https://sourceware.org/bugzilla/show_bug.cgi?id=32659
Bug ID: 32659
Summary: Bad PLT asm generated on ARM thumb with PIC and LTO
Product: binutils
Version: 2.45 (HEAD)
Status: NEW
Severity: normal
Priority: P2
Component: ld
Assignee: unassigned at sourceware dot org
Reporter: clyon at gcc dot gnu.org
Target Milestone: ---
As reported in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118715 we have a
case where the linker generates the PLT at the wrong offset.
$ cat pr118715.c
extern void foo(void);
void _start(void) {
foo();
}
$ arm-eabi-gcc -O2 -Wall -Wextra -fPIC -ffreestanding -nostdlib -mthumb
-mcpu=cortex-m4 --entry=_start -shared pr118715.c -o pr118715.exe.lto -flto
-save-temps
$ arm-eabi-objdump -rdth ./pr118715.exe.lto
[...]
00000168 <foo@plt>:
168: 0000 movs r0, r0
16a: 0000 movs r0, r0
16c: f241 0c88 movw ip, #4232 @ 0x1088
170: f2c0 0c00 movt ip, #0
174: 44fc add ip, pc
176: Address 0x176 is out of bounds.
The problem is that elf32_arm_create_dynamic_sections is called with a BFD
pointing to pr118715.exe.lto-pr118715.o, after plugin_object_p has called
bfd_make_readable (abfd);
pr118715.exe.lto-pr118715.o contains an attributes section, but
bfd_make_readable replaces it with an empty one.
So when elf32_arm_create_dynamic_sections calls using_thumb_only, there's no
profile info, so using_thumb_only returns false and htab->plt_header_size /
htab->plt_entry_size are not adjusted as they should.
Later calls to using_thumb_only correctly see that M profile is used, and
return true.
What's the best way to make sure the attributes section is kept?
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