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From: "vluchits at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/100163] New: -falign-loops sometimes produces invalid code for SH-2
Date: Tue, 20 Apr 2021 19:44:17 +0000 [thread overview]
Message-ID: <bug-100163-4@http.gcc.gnu.org/bugzilla/> (raw)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100163
Bug ID: 100163
Summary: -falign-loops sometimes produces invalid code for SH-2
Product: gcc
Version: 9.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: vluchits at gmail dot com
Target Milestone: ---
Hello,
relocating functions to .data segment causes gcc to produce invalid code for
'nop' instruction on SH2 architecture when -O2 optimization flag is specified
or -falign-loops is enabled explicitly.
Here's disassembly of a C function R_SegCommand that demonstrates the code that
works:
0000050c <_R_SegCommands>:
50c: 2f 86 mov.l r8,@-r15
50e: 2f 96 mov.l r9,@-r15
510: 2f a6 mov.l r10,@-r15
512: 2f b6 mov.l r11,@-r15
514: 2f c6 mov.l r12,@-r15
516: 2f d6 mov.l r13,@-r15
518: 2f e6 mov.l r14,@-r15
51a: 91 b1 mov.w 680 <_R_SegCommands+0x174>,r1 ! 258
51c: 4f 22 sts.l pr,@-r15
51e: d2 5a mov.l 688 <_R_SegCommands+0x17c>,r2 ! 20004024
520: 3f 18 sub r1,r15
522: 00 09 nop
524: 60 21 mov.w @r2,r0
526: 64 0d extu.w r0,r4
528: 24 48 tst r4,r4
52a: 8f fb bf.s 524 <_R_SegCommands+0x18>
52c: e7 03 mov #3,r7
...
Please note the 'nop' command at offset 522, which is encoded as 00 09, which
is the correct opcode for nop on SH2.
Now if -O2 or -Os -align-loops are specified and R_SegCommands is relocated to
the .data segment and aligned to 16-byte boundary:
void R_SegCommands(void) __attribute__((section(".data"), aligned(16)));
the following code is produced:
000000d0 <_R_SegCommands>:
d0: 2f 86 mov.l r8,@-r15
d2: 2f 96 mov.l r9,@-r15
d4: 2f a6 mov.l r10,@-r15
d6: 2f b6 mov.l r11,@-r15
d8: 2f c6 mov.l r12,@-r15
da: 2f d6 mov.l r13,@-r15
dc: 2f e6 mov.l r14,@-r15
de: 91 b1 mov.w 244 <_R_SegCommands+0x174>,r1 ! 258
e0: 4f 22 sts.l pr,@-r15
e2: d2 5a mov.l 24c <_R_SegCommands+0x17c>,r2 ! 20004024
e4: 3f 18 sub r1,r15
e6: 00 00 .word 0x0000
e8: 60 21 mov.w @r2,r0
ea: 64 0d extu.w r0,r4
ec: 24 48 tst r4,r4
ee: 8f fb bf.s e8 <_R_SegCommands+0x18>
f0: e7 03 mov #3,r7
f2: d5 57 mov.l 250 <_R_SegCommands+0x180>,r5 ! 0
<_R_DrawTexture>
f4: e3 01 mov #1,r3
...
Note the opcode at offset e6, which is a nop instruction and was 00 09 in the
previous version and which is 00 00 now. When this opcode is encountered during
the program's execution, it an causes immediate crash.
Replacing all occurrences of 00 00 in the binary code with 00 09 makes the
makes the program run fine again.
next reply other threads:[~2021-04-20 19:44 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-20 19:44 vluchits at gmail dot com [this message]
2021-04-20 20:57 ` [Bug target/100163] " pinskia at gcc dot gnu.org
2021-04-20 22:25 ` vluchits at gmail dot com
2021-04-20 23:50 ` pinskia at gcc dot gnu.org
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