https://sourceware.org/bugzilla/show_bug.cgi?id=32367
Bug ID: 32367
Summary: Cannot b.w to thumb symbol from symbol
Product: binutils
Version: 2.43.1
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: ld
Assignee: unassigned at sourceware dot org
Reporter: maxmsonderegger at gmail dot com
Target Milestone: ---
Running the below command generates a stub to transition from thumb to arm,
when branching to a provided symbol. The symbol is not marked as arm
explicitly, so I expect the compiler and linker to assume it is thumb and emit
a b.w to the target. This prevents linking multiple large thumb object files
together and I do not believe it is intended behavior. I am happy to submit a
bug fix, but am new to contributing to binutils and would like to know what you
all believe is the best way to address this? Assembly directives, linker
patching, linker script hints?
Things I tried:
Setting . = 0x40001 has no effect. Using .thumb_set, .set, etc. on
___top_of_text to provide hints to the assembler has no effect. Compiling with
-mthumb has no effect. Setting the arch to one of the thumb only architectures
(e.g. armv7-m) does make it do the expected behavior and emit a b.w to the
location, however this feels like a kludge and limits my target architectures.
script.ld:
SECTIONS {
. = 0x40000;
PROVIDE( ___top_of_text = .);
.text : {
*(.text)
}
}
---
test.s:
.syntax unified
.thumb
mov r1, r2
mov r3, r4
b.w ___top_of_text
---
%> arm-none-eabi-as -o test.o test.s && arm-none-eabi-ld -o test test.o -T
script.ld && arm-none-eabi-objdump -d test.o && arm-none-eabi-objdump -x test.o
&& arm-none-eabi-objdump -d test
test.o: file format elf32-littlearm
Disassembly of section .text:
00000000 <.text>:
0: 4611 mov r1, r2
2: 4623 mov r3, r4
4: f7ff bffe b.w 0 <___top_of_text>
test.o: file format elf32-littlearm
test.o
architecture: armv6t2, flags 0x00000011:
HAS_RELOC, HAS_SYMS
start address 0x00000000
private flags = 0x5000000: [Version5 EABI]
Sections:
Idx Name Size VMA LMA File off Algn
0 .text 00000008 00000000 00000000 00000034 2**1
CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
1 .data 00000000 00000000 00000000 0000003c 2**0
CONTENTS, ALLOC, LOAD, DATA
2 .bss 00000000 00000000 00000000 0000003c 2**0
ALLOC
3 .ARM.attributes 00000014 00000000 00000000 0000003c 2**0
CONTENTS, READONLY
SYMBOL TABLE:
00000000 l d .text 00000000 .text
00000000 l d .data 00000000 .data
00000000 l d .bss 00000000 .bss
00000000 l d .ARM.attributes 00000000 .ARM.attributes
00000000 *UND* 00000000 ___top_of_text
RELOCATION RECORDS FOR [.text]:
OFFSET TYPE VALUE
00000004 R_ARM_THM_JUMP24 ___top_of_text
test: file format elf32-littlearm
Disassembly of section .text:
00040000 <___top_of_text>:
40000: 4611 mov r1, r2
40002: 4623 mov r3, r4
40004: f000 b800 b.w 40008 <_____top_of_text_from_thumb>
00040008 <_____top_of_text_from_thumb>:
40008: 4778 bx pc
4000a: e7fd b.n 40008 <_____top_of_text_from_thumb>
4000c: eafffffb b 40000 <___top_of_text>
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