https://sourceware.org/bugzilla/show_bug.cgi?id=24456
Bug ID: 24456
Summary: bfd elf.c assertion for multiple relocations to same
section
Product: binutils
Version: 2.23
Status: NEW
Severity: normal
Priority: P2
Component: binutils
Assignee: unassigned at sourceware dot org
Reporter: joe.lawrence at redhat dot com
Target Milestone: ---
We're working on an upstream kernel feature [1] which adds a new
relocation section to kernel modules and when loading the .ko's symbol
information into crash utility (which includes gdb, which includes bfd)
it's hitting an assertion in elf.c that isn't giving much information to
debug.
Here is the assertion when running crash (with a bit of extra
debugging):
% insmod
/lib/modules/5.1.0-rc4+/kernel/samples/livepatch/livepatch-annotated-sample.ko
% crash
...
crash> mod -s livepatch_annotated_sample
/lib/modules/5.1.0-rc4+/kernel/samples/livepatch/livepatch-annotated-sample.ko
shindex=34, name=.klp.rela.vmlinux..text
*p_hdr(0x57f6150) == NULL = 0, this_idx=3
BFD: BFD (GNU Binutils) 2.23.52.20130312 assertion fail elf.c:1881
MODULE NAME SIZE OBJECT FILE
ffffffffc05cb380 livepatch_annotated_sample 16384
/lib/modules/5.1.0-rc4+/kernel/samples/livepatch/livepatch-annotated-sample.ko
and the corresponding assertion, with extra debugging, in elf.c:
1545 bfd_section_from_shdr (bfd *abfd, unsigned int shindex)
....
1563 switch (hdr->sh_type)
1564 {
....
1784 case SHT_REL:
1785 case SHT_RELA:
....
1871 esdt = elf_section_data (target_sect);
1872 if (hdr->sh_type == SHT_RELA)
1873 p_hdr = &esdt->rela.hdr;
1874 else
1875 p_hdr = &esdt->rel.hdr;
1876
1877 if (*p_hdr != NULL) {
1878 printf("shindex=%d\nname=%s\n", shindex, name);
1879 printf("*p_hdr(%p) == NULL = %d, this_idx=%d\n", *p_hdr, (*p_hdr
== NULL), esdt->this_idx);
1880 }
1881 BFD_ASSERT (*p_hdr == NULL);
I noticed that it is processing our new section, index 34,
.klp.rela.vmlinux..text and finds an existing p_hdr to section
index 3, .text:
% eu-readelf --relocs
/lib/modules/5.1.0-rc4+/kernel/samples/livepatch/livepatch-annotated-sample.ko
Relocation section [ 4] '.rela.text' for section [ 3] '.text' at offset 0xc8
contains 7 entries:
Offset Type Value Addend Name
0x0000000000000001 X86_64_PC32 000000000000000000 -4 __fentry__
0x000000000000000f X86_64_32S 000000000000000000 +0
.rodata.str1.1
0x0000000000000014 X86_64_PC32 000000000000000000 -4 seq_printf
0x0000000000000021 X86_64_PC32 000000000000000000 -4 __fentry__
0x0000000000000028 X86_64_32S 000000000000000000 +0 .data
0x000000000000002d X86_64_PC32 000000000000000000 -4
klp_enable_patch
0x0000000000000041 X86_64_PC32 000000000000000000 -4 __fentry__
Relocation section [34] '.klp.rela.vmlinux..text' for section [ 3] '.text' at
offset 0x4a080 contains 1 entry:
Offset Type Value Addend Name
0x0000000000000008 X86_64_PC32 000000000000000000 -4
.klp.sym.vmlinux.saved_command_line,0
Unfortunately it is less than trivial to move crash utility's version of
gdb / binutils forward, so I couldn't directly test with a newer version
of binutils. However, elf.c :: bfd_section_from_shdr() still seems to
contain this assertion, though in a slightly more direct format:
/* PR 17512: file: 0b4f81b7. */
if (*p_hdr != NULL)
goto fail;
There other binutils utilities that are also reporting problems, but
with an error message too vague to determine why they are failing. They
are perhaps related, and possibly easier to debug/verify for our
purposes here.
Here's what a fresh clone + build of binutils-gdb tree versions of
objdump and gdb think of our new object file [2]:
% git describe HEAD
users/ARM/embedded-gdb-master-2018q4-978-g48574d91bf12
% ./binutils/objdump -D /tmp/bug/livepatch-annotated-sample.ko
./binutils/objdump: /tmp/bug/livepatch-annotated-sample.ko: bad value
% ./gdb/gdb -q /tmp/bug/livepatch-annotated-sample.ko
"/tmp/bug/livepatch-annotated-sample.ko": not in executable format: bad value
Both of those tools work as expected with an ordinary kernel module [3]
(ie, one with any extra relocation sections to '.text').
[1] https://lore.kernel.org/lkml/20190410155058.9437-1-joe.lawre...@redhat.com/
[2] http://people.redhat.com/~jolawren/bug/livepatch-annotated-sample.ko
[3] http://people.redhat.com/~jolawren/bug/livepatch-sample.ko
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