Re: Refactoring backend fork+exec code

On Mon, Mar 18, 2024 at 10:41 PM Heikki Linnakangas <hlinnaka@iki.fi> wrote:
> Committed, with some final cosmetic cleanups. Thanks everyone!

Nitpicking from UBSan with EXEC_BACKEND on Linux (line numbers may be
a bit off, from a branch of mine):

../src/backend/postmaster/launch_backend.c:772:2: runtime error: null
pointer passed as argument 2, which is declared to never be null
==13303==Using libbacktrace symbolizer.
    #0 0x5555564b0202 in save_backend_variables
../src/backend/postmaster/launch_backend.c:772
    #1 0x5555564b0242 in internal_forkexec
../src/backend/postmaster/launch_backend.c:311
    #2 0x5555564b0bdd in postmaster_child_launch
../src/backend/postmaster/launch_backend.c:244
    #3 0x5555564b3121 in StartChildProcess
../src/backend/postmaster/postmaster.c:3928
    #4 0x5555564b933a in PostmasterMain
../src/backend/postmaster/postmaster.c:1357
    #5 0x5555562de4ad in main ../src/backend/main/main.c:197
    #6 0x7ffff667ad09 in __libc_start_main
(/lib/x86_64-linux-gnu/libc.so.6+0x23d09)
    #7 0x555555e34279 in _start
(/tmp/cirrus-ci-build/build/tmp_install/usr/local/pgsql/bin/postgres+0x8e0279)

This silences it:

-       memcpy(param->startup_data, startup_data, startup_data_len);
+       if (startup_data_len > 0)
+               memcpy(param->startup_data, startup_data, startup_data_len);

(I found that out by testing EXEC_BACKEND on CI.  I also learned that
the Mac and FreeBSD tasks fail with EXEC_BACKEND because of SysV shmem
bleating.  We probably should go and crank up the relevant sysctls in
the .cirrus.tasks.yml...)