On 2020-04-26 17:17:56+0100, Ramsay Jones <ramsay@xxxxxxxxxxxxxxxxxxxx> wrote: > > > On 26/04/2020 01:54, Danh Doan wrote: > > On 2020-04-25 21:28:05+0100, Ramsay Jones <ramsay@xxxxxxxxxxxxxxxxxxxx> wrote: > [snip] > >> OK, I had a quick look at the <alloca.h> header file on a glibc > >> system (linux) and new-lib system (cygwin) and they both do > >> (more or less) the same thing: first #undef alloca, and then > >> if being compiled by