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From: Florian Weimer <fweimer@redhat.com>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: GNU C Library <libc-alpha@sourceware.org>,
	 Jakub Jelinek <jakub@redhat.com>
Subject: Re: [PATCH 0/2] Remove some i386 system call optimizations
Date: Tue, 11 Jan 2022 23:52:39 +0100	[thread overview]
Message-ID: <87bl0hriko.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <CAMe9rOowcGPjbSK5KUXDMJyu7Em=gEyujV4kwhEHnffPVMGkHQ@mail.gmail.com> (H. J. Lu's message of "Tue, 11 Jan 2022 14:20:29 -0800")

* H. J. Lu:

>> > There are
>> >
>> > /* Since GCC 5 and above can properly spill %ebx with PIC when needed,
>> >    we can inline syscalls with 6 arguments if GCC 5 or above is used
>> >    to compile glibc.  Disable GCC 5 optimization when compiling for
>> >    profiling or when -fno-omit-frame-pointer is used since asm ("ebp")
>> >    can't be used to put the 6th argument in %ebp for syscall.  */
>> > #if !defined PROF && CAN_USE_REGISTER_ASM_EBP
>> > # define OPTIMIZE_FOR_GCC_5
>> > #endif
>> >
>> > If we want to support profiling or -fno-omit-frame-pointer,
>> > we need to keep these codes.
>>
>> This is strictly for %ebp, I think, as indicated by the comment.  %ebx
>> does not need to be special-cased for profiling.
>>
>> I assume that building glibc (with profiling) is proof enough that this
>> works?
>
> You need to test glibc build with -fno-omit-frame-pointer.

I tried it, it works (with both patches applied).
-fno-omit-frame-pointer is about %ebp, not %ebx.

Thanks,
Florian


  reply	other threads:[~2022-01-11 22:52 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-11 10:05 Florian Weimer
2022-01-11 10:06 ` [PATCH 1/2] i386: Always treat %ebx as an allocatable register Florian Weimer
2022-01-11 10:06 ` [PATCH 2/2] i386: Always use __libc_do_syscall for 6-argument syscalls (bug 27997) Florian Weimer
2022-01-11 14:00 ` [PATCH 0/2] Remove some i386 system call optimizations H.J. Lu
2022-01-11 20:30   ` H.J. Lu
2022-01-11 20:37     ` Florian Weimer
2022-01-11 22:20       ` H.J. Lu
2022-01-11 22:52         ` Florian Weimer [this message]
2022-01-12 18:49           ` H.J. Lu
2022-01-12 19:37             ` Florian Weimer
2022-01-12 19:56               ` H.J. Lu
2022-01-12 20:12                 ` Florian Weimer
2022-01-12 21:59                   ` H.J. Lu
2022-01-12 22:33                     ` Florian Weimer

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