Don't clobber /dev/null when compiling as root

Compiling as root is highly discouraged, but some people do it anyway.
gcc_ok, however, can clobber /dev/null due to "-o /dev/null"; this is
bad.  Instead, write a temporary file and delete it.

13 files changed, 52 insertions, 26 deletions

diff --git a/Makefile b/Makefile
index 5a27526c..24450357 100644
--- a/Makefile
+++ b/Makefile
@@ -17,8 +17,10 @@
 # No builtin rules
 MAKEFLAGS = -r
 
-gcc_ok   = $(shell if gcc $(1) dummy.c -o /dev/null 2>/dev/null; \
-	           then echo '$(1)'; else echo '$(2)'; fi)
+TMPFILE = $(shell mktemp /tmp/gcc_ok.XXXXXX)
+
+gcc_ok   = $(shell tmpf=$(TMPFILE); if gcc $(1) dummy.c -o $$tmpf 2>/dev/null; \
+	           then echo '$(1)'; else echo '$(2)'; fi; rm -f $$tmpf)
 
 comma   := ,
 LDHASH  := $(call gcc_ok,-Wl$(comma)--hash-style=both,)
diff --git a/com32/lib/MCONFIG b/com32/lib/MCONFIG
index 461ada44..781292ba 100644
--- a/com32/lib/MCONFIG
+++ b/com32/lib/MCONFIG
@@ -1,7 +1,9 @@
 # -*- makefile -*-
 
-gcc_ok  = $(shell if gcc $(1) -c -x c /dev/null -o /dev/null 2>/dev/null; \
-	  then echo $(1); else echo $(2); fi)
+TMPFILE = $(shell mktemp /tmp/gcc_ok.XXXXXX)
+
+gcc_ok  = $(shell tmpf=$(TMPFILE); if gcc $(1) -c -x c /dev/null -o $$tmpf 2>/dev/null; \
+	  then echo $(1); else echo $(2); fi; rm -f $$tmpf)
 
 GCCOPT := $(call gcc_ok,-m32,) $(call gcc_ok,-fno-stack-protector,)
 
diff --git a/com32/libutil/Makefile b/com32/libutil/Makefile
index 1dac1f76..15393533 100644
--- a/com32/libutil/Makefile
+++ b/com32/libutil/Makefile
@@ -29,8 +29,10 @@
 ## Utility companion library for the COM32 library
 ##
 
-gcc_ok   = $(shell if gcc $(1) -c -x c /dev/null -o /dev/null 2>/dev/null; \
-	           then echo $(1); else echo $(2); fi)
+TMPFILE = $(shell mktemp /tmp/gcc_ok.XXXXXX)
+
+gcc_ok   = $(shell tmpf=$(TMPFILE); if gcc $(1) -c -x c /dev/null -o $$tmpf 2>/dev/null; \
+	           then echo $(1); else echo $(2); fi; rm -f $$tmpf)
 
 M32     := $(call gcc_ok,-m32,) $(call gcc_ok,-fno-stack-protector,)
 
diff --git a/com32/modules/Makefile b/com32/modules/Makefile
index bef45a87..9be0b85a 100644
--- a/com32/modules/Makefile
+++ b/com32/modules/Makefile
@@ -14,8 +14,10 @@
 ## samples for syslinux users
 ##
 
-gcc_ok   = $(shell if gcc $(1) -c -x c /dev/null -o /dev/null 2>/dev/null; \
-	           then echo $(1); else echo $(2); fi)
+TMPFILE = $(shell mktemp /tmp/gcc_ok.XXXXXX)
+
+gcc_ok   = $(shell tmpf=$(TMPFILE); if gcc $(1) -c -x c /dev/null -o $$tmpf 2>/dev/null; \
+	           then echo $(1); else echo $(2); fi; rm -f $$tmpf)
 
 M32     := $(call gcc_ok,-m32,) $(call gcc_ok,-fno-stack-protector,)
 
diff --git a/com32/samples/Makefile b/com32/samples/Makefile
index b694a489..b2544e6d 100644
--- a/com32/samples/Makefile
+++ b/com32/samples/Makefile
@@ -14,8 +14,10 @@
 ## samples for syslinux users
 ##
 
