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    SubjectRe: [PATCH v1.1 3/3] x86/static_call: Add support for Jcc tail-calls
    On Thu, 26 Jan 2023 10:14:49 -0800
    Nick Desaulniers <ndesaulniers@google.com> wrote:

    > On Thu, Jan 26, 2023 at 7:34 AM Peter Zijlstra <peterz@infradead.org> wrote:
    > >
    > > On Tue, Jan 24, 2023 at 10:07:53AM -0500, Steven Rostedt wrote:
    > > > On Tue, 24 Jan 2023 14:06:49 +0100
    > > > Peter Zijlstra <peterz@infradead.org> wrote:
    > > >
    > > > > > Just to confirm, as it's not clear if this is the static call site or one
    > > > > > of the functions that is being called.
    > > > >
    > > > > Ah, you've not looked at enough asm then? ;-) Yes this is the static
    > > > > call site, see the __SCT_ target (instruction at 0x35d).
    > > >
    > > > Yeah, could you specify it a bit more in the change log such that those
    > > > looking back at this don't have to have that requirement of staring at
    > > > enough asm ;-)
    > >
    > > How's this then?

    Better :-)

    Anyway... Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>

    > >
    > > ---
    > > Subject: x86/static_call: Add support for Jcc tail-calls
    > > From: Peter Zijlstra <peterz@infradead.org>
    > > Date: Fri Jan 20 16:40:33 CET 2023
    > >
    > > Clang likes to create conditional tail calls like:
    > >
    > > 0000000000000350 <amd_pmu_add_event>:
    > > 350: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1) 351: R_X86_64_NONE __fentry__-0x4
    > > 355: 48 83 bf 20 01 00 00 00 cmpq $0x0,0x120(%rdi)
    > > 35d: 0f 85 00 00 00 00 jne 363 <amd_pmu_add_event+0x13> 35f: R_X86_64_PLT32 __SCT__amd_pmu_branch_add-0x4
    > > 363: e9 00 00 00 00 jmp 368 <amd_pmu_add_event+0x18> 364: R_X86_64_PLT32 __x86_return_thunk-0x4
    >
    > If it helps reduce the line width in the commit message to focus on
    > just the instructions, lately I've been using
    > `--no-addresses --no-show-raw-insn` flags to llvm-objdump.

    Actually, I like the full output. Even if we do reduce it, it will
    still be over 80.

    -- Steve

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