https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79023
Bug ID: 79023
Summary: ARM: Compiler optimizations cause branch instruction
within while loop to call itself infinitely.
Product: gcc
Version: 6.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: geo...@george-morgan.com
Target Milestone: ---
The code compiled with "arm-none-eabi-gcc -nostartfiles -ffreestanding -Os
bug.c -o bug.o"
-----------------
volatile void *ptr;
void func(void) {
while (!ptr);
}
-----------------
Produces the following assembly output:
-------------------------------------------------------------------------------
bug.o: file format elf32-littlearm
Disassembly of section .text:
00008000 <func>:
8000: 4b02 ldr r3, [pc, #8] ; (800c <func+0xc>)
8002: 681b ldr r3, [r3, #0]
8004: b903 cbnz r3, 8008 <func+0x8>
8006: e7fe b.n 8006 <func+0x6>
8008: 4770 bx lr
800a: bf00 nop
800c: 00018010 andeq r8, r1, r0, lsl r0
Disassembly of section .bss:
00018010 <ptr>:
18010: 00000000 andeq r0, r0, r0
Disassembly of section .comment:
00000000 <.comment>:
0: 3a434347 bcc 10d0d24 <_stack+0x1050d24>
4: 4e472820 cdpmi 8, 4, cr2, cr7, cr0, {1}
8: 36202955 ; <UNDEFINED> instruction: 0x36202955
c: 302e332e eorcc r3, lr, lr, lsr #6
...
Disassembly of section .ARM.attributes:
00000000 <_stack-0x80000>:
0: 00003241 andeq r3, r0, r1, asr #4
4: 61656100 cmnvs r5, r0, lsl #2
8: 01006962 tsteq r0, r2, ror #18
c: 00000028 andeq r0, r0, r8, lsr #32
10: 726f4305 rsbvc r4, pc, #335544320 ; 0x14000000
14: 2d786574 cfldr64cs mvdx6, [r8, #-464]! ; 0xfffffe30
18: 0600344d streq r3, [r0], -sp, asr #8
1c: 094d070d stmdbeq sp, {r0, r2, r3, r8, r9, sl}^
20: 14041202 strne r1, [r4], #-514 ; 0xfffffdfe
24: 17011501 strne r1, [r1, -r1, lsl #10]
28: 19011803 stmdbne r1, {r0, r1, fp, ip}
2c: 1e011a01 vmlane.f32 s2, s2, s2
30: Address 0x0000000000000030 is out of bounds.
------------------------------------------------------------------------------
As you can see, the instruction at 8006 calls itself infinitely.
