illumos gate

This is reproducible as long as the process you're taking a core file of is larger than the amount of free space in the ramdisk. trussing it shows:

pread(256, "02\\0\\0\\0 X05FAFE N %FDFE".., 4096, 0xFEFFB000) = 4096
pwrite(3, "02\\0\\0\\0 X05FAFE N %FDFE".., 4096, 0x0162483C) = 1988
pwrite(3, "02\\0\\0\\0", 4, 0x0162483C)        = 4
fcntl(3, F_FREESP, 0xFFFFFD7FFFDFE360)        = 0
pwrite(3, "01\\0\\0\\0\\0\\0\\0\\0\\0B0FFFE".., 32, 4756) = 32
pread(256, "\\0\\0\\0\\0\\0\\0\\0\\0\\0\\0\\0\\0".., 4096, 0xFEFFD000) = 4096
pwrite(3, "\\0\\0\\0\\0\\0\\0\\0\\0\\0\\0\\0\\0".., 4096, 0x01624844) = 1980
pwrite(3, "02\\0\\0\\0", 4, 0x01624844)        = 4
fcntl(3, F_FREESP, 0xFFFFFD7FFFDFE360)        = 0
pwrite(3, "01\\0\\0\\0\\0\\0\\0\\0\\0D0FFFE".., 32, 4788) = 32
pwrite(3, "\\0\\0\\0\\0\\0\\0\\0\\0\\0\\0\\0\\0".., 677712, 0x0162484C) = 1972
fcntl(3, F_FREESP, 0xFFFFFD7FFFDFE4E0)        = 0
close(3)                    = 0
unlink("core.85530")                = 0
fstat(2, 0xFFFFFD7FFFDFDF40)            = 0
gcorewrite(2, " g c o r e", 5)            = 5
: write(2, " :  ", 2)                = 2
core.85530write(2, " c o r e . 8 5 5 3 0", 10)        = 10
 dump failed: write(2, "   d u m p   f a i l e d".., 14)    = 14
No such file or directorywrite(2, " N o   s u c h   f i l e".., 25)    = 25

If the pwrite64() call in dump_sections() doesn't return indicating that all bytes were written, dump_sections() returns -1. That gets propagated back up to Pgcore() in libproc, then gcore() in gcore(1), which prints the error message using "strerror(errno)". The problem is that errno was never set because no system call failed here: pwrite() just returned less than the full byte count. Even if an errno had been set by pwrite(), we make several system calls between that call and the return from Pgcore(), and any of them could clobber errno.