Re: pg_preadv() and pg_pwritev()

From: Sergey Shinderuk <s(dot)shinderuk(at)postgrespro(dot)ru>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: pg_preadv() and pg_pwritev()
Date: 2021-01-15 01:53:46
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On 15.01.2021 01:13, Tom Lane wrote:

> than relying entirely on xcodebuild. Maybe there's a case for trying
> "xcrun --sdk macosx --show-sdk-path" in between; in my tests that
> seemed noticeably faster than invoking xcodebuild, and I've not yet
> seen a case where it gave a different answer.

I see that "xcrun --sdk macosx --show-sdk-path" really calls
"/Applications/ -sdk
macosx -version Path" under the hood.

% lldb -- xcrun --no-cache --sdk macosx --show-sdk-path
(lldb) target create "xcrun"
Current executable set to 'xcrun' (x86_64).
(lldb) settings set -- "--no-cache" "--sdk" "macosx"
(lldb) settings set target.unset-env-vars SDKROOT
(lldb) b popen
Breakpoint 1: where = libsystem_c.dylib`popen, address = 0x00007fff67265607
(lldb) r
Process 26857 launched: '/usr/bin/xcrun' (x86_64)
Process 26857 stopped
* thread #1, queue = '', stop reason = breakpoint 1.1
frame #0: 0x00007fff6e313607 libsystem_c.dylib`popen
-> 0x7fff6e313607 <+0>: pushq %rbp
0x7fff6e313608 <+1>: movq %rsp, %rbp
0x7fff6e31360b <+4>: pushq %r15
0x7fff6e31360d <+6>: pushq %r14
Target 0: (xcrun) stopped.
(lldb) p (char *)$arg1
(char *) $1 = 0x0000000100406960
"/Applications/ -sdk
macosx -version Path"

% sudo dtrace -n 'pid$target::popen:entry { trace(copyinstr(arg0)) }' -c
'xcrun --sdk macosx --show-sdk-path'
dtrace: description 'pid$target::popen:entry ' matched 1 probe
0 413269 popen:entry
/Applications/ -sdk
macosx -version Path
dtrace: pid 26905 has exited

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