[Buildroot] [PATCH] toolchain/external: fix wrapper by not passing conflicting flags

Yann E. MORIN yann.morin.1998 at free.fr
Mon Jan 6 00:12:22 UTC 2014

From: "Yann E. MORIN" <yann.morin.1998 at free.fr>

In our wrapper, we forcibly add the -march=, -mcpu= and-mtune= flags
to the actual copmpiler, this in an attempt to always generate correct
and optimised code for the target.

But in some cases, the caller knows better than we do, and passes its
own set, or subset of those flags. In this case, some may conflict with
the ones we pass. The most prominent offender being the Linux kernel.

For example, on the ARM Rapsberry Pi, the Linux kernel will set the
-march=armv6 flag and no -mcpu= flag, but we pass -mcpu=arm1176jzf-s,
which conflicts:

    drivers/scsi/scsi_trace.c:1:0: warning: switch -mcpu=arm1176jzf-s
    conflicts with -march=armv6 switch

(and so for all the files the kernel compiles, pretty messy)
(note: arm1176jzf-s is not an armv6, it is an armv6zk. Yeah...)

To avoid this situation, we scan our commandline for any occurence of
the possibly conflicting flags. If none is found, then we add our owns.
If any is found, then we don't add any of our owns.

The idea behind this is that we trust the caller to know better than
we do what it is doing. Since the biggest, and sole so far, offender
is the Linux kernel, then this is a rather safe bet.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998 at free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni at free-electrons.com>
Cc: Peter Korsgaard <jacmet at uclibc.org>
Cc: Arnout Vandecappelle <arnout at mind.be>
 .../toolchain-external/ext-toolchain-wrapper.c     | 41 ++++++++++++++++------
 1 file changed, 31 insertions(+), 10 deletions(-)

diff --git a/toolchain/toolchain-external/ext-toolchain-wrapper.c b/toolchain/toolchain-external/ext-toolchain-wrapper.c
index d54f1f5..dd84a5d 100644
--- a/toolchain/toolchain-external/ext-toolchain-wrapper.c
+++ b/toolchain/toolchain-external/ext-toolchain-wrapper.c
@@ -30,21 +30,17 @@ static char sysroot[PATH_MAX];
  * that we only pass the predefined one to the real compiler if the inverse
  * option isn't in the argument list.
  * This specifies the worst case number of extra arguments we might pass
+ * Currently, we have:
+ * 	-mfloat-abi=
+ * 	-march=
+ * 	-mtune=
+ * 	-mcpu=
 static char *predef_args[] = {
 	"--sysroot", sysroot,
-#ifdef BR_ARCH
-	"-march=" BR_ARCH,
-#endif /* BR_ARCH */
-#ifdef BR_TUNE
-	"-mtune=" BR_TUNE,
-#endif /* BR_TUNE */
-#ifdef BR_CPU
-	"-mcpu=" BR_CPU,
 #ifdef BR_ABI
 	"-mabi=" BR_ABI,
@@ -157,6 +153,31 @@ int main(int argc, char **argv)
 		*cur++ = "-mfloat-abi=" BR_FLOAT_ABI;
+#if defined(BR2_ARCH) || \
+    defined(BR2_TUNE) || \
+    defined(BR2_CPU)
+	/* Add our -march/cpu/tune/abi flags, but only if none are
+	 * already specified on the commandline
+	 */
+	for (i = 1; i < argc; i++) {
+		if (!strncmp(argv[i], "-march=", strlen("-march=")) ||
+		    !strncmp(argv[i], "-mtune=", strlen("-mtune=")) ||
+		    !strncmp(argv[i], "-mcpu=",  strlen("-mcpu=" )))
+			break;
+	}
+	if (i == argc) {
+#ifdef BR_ARCH
+		*cur++ = "-march=" BR_ARCH;
+#ifdef BR_TUNE
+		*cur++ = "-mtune=" BR_TUNE;
+#ifdef BR_CPU
+		*cur++ = "-mcpu=" BR_CPU;
+	}
+#endif /* ARCH || TUNE || CPU */
 	/* append forward args */
 	memcpy(cur, &argv[1], sizeof(char *) * (argc - 1));
 	cur += argc - 1;

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