Messages in this thread | | | Date | Fri, 30 May 2014 13:02:55 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH v2 2/2] x86,vdso: Fix cross-compilation from big-endian architectures |
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On 05/30/2014 08:48 AM, Andy Lutomirski wrote: > This adds a macro GET(x) to convert x from big-endian to > little-endian. Hopefully I put it everywhere it needs to go and got > all the cases needed for everyone's linux/elf.h. > > Signed-off-by: Andy Lutomirski <luto@amacapital.net> > --- > arch/x86/vdso/vdso2c.c | 15 ++++++++++++ > arch/x86/vdso/vdso2c.h | 63 ++++++++++++++++++++++++++++---------------------- > 2 files changed, 50 insertions(+), 28 deletions(-)
A couple of observations:
1. We shouldn't use double-underscore in host C code.
2. It would be nice if we can take these sort of things (host-build helper macros) and move them to some common file in the Linux kernel eventually, so it would be a good thing to make the naming a little less general.
3. Even though it isn't necessary, making it work on 8-bit values so one doesn't have to worry about the type would seem like a good thing.
I came up with the following, it seems like a reasonable simplification:
> #define _LE(x, bits, ifnot) \ > __builtin_choose_expr( \ > (sizeof(x) == bits/8), \ > (__typeof__(x))le##bits##toh(x), ifnot) > > extern void bad_le(uint64_t); > #define _LAST_LE(x) \ > __builtin_choose_expr(sizeof(x) == 1, (x), bad_le(x)) > > #define LE(x) \ > _LE(x, 64, _LE(x, 32, _LE(x, 16, _LAST_LE(x))))
What do you think?
-hpa
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