Add support for inlined functions

[maxgio92]

When compiler optimization inlines functions, related symbols are tricky to retrieve since they are no longer explicitely listed in the ELF symbol table.

Support for such cases would be highly beneficial.

For instance, the Go compiler often inlines functions with low LoC:

package main

import (
	"fmt"
	"os"
)

//go:noinline
func add(a, b int) int {
	return a + b
}

//go:noinline
func multiply(a, b int) int {
	return a * b
}

//go:noinline
func subtract(a, b int) int {
	return a - b
}

//go:noinline
func divide(a, b int) int {
	if b == 0 {
		return 0
	}
	return a / b
}

//go:noinline
func greet(name string) {
	fmt.Printf("Hello, %s!\n", name)
}

func main() {
	if len(os.Args) < 2 {
		fmt.Println("Usage: demo-app <command>")
		fmt.Println("Commands: add, multiply, greet")
		os.Exit(1)
	}

	cmd := os.Args[1]

	switch cmd {
	case "add":
		result := add(10, 20)
		fmt.Printf("10 + 20 = %d\n", result)
	case "multiply":
		result := multiply(5, 6)
		fmt.Printf("5 * 6 = %d\n", result)
	case "greet":
		greet("xcover")
	case "all":
		// Call all functions for maximum coverage
		fmt.Println("Running all functions:")
		fmt.Printf("Add: %d\n", add(10, 20))
		fmt.Printf("Multiply: %d\n", multiply(5, 6))
		fmt.Printf("Subtract: %d\n", subtract(30, 10))
		fmt.Printf("Divide: %d\n", divide(100, 5))
		greet("xcover")
	default:
		fmt.Printf("Unknown command: %s\n", cmd)
	}
}

$ go build .
$ go tool nm tmp | grep -E " main\."
  499e00 T main.add
  499e60 T main.divide
  499e80 T main.greet
  499f00 T main.main
  499e20 T main.multiply
  499e40 T main.subtract

without the noinline annotation, Go compiler would inline all the functions into the main one:

$ go build .
$ go tool nm demo-inlined | grep -E " main\."
  499e00 T main.main

VA range from the DWARF info:

With inlined functions:

$ readelf -wi ./demo-inline | grep -A2 " main\."
    <1dd2>   DW_AT_name        : main.greet
    <1ddd>   DW_AT_inline      : 1      (inlined)
    <1dde>   DW_AT_decl_line   : 27
--
    <1e46>   DW_AT_name        : main.main
    <1e50>   DW_AT_low_pc      : (index: 0x1): 0x499e00
    <1e51>   DW_AT_high_pc     : 1174

Without:

$ readelf -wi ./demo-noinline | grep -A2 " main\."
    <1e2b>   DW_AT_name        : main.add
    <1e34>   DW_AT_low_pc      : (index: 0x1): 0x499e00
    <1e35>   DW_AT_high_pc     : 4
--
    <1e66>   DW_AT_name        : main.multiply
    <1e74>   DW_AT_low_pc      : (index: 0x2): 0x499e20
    <1e75>   DW_AT_high_pc     : 5
--
    <1ea6>   DW_AT_name        : main.subtract
    <1eb4>   DW_AT_low_pc      : (index: 0x3): 0x499e40
    <1eb5>   DW_AT_high_pc     : 4
--
    <1ee6>   DW_AT_name        : main.divide
    <1ef2>   DW_AT_low_pc      : (index: 0x4): 0x499e60
    <1ef3>   DW_AT_high_pc     : 27
--
    <1f24>   DW_AT_name        : main.greet
    <1f2f>   DW_AT_low_pc      : (index: 0x5): 0x499e80
    <1f30>   DW_AT_high_pc     : 125
--
    <1f66>   DW_AT_name        : main.main
    <1f70>   DW_AT_low_pc      : (index: 0x6): 0x499f00
    <1f71>   DW_AT_high_pc     : 1110

[maxgio92]

When debug info is not stripped away, DWARF 's DW_AT_abstract_origin which should link to the debug info offset in the non-optimized binary.