Hi,
It seems to me that both GCC 6.3 and 6.4 mis-compiles
arch/arm/mach-imx/syscounter.c.
I'm attaching two files, bad.txt is the original syscounter.c and
good.txt is the one
with the following patch.
diff --git a/arch/arm/mach-imx/syscounter.c b/arch/arm/mach-imx/syscounter.c
index 9290918dca..30ed0109a2 100644
--- a/arch/arm/mach-imx/syscounter.c
+++ b/arch/arm/mach-imx/syscounter.c
@@ -82,7 +82,7 @@ unsigned long long get_ticks(void)
{
unsigned long long now;
- asm("mrrc p15, 0, %Q0, %R0, c14" : "=r" (now));
+ asm volatile("mrrc p15, 0, %Q0, %R0, c14" : "=r" (now));
gd->arch.tbl = (unsigned long)(now & 0xffffffff);
gd->arch.tbu = (unsigned long)(now >> 32);
The target code is the while loop in the __udelay.
void __udelay(unsigned long usec)
{
unsigned long long tmp;
ulong tmo;
tmo = us_to_tick(usec);
tmp = get_ticks() + tmo; /* get current timestamp */
while (get_ticks() < tmp) /* loop till event */
/*NOP*/;
}
Here is the mis compiled asm from the above code (whole function is
attached as bad.txt)
88: 428b cmp r3, r1
8a: f8ce 20a4 str.w r2, [lr, #164] ; 0xa4
8e: bf08 it eq
90: 4282 cmpeq r2, r0
92: f8ce 30a0 str.w r3, [lr, #160] ; 0xa0
96: d3f7 bcc.n 88 <__udelay+0x88>
Note that the last bcc.n to 88 and we don't see mrrc.
This seems to be that both get_ticks() are inlined and "mrrc"s are
duplicated in the
__udealy() and GCC sees it as an opportunity to optimize out.
GCC 5 and 8 seems to work fine. Unfortunately I don't have GCC 7 ATM so no
idea how it compiles.
Does anyone see this?
--
yashi
Disassembly of section .text.__udelay:
00000000 <__udelay>:
0: e92d 4cf0 stmdb sp!, {r4, r5, r6, r7, sl, fp, lr}
4: ee1e 1f10 mrc 15, 0, r1, cr14, cr0, {0}
8: f244 243f movw r4, #16959 ; 0x423f
c: f2c0 040f movt r4, #15
10: 2500 movs r5, #0
12: f243 4edb movw lr, #13531 ; 0x34db
16: fbe1 4500 umlal r4, r5, r1, r0
1a: f2cd 7eb6 movt lr, #55222 ; 0xd7b6
1e: f64d 6c82 movw ip, #56962 ; 0xde82
22: f2c4 3c1b movt ip, #17179 ; 0x431b
26: 2300 movs r3, #0
28: fba4 670e umull r6, r7, r4, lr
2c: 4629 mov r1, r5
2e: 2500 movs r5, #0
30: 2600 movs r6, #0
32: fba4 ab0c umull sl, fp, r4, ip
36: fb0e 7205 mla r2, lr, r5, r7
3a: fb0c bb05 mla fp, ip, r5, fp
3e: 2500 movs r5, #0
40: fbee 2301 umlal r2, r3, lr, r1
44: 46ce mov lr, r9
46: eb1a 0a02 adds.w sl, sl, r2
4a: eb4b 0b03 adc.w fp, fp, r3
4e: 459b cmp fp, r3
50: f64d 6382 movw r3, #56962 ; 0xde82
54: f2c4 331b movt r3, #17179 ; 0x431b
58: 465c mov r4, fp
5a: bf08 it eq
5c: 4592 cmpeq sl, r2
5e: fbe3 4501 umlal r4, r5, r3, r1
62: ec51 0f0e mrrc 15, 0, r0, r1, cr14
66: bf2c ite cs
68: 2700 movcs r7, #0
6a: 2701 movcc r7, #1
6c: f8c9 00a4 str.w r0, [r9, #164] ; 0xa4
70: 19a4 adds r4, r4, r6
72: 4602 mov r2, r0
74: 417d adcs r5, r7
76: f8c9 10a0 str.w r1, [r9, #160] ; 0xa0
7a: 0ca4 lsrs r4, r4, #18
7c: 460b mov r3, r1
7e: ea44 3485 orr.w r4, r4, r5, lsl #14
82: 1900 adds r0, r0, r4
84: f141 0100 adc.w r1, r1, #0
88: 428b cmp r3, r1
8a: f8ce 20a4 str.w r2, [lr, #164] ; 0xa4
8e: bf08 it eq
90: 4282 cmpeq r2, r0
92: f8ce 30a0 str.w r3, [lr, #160] ; 0xa0
96: d3f7 bcc.n 88 <__udelay+0x88>
98: e8bd 8cf0 ldmia.w sp!, {r4, r5, r6, r7, sl, fp, pc}
Disassembly of section .text.__udelay:
00000000 <__udelay>:
0: e92d 4cf0 stmdb sp!, {r4, r5, r6, r7, sl, fp, lr}
4: ee1e 1f10 mrc 15, 0, r1, cr14, cr0, {0}
8: f244 243f movw r4, #16959 ; 0x423f
c: f2c0 040f movt r4, #15
10: 2500 movs r5, #0
12: f243 4edb movw lr, #13531 ; 0x34db
16: fbe1 4500 umlal r4, r5, r1, r0
1a: f2cd 7eb6 movt lr, #55222 ; 0xd7b6
1e: f64d 6c82 movw ip, #56962 ; 0xde82
22: f2c4 3c1b movt ip, #17179 ; 0x431b
26: 2300 movs r3, #0
28: f64d 6082 movw r0, #56962 ; 0xde82
2c: f2c4 301b movt r0, #17179 ; 0x431b
30: fba4 670e umull r6, r7, r4, lr
34: 4629 mov r1, r5
36: 2500 movs r5, #0
38: fba4 ab0c umull sl, fp, r4, ip
3c: fb0e 7205 mla r2, lr, r5, r7
40: fb0c bb05 mla fp, ip, r5, fp
44: 2500 movs r5, #0
46: fbee 2301 umlal r2, r3, lr, r1
4a: eb1a 0a02 adds.w sl, sl, r2
4e: eb4b 0b03 adc.w fp, fp, r3
52: 459b cmp fp, r3
54: 465c mov r4, fp
56: bf08 it eq
58: 4592 cmpeq sl, r2
5a: fbe0 4501 umlal r4, r5, r0, r1
5e: f04f 0200 mov.w r2, #0
62: bf2c ite cs
64: 2300 movcs r3, #0
66: 2301 movcc r3, #1
68: 4620 mov r0, r4
6a: 4629 mov r1, r5
6c: ec55 4f0e mrrc 15, 0, r4, r5, cr14
70: 1812 adds r2, r2, r0
72: f8c9 40a4 str.w r4, [r9, #164] ; 0xa4
76: 414b adcs r3, r1
78: f8c9 50a0 str.w r5, [r9, #160] ; 0xa0
7c: 0c92 lsrs r2, r2, #18
7e: 4649 mov r1, r9
80: ea42 3283 orr.w r2, r2, r3, lsl #14
84: 18a4 adds r4, r4, r2
86: f145 0500 adc.w r5, r5, #0
8a: ec53 2f0e mrrc 15, 0, r2, r3, cr14
8e: 42ab cmp r3, r5
90: f8c1 20a4 str.w r2, [r1, #164] ; 0xa4
94: bf08 it eq
96: 42a2 cmpeq r2, r4
98: f8c1 30a0 str.w r3, [r1, #160] ; 0xa0
9c: d3f5 bcc.n 8a <__udelay+0x8a>
9e: e8bd 8cf0 ldmia.w sp!, {r4, r5, r6, r7, sl, fp, pc}
a2: bf00 nop
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