On 27/04/2020 02:08, Danh Doan wrote: [snip] >>> musl's alloca.h is available here: >>> >>> https://git.musl-libc.org/cgit/musl/tree/include/alloca.h >> >> Hmm, OK, so that partly explains the problem. I wonder if the >> musl guys would accept a bug report? > > I don't think they have a policy of no `#undef` whatsoever. That's fair enough. > But, I think they're picky when come to C-correctly and > POSIX-correctly. > Does C or POSIX define alloca(3) at all? No alloca() is not in either the POSIX or C standard(s). This was an extension from the early days of BSD Unix. For some reason, I thought you had to explicitly '#include <alloca.h>' to use it, but it appears that (by default) you get a bonus include from the <stdlib.h> header, unless you restrict the headers using the various macros and/or compiler command-line options. As it happens, even on glibc systems, the <alloca.h> header is included by the <stdlib.h> header, unless you take steps to suppress it. So, we would have had the same issue, if it wasn't for the aforementioned '#undef alloca' the the glibc header file. When I need to look at pp output, while debugging things like this, I cherry-pick a patch to the Makefile: $ git diff diff --git a/Makefile b/Makefile index 6d5cee270c..cd8753bf54 100644 --- a/Makefile +++ b/Makefile @@ -2423,6 +2423,9 @@ $(ASM_OBJ): %.o: %.S GIT-CFLAGS $(missing_dep_dirs) %.s: %.c GIT-CFLAGS FORCE $(QUIET_CC)$(CC) -o $@ -S $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) $< +%.i: %.c GIT-CFLAGS FORCE + $(QUIET_CC)$(CC) $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) -E $< >$*.i + ifdef USE_COMPUTED_HEADER_DEPENDENCIES # Take advantage of gcc's on-the-fly dependency generation # See <http://gcc.gnu.org/gcc-3.0/features.html>. @@ -2474,7 +2477,7 @@ http-walker.sp http-walker.s http-walker.o: EXTRA_CPPFLAGS = -DNO_EXPAT endif ifdef NO_REGEX -compat/regex/regex.sp compat/regex/regex.o: EXTRA_CPPFLAGS = \ +compat/regex/regex.i compat/regex/regex.sp compat/regex/regex.o: EXTRA_CPPFLAGS = \ -DGAWK -DNO_MBSUPPORT endif $ [The second hunk above is not actually part of the cherry-picked patch, but I needed it in this instance to get GAWK and NO_MBSUPPORT passed to the compiler!] $ make NO_REGEX=1 compat/regex/regex.i CC compat/regex/regex.i $ vim compat/regex/regex.i $ ... which shows <alloca.h> is indeed being #included from <stdlib.h>. [it is protected by a __USE_MISC pp variable, but I didn't bother to track it down! ;-)] ATB, Ramsay Jones