-gcc_ok   = $(shell if gcc $(1) -c -x c /dev/null -o /dev/null 2>/dev/null; \
-	           then echo $(1); else echo $(2); fi)
+TMPFILE = $(shell mktemp /tmp/gcc_ok.XXXXXX)
+
+gcc_ok   = $(shell tmpf=$(TMPFILE); if gcc $(1) -c -x c /dev/null -o $$tmpf 2>/dev/null; \
+	           then echo $(1); else echo $(2); fi; rm -f $$tmpf)
 
 M32     := $(call gcc_ok,-m32,) $(call gcc_ok,-fno-stack-protector,)
 
diff --git a/dos/Makefile b/dos/Makefile
index 5fd52d1b..53406b19 100644
--- a/dos/Makefile
+++ b/dos/Makefile
@@ -1,5 +1,7 @@
-gcc_ok   = $(shell if gcc $(1) -c -x c /dev/null -o /dev/null 2>/dev/null; \
-	           then echo $(1); else echo $(2); fi)
+TMPFILE = $(shell mktemp /tmp/gcc_ok.XXXXXX)
+
+gcc_ok   = $(shell tmpf=$(TMPFILE); if gcc $(1) -c -x c /dev/null -o $$tmpf 2>/dev/null; \
+	           then echo $(1); else echo $(2); fi; rm -f $$tmpf)
 
 M32       := $(call gcc_ok,-m32,) $(call gcc_ok,-ffreestanding,) $(call gcc_ok,-fno-stack-protector,)
 
diff --git a/extlinux/Makefile b/extlinux/Makefile
index 8d347a98..d2ea6f9b 100644
--- a/extlinux/Makefile
+++ b/extlinux/Makefile
@@ -1,5 +1,7 @@
-gcc_ok   = $(shell if gcc $(1) ../dummy.c -o /dev/null 2>/dev/null; \
-	           then echo '$(1)'; else echo '$(2)'; fi)
+TMPFILE = $(shell mktemp /tmp/gcc_ok.XXXXXX)
+
+gcc_ok   = $(shell tmpf=$(TMPFILE); if gcc $(1) ../dummy.c -o $$tmpf 2>/dev/null; \
+	           then echo '$(1)'; else echo '$(2)'; fi; rm -f $$tmpf)
 
 comma   := ,
 LDHASH  := $(call gcc_ok,-Wl$(comma)--hash-style=both,)
diff --git a/mbr/Makefile b/mbr/Makefile
index 7662a0a3..87744131 100644
--- a/mbr/Makefile
+++ b/mbr/Makefile
@@ -14,8 +14,10 @@
 # Makefile for MBR
 #
 
-gcc_ok   = $(shell if gcc $(1) -c -x c /dev/null -o /dev/null 2>/dev/null; \
-	           then echo $(1); else echo $(2); fi)
+TMPFILE = $(shell mktemp /tmp/gcc_ok.XXXXXX)
+
+gcc_ok   = $(shell tmpf=$(TMPFILE); if gcc $(1) -c -x c /dev/null -o $$tmpf 2>/dev/null; \
+	           then echo $(1); else echo $(2); fi; rm -f $$tmpf)
 
 M32       := $(call gcc_ok,-m32,) $(call gcc_ok,-ffreestanding,) $(call gcc_ok,-fno-stack-protector)
 
diff --git a/memdisk/Makefile b/memdisk/Makefile
index 72234cab..161a163e 100644
--- a/memdisk/Makefile
+++ b/memdisk/Makefile
@@ -12,8 +12,10 @@
 
 VERSION := $(shell cat ../version)
 
