Messages in this thread | | | Date | Tue, 07 Feb 2006 00:43:01 -0800 (PST) | Subject | Re: [PATCH] compat: add compat functions for *at syscalls | From | "David S. Miller" <> |
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From: Stephen Rothwell <sfr@canb.auug.org.au> Date: Tue, 7 Feb 2006 11:27:13 +1100
> *If* we do get is_compat_task(), what would be you reaction to something > like this: ... > + if (is_compat_task()) > + dfd = compat_sign_extend(dfd);
A load and a test is more expensive than the assembler stubs where we _know_ we are compat.
The alternative suggestions get less and less efficient :-) My whole desire is to optimize this as much as possible, without the overhead of an extra stack frame or "is_compat_task()" kinds of runtime tests.
Really, the way to do this is to have a description header file, that does stuff like:
SIGN1(STUB_NAME, REAL_SYSCALL, ARG1_TO_EXTEND) SIGN2(STUB_NAME, REAL_SYSCALL, ARG1_TO_EXTEND, ARG2_TO_EXTEND)
etc. etc. for each syscall that only needs sign extension compat handling, and the platform provides definitions of these macros which expand the above as appropriate. Use arch/sparc64/kernel/sys32.S as a guide.
So for sys_exit_group you'd list something like:
SIGN1(sys32_exit_group, sys_exit_group, ARG0)
"ARG0" would get defined to whatever register mnemonic the first argument to a function gets passed into, ARG1 to the second, etc. So on Sparc64 that would be:
#define ARG0 %o0 #define ARG1 %o1 #define ARG2 %o2 #define ARG3 %o3 #define ARG4 %o4 #define ARG5 %o5
and you'd use "sys32_exit_group" in the compat syscall table. The SIGN1 definition on sparc64 would be exactly what it is right now in that sys32.S file.
Such a header can be use to generate stubs on every platform. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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