Using valgrind trunk (revision 15637) compiled from sources on Mac OS 10.11 (El Capitan), I get the following error on certain executables (in this case, the GCC compilers):
$ valgrind --version
$ valgrind ./f951
valgrind: mmap-FIXED(0x1015a2000, 1075085312) failed in UME (load_segment2) with error 22 (Invalid argument).
The bzip2'ed executable "f951" can be found at this URL: https://www.dropbox.com/s/wzzj20gte9dm8vh/f951.bz2?dl=0
To these executables have any packers like UPX run on them?
(In reply to Rhys Kidd from comment #1)
> To these executables have any packers like UPX run on them?
I'm removing this as a blocker on OS X 10.11 support, as the same error is reported with current and prior OS X releases.
The underlying issue here is related to other reports of failure mmap'ing low addresses within the executable, where Valgrind also maps itself. e.g. can be caused by executables with very large text, data or bss segments.
There is some further discussion that can be found here: bz#138424 or with a quick search through closed bug reports with "mmap-FIXED".