[PATCH] kbuild: Disallow GCC 4.1.0 / 4.1.1

[Ingo Molnar]

Impact: fix crashes that can trigger if built with GCC 4.1.0 or 4.1.1

GCC 4.1.0 and 4.1.1 has a bug that can miscompile __weak symbols,
by inlining __weak functions into same-file call sites - breaking the
kernel if the __weak symbol is overriden later on.

In the past we tried to work around this problem by artificially
isolating call site and definition site - but these bugs tend to
pop up regularly:

 43a2563: sparseirq: move __weak symbols into separate compilation unit
 13a0c3c: sparseirq: work around compiler optimizing away __weak functions

And Linus has extended Sparse to report same-file callsites for __weak
symbols - which gave two dozen hits.

We have not found a clean way to work around this bug on the source
code level (noinline and explicit barrier()s are ignored by GCC), so we do
not allow these compilers (which are quite rare these days, have other bugs
and are superceded by the 4.1.2 bugfix release anyway).

Kernel builds under gcc 410 or 411 will now fail with this error message:

  Sorry, your compiler is too old, too buggy or not recognized.

Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
 include/linux/compiler.h |   17 +++++++++++++++--
 1 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index ea7c6be..dd558ce 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -36,12 +36,25 @@ extern void __chk_io_ptr(const volatile void __iomem *);
 
 #ifdef __KERNEL__
 
-#if __GNUC__ >= 4
+/*
+ * GCC 4.1.0 and 4.1.1 has a bug that can miscompile __weak symbols,
+ * by inlining __weak functions into same-file call sites - breaking the
+ * kernel if the __weak symbol is overriden later on.
+ *
+ * We have not found a clean way to work around this bug on the source
+ * code level, so we do not allow these compilers (which are quite
+ * rare these days, have other bugs and are superceded by the 4.1.2
+ * bugfix release anyway):
+ */
+#define gcc41_inlining_bug \
+	(__GNUC__ == 4 && __GNUC_MINOR__ == 1 && __GNUC_PATCHLEVEL__ <= 1)
+
+#if __GNUC__ >= 4 && !gcc41_inlining_bug
 # include <linux/compiler-gcc4.h>
 #elif __GNUC__ == 3 && __GNUC_MINOR__ >= 2
 # include <linux/compiler-gcc3.h>
 #else
-# error Sorry, your compiler is too old/not recognized.
+# error Sorry, your compiler is too old, too buggy or not recognized.
 #endif
 
 #define notrace __attribute__((no_instrument_function))
--
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