truss: handle shm_open's special SHM_ANON value better.

[munro_ip9.org]

Summary

The support for decoding shm_open(2) just added in D17457 causes truss to display shmopen("(null"), ...) if you use the special SHM_ANON value as a segment name. Maybe that's OK, but it'd be better to detect that value and show it properly.

Test Plan

$ cat test.c
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/types.h>

int main(int argc, char *argv[])
{
    shm_open(SHM_ANON, O_RDWR | O_CREAT | O_EXCL, 0600);
    shm_open("/test-shm-segment", O_RDWR | O_CREAT | O_EXCL, 0600);
    shm_unlink("/test-shm-segment");
    return 0;
}
$ cc test.c
$ truss ./a.out

As of r339224 that shows:

shm_open("(null)",O_RDWR|O_CREAT|O_EXCL,0600)    = 3 (0x3)
shm_open("/test-shm-segment",O_RDWR|O_CREAT|O_EXCL,0600) = 4 (0x4)

With this patch it shows:

shm_open(SHM_ANON,O_RDWR|O_CREAT|O_EXCL,0600)    = 3 (0x3)
shm_open("/test-shm-segment",O_RDWR|O_CREAT|O_EXCL,0600) = 4 (0x4)

[jhb]

Looks good apart from a sorting nit.

usr.bin/truss/syscall.h

43 ↗

(On Diff #48875)

I think I probably haven't bothered updating the comment block of new types FWIW.

150 ↗

(On Diff #48875)

These enum lists are sorted first by type and then alphabetically within each type.

[jhb]

usr.bin/truss/syscalls.c

1599 ↗

(On Diff #48875)

No space after cast in FreeBSD's style.

1603 ↗

(On Diff #48875)

Best to use the style-mandated '/* FALLTHROUGH */' as it is also recognized by compilers and static analyzers.

[munro_ip9.org]

Fixes for style feedback from jhb. Thanks!

[allanjude]

Approved By: allanjude