## Compiler {#compiler}

## Assembler {#assembler}

the host linker. The default value for the host linker is $CC, split
into fields, or else "gcc". The specific host linker command line can
be overridden using command line flags: cmd/link -extld=clang
-extldflags='-ggdb -O3'. If any package in a build includes a .cc or
other file compiled by the C++ compiler, the go tool will use the
-extld option to set the host linker to the C++ compiler.

			argvPtrs.push(0);

			const argv = offset;
			argvPtrs.forEach((ptr) => {
				this.mem.setUint32(offset, ptr, true);
				this.mem.setUint32(offset + 4, 0, true);
				offset += 8;
			});

			// The linker guarantees global data starts from at least wasmMinDataAddr.
			// Keep in sync with cmd/link/internal/ld/data.go:wasmMinDataAddr.
			const wasmMinDataAddr = 4096 + 8192;
			if (offset >= wasmMinDataAddr) {

// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

//go:build cgo && !windows

// Issue 29563: internal linker fails on duplicate weak symbols.
// No runtime test; just make sure it compiles.

package cgotest

		if f == nil {
			continue
		}
		fname := f.Name()
		switch fname {
		case "goCallback":
			// TODO(qmuntal): investigate why this function doesn't appear
			// when using the external linker.
			continue
		}
		// In module mode, this package has a fully-qualified import path.
		// Remove it if present.
		fname = strings.TrimPrefix(fname, "cmd/cgo/internal/")
		if !strings.HasPrefix(fname, "test.") {

		}
		a.Offset = int64(p.expr())
		if p.peek() != '(' {
			switch prefix {
			case '$':
				a.Type = obj.TYPE_CONST
			case '*':
				a.Type = obj.TYPE_INDIR // Can appear but is illegal, will be rejected by the linker.
			default:
				a.Type = obj.TYPE_MEM
			}
			// fmt.Printf("CONST %d %s\n", a.Offset, obj.Dconv(&emptyProg, 0, a))
			p.expectOperandEnd()
			return
		}
		// fmt.Printf("offset %d \n", a.Offset)
	}

Previously, large builds could see 100%+ build time increase from enabling PGO.
In Go 1.23, overhead should be in the single digit percentages.

## Assembler {#assembler}

package cgotest

import "testing"

// If gcc is used, and linking internally, __mulsc3 and __muldc3
// will be linked in from libgcc which make several R_PPC64_TOC16_DS
// relocations which may not be resolvable with the internal linker.
func test8694(t *testing.T) { t.Skip("not supported on ppc64/ppc64le with internal linking") }

	JMP	2(PC)					// 6f008000
	JMP	(X5)					// 67800200
	JMP	4(X5)					// 67804200

	// CALL and JMP to symbol are encoded as JAL (using LR or ZERO
	// respectively), with a R_RISCV_JAL relocation. The linker resolves
	// the real address and updates the immediate, using a trampoline in
	// the case where the address is not directly reachable.
	CALL	asmtest(SB)				// ef000000
	JMP	asmtest(SB)				// 6f000000

// license that can be found in the LICENSE file.

package cgotest

// Test that we have no more than one build ID.  In the past we used
// to generate a separate build ID for each package using cgo, and the
// linker concatenated them all.  We don't want that--we only want
// one.

import (
	"bytes"
	"debug/elf"
	"os"
	"testing"
)

func testBuildID(t *testing.T) {
	f, err := elf.Open("/proc/self/exe")