build: improve detection of eBPF support #22238

1. 
   fanquake commented at 5:49 am on June 14, 2021: member

   Just checking for the sys/sdt.h header isn’t enough, as systems like macOS have the header, but it doesn’t actually have the DTRACE_PROBE* probes, which leads to compile failures. The contents of sys/sdt.h in the macOS SDK is:

    0#ifndef _SYS_SDT_H
    1#define _SYS_SDT_H
    2
    3/*
    4 * This is a wrapper header that wraps the mach visible sdt.h header so that
    5 * the header file ends up visible where software expects it to be.  We also
    6 * do the C/C++ symbol wrapping here, since Mach headers are technically C
    7 * interfaces.
    8 *
    9 * Note:  The process of adding USDT probes to code is slightly different
   10 * than documented in the "Solaris Dynamic Tracing Guide".
   11 * The DTRACE_PROBE*() macros are not supported on Mac OS X -- instead see
   12 * "BUILDING CODE CONTAINING USDT PROBES" in the dtrace(1) manpage
   13 *
   14 */
   15#include <sys/cdefs.h>
   16__BEGIN_DECLS
   17#include <mach/sdt.h>
   18__END_DECLS
   19
   20#endif  /* _SYS_SDT_H */
   

   The BUILDING CODE CONTAINING USDT PROBES section from the dtrace manpage is available here, and outlines the more involved process of using USDT probes on macOS.

2. fanquake added the label Build system on Jun 14, 2021
3. 
   theStack commented at 4:40 pm on June 14, 2021: member

   Concept ACK
4. 
   practicalswift commented at 11:14 am on June 15, 2021: contributor

   Concept ACK
5. build: improve detection of eBPF support

   Just checking for the `sys/sdt.h` header isn't enough, as systems like
   macOS have the header, but it doesn't actually have the dtrace probes,
   which leads to compile failures.

   8f7704d032
6. fanquake force-pushed on Jun 16, 2021
7. 
   jb55 commented at 7:38 pm on June 17, 2021: member

   utACK 8f7704d0321a71c1691837a6bd3b4e05f84d3031
8. 
   practicalswift commented at 8:01 pm on June 17, 2021: contributor

   cr ACK 8f7704d0321a71c1691837a6bd3b4e05f84d3031
9. hebasto approved
10. 
    hebasto commented at 9:43 pm on June 17, 2021: member

    ACK 8f7704d0321a71c1691837a6bd3b4e05f84d3031, tested on macOS Big Sur 11.4 (20F71) and on Linux Mint 20.1 (x86_64) with depends.

    It would be nice to have the default value of --enable-ebpf equal to auto, and emit an error message when --enable-ebpf=yes but its conditions are not met.

11. fanquake merged this on Jun 18, 2021
12. fanquake closed this on Jun 18, 2021

    ---

13. fanquake deleted the branch on Jun 18, 2021
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Contributors
fanquake theStack practicalswift jb55 hebasto

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