ARM: 8429/1: disable GCC SRA optimization
authorArd Biesheuvel <ard.biesheuvel@linaro.org>
Thu, 3 Sep 2015 12:24:40 +0000 (13:24 +0100)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Thu, 22 Oct 2015 21:37:49 +0000 (14:37 -0700)
commita18006390cf8f53f73a7e5e08e7102212807e2e8
tree8f27ad2cb2ef7f89879c9f023b94f5446d853d82
parentb200a84e6b618fc37d04f74d7228cf5acd6fb221
ARM: 8429/1: disable GCC SRA optimization

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@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
arch/arm/Makefile