From: Josh Poimboeuf <[email protected]> Sent: Tuesday, November 11, 2025 8:04 PM > > On Wed, Nov 12, 2025 at 02:26:18AM +0000, Michael Kelley wrote: > > > I've been able to debug this. Two problems: > > > > > > 1) On Ubuntu (both 20.04 and 24.04), /bin/sh and /usr/bin/sh are symlinks > > > to "dash" (not "bash"). So the "shell" command in "make" invokes dash. The > > > man page for dash shows that the built-in echo command accepts only -n as > > > an option. The -e behavior of processing "\n" and similar sequences is > > > always > > > enabled. So on my Ubuntu systems, the "-e" is ignored by echo and becomes > > > part of the C source code sent to gcc, and of course it barfs. Dropping > > > the -e > > > makes it work for me (and the \n is handled correctly), but that might > > > not work > > > with other shells. Using "/bin/echo" with the -e solves the problem in a > > > more > > > compatible way across different shells. > > Ah. I think we can use "printf" here. > > > > 2) With make v4.2.1 on my Ubuntu 20.04 system, the "#" character in the > > > "#include" added to the echo command is problematic. "make" seems to be > > > treating it as a comment character, though I'm not 100% sure of that > > > interpretation. Regardless, the "#" causes a syntax error in the "make" > > > shell > > > command. Adding a backslash before the "#" solves that problem. On an > > > Ubuntu > > > 24.04 system with make v4.3, the "#" does not cause any problems. (I > > > tried to put > > > make 4.3 on my Ubuntu 20.04 system, but ran into library compatibility > > > problems > > > so I wasn’t able to definitively confirm that it is the make version that > > > changes the > > > handling of the "#"). Unfortunately, adding the backslash before the # > > > does *not* > > > work with make v4.3. The backslash becomes part of the C source code sent > > > to > > > gcc, which barfs. I don't immediately have a suggestion on how to resolve > > > this > > > in a way that is compatible across make versions. > > > > Using "\043" instead of the "#" is a compatible solution that works in make > > v4.2.1 and v4.3 and presumably all other versions as well. > > Hm... I've seen similar portability issues with "," for which we had to > change it to "$(comma)" which magically worked for some reason that I am > forgetting. > > Does "$(pound)" work? This seems to work here: > > HAVE_XXHASH = $(shell printf "$(pound)include > <xxhash.h>\nXXH3_state_t *state;int main() {}" | \ >
Yes, the above line works in my Ubuntu 20.04 and 24.04 environments. It properly detects the presence and absence of xxhash 0.8. Seems like a good solution to me. Michael
