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cmd/link: avoid exporting all symbols on windows buildmode=pie

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Marking one functions with __declspec(dllexport) forces mingw to
create .reloc section without having to export all symbols.

See https://insights.sei.cmu.edu/cert/2018/08/when-aslr-is-not-really-aslr---the-case-of-incorrect-assumptions-and-bad-defaults.html for more info.

This change cuts 73kb of a "hello world" pie binary.

Updates #6853
Fixes #40795

Change-Id: I3cc57c3b64f61187550bc8751dfa085f106c8475
Reviewed-on: https://go-review.googlesource.com/c/go/+/264459
Trust: Alex Brainman <alex.brainman@gmail.com>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Austin Clements <austin@google.com>
This commit is contained in:
Quim Muntal 2020-10-22 22:32:20 +02:00 • committed by Austin Clements
parent 333d2010ec
commit e463c28cc1
6 changed files with 52 additions and 7 deletions
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9
misc/cgo/testcshared/cshared_test.go
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@ -401,7 +401,7 @@ func main() {
defer f.Close()
section := f.Section(".edata")
if section == nil {
t.Error(".edata section is not present")
t.Fatalf(".edata section is not present")
}
// TODO: deduplicate this struct from cmd/link/internal/ld/pe.go
@ -418,7 +418,8 @@ func main() {
t.Fatalf("binary.Read failed: %v", err)
}
expectedNumber := uint32(2)
// Only the two exported functions and _cgo_dummy_export should be exported
expectedNumber := uint32(3)
if exportAllSymbols {
if e.NumberOfFunctions <= expectedNumber {
@ -429,10 +430,10 @@ func main() {
}
} else {
if e.NumberOfFunctions != expectedNumber {
t.Fatalf("too many exported functions: %v", e.NumberOfFunctions)
t.Fatalf("got %d exported functions; want %d", e.NumberOfFunctions, expectedNumber)
}
if e.NumberOfNames != expectedNumber {
t.Fatalf("too many exported names: %v", e.NumberOfNames)
t.Fatalf("got %d exported names; want %d", e.NumberOfNames, expectedNumber)
}
}
}