cmd/link: handle grouped resource sections

The Go PE linker does not support enough generalized PE logic to
properly handle .rsrc sections gracefully. Instead a few things are
special cased for these. The linker also does not support PE's "grouped
sections" features, in which input objects have several named sections
that are sorted, merged, and renamed in the output file. In the past,
more sophisticated support for resources or for PE features like grouped
sections have not been necessary, as Go's own object formats are pretty
vanilla, and GNU binutils also produces pretty vanilla objects where all
sections are already merged.

However, GNU binutils is lagging with arm support, and here LLVM has
picked up the slack. In particular, LLVM has its own rc/cvtres combo,
which are glued together in mingw LLVM distributions as windres, a
command line compatible tool with binutils' windres, which supports arm
and arm64. But there's a key difference between binutils' windres and
LLVM's windres: the LLVM one uses proper grouped sections.

So, this commit adds grouped sections support for resource sections to
the linker. We don't attempt to plumb generic support for grouped
sections, just as there isn't generic support already for what resources
require. Instead we augment the resource handling logic to deal with
standard two-section resource objects.

We also add a test for this, akin to the current test for more vanilla
binutils resource objects, and make sure that the rsrc tests are always
performed.

Fixes #42866.
Fixes #43182.

Change-Id: I059450021405cdf2ef1c195ddbab3960764ad711
Reviewed-on: https://go-review.googlesource.com/c/go/+/268337
Run-TryBot: Jason A. Donenfeld <Jason@zx2c4.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Trust: Alex Brainman <alex.brainman@gmail.com>
Trust: Jason A. Donenfeld <Jason@zx2c4.com>

2 files changed, 43 insertions, 0 deletions

diff --git a/src/cmd/link/testdata/testPErsrc-complex/main.go b/src/cmd/link/testdata/testPErsrc-complex/main.go
new file mode 100644
index 0000000000..affd6eada2
--- /dev/null
+++ b/src/cmd/link/testdata/testPErsrc-complex/main.go
@@ -0,0 +1,43 @@
+// Copyright 2020 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.
+
+// Test that a PE rsrc section is handled correctly, when the object files
+// have been created by llvm-rc or msvc's rc.exe, which means there's the
+// @feat.00 symbol as well as split .rsrc$00 and .rsrc$01 section to deal with.
+//
+// rsrc.syso is created with:
+//    windres -i a.rc -o rsrc.syso -O coff
+// where this windres calls into llvm-rc and llvm-cvtres. The source file,
+// a.rc, simply contains a reference to its own bytes:
+//
+//    resname RCDATA a.rc
+//
+// Object dumping the resultant rsrc.syso, we can see the split sections and
+// the @feat.00 SEH symbol:
+//
+//     rsrc.syso:      file format coff-x86-64
+//
+//     architecture: x86_64
+//     start address: 0x0000000000000000
+//
+//     Export Table:
+//     Sections:
+//     Idx Name          Size     VMA              Type
+//       0 .rsrc$01      00000068 0000000000000000 DATA
+//       1 .rsrc$02      00000018 0000000000000000 DATA
+//
+//     SYMBOL TABLE:
+//     [ 0](sec -1)(fl 0x00)(ty   0)(scl   3) (nx 0) 0x00000011 @feat.00
+//     [ 1](sec  1)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .rsrc$01
+//     AUX scnlen 0x68 nreloc 1 nlnno 0 checksum 0x0 assoc 0 comdat 0
+//     [ 3](sec  2)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .rsrc$02
+//     AUX scnlen 0x18 nreloc 0 nlnno 0 checksum 0x0 assoc 0 comdat 0
+//     [ 5](sec  2)(fl 0x00)(ty   0)(scl   3) (nx 0) 0x00000000 $R000000
+//     RELOCATION RECORDS FOR [.rsrc$01]:
+//     OFFSET           TYPE                     VALUE
+//     0000000000000048 IMAGE_REL_AMD64_ADDR32NB $R000000
+
+package main
+
+func main() {}
diff --git a/src/cmd/link/testdata/testPErsrc-complex/rsrc.syso b/src/cmd/link/testdata/testPErsrc-complex/rsrc.syso
new file mode 100644
index 0000000000..eff630b8a2
--- /dev/null
+++ b/src/cmd/link/testdata/testPErsrc-complex/rsrc.syso