$ perf trace -S ./trivial 
         ? (         ): trivial/84044  ... [continued]: execve())                                           = 0
     0.038 ( 0.002 ms): trivial/84044 brk()                                                                 = 0xe02000
     0.048 ( 0.001 ms): trivial/84044 arch_prctl(option: 0x3001, arg2: 0x7ffe4bdf0d60)                      = -1 EINVAL (Invalid argument)
     0.067 ( 0.007 ms): trivial/84044 access(filename: 0xee77b500, mode: R)                                 = -1 ENOENT (No such file or directory)
     0.080 ( 0.006 ms): trivial/84044 openat(dfd: CWD, filename: 0xee777ee0, flags: RDONLY|CLOEXEC)         = 3
     0.087 ( 0.003 ms): trivial/84044 newfstatat(dfd: 3, filename: 0xee7776f5, statbuf: 0x7ffe4bdeff90, flag: 4096) = 0
     0.092 ( 0.004 ms): trivial/84044 mmap(len: 271188, prot: READ, flags: PRIVATE, fd: 3)                  = 0x7fc2ee70d000
     0.097 ( 0.001 ms): trivial/84044 close(fd: 3)                                                          = 0
     0.118 ( 0.006 ms): trivial/84044 openat(dfd: CWD, filename: 0xee783e50, flags: RDONLY|CLOEXEC)         = 3
     0.126 ( 0.003 ms): trivial/84044 read(fd: 3, buf: 0x7ffe4bdf00e8, count: 832)                          = 832
     0.130 ( 0.002 ms): trivial/84044 pread64(fd: 3, buf: 0x7ffe4bdefcf0, count: 784, pos: 64)              = 784
     0.134 ( 0.002 ms): trivial/84044 pread64(fd: 3, buf: 0x7ffe4bdefcb0, count: 48, pos: 848)              = 48
     0.137 ( 0.002 ms): trivial/84044 pread64(fd: 3, buf: 0x7ffe4bdefc60, count: 68, pos: 896)              = 68
     0.140 ( 0.002 ms): trivial/84044 newfstatat(dfd: 3, filename: 0xee7776f5, statbuf: 0x7ffe4bdeff90, flag: 4096) = 0
     0.144 ( 0.003 ms): trivial/84044 mmap(len: 8192, prot: READ|WRITE, flags: PRIVATE|ANONYMOUS)           = 0x7fc2ee70b000
     0.151 ( 0.013 ms): trivial/84044 pread64(fd: 3, buf: 0x7ffe4bdefbe0, count: 784, pos: 64)              = 784
     0.166 ( 0.006 ms): trivial/84044 mmap(len: 1892824, prot: READ, flags: PRIVATE|DENYWRITE, fd: 3)       = 0x7fc2ee53c000
     0.173 ( 0.010 ms): trivial/84044 mprotect(start: 0x7fc2ee562000, len: 1679360)                         = 0
     0.185 ( 0.009 ms): trivial/84044 mmap(addr: 0x7fc2ee562000, len: 1363968, prot: READ|EXEC, flags: PRIVATE|FIXED|DENYWRITE, fd: 3, off: 0x26000) = 0x7fc2ee562000
     0.196 ( 0.005 ms): trivial/84044 mmap(addr: 0x7fc2ee6af000, len: 311296, prot: READ, flags: PRIVATE|FIXED|DENYWRITE, fd: 3, off: 0x173000) = 0x7fc2ee6af000
     0.202 ( 0.006 ms): trivial/84044 mmap(addr: 0x7fc2ee6fc000, len: 24576, prot: READ|WRITE, flags: PRIVATE|FIXED|DENYWRITE, fd: 3, off: 0x1bf000) = 0x7fc2ee6fc000
     0.214 ( 0.004 ms): trivial/84044 mmap(addr: 0x7fc2ee702000, len: 33240, prot: READ|WRITE, flags: PRIVATE|FIXED|ANONYMOUS) = 0x7fc2ee702000
     0.229 ( 0.001 ms): trivial/84044 close(fd: 3)                                                          = 0
     0.242 ( 0.003 ms): trivial/84044 mmap(len: 8192, prot: READ|WRITE, flags: PRIVATE|ANONYMOUS)           = 0x7fc2ee53a000
     0.248 ( 0.002 ms): trivial/84044 arch_prctl(option: SET_FS, arg2: 0x7fc2ee70c580)                      = 0
     0.304 ( 0.005 ms): trivial/84044 mprotect(start: 0x7fc2ee6fc000, len: 12288, prot: READ)               = 0
     0.312 ( 0.004 ms): trivial/84044 mprotect(start: 0x403000, len: 4096, prot: READ)                      = 0
     0.320 ( 0.006 ms): trivial/84044 mprotect(start: 0x7fc2ee780000, len: 8192, prot: READ)                = 0
     0.337 ( 0.011 ms): trivial/84044 munmap(addr: 0x7fc2ee70d000, len: 271188)                             = 0
     0.365 ( 0.001 ms): trivial/84044 brk()                                                                 = 0xe02000
     0.368 ( 0.002 ms): trivial/84044 brk(brk: 0xe23000)                                                    = 0xe23000
     0.377 ( 0.010 ms): trivial/84044 openat(dfd: CWD, filename: 0x402012, flags: CREAT|TRUNC|WRONLY, mode: IRUGO|IWUGO) = 3
     0.398 ( 0.002 ms): trivial/84044 newfstatat(dfd: 3, filename: 0xee6c995a, statbuf: 0x7ffe4bdf0650, flag: 4096) = 0
     0.401 ( 0.002 ms): trivial/84044 ioctl(fd: 3, cmd: TCGETS, arg: 0x7ffe4bdf05b0)                        = -1 ENOTTY (Inappropriate ioctl for device)
     0.408 ( 0.002 ms): trivial/84044 write(fd: 3, buf: 0xe02480, count: 10)                                = 10
     0.413 (         ): trivial/84044 exit_group()                                                          = ?

   Summary of events:

   trivial (84044), 70 events, 92.1%

   syscall            calls  errors  total       min       avg       max       stddev
                                     (msec)    (msec)    (msec)    (msec)        (%)
   --------------- --------  ------ -------- --------- --------- ---------     ------
   mmap                   8      0     0.041     0.003     0.005     0.009     14.32%
   mprotect               4      0     0.025     0.004     0.006     0.010     21.35%
   openat                 3      0     0.022     0.006     0.007     0.010     19.30%
   pread64                4      0     0.018     0.002     0.004     0.013     62.41%
   munmap                 1      0     0.011     0.011     0.011     0.011      0.00%
   newfstatat             3      0     0.008     0.002     0.003     0.003     17.21%
   access                 1      1     0.007     0.007     0.007     0.007      0.00%
   brk                    3      0     0.006     0.001     0.002     0.002     13.93%
   arch_prctl             2      1     0.003     0.001     0.001     0.002      1.69%
   close                  2      0     0.003     0.001     0.001     0.001      0.00%
   read                   1      0     0.003     0.003     0.003     0.003      0.00%
   write                  1      0     0.002     0.002     0.002     0.002      0.00%
   ioctl                  1      1     0.002     0.002     0.002     0.002      0.00%
   execve                 1      0     0.000     0.000     0.000     0.000      0.00%

So, looks like total syscall overhead is on the order of 0.1 ms? Granted, it's a significant part of the runtime, but I think all the relocations and such are driving the libc overhead (as shown in callgrind output: https://i.imgur.com/Yligh7S.png )

And great, now I know a new way to use perf! (I initially tried profiling with perf but it doesn't get enough samples to be useful!).