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| author | Kees Cook <keescook@chromium.org> | 2018-05-31 11:45:25 -0700 |
|---|---|---|
| committer | Boris Brezillon <boris.brezillon@bootlin.com> | 2018-06-22 00:29:39 +0200 |
| commit | 02361bc7788852f33dd0a05235a52b9ccf097916 (patch) | |
| tree | 1e07e38295627ab67e6794150fa0c7015adde300 /lib/Makefile | |
| parent | ce397d215ccd07b8ae3f71db689aedb85d56ab40 (diff) | |
| download | lwn-02361bc7788852f33dd0a05235a52b9ccf097916.tar.gz lwn-02361bc7788852f33dd0a05235a52b9ccf097916.zip | |
lib/bch: Remove VLA usage
In the quest to remove all stack VLA usage from the kernel[1], this
allocates a fixed size stack array to cover the range needed for
bch. This was done instead of a preallocation on the SLAB due to
performance reasons, shown by Ivan Djelic:
little-endian, type sizes: int=4 long=8 longlong=8
cpu: Intel(R) Core(TM) i5 CPU 650 @ 3.20GHz
calibration: iter=4.9143µs niter=2034 nsamples=200 m=13 t=4
Buffer allocation | Encoding throughput (Mbit/s)
---------------------------------------------------
on-stack, VLA | 3988
on-stack, fixed | 4494
kmalloc | 1967
So this change actually improves performance too, it seems.
The resulting stack allocation can get rather large; without
CONFIG_BCH_CONST_PARAMS, it will allocate 4096 bytes, which
trips the stack size checking:
lib/bch.c: In function ‘encode_bch’:
lib/bch.c:261:1: warning: the frame size of 4432 bytes is larger than 2048 bytes [-Wframe-larger-than=]
Even the default case for "allmodconfig" (with CONFIG_BCH_CONST_M=14 and
CONFIG_BCH_CONST_T=4) would have started throwing a warning:
lib/bch.c: In function ‘encode_bch’:
lib/bch.c:261:1: warning: the frame size of 2288 bytes is larger than 2048 bytes [-Wframe-larger-than=]
But this is how large it's always been; it was just hidden from
the checker because it was a VLA. So the Makefile has been adjusted to
silence this warning for anything smaller than 4500 bytes, which should
provide room for normal cases, but still low enough to catch any future
pathological situations.
[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Ivan Djelic <ivan.djelic@parrot.com>
Tested-by: Ivan Djelic <ivan.djelic@parrot.com>
Acked-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Diffstat (limited to 'lib/Makefile')
| -rw-r--r-- | lib/Makefile | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/lib/Makefile b/lib/Makefile index 956b320292fe..e1ee1046abf0 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -123,6 +123,7 @@ obj-$(CONFIG_ZLIB_INFLATE) += zlib_inflate/ obj-$(CONFIG_ZLIB_DEFLATE) += zlib_deflate/ obj-$(CONFIG_REED_SOLOMON) += reed_solomon/ obj-$(CONFIG_BCH) += bch.o +CFLAGS_bch.o := $(call cc-option,-Wframe-larger-than=4500) obj-$(CONFIG_LZO_COMPRESS) += lzo/ obj-$(CONFIG_LZO_DECOMPRESS) += lzo/ obj-$(CONFIG_LZ4_COMPRESS) += lz4/ |