[syslinux] extlinux VPATH build issue

[H. Peter Anvin]

Zach Carter wrote:
> Hi:
> 
> I've been seeing intermittent build failures with the extlinux target,
> and I believe I've tracked it down to a VPATH issue.  See this make -d
> log: 
> 
>      Finished prerequisites of target file `extlinux'.
>      Prerequisite `extlinux.o' is newer than target `extlinux'.
>      Prerequisite `setadv.o' is newer than target `extlinux'.
>      Prerequisite `extlinux_bss_bin.o' is newer than target `extlinux'.
>      Prerequisite `extlinux_sys_bin.o' is newer than target `extlinux'.
>     No need to remake target `extlinux'; using VPATH name `../extlinux'.
> 
> Since the CWD is named extlinux, and the VPATH includes '..', make is
> using the timestamp on the '../extlinux' directory to decide whether to
> remake the 'extlinux' executable.  
> 
> I believe the included fix should resolve the issue.  It tells make to
> only use the VPATH for *.c and *.o files, which means the VPATH will not
> be searched for the 'extlinux' executable.  
> 

Interesting, I wasn't familiar with that construct.

Either way, I don't know how useful it is, since have massively revamped 
the Makefiles in the 3.70 branch of the Syslinux development tree (see 
Syslinux 3.70-pre12); this should hopefully avoid this problem as well.

Even so, it's a useful construct that might come in handy.

	-hpa