Getting started. Roel Jordans

Transcription

1 Getting started Roel Jordans

2 Goal Translate a program from a high level language into something the processor can execute efficiently So before we start we need to know how this processor executes a program 2

3 Processor architecture by example: AVR

4 AVR CPU core Separate instruction and Data memories All 32 General purpose registers connected to ALU 4 IO Modules connected to Data Bus and accessible via Special Function Registers

5 Memory organization One general purpose register file Two memories Program memory Data memory And some peripherals Memory mapped e.g. IO ports, timers, EEPROM,... 5

6 General purpose registers 32x8-bit registers 16-bit registers formed using pairs of 8 bit registers X, Y, and Z 16-bit registers Can be used for indirect addressing Operation input/output schemes: One 8-bit operand, 8-bit result Two 8-bit operands, 8-bit result Two 8-bit operands, 16-bit result One 16-bit operand, 16-bit result Hardware stack pointer 6

7 Program memory On chip, in system programmable 32K bytes, in 16K 2 byte instructions Accessible via special instructions (LPM,SPM) Bootloader support from boot flash section Contains interrupt vector table Program starts with reset (IRQ0) 7

8 Data memory Registers mapped in SRAM memory space 32 GPR 64 SFR SFR's accessed through in/out instructions (IO registers) 2KB of internal SRAM from address 0x060 Holds the stack! Required for call instruction Stack grows down from the top of memory 8

9 Important information The AVR datasheet Only 448 pages long! Also includes info on the available peripherals Focus on the following sections 6 & 7 for the architecture and memory organization 31 for the instruction-set overview 30 for the special function register Provided on the oncourse website 9

10 Compilation stages

11 Compilation flow overview User-created files Makefile Make Utility C/C++ Source and Header Files Assembly Assembly Source Source Files Files Shared Object File 11 Object Files Archive Utility Library Files Linker Script File Linkable Image File Executable Image File Link Map File

12 12

13 Preprocessor Adds some really useful extra features #include #define #ifdef Also useful for other languages Like the 13

14 The Compilation in three steps AST, IR, Code generation 14

15 An example from C int foo(int a, int b) { return a + b; } 15

16 int foo(int a, int b) { return a + b; } Abstract Syntax Tree (AST) $ clang Xclang ast dump fsyntax only f.c TranslationUnitDecl... TypedefDecl... ` FunctionDecl... <f.c:1:1, line:3:1> line:1:5 foo 'int(int,int)' ParmVarDecl... <col:9, col:13> col:13 used a 'int' ParmVarDecl... <col:16, col:20> col:20 used b 'int' ` CompoundStmt... <col:23, line:3:1> ` ReturnStmt... <line:2:2, col:11> ` BinaryOperator... 'int' '+' ImplicitCastExpr... 'int' <LValueToRValue> ` DeclRefExpr... 'int' lvalue ParmVar... 'a' 'int' ` ImplicitCastExpr... 'int' <LValueToRValue> ` DeclRefExpr... 'int' lvalue ParmVar... 'b' 'int' 16

17 AST Tools Direct translation back to C Code formatting with clang-format AST analysis clang-check Buffer checking C code clang-tidy Cleans up common programming mistakes Transforming AST Source-to-source transformations clang-modernize Update code to use newer language features 17

18 int foo(int a, int b) { return a + b; } Intermediate Representation (IR) $ clang target=avr emit llvm S f.c ; ModuleID = 'f.c' target datalayout = "..." target triple = "avr unknown unknown" ; Function Attrs: nounwind define %a, i16 %b) #0 { %1 = alloca i16, align 2 %2 = alloca i16, align 2 store i16 %a, i16* %1, align 2 store i16 %b, i16* %2, align 2 %3 = load i16* %1, align 2 %4 = load i16* %2, align 2 %5 = add nsw i16 %3, %4 ret i16 %5 } 18

19 IR optimizations Code simplification Dead-code elimination (DCE) Common sub-expression elimination (CSE) Code analysis Alias analysis Control-flow analysis Code transformation Loop transformation Auto vectorization 19

20 int foo(int a, int b) { return a + b; } Enabling IR optimizations $ opt S O1 f.ll o f.opt.ll ; ModuleID = 'f.ll' target datalayout = "..." target triple = "avr unknown unknown" ; Function Attrs: nounwind define %a, i16 %b) #0 { %add = add nsw i16 %a, %b ret i16 %add } 20

21 int foo(int a, int b) { return a + b; } CodeGen $ llc f.opt.ll.text.file.globl.align.type "f.opt.ll" foo 2 foo,@function foo: ; BB#0: add adc ret.lfunc_end0:.size ; %entry r24, r22 r25, r23 foo,.lfunc_end0 foo 21

22 The From human readable to executable Produces object files Usually in ELF or COFF format 22

23 Executable and Linkable Format Contains the binary data for the processor Code & Data Optionally contains extra information Debug information Symbol tables Relocation information 23

24 Linux Executable ELF files The Executable ELF files produced by the Linux linker are configured for execution in a private virtual address space, whereby every program gets loaded at the identical virtual memory-address 24

25 Executable versus Linkable ELF Header ELF Header Program-Header Table (optional) Program-Header Table Section 1 Data Segment 1 Data Section 2 Data Segment 2 Data Section 3 Data Segment 3 Data Section n Data Segment n Data Section-Header Table Section-Header Table (optional) Linkable File Executable File 25

26 Role of the Linker ELF Header ELF Header Section 1 Data Section 2 Data Program-Header Table Section n Data Segment 1 Data Section-Header Table Segment 2 Data Linkable File ELF Header Segment n Data Section 1 Data Section 2 Data Executable File Section n Data Section-Header Table Linkable File 26

27 The linker Controllable by a linker script Default provided for simple architectures Required when the mapping of sections to memories becomes more complex Multiple data memories Moving code around at runtime Fat binaries: supporting multiple architectures Encrypted binaries 27

28 C runtime Initializing the processor What happens before and after main Setting up the stack Calling main Stopping execution 28

29 To summarize User-created files Makefile Make Utility C/C++ Source and Header Files Assembly Assembly Source Source Files Files Archive Utility Library Files Shared Object File 29 Linker Script File Object Files Linkable Executable The driver Image File Image File Link Map File

30 The driver Many different tools in the compilation process Mostly useful when debugging the Needs simple interface The frontend program (clang) can actually call the right programs for you! 30

31 PCP Assignment 1: AVR backend

32 The application

33 Overview Practice makes perfect Assignments on the ES group servers 33 Login information can be found on oncourse.tue.nl Password distributed in My grades Start with Tool setup Download and follow the assignment instructions Answer the Assignment 1.A quiz questions on oncourse

34 Bonus exercise 1 Make (or Makefiles) As mentioned earlier in this lecture Manages compilation steps Very useful to know (Ab)used for many other purposes Also available on oncourse Take home exercise with questions online Try to automate the build process of assignment 1

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36 Acknowledgements These slides were partially based on the following: