensure regressions don't happen
in the future. I've bundled these selftests changes together with libbpf
changes to keep the above description tied with both libbpf and
selftests changes.

Fixes: 74cc6311ce ("libbpf: Add USDT notes parsing and resolution logic")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220616055543.3285835-1-andrii@kernel.org
2022-06-17 01:20:10 +02:00
..
accounting taskstats: version 12 with thread group and exe info 2022-04-29 14:38:03 -07:00
arch perf tools changes for v5.19: 2nd batch 2022-05-29 10:10:15 -07:00
bootconfig
bpf bpftool: Do not check return value from libbpf_set_strict_mode() 2022-06-14 22:18:56 +02:00
build perf build: Stop using __weak bpf_map_create() to handle older libbpf versions 2022-05-26 12:36:56 -03:00
certs tools/certs: Add print-cert-tbs-hash.sh 2022-05-23 18:47:49 +03:00
cgroup tools/cgroup/slabinfo: update to work with struct slab 2022-02-21 11:34:49 +01:00
counter
debugging
edid
firewire
firmware
gpio
hv
iio Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
include bpf: Add btf enum64 support 2022-06-07 10:20:42 -07:00
io_uring
kvm/kvm_stat
laptop
leds
lib libbpf: Fix internal USDT address translation logic for shared libraries 2022-06-17 01:20:10 +02:00
memory-model tools/memory-model/README: Update klitmus7 compat table 2022-05-03 10:12:48 -07:00
objtool Kbuild updates for v5.19 2022-05-26 12:09:50 -07:00
pci
pcmcia
perf perf scripts python: Support Arm CoreSight trace data disassembly 2022-05-27 13:22:14 -03:00
power Power management updates for 5.19-rc1 2022-05-24 16:04:25 -07:00
rcu
scripts Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
spi
testing libbpf: Fix internal USDT address translation logic for shared libraries 2022-06-17 01:20:10 +02:00
thermal tools/thermal: remove unneeded semicolon 2022-05-19 12:11:52 +02:00
time
tracing rtla: Remove procps-ng dependency 2022-05-26 15:20:46 -04:00
usb
virtio tools/virtio: compile with -pthread 2022-03-28 16:52:59 -04:00
vm mm/page-flags: reuse PG_mappedtodisk as PG_anon_exclusive for PageAnon() pages 2022-05-09 18:20:44 -07:00
wmi
Makefile Thermal control updates for 5.19-rc1 2022-05-24 16:19:30 -07:00