XeLaTeX doesn't have complete fonts I've just moved to OS X form Ubuntu. I'm using OS X 10.8.2 unfortunately I'm not able to say what TeX distribution is installed on the computer since it wasn't me who installed it, I guess it was installation form tug.org. 

I have problem with my .tex files. While LaTeX documents are compiled correctly, XeLateX generate a warning: 


  Missing character: There is no ẖ in font [lmroman10-regular]:mapping=tex-text
  !


All other diacritics signes are found (\d{h}, \b{d} etc).

I was compiling file in TeXworks and TeXshop and I guess it's not a problem of editor since in both editors I get the same warning.

If LaTeX is using special fonts installed in it's directory, XeLaTeX is supposed to use the fonts available in general in the system.

Thanks

Here is the output of the content of /Applications/TeX directory:

MacBook-Pro-Marek:TeX user$ ls
BibDesk.app             LaTeXiT.app             TeXShop.app
Eps-Tiff-Conversion.pdf LuaTeX-and-XeTeX        TeXworks.app
Excalibur-4.0.7         READ ME FIRST.pdf       What Is Installed.pdf
FixMacTeX2012.pkg       TeX Live Utility.app
The problem was that in the fonts I was trying to use this particular diacritic sing doesn't exist. Solution given to me on tex.stackexchange is to add this character in the preamble of .tex document. The code for simple XeLaTeX document containing ẖ is: 

\documentclass{article}

\usepackage{fontspec}
\usepackage{newunicodechar}

\UndeclareUTFcomposite[\UTFencname]{x1E96}{\b}{h}
\makeatletter
\DeclareRobustCommand{\b}[1]
{\hmode@bgroup\o@lign{\relax#1\crcr\hidewidth\ltx@sh@ft{-3ex}%
\vbox to.2ex{\hbox{\char"AF}\vss}\hidewidth}\egroup}
\makeatother

\newunicodechar{ẖ}{\b{h}}

\begin{document}

\b{h}ur\=u\v g

\end{document}


Other possibility is to install fonts, like Linux Libertine, which do have this character.

To see all question and original reply and comments, see here.