-gcc_ok   = $(shell if gcc $(1) -c -x c /dev/null -o /dev/null 2>/dev/null; \
-	           then echo $(1); else echo $(2); fi)
+TMPFILE = $(shell mktemp /tmp/gcc_ok.XXXXXX)
+
+gcc_ok   = $(shell tmpf=$(TMPFILE); if gcc $(1) -c -x c /dev/null -o $$tmpf 2>/dev/null; \
+	           then echo $(1); else echo $(2); fi; rm -f $$tmpf)
 
 M32     := $(call gcc_ok,-m32,)
 ALIGN   := $(call gcc_ok,-falign-functions=0 -falign-jumps=0 -falign-loops=0,-malign-functions=0 -malign-jumps=0 -malign-loops=0)
diff --git a/menu/Makefile b/menu/Makefile
index cee1c3af..702f4563 100644
--- a/menu/Makefile
+++ b/menu/Makefile
@@ -14,8 +14,10 @@
 ## samples for syslinux users
 ##
 
-gcc_ok   = $(shell if gcc $(1) -c -x c /dev/null -o /dev/null 2>/dev/null; \
-	           then echo $(1); else echo $(2); fi)
+TMPFILE = $(shell mktemp /tmp/gcc_ok.XXXXXX)
+
+gcc_ok   = $(shell tmpf=$(TMPFILE); if gcc $(1) -c -x c /dev/null -o $$tmpf 2>/dev/null; \
+	           then echo $(1); else echo $(2); fi; rm -f $$tmpf)
 
 M32     := $(call gcc_ok,-m32,) $(call gcc_ok,-fno-stack-protector,)
 
diff --git a/mtools/Makefile b/mtools/Makefile
index 546e3d14..16d63a69 100644
--- a/mtools/Makefile
+++ b/mtools/Makefile
@@ -1,5 +1,7 @@
-gcc_ok   = $(shell if gcc $(1) ../dummy.c -o /dev/null 2>/dev/null; \
-	           then echo '$(1)'; else echo '$(2)'; fi)
+TMPFILE = $(shell mktemp /tmp/gcc_ok.XXXXXX)
+
+gcc_ok   = $(shell tmpf=$(TMPFILE); if gcc $(1) ../dummy.c -o $$tmpf 2>/dev/null; \
+	           then echo '$(1)'; else echo '$(2)'; fi; rm -f $$tmpf)
 
 comma   := ,
 LDHASH  := $(call gcc_ok,-Wl$(comma)--hash-style=both,)
diff --git a/sample/Makefile b/sample/Makefile
index f301b9f1..cc22a984 100644
--- a/sample/Makefile
+++ b/sample/Makefile
@@ -14,8 +14,10 @@
 ## samples for syslinux users
 ##
 
-gcc_ok   = $(shell if gcc $(1) -c -x c /dev/null -o /dev/null 2>/dev/null; \
-	           then echo $(1); else echo $(2); fi)
+TMPFILE = $(shell mktemp /tmp/gcc_ok.XXXXXX)
+
+gcc_ok   = $(shell tmpf=$(TMPFILE); if gcc $(1) -c -x c /dev/null -o $$tmpf 2>/dev/null; \
+	           then echo $(1); else echo $(2); fi; rm -f $$tmpf)
 
 M32       := $(call gcc_ok,-m32,) $(call gcc_ok,-ffreestanding,) $(call gcc_ok,-fno-stack-protector,)
 
diff --git a/unix/Makefile b/unix/Makefile
index f0ab279a..b0465299 100644
--- a/unix/Makefile
+++ b/unix/Makefile
@@ -1,5 +1,7 @@
-gcc_ok   = $(shell if gcc $(1) ../dummy.c -o /dev/null 2>/dev/null; \
-	           then echo '$(1)'; else echo '$(2)'; fi)
+TMPFILE = $(shell mktemp /tmp/gcc_ok.XXXXXX)
+
+gcc_ok   = $(shell tmpf=$(TMPFILE); if gcc $(1) ../dummy.c -o $$tmpf 2>/dev/null; \
+	           then echo '$(1)'; else echo '$(2)'; fi; rm -f $$tmpf)
 
 comma   := ,
 LDHASH  := $(call gcc_ok,-Wl$(comma)--hash-style=both,)