[release-branch.go1.15] cmd/go: don't lookup the path for CC when invoking cgo

Previously, if CC was a path without separators (like gcc or clang),
we'd look it up in PATH in cmd/go using internal/execabs.LookPath,
then pass the resolved path to cgo in CC.

This caused a regression: if the directory in PATH containing CC has a
space, cgo splits it and interprets it as multiple arguments.

With this change, cmd/go no longer resolves CC before invoking
cgo. cgo does the path lookup on each invocation. This reverts the
security fix CL 284780, but that was redundant with the addition of
internal/execabs (CL 955304), which still protects us.

NOTE: This CL includes a related test fix from CL 286292.

Fixes #43860

Change-Id: I65d91a1e303856df8653881eb6e2e75a3bf95c49
Reviewed-on: https://go-review.googlesource.com/c/go/+/285873
Trust: Jay Conrod <jayconrod@google.com>
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
(cherry picked from commit a2cef9b544708ecae983ed8836ee2425a28aab68)
Reviewed-on: https://go-review.googlesource.com/c/go/+/285954
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>

1 files changed, 56 insertions, 0 deletions

diff --git a/src/cmd/go/testdata/script/cgo_path_space.txt b/src/cmd/go/testdata/script/cgo_path_space.txt
new file mode 100644
index 0000000000..654295dc69
--- /dev/null
+++ b/src/cmd/go/testdata/script/cgo_path_space.txt
@@ -0,0 +1,56 @@
+# Check that if the PATH directory containing the C compiler has a space,
+# we can still use that compiler with cgo.
+# Verifies #43808.
+[!cgo] skip
+
+# Set CC explicitly to something that requires a PATH lookup.
+# Normally, the default is gcc or clang, but if CC was set during make.bash,
+# that becomes the default.
+[exec:clang] env CC=clang
+[exec:gcc] env CC=gcc
+[!exec:clang] [!exec:gcc] skip 'Unknown C compiler'
+
+[!windows] chmod 0755 $WORK/'program files'/clang
+[!windows] chmod 0755 $WORK/'program files'/gcc
+[!windows] exists -exec $WORK/'program files'/clang
+[!windows] exists -exec $WORK/'program files'/gcc
+[!windows] env PATH=$WORK/'program files':$PATH
+[windows] exists -exec $WORK/'program files'/gcc.bat
+[windows] exists -exec $WORK/'program files'/clang.bat
+[windows] env PATH=$WORK\'program files';%PATH%
+
+! exists $WORK/log.txt
+? go build -x
+exists $WORK/log.txt
+rm $WORK/log.txt
+
+# TODO(#41400, #43078): when CC is set explicitly, it should be allowed to
+# contain spaces separating arguments, and it should be possible to quote
+# arguments with spaces (including the path), as in CGO_CFLAGS and other
+# variables. For now, this doesn't work.
+[!windows] env CC=$WORK/'program files'/gcc
+[windows] env CC=$WORK\'program files'\gcc.bat
+! go build -x
+! exists $WORK/log.txt
+
+-- go.mod --
+module m
+
+-- m.go --
+package m
+
+// #define X 1
+import "C"
+
+-- $WORK/program files/gcc --
+#!/bin/sh
+
+echo ok >$WORK/log.txt
+-- $WORK/program files/clang --
+#!/bin/sh
+
+echo ok >$WORK/log.txt
+-- $WORK/program files/gcc.bat --
+echo ok >%WORK%\log.txt
+-- $WORK/program files/clang.bat --
+echo ok >%WORK%\log.txt