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Diffstat (limited to '2026-linuxdays/pres.typ')
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diff --git a/2026-linuxdays/pres.typ b/2026-linuxdays/pres.typ new file mode 100644 index 0000000..1e15bac --- /dev/null +++ b/2026-linuxdays/pres.typ @@ -0,0 +1,359 @@ +#import "@preview/polylux:0.4.0": * +#import "@preview/metropolis-polylux:0.1.0" as metropolis + +#show: metropolis.setup +#show: metropolis.setup.with(footer: [Má smysl rozumět assembleru?]) + +#slide[ + #set page(header: none, footer: none, margin: 3em) + + #text(size: 1.3em)[*Má smysl rozumět assembleru?*] + + LinuxDays 2026 + + #metropolis.divider + + #set text(size: .8em, weight: "light") + Karel Kočí + + 4.10.2026 + + https://git.cynerd.cz/presentations/tree/2026-linuxdays +] + +#slide[ + = Co je Assembler? + + - Programovací jazyk + - Syntaxe + - Komentáře + - Makra + + - Čitelný zápis programového kódu + - 1:1 asociace mezi instrukcemi + - rozhraní mezi programem a procesorem +] + +#slide[ + = Crash course CPU + + #image("intro.webp") +] + +#slide[ + = Crash course Assembler + + #columns(2)[ + ```asm + .globl _start + .option norelax + + .text + + _start: + loop: + lw x2, 0x400(x0) + sw x2, 0x404(x0) + beq x0, x0, loop + nop + nop + ebreak + ``` + #colbreak() + ```asm + .data + .org 0x400 + + src_val: + .word 0x12345678 + dst_val: + .word 0 + ``` + ] +] + +#slide[ + = Proč tohle nefunguje? + + ```c + void *buf = malloc(BUFSIZ); + uint64_t *num = buf + 1; + *num = 42; + ``` + ``` + $ gcc align.c -o align + $ ./align + $ + ``` + ``` + $ armv7l-unknown-linux-gnueabihf-gcc -ggdb align.c -o align + $ ./align + qemu: uncaught target signal 7 (Bus error) - core dumped + $ + ``` +] +#slide[ + = Disassembly + #text(size: .8em)[ + ``` + $ armv7l-unknown-linux-gnueabihf-objdump -S align + ... + void *buf = malloc(BUFSIZ); + 6d4: e3a00a02 mov r0, #8192 @ 0x2000 + 6d8: ebffff97 bl 53c <malloc@plt> + 6dc: e1a03000 mov r3, r0 + 6e0: e50b3008 str r3, [fp, #-8] + uint64_t *num = buf + 1; + 6ec: e51b3008 ldr r3, [fp, #-8] + 6f0: e2833001 add r3, r3, #1 + 6f4: e50b3010 str r3, [fp, #-16] + *num = 42; + 6f8: e51b1010 ldr r1, [fp, #-16] + 6fc: e3a0202a mov r2, #42 @ 0x2a + 700: e3a03000 mov r3, #0 + 704: e1c120f0 strd r2, [r1] + ... + ``` + ] +] +#slide[ + = Malá oprava + + ```c + typedef uint64_t uint64_unaligned_t [[gnu::aligned(1)]]; + void *buf = malloc(BUFSIZ); + uint64_unaligned_t *num = buf + 1; + *num = 42; + ``` + + #text(size: .7em)[ + ``` + uint64_unaligned_t *num = buf + 1; + 6ec: e51b3008 ldr r3, [fp, #-8] + 6f0: e2833001 add r3, r3, #1 + 6f4: e50b3010 str r3, [fp, #-16] + *num = 42; + 6f8: e51b3010 ldr r3, [fp, #-16] + 6fc: e3a0202a mov r2, #42 @ 0x2a + 700: e5832000 str r2, [r3] + 704: e3a02000 mov r2, #0 + 708: e5832004 str r2, [r3, #4] + ``` + ] +] + +#slide[ + = Použití speciálních instrukcí + Například SIMD: + + ```c + typedef int v4si [[gnu::vector_size(16)]]; + + v4si v4add(v4si a, v4si b) { + asm("paddd %[b], %[a]" : [a] "+x"(a) : [b] "x"(b)); + return a; + } + ``` +] + +#metropolis.new-section[TLDR; Ano, vyplatí se ho znát.] + +#slide[ + = Ale SIMD... + + ```c + typedef int v4si [[gnu::vector_size(16)]]; + v4si v4add2(v4si a, v4si b) { return a + b; } + ``` + \ + + ```asm + 0000000000000025 <v4add2>: + 25: 55 push %rbp + 26: 48 89 e5 mov %rsp,%rbp + 29: 0f 29 45 f0 movaps %xmm0,-0x10(%rbp) + 2d: 0f 29 4d e0 movaps %xmm1,-0x20(%rbp) + 31: 66 0f 6f 45 f0 movdqa -0x10(%rbp),%xmm0 + 36: 66 0f fe 45 e0 paddd -0x20(%rbp),%xmm0 + 3b: 5d pop %rbp + 3c: c3 ret + ``` +] + +#slide[ + = A zarovnání... + + - Python, JavaScript, ... + - Ehm... RUST! RUST! RUST! RUST! RUST! + - Btw.. v Go to taky bez unsafe nejde + + A kdo dneska píše programy v assembleru? +] + +#metropolis.new-section[TLDR; Takže ho nemusím znát?] + +#slide[ + = Pochopení jak fungují struktury + ```c + struct px { int x, y;}; + int x_plus_y(struct px *p) { + return p->x + p->y; + } + ``` + ``` + p->x + p->y; + 66: 411c lw a5,0(a0) + 68: 4148 lw a0,4(a0) + 6a: 9d3d addw a0,a0,a5 + ``` +] + +#slide[ + = Jak funguje volání funkce + #text(size: .8em)[ + ```c + add2(1, 2); + ``` + ``` + fc: 4589 li a1,2 + fe: 4505 li a0,1 + 100: 00000097 auipc ra,0x0 + 104: 000080e7 jalr ra # 100 <call_add+0xc> + ``` + ```c + add9(1, 2, 3, 4, 5, 6, 7, 8, 9); + ``` + ``` + 108: 47a5 li a5,9 + 10a: e03e sd a5,0(sp) + 10c: 48a1 li a7,8 + 10e: 481d li a6,7 + 110: 4799 li a5,6 + 112: 4715 li a4,5 + 114: 4691 li a3,4 + 116: 460d li a2,3 + 118: 4589 li a1,2 + 11a: 4505 li a0,1 + 11c: 00000097 auipc ra,0x0 + 120: 000080e7 jalr ra # 11c <call_add+0x28> + ``` + ] +] + +#slide[ + = Staré zvyky + #text(size: .8em)[ + #columns(2)[ + ```c + int div2_a(unsigned x) { + return x / 2; + } + ``` + ``` + 0: 1101 addi sp,sp,-32 + 2: ec06 sd ra,24(sp) + 4: e822 sd s0,16(sp) + 6: 1000 addi s0,sp,32 + 8: 87aa mv a5,a0 + a: fef42623 sw a5,-20(s0) + e: fec42783 lw a5,-20(s0) + 12: 0017d79b srliw a5,a5,0x1 + 16: 2781 sext.w a5,a5 + 18: 853e mv a0,a5 + 1a: 60e2 ld ra,24(sp) + 1c: 6442 ld s0,16(sp) + 1e: 6105 addi sp,sp,32 + 20: 8082 ret + ``` + #colbreak() + ```c + int div2_b(unsigned x) { + return x >> 1; + } + ``` + ``` + 22: 1101 addi sp,sp,-32 + 24: ec06 sd ra,24(sp) + 26: e822 sd s0,16(sp) + 28: 1000 addi s0,sp,32 + 2a: 87aa mv a5,a0 + 2c: fef42623 sw a5,-20(s0) + 30: fec42783 lw a5,-20(s0) + 34: 0027d79b srliw a5,a5,0x1 + 38: 2781 sext.w a5,a5 + 3a: 853e mv a0,a5 + 3c: 60e2 ld ra,24(sp) + 3e: 6442 ld s0,16(sp) + 40: 6105 addi sp,sp,32 + 42: 8082 ret + ``` + ]] +] + +#slide[ + = Opravdu optimální? + #text(size: .8em)[ + #columns(2)[ + ```c + int abs_a(int x) { + return x < 0 ? -x : x; + } + ``` + ``` + 52: fec42783 lw a5,-20(s0) + 56: 41f7d79b sraiw a5,a5,0x1f + 5a: fec42703 lw a4,-20(s0) + 5e: 8f3d xor a4,a4,a5 + 60: 40f707bb subw a5,a4,a5 + 64: 2781 sext.w a5,a5 + ``` + #colbreak() + ```c + int abs_b(int x) { + int m = x >> (sizeof(x) * CHAR_BIT - 1); + return (x + m) ^ m; + } + ``` + ``` + 7e: fdc42783 lw a5,-36(s0) + 82: 41f7d79b sraiw a5,a5,0x1f + 86: fef42623 sw a5,-20(s0) + 8a: fdc42783 lw a5,-36(s0) + 8e: 873e mv a4,a5 + 90: fec42783 lw a5,-20(s0) + 94: 9fb9 addw a5,a5,a4 + 96: 2781 sext.w a5,a5 + 98: fec42703 lw a4,-20(s0) + 9c: 8fb9 xor a5,a5,a4 + 9e: 2781 sext.w a5,a5 + ``` + ] + ] +] + +#slide[ + = Takže k čemu se hodí? + - Pochopení jak procesory fungují + - Optimalizuji, nebo to kazím kompilátoru? + - -> Porozumění kódu (https://godbolt.org/) + - Debuggování kompilovaných jazyků, když už dojde na nehorší + - Implementace kritických sekcí v OS a embedded + - Vývoj kompilátoru (i JIT) +] + +#slide[ + #show: metropolis.focus + Děkuji za pozornost + + Karel Kočí + + #metropolis.divider + + #text(size: 0.7em)[ + https://git.cynerd.cz + + https://gitlab.com/cynerd + + https://git.cynerd.cz/presentations/tree/2026-linuxdays + ] +] |