Re: [PATCH] lib: fix 842 build on 32-bit architectures
From: Dan Streetman <hidden>
Date: 2015-05-14 08:54:33
Also in:
linux-arm-kernel, lkml
On Wed, May 13, 2015 at 7:52 PM, Dan Streetman [off-list ref] wrote:
quoted
Building the 842 code on 32-bit ARM currently results in this link error: ERROR: "__aeabi_uldivmod" [lib/842/842_decompress.ko] undefined!Oops! Guess I should build/test on 32 bit more.quoted
The reason is that the __do_index function performs a 64-bit division by a power-of-two number, but it has no insight into the function arguments.
wait, do you mean the 64 bit mod, total % fsize? That should already be fixed in Herbert's tree, I changed it to subtraction instead. In any case, I looked at the code again and I think the fsize parameter can be removed, and just simply calculated in the function, it's just a shift. I'll send a patch.
quoted hunk ↗ jump to hunk
quoted
By marking that function inline, the fsize argument is always known at the time that do_index is called, and the compiler is able to replace the extremely expensive 64-bit division with a cheap constant shift operation.alternately, we know that fsize will always be less than 64 bits, at most it's 4<<9 or 8<<8 (both == 1<<11). So we could just change its type to u16.diff --git a/lib/842/842_decompress.c b/lib/842/842_decompress.c index 6b2b45aecde3..285bf6b6959c 100644 --- a/lib/842/842_decompress.c +++ b/lib/842/842_decompress.c@@ -169,7 +169,7 @@ static int do_data(struct sw842_param *p, u8 n) return 0; } -static int __do_index(struct sw842_param *p, u8 size, u8 bits, u64 fsize) +static int __do_index(struct sw842_param *p, u8 size, u8 bits, u16 fsize) { u64 index, offset, total = round_down(p->out - p->ostart, 8); int ret;Or, we could inline it and change the type to u16. In any case, Acked-by: Dan Streetman <redacted>quoted
Aside from fixing that link error, this approach should also improve both code size and performance on 32-bit architectures significantly. Signed-off-by: Arnd Bergmann <arnd@arndb.de> --- Found while building arm32 allmodconfig with gcc-5.0diff --git a/lib/842/842_decompress.c b/lib/842/842_decompress.c index 6b2b45aecde3..285bf6b6959c 100644 --- a/lib/842/842_decompress.c +++ b/lib/842/842_decompress.c@@ -169,7 +169,7 @@ static int do_data(struct sw842_param *p, u8 n) return 0; } -static int __do_index(struct sw842_param *p, u8 size, u8 bits, u64 fsize) +static inline int __do_index(struct sw842_param *p, u8 size, u8 bits, u64 fsize) { u64 index, offset, total = round_down(p->out - p->ostart, 8); int ret;