4.2-stable review patch. If anyone has any objections, please let me know.
------------------
From: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
commit a077224fd35b2f7fbc93f14cf67074fc792fbac2 upstream.
While working on the 32-bit ARM port of UEFI, I noticed a strange
corruption in the kernel log. The following snprintf() statement
(in drivers/firmware/efi/efi.c:efi_md_typeattr_format())
snprintf(pos, size, "|%3s|%2s|%2s|%2s|%3s|%2s|%2s|%2s|%2s]",
was producing the following output in the log:
| | | | | |WB|WT|WC|UC]
| | | | | |WB|WT|WC|UC]
| | | | | |WB|WT|WC|UC]
|RUN| | | | |WB|WT|WC|UC]*
|RUN| | | | |WB|WT|WC|UC]*
| | | | | |WB|WT|WC|UC]
|RUN| | | | |WB|WT|WC|UC]*
| | | | | |WB|WT|WC|UC]
|RUN| | | | | | | |UC]
|RUN| | | | | | | |UC]
As it turns out, this is caused by incorrect code being emitted for
the string() function in lib/vsprintf.c. The following code
if (!(spec.flags & LEFT)) {
while (len < spec.field_width--) {
if (buf < end)
*buf = ' ';
++buf;
}
}
for (i = 0; i < len; ++i) {
if (buf < end)
*buf = *s;
++buf; ++s;
}
while (len < spec.field_width--) {
if (buf < end)
*buf = ' ';
++buf;
}
when called with len == 0, triggers an issue in the GCC SRA optimization
pass (Scalar Replacement of Aggregates), which handles promotion of signed
struct members incorrectly. This is a known but as yet unresolved issue.
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65932). In this particular
case, it is causing the second while loop to be executed erroneously a
single time, causing the additional space characters to be printed.
So disable the optimization by passing -fno-ipa-sra.
Acked-by: Nicolas Pitre <nico@xxxxxxxxxx>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm/Makefile | 8 ++++++++
1 file changed, 8 insertions(+)
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -54,6 +54,14 @@ AS += -EL
LD += -EL
endif
+#
+# The Scalar Replacement of Aggregates (SRA) optimization pass in GCC 4.9 and
+# later may result in code being generated that handles signed short and signed
+# char struct members incorrectly. So disable it.
+# (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65932)
+#
+KBUILD_CFLAGS += $(call cc-option,-fno-ipa-sra)
+
# This selects which instruction set is used.
# Note that GCC does not numerically define an architecture version
# macro, but instead defines a whole series of macros which makes
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