https://sourceware.org/bugzilla/show_bug.cgi?id=19744
Bug ID: 19744
Summary: Thumb-1 pcrop relocations don't work on Thumb-2
targets
Product: binutils
Version: 2.27 (HEAD)
Status: NEW
Severity: normal
Priority: P2
Component: gas
Assignee: unassigned at sourceware dot org
Reporter: cbaylis at gcc dot gnu.org
Target Milestone: ---
Created attachment 9052
--> https://sourceware.org/bugzilla/attachment.cgi?id=9052&action=edit
test case
There are two problems when using the Thumb-1 pcrop relocations on Thumb-2
targets. Firstly, incorrect "undefined symbol" errors are triggered. Secondly,
the assembler may generate 32 bit instructions when 16bit encodings are
available.
The attached test-case works as expected for Thumb-1 targets.
$ arm-unknown-linux-gnueabihf-gcc -c pcrop.S -march=armv4t
$ arm-unknown-linux-gnueabihf-objdump -d pcrop.o
pcrop.o: file format elf32-littlearm
Disassembly of section .text:
00000000 <foo>:
0: 2300 movs r3, #0
2: 021b lsls r3, r3, #8
4: 3300 adds r3, #0
6: 021b lsls r3, r3, #8
8: 3300 adds r3, #0
a: 021b lsls r3, r3, #8
c: 3300 adds r3, #0
With a Thumb-2 target, undefined symbol errors are reported instead:
$ arm-unknown-linux-gnueabihf-gcc -c pcrop.S -march=armv7-m
pcrop.S: Assembler messages:
pcrop.S:7: Error: undefined symbol foo used as an immediate value
pcrop.S:9: Error: undefined symbol foo used as an immediate value
pcrop.S:11: Error: undefined symbol foo used as an immediate value
pcrop.S:13: Error: undefined symbol foo used as an immediate value
With a Thumb-2 target, and working around the undefined symbol error, the
assembler generates 32 bit instructions, even though 16 bit encodings are
available.
$ arm-unknown-linux-gnueabihf-gcc -c pcrop.S -march=armv7-m -DDEF_SYM
$ arm-unknown-linux-gnueabihf-objdump -d pcrop.o
pcrop.o: file format elf32-littlearm
Disassembly of section .text:
00000000 <foo>:
0: f05f 0300 movs.w r3, #0 ;// 32 bit
4: 021b lsls r3, r3, #8
6: f113 0300 adds.w r3, r3, #0 ;// 32 bit
a: 021b lsls r3, r3, #8
c: f113 0300 adds.w r3, r3, #0 ;// 32 bit
10: 021b lsls r3, r3, #8
12: f113 0300 adds.w r3, r3, #0 ;// 32 bit
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