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the-led-and-delay-abstraction.md set half_period is broken. #280

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vringar opened this issue Dec 29, 2020 · 1 comment
Open

the-led-and-delay-abstraction.md set half_period is broken. #280

vringar opened this issue Dec 29, 2020 · 1 comment

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@vringar
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vringar commented Dec 29, 2020 •
edited
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discovery/src/05-led-roulette/the-led-and-delay-abstractions.md

Lines 207 to 220 in b2b1624

Now, we are going to modify this variable using the `set` command:
```
(gdb) set half_period = 100
(gdb) print half_period
$1 = 100
```
If you let program run free again using the `continue` command, you should see that the LED will
blink at a much faster rate now!
Question! What happens if you keep lowering the value of `half_period`? At what value of
`half_period` you can no longer see the LED blink?

Doesn't work anymore on rustc 1.48.0 (7eac88abb 2020-11-16).

Full asm output (built with RUSTFLAGS="--emit asm" cargo build --target thumbv7em-none-eabi 
	.text
	.syntax unified
	.eabi_attribute	67, "2.09"
	.eabi_attribute	6, 13
	.eabi_attribute	7, 77
	.eabi_attribute	8, 0
	.eabi_attribute	9, 2
	.eabi_attribute	34, 1
	.eabi_attribute	17, 1
	.eabi_attribute	20, 1
	.eabi_attribute	21, 0
	.eabi_attribute	23, 3
	.eabi_attribute	24, 1
	.eabi_attribute	25, 1
	.eabi_attribute	38, 1
	.eabi_attribute	14, 0
	.file	"33ne5uerfjn3u8oj"
	.section	.text.main,"ax",%progbits
	.globl	main
	.p2align	1
	.type	main,%function
	.code	16
	.thumb_func
main:
.Lfunc_begin0:
	.file	1 "/home/stefan/projects/discovery/src/05-led-roulette/src/main.rs"
	.loc	1 7 0
	.fnstart
	.cfi_sections .debug_frame
	.cfi_startproc
	.save	{r7, lr}
	push	{r7, lr}
	.cfi_def_cfa_offset 8
	.cfi_offset lr, -4
	.cfi_offset r7, -8
	.setfp	r7, sp
	mov	r7, sp
	.cfi_def_cfa_register r7
.Ltmp0:
	.loc	1 7 1 prologue_end
	bl	_ZN12led_roulette18__cortex_m_rt_main17h0b2223cb0e38e500E
	.inst.n	0xdefe
.Ltmp1:
.Lfunc_end0:
	.size	main, .Lfunc_end0-main
	.cfi_endproc
	.cantunwind
	.fnend

	.section	.text._ZN12led_roulette18__cortex_m_rt_main17h0b2223cb0e38e500E,"ax",%progbits
	.p2align	1
	.type	_ZN12led_roulette18__cortex_m_rt_main17h0b2223cb0e38e500E,%function
	.code	16
	.thumb_func
_ZN12led_roulette18__cortex_m_rt_main17h0b2223cb0e38e500E:
.Lfunc_begin1:
	.loc	1 8 0
	.fnstart
	.cfi_startproc
	.save	{r7, lr}
	push	{r7, lr}
	.cfi_def_cfa_offset 8
	.cfi_offset lr, -4
	.cfi_offset r7, -8
	.setfp	r7, sp
	mov	r7, sp
	.cfi_def_cfa_register r7
	.pad	#72
	sub	sp, #72
	add	r0, sp, #40
.Ltmp2:
	.loc	1 9 48 prologue_end
	bl	_ZN4aux54init17ha90da604cbc87758E
	b	.LBB1_1
.LBB1_1:
	.loc	1 0 48 is_stmt 0
	add	r0, sp, #40
	add	r1, sp, #12
	.loc	1 9 10
	ldm.w	r0, {r2, r3, r4, r12, lr}
	stm.w	r1, {r2, r3, r4, r12, lr}
	.loc	1 9 21
	ldr	r0, [sp, #60]
	ldr	r1, [sp, #64]
	str	r1, [sp, #36]
	str	r0, [sp, #32]
	mov.w	r0, #500
.Ltmp3:
	.loc	1 11 23 is_stmt 1
	strh	r0, [r7, #-2]
.Ltmp4:
	.loc	1 13 5
	b	.LBB1_2
.LBB1_2:
	.loc	1 14 9
	movw	r2, :lower16:.L__unnamed_1
	movt	r2, :upper16:.L__unnamed_1
	add	r0, sp, #32
	movs	r1, #0
	bl	_ZN73_$LT$f3..led..Leds$u20$as$u20$core..ops..index..IndexMut$LT$usize$GT$$GT$9index_mut17h381d5f4e0c621798E
	str	r0, [sp, #8]
	b	.LBB1_3
.LBB1_3:
	ldr	r0, [sp, #8]
	bl	_ZN2f33led3Led2on17hd271365517c0b11cE
	b	.LBB1_4
.LBB1_4:
	.loc	1 0 9 is_stmt 0
	add	r0, sp, #12
	mov.w	r1, #500
	.loc	1 15 9 is_stmt 1
	bl	_ZN97_$LT$stm32f30x_hal..delay..Delay$u20$as$u20$embedded_hal..blocking..delay..DelayMs$LT$u16$GT$$GT$8delay_ms17h5400aa5c3c87f438E
	b	.LBB1_5
.LBB1_5:
	.loc	1 17 9
	movw	r2, :lower16:.L__unnamed_2
	movt	r2, :upper16:.L__unnamed_2
	add	r0, sp, #32
	movs	r1, #0
	bl	_ZN73_$LT$f3..led..Leds$u20$as$u20$core..ops..index..IndexMut$LT$usize$GT$$GT$9index_mut17h381d5f4e0c621798E
	str	r0, [sp, #4]
	b	.LBB1_6
.LBB1_6:
	ldr	r0, [sp, #4]
	bl	_ZN2f33led3Led3off17hef007257bef9f451E
	b	.LBB1_7
.LBB1_7:
	.loc	1 0 9 is_stmt 0
	add	r0, sp, #12
	mov.w	r1, #500
	.loc	1 18 9 is_stmt 1
	bl	_ZN97_$LT$stm32f30x_hal..delay..Delay$u20$as$u20$embedded_hal..blocking..delay..DelayMs$LT$u16$GT$$GT$8delay_ms17h5400aa5c3c87f438E
	b	.LBB1_8
.LBB1_8:
	.loc	1 13 5
	b	.LBB1_2
.Ltmp5:
.Lfunc_end1:
	.size	_ZN12led_roulette18__cortex_m_rt_main17h0b2223cb0e38e500E, .Lfunc_end1-_ZN12led_roulette18__cortex_m_rt_main17h0b2223cb0e38e500E
	.cfi_endproc
	.cantunwind
	.fnend

	.type	.L__unnamed_3,%object
	.section	.rodata..L__unnamed_3,"a",%progbits
.L__unnamed_3:
	.ascii	"src/05-led-roulette/src/main.rs"
	.size	.L__unnamed_3, 31

	.type	.L__unnamed_1,%object
	.section	.rodata..L__unnamed_1,"a",%progbits
	.p2align	2
.L__unnamed_1:
	.long	.L__unnamed_3
	.asciz	"\037\000\000\000\016\000\000\000\t\000\000"
	.size	.L__unnamed_1, 16

	.type	.L__unnamed_2,%object
	.section	.rodata..L__unnamed_2,"a",%progbits
	.p2align	2
.L__unnamed_2:
	.long	.L__unnamed_3
	.asciz	"\037\000\000\000\021\000\000\000\t\000\000"
	.size	.L__unnamed_2, 16

	.section	.debug_abbrev,"",%progbits
	.byte	1
	.byte	17
	.byte	1
	.byte	37
	.byte	14
	.byte	19
	.byte	5
	.byte	3
	.byte	14
	.byte	16
	.byte	23
	.byte	27
	.byte	14
	.ascii	"\264B"
	.byte	25
	.byte	17
	.byte	1
	.byte	85
	.byte	23
	.byte	0
	.byte	0
	.byte	2
	.byte	57
	.byte	1
	.byte	3
	.byte	14
	.byte	0
	.byte	0
	.byte	3
	.byte	46
	.byte	0
	.byte	17
	.byte	1
	.byte	18
	.byte	6
	.byte	64
	.byte	24
	.byte	110
	.byte	14
	.byte	3
	.byte	14
	.byte	58
	.byte	11
	.byte	59
	.byte	11
	.byte	63
	.byte	25
	.byte	0
	.byte	0
	.byte	4
	.byte	46
	.byte	1
	.byte	17
	.byte	1
	.byte	18
	.byte	6
	.byte	64
	.byte	24
	.byte	110
	.byte	14
	.byte	3
	.byte	14
	.byte	58
	.byte	11
	.byte	59
	.byte	11
	.ascii	"\207\001"
	.byte	25
	.byte	0
	.byte	0
	.byte	5
	.byte	11
	.byte	1
	.byte	17
	.byte	1
	.byte	18
	.byte	6
	.byte	0
	.byte	0
	.byte	6
	.byte	52
	.byte	0
	.byte	2
	.byte	24
	.byte	3
	.byte	14
	.byte	58
	.byte	11
	.byte	59
	.byte	11
	.byte	73
	.byte	19
	.byte	0
	.byte	0
	.byte	7
	.byte	19
	.byte	1
	.byte	3
	.byte	14
	.byte	11
	.byte	11
	.ascii	"\210\001"
	.byte	15
	.byte	0
	.byte	0
	.byte	8
	.byte	13
	.byte	0
	.byte	3
	.byte	14
	.byte	73
	.byte	19
	.ascii	"\210\001"
	.byte	15
	.byte	56
	.byte	11
	.byte	0
	.byte	0
	.byte	9
	.byte	47
	.byte	0
	.byte	73
	.byte	19
	.byte	3
	.byte	14
	.byte	0
	.byte	0
	.byte	10
	.byte	19
	.byte	0
	.byte	3
	.byte	14
	.byte	11
	.byte	11
	.ascii	"\210\001"
	.byte	15
	.byte	0
	.byte	0
	.byte	11
	.byte	36
	.byte	0
	.byte	3
	.byte	14
	.byte	62
	.byte	11
	.byte	11
	.byte	11
	.byte	0
	.byte	0
	.byte	12
	.byte	15
	.byte	0
	.byte	73
	.byte	19
	.byte	3
	.byte	14
	.byte	51
	.byte	6
	.byte	0
	.byte	0
	.byte	13
	.byte	1
	.byte	1
	.byte	73
	.byte	19
	.byte	0
	.byte	0
	.byte	14
	.byte	33
	.byte	0
	.byte	73
	.byte	19
	.byte	34
	.byte	13
	.byte	55
	.byte	11
	.byte	0
	.byte	0
	.byte	15
	.byte	36
	.byte	0
	.byte	3
	.byte	14
	.byte	11
	.byte	11
	.byte	62
	.byte	11
	.byte	0
	.byte	0
	.byte	0
	.section	.debug_info,"",%progbits
.Lcu_begin0:
	.long	.Ldebug_info_end0-.Ldebug_info_start0
.Ldebug_info_start0:
	.short	4
	.long	.debug_abbrev
	.byte	4
	.byte	1
	.long	.Linfo_string0
	.short	28
	.long	.Linfo_string1
	.long	.Lline_table_start0
	.long	.Linfo_string2

	.long	0
	.long	.Ldebug_ranges0
	.byte	2
	.long	.Linfo_string3
	.byte	3
	.long	.Lfunc_begin0
	.long	.Lfunc_end0-.Lfunc_begin0
	.byte	1
	.byte	87
	.long	.Linfo_string4
	.long	.Linfo_string5
	.byte	1
	.byte	7

	.byte	4
	.long	.Lfunc_begin1
	.long	.Lfunc_end1-.Lfunc_begin1
	.byte	1
	.byte	87
	.long	.Linfo_string6
	.long	.Linfo_string7
	.byte	1
	.byte	8

	.byte	5
	.long	.Ltmp3
	.long	.Ltmp5-.Ltmp3
	.byte	6
	.byte	2
	.byte	125
	.byte	12
	.long	.Linfo_string8
	.byte	1
	.byte	9
	.long	159
	.byte	6
	.byte	2
	.byte	125
	.byte	32
	.long	.Linfo_string36
	.byte	1
	.byte	9
	.long	520
	.byte	5
	.long	.Ltmp4
	.long	.Ltmp5-.Ltmp4
	.byte	6
	.byte	2
	.byte	145
	.byte	126
	.long	.Linfo_string53
	.byte	1
	.byte	11
	.long	580
	.byte	0
	.byte	0
	.byte	0
	.byte	0
	.byte	2
	.long	.Linfo_string9
	.byte	2
	.long	.Linfo_string8
	.byte	7
	.long	.Linfo_string35
	.byte	20
	.byte	4
	.byte	8
	.long	.Linfo_string10
	.long	195
	.byte	4
	.byte	0
	.byte	8
	.long	.Linfo_string24
	.long	406
	.byte	1
	.byte	0
	.byte	0
	.byte	0
	.byte	2
	.long	.Linfo_string11
	.byte	7
	.long	.Linfo_string23
	.byte	20
	.byte	4
	.byte	8
	.long	.Linfo_string12
	.long	275
	.byte	4
	.byte	0
	.byte	8
	.long	.Linfo_string17
	.long	275
	.byte	4
	.byte	4
	.byte	8
	.long	.Linfo_string18
	.long	275
	.byte	4
	.byte	8
	.byte	8
	.long	.Linfo_string19
	.long	389
	.byte	1
	.byte	16
	.byte	8
	.long	.Linfo_string21
	.long	389
	.byte	1
	.byte	17
	.byte	8
	.long	.Linfo_string22
	.long	275
	.byte	4
	.byte	12
	.byte	0
	.byte	0
	.byte	2
	.long	.Linfo_string13
	.byte	7
	.long	.Linfo_string16
	.byte	4
	.byte	4
	.byte	8
	.long	.Linfo_string14
	.long	382
	.byte	4
	.byte	0
	.byte	0
	.byte	0
	.byte	2
	.long	.Linfo_string40
	.byte	2
	.long	.Linfo_string41
	.byte	7
	.long	.Linfo_string49
	.byte	1
	.byte	1
	.byte	8
	.long	.Linfo_string42
	.long	389
	.byte	1
	.byte	0
	.byte	8
	.long	.Linfo_string43
	.long	454
	.byte	1
	.byte	0
	.byte	9
	.long	345
	.long	.Linfo_string46
	.byte	0
	.byte	0
	.byte	7
	.long	.Linfo_string47
	.byte	0
	.byte	1
	.byte	8
	.long	.Linfo_string43
	.long	471
	.byte	1
	.byte	0
	.byte	9
	.long	373
	.long	.Linfo_string46
	.byte	0
	.byte	10
	.long	.Linfo_string44
	.byte	0
	.byte	1
	.byte	0
	.byte	0
	.byte	11
	.long	.Linfo_string15
	.byte	7
	.byte	4
	.byte	11
	.long	.Linfo_string20
	.byte	7
	.byte	1
	.byte	2
	.long	.Linfo_string25
	.byte	2
	.long	.Linfo_string26
	.byte	7
	.long	.Linfo_string34
	.byte	0
	.byte	1
	.byte	8
	.long	.Linfo_string27
	.long	437
	.byte	1
	.byte	0
	.byte	0
	.byte	0
	.byte	0
	.byte	2
	.long	.Linfo_string28
	.byte	2
	.long	.Linfo_string29
	.byte	7
	.long	.Linfo_string33
	.byte	0
	.byte	1
	.byte	9
	.long	490
	.long	.Linfo_string32
	.byte	0
	.byte	7
	.long	.Linfo_string48
	.byte	0
	.byte	1
	.byte	9
	.long	345
	.long	.Linfo_string32
	.byte	0
	.byte	7
	.long	.Linfo_string45
	.byte	0
	.byte	1
	.byte	9
	.long	373
	.long	.Linfo_string32
	.byte	0
	.byte	0
	.byte	0
	.byte	12
	.long	503
	.long	.Linfo_string31
	.long	0
	.byte	11
	.long	.Linfo_string30
	.byte	7
	.byte	0
	.byte	2
	.long	.Linfo_string37
	.byte	2
	.long	.Linfo_string38
	.byte	7
	.long	.Linfo_string52
	.byte	8
	.byte	1
	.byte	8
	.long	.Linfo_string36
	.long	560
	.byte	1
	.byte	0
	.byte	0
	.byte	7
	.long	.Linfo_string50
	.byte	1
	.byte	1
	.byte	8
	.long	.Linfo_string39
	.long	305
	.byte	1
	.byte	0
	.byte	0
	.byte	0
	.byte	0
	.byte	13
	.long	539
	.byte	14
	.long	573
	.byte	0
	.byte	8
	.byte	0
	.byte	15
	.long	.Linfo_string51
	.byte	8
	.byte	7
	.byte	11
	.long	.Linfo_string54
	.byte	7
	.byte	2
	.byte	0
.Ldebug_info_end0:
	.section	.text.main,"ax",%progbits
.Lsec_end0:
	.section	.text._ZN12led_roulette18__cortex_m_rt_main17h0b2223cb0e38e500E,"ax",%progbits
.Lsec_end1:
	.section	.debug_aranges,"",%progbits
	.long	36
	.short	2
	.long	.Lcu_begin0
	.byte	4
	.byte	0
	.zero	4,255
	.long	.Lfunc_begin0
	.long	.Lsec_end0-.Lfunc_begin0
	.long	.Lfunc_begin1
	.long	.Lsec_end1-.Lfunc_begin1
	.long	0
	.long	0
	.section	.debug_ranges,"",%progbits
.Ldebug_ranges0:
	.long	.Lfunc_begin0
	.long	.Lfunc_end0
	.long	.Lfunc_begin1
	.long	.Lfunc_end1
	.long	0
	.long	0
	.section	.debug_str,"MS",%progbits,1
.Linfo_string0:
	.asciz	"clang LLVM (rustc version 1.48.0 (7eac88abb 2020-11-16))"
.Linfo_string1:
	.asciz	"src/05-led-roulette/src/main.rs"
.Linfo_string2:
	.asciz	"/home/stefan/projects/discovery"
.Linfo_string3:
	.asciz	"led_roulette"
.Linfo_string4:
	.asciz	"main"
.Linfo_string5:
	.asciz	"__cortex_m_rt_main_trampoline"
.Linfo_string6:
	.asciz	"_ZN12led_roulette18__cortex_m_rt_main17h0b2223cb0e38e500E"
.Linfo_string7:
	.asciz	"__cortex_m_rt_main"
.Linfo_string8:
	.asciz	"delay"
.Linfo_string9:
	.asciz	"stm32f30x_hal"
.Linfo_string10:
	.asciz	"clocks"
.Linfo_string11:
	.asciz	"rcc"
.Linfo_string12:
	.asciz	"hclk"
.Linfo_string13:
	.asciz	"time"
.Linfo_string14:
	.asciz	"__0"
.Linfo_string15:
	.asciz	"u32"
.Linfo_string16:
	.asciz	"Hertz"
.Linfo_string17:
	.asciz	"pclk1"
.Linfo_string18:
	.asciz	"pclk2"
.Linfo_string19:
	.asciz	"ppre1"
.Linfo_string20:
	.asciz	"u8"
.Linfo_string21:
	.asciz	"ppre2"
.Linfo_string22:
	.asciz	"sysclk"
.Linfo_string23:
	.asciz	"Clocks"
.Linfo_string24:
	.asciz	"syst"
.Linfo_string25:
	.asciz	"cortex_m"
.Linfo_string26:
	.asciz	"peripheral"
.Linfo_string27:
	.asciz	"_marker"
.Linfo_string28:
	.asciz	"core"
.Linfo_string29:
	.asciz	"marker"
.Linfo_string30:
	.asciz	"()"
.Linfo_string31:
	.asciz	"*const ()"
.Linfo_string32:
	.asciz	"T"
.Linfo_string33:
	.asciz	"PhantomData<*const ()>"
.Linfo_string34:
	.asciz	"SYST"
.Linfo_string35:
	.asciz	"Delay"
.Linfo_string36:
	.asciz	"leds"
.Linfo_string37:
	.asciz	"f3"
.Linfo_string38:
	.asciz	"led"
.Linfo_string39:
	.asciz	"pex"
.Linfo_string40:
	.asciz	"gpio"
.Linfo_string41:
	.asciz	"gpioe"
.Linfo_string42:
	.asciz	"i"
.Linfo_string43:
	.asciz	"_mode"
.Linfo_string44:
	.asciz	"PushPull"
.Linfo_string45:
	.asciz	"PhantomData<stm32f30x_hal::gpio::PushPull>"
.Linfo_string46:
	.asciz	"MODE"
.Linfo_string47:
	.asciz	"Output<stm32f30x_hal::gpio::PushPull>"
.Linfo_string48:
	.asciz	"PhantomData<stm32f30x_hal::gpio::Output<stm32f30x_hal::gpio::PushPull>>"
.Linfo_string49:
	.asciz	"PEx<stm32f30x_hal::gpio::Output<stm32f30x_hal::gpio::PushPull>>"
.Linfo_string50:
	.asciz	"Led"
.Linfo_string51:
	.asciz	"__ARRAY_SIZE_TYPE__"
.Linfo_string52:
	.asciz	"Leds"
.Linfo_string53:
	.asciz	"half_period"
.Linfo_string54:
	.asciz	"u16"
	.section	.debug_pubnames,"",%progbits
	.long	.LpubNames_end0-.LpubNames_begin0
.LpubNames_begin0:
	.short	2
	.long	.Lcu_begin0
	.long	588
	.long	396
	.asciz	"cortex_m"
	.long	43
	.asciz	"__cortex_m_rt_main_trampoline"
	.long	432
	.asciz	"marker"
	.long	38
	.asciz	"led_roulette"
	.long	64
	.asciz	"__cortex_m_rt_main"
	.long	427
	.asciz	"core"
	.long	401
	.asciz	"peripheral"
	.long	149
	.asciz	"stm32f30x_hal"
	.long	270
	.asciz	"time"
	.long	154
	.asciz	"delay"
	.long	295
	.asciz	"gpio"
	.long	300
	.asciz	"gpioe"
	.long	515
	.asciz	"led"
	.long	190
	.asciz	"rcc"
	.long	510
	.asciz	"f3"
	.long	0
.LpubNames_end0:
	.section	.debug_pubtypes,"",%progbits
	.long	.LpubTypes_end0-.LpubTypes_begin0
.LpubTypes_begin0:
	.short	2
	.long	.Lcu_begin0
	.long	588
	.long	490
	.asciz	"*const ()"
	.long	580
	.asciz	"u16"
	.long	520
	.asciz	"Leds"
	.long	437
	.asciz	"PhantomData<*const ()>"
	.long	275
	.asciz	"Hertz"
	.long	159
	.asciz	"Delay"
	.long	389
	.asciz	"u8"
	.long	503
	.asciz	"()"
	.long	406
	.asciz	"SYST"
	.long	539
	.asciz	"Led"
	.long	345
	.asciz	"Output<stm32f30x_hal::gpio::PushPull>"
	.long	305
	.asciz	"PEx<stm32f30x_hal::gpio::Output<stm32f30x_hal::gpio::PushPull>>"
	.long	382
	.asciz	"u32"
	.long	471
	.asciz	"PhantomData<stm32f30x_hal::gpio::PushPull>"
	.long	454
	.asciz	"PhantomData<stm32f30x_hal::gpio::Output<stm32f30x_hal::gpio::PushPull>>"
	.long	373
	.asciz	"PushPull"
	.long	195
	.asciz	"Clocks"
	.long	0
.LpubTypes_end0:
	.section	".note.GNU-stack","",%progbits
	.eabi_attribute	30, 5
	.section	.debug_line,"",%progbits
.Lline_table_start0:

I think the relevant part of this output is section .LBB1_4 where we see that the constant 500 gets moved into r1 before calling the delay function instead of loading the variable from the stack.
@pevandenburie pevandenburie mentioned this issue Feb 7, 2021
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@pevandenburie
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Explanation is given in issue #236 , although this does not resolve it. Maybe simply remove this gdb example from the book?

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@pevandenburie @vringar