[llvm-bugs] [Bug 43212] New: After r360593, badly aligned offsets when using -N (aka --omagic)
via llvm-bugs
llvm-bugs at lists.llvm.org
Tue Sep 3 12:23:18 PDT 2019
https://bugs.llvm.org/show_bug.cgi?id=43212
Bug ID: 43212
Summary: After r360593, badly aligned offsets when using -N
(aka --omagic)
Product: lld
Version: unspecified
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: ELF
Assignee: unassignedbugs at nondot.org
Reporter: dimitry at andric.com
CC: llvm-bugs at lists.llvm.org, peter.smith at linaro.org
While attempting to build FreeBSD head with clang and lld 9.0.0, I ran into an
error message from our elftoolchain-based objcopy, when stripping a boot loader
related binary which was linked with lld:
objcopy: elf_update() failed: Layout constraint violation
The problem turns out to be the alignment of the .rodata section:
$ readelf -lSW
/usr/obj/share/dim/src/freebsd/clang900-import/amd64.amd64/stand/i386/gptboot/gptboot.out
There are 19 section headers, starting at offset 0x2e454:
Section Headers:
[Nr] Name Type Addr Off Size ES Flg Lk Inf
Al
[ 0] NULL 00000000 000000 000000 00 0 0
0
[ 1] .text PROGBITS 00000000 000094 00a504 00 AX 0 0
4
[ 2] .rodata PROGBITS 0000a508 00a59c 0038fb 00 AMS 0 0
8
...
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
LOAD 0x000094 0x00000000 0x00000000 0x0df3c 0x0df3c RWE 0x8
GNU_STACK 0x000000 0x00000000 0x00000000 0x00000 0x00000 RW 0
E.g., .rodata starts at offset 0xa59c, while its alignment is supposed to be 8
bytes. Similarly, the LOAD segment has an offset of 0x94, while its alignment
is 8 bytes.
This problem started occurring after https://reviews.llvm.org/rLLD360593
("[ELF] Full support for -n (--nmagic) and -N (--omagic) via common page").
Before this change, the -N option got largely ignored, which is why we never
saw this issue before.
Minimal test case:
$ cat align-test.s
.text
.globl _start
_start:
xor %eax,%eax
retl
.rodata
.align 8
.quad 42
$ cc -m32 -c align-test.s
$ readelf -S align-test.o
There are 5 section headers, starting at offset 0x88:
Section Headers:
[Nr] Name Type Addr Off Size ES Flg Lk Inf
Al
[ 0] NULL 00000000 000000 000000 00 0 0
0
[ 1] .strtab STRTAB 00000000 000060 000026 00 0 0
1
[ 2] .text PROGBITS 00000000 000034 000003 00 AX 0 0
4
[ 3] .rodata PROGBITS 00000000 000038 000008 00 A 0 0
8
[ 4] .symtab SYMTAB 00000000 000040 000020 10 1 1
4
################################################################
# with ld.lld r360592, everything is page-aligned, even while -N is used:
$ ~/llvm/trunk-r360592/bin/ld.lld -m elf_i386_fbsd -N -Ttext 0x0 -o
align-test-r360592.out align-test.o
$ readelf -lS align-test-r360592.out
Elf file type is EXEC (Executable file)
Entry point 0x0
There are 2 program headers, starting at offset 52
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
LOAD 0x001000 0x00000000 0x00000000 0x01000 0x01000 RWE 0x1000
GNU_STACK 0x000000 0x00000000 0x00000000 0x00000 0x00000 RW 0
Section to Segment mapping:
Segment Sections...
00 .text .rodata
01
There are 7 section headers, starting at offset 0x20a4:
Section Headers:
[Nr] Name Type Addr Off Size ES Flg Lk Inf
Al
[ 0] NULL 00000000 000000 000000 00 0 0
0
[ 1] .text PROGBITS 00000000 001000 000003 00 AX 0 0
4
[ 2] .rodata PROGBITS 00000008 001008 000008 00 A 0 0
8
[ 3] .comment PROGBITS 00000000 002000 000047 01 MS 0 0
1
[ 4] .symtab SYMTAB 00000000 002048 000020 10 6 1
4
[ 5] .shstrtab STRTAB 00000000 002068 000032 00 0 0
1
[ 6] .strtab STRTAB 00000000 00209a 000008 00 0 0
1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings)
I (info), L (link order), G (group), x (unknown)
O (extra OS processing required) o (OS specific), p (processor specific)
################################################################
# with ld.lld r360593, -N does much more, but messes up the offsets:
$ ~/llvm/trunk-r360593/bin/ld.lld -m elf_i386_fbsd -N -Ttext 0x0 -o
align-test-r360593.out align-test.o
$ readelf -lS align-test-r360593.out
Elf file type is EXEC (Executable file)
Entry point 0x0
There are 2 program headers, starting at offset 52
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
LOAD 0x000094 0x00000000 0x00000000 0x00010 0x00010 RWE 0x8
GNU_STACK 0x000000 0x00000000 0x00000000 0x00000 0x00000 RW 0
Section to Segment mapping:
Segment Sections...
00 .text .rodata
01
There are 7 section headers, starting at offset 0x148:
Section Headers:
[Nr] Name Type Addr Off Size ES Flg Lk Inf
Al
[ 0] NULL 00000000 000000 000000 00 0 0
0
[ 1] .text PROGBITS 00000000 000094 000003 00 AX 0 0
4
[ 2] .rodata PROGBITS 00000008 00009c 000008 00 A 0 0
8
[ 3] .comment PROGBITS 00000000 0000a4 000047 01 MS 0 0
1
[ 4] .symtab SYMTAB 00000000 0000ec 000020 10 6 1
4
[ 5] .shstrtab STRTAB 00000000 00010c 000032 00 0 0
1
[ 6] .strtab STRTAB 00000000 00013e 000008 00 0 0
1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings)
I (info), L (link order), G (group), x (unknown)
O (extra OS processing required) o (OS specific), p (processor specific)
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