On 2011年12月18日 01:08, Brian Gerst wrote:
On Sat, Dec 17, 2011 at 9:58 AM, Nai Xia<nai.xia@xxxxxxxxx> wrote:
Hi Andi,
Seems I used a stale email address of you from a related git commit log,
so this is a resend, sorry.
=======
Hi,
I notice that all x86 assembly code for string operations containing
"scasb, lodsb", etc does not have "cld" at the beginning.
Is this 100% safe?
Or in other words, how could we be sure that
there is no "std" generated by compiler somewhere just before
the string operations?
Thanks,
Nai
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The i386 ELF ABI states "The direction flag must be set to the
‘‘forward’’ (that is, zero) direction before entry and upon exit from
a function." Therefore it can be assumed to be clear, unless
explicitly set.
Hmm, I get those lines now. Thanks for reply.
Seems gcc started to strictly conform to this ABI since 4.3 . But glibc
seems still have some leading "cld" string code, maybe just prepared for
non-conforming kernels other than Linux.
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Brian Gerst
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