Em 26-11-2013 17:27, Daniel Borkmann escreveu:
On 11/26/2013 01:00 AM, Cesar Eduardo Barros wrote:
Compile-tested on x86_64.
Actually with yet another version, I hoped that the "compile-tested"-only
statement would eventually disappear, ohh well. ;)
I did compile test each version ;-) including verifying (with "make
crypto/memneq.i") that the macro was really generating the expected
inline assembly (with these #ifdef chains, one has to be careful with
typos).
(Actually, I compile tested with "make crypto/memneq.o crypto/memneq.s
crypto/memneq.i". I took a peek at the assembly to see if it made sense.)
Resolving the OPTIMIZER_HIDE_VAR() macro for others than GCC jnto a
barrier() seems a bit suboptimal, but assuming 99% of people will use
GCC anyway, then for the minority of the remaining, they will worst case
have a clever compiler and eventually mimic memcmp() in some situations,
or have a not-so-clever compiler and execute the full code as is.
I do not think any compiler other than gcc and icc can compile
unmodified upstream kernel code. LLVM's clang would be the one which
comes closest, but it has gcc-compatible inline assembly, as does icc AFAIK.
The #define to barrier() within compiler-intel.h is for some compiler
called ECC (not icc). From what I could find about it on a quick search,
it appears to be some kind of Itanium compiler.
That part of the header was added back in 2003, and I do not believe it
is still relevant. A comment within that #ifdef block says "Intel ECC
compiler doesn't support gcc specific asm stmts", but there are many
uses of unprotected inline assembly all over the kernel (including on
the ia64 headers), so if that comment is true, the kernel will not
compile with that compiler. It is probably a piece of leftover dead
code. I only added to it because I am following RELOC_HIDE's example,
and RELOC_HIDE is there.
Anyway, I think still better than the rather ugly Makefile workaround
imho, so I'm generally fine with this.
--
Cesar Eduardo Barros
cesarb@xxxxxxxxxxxxx
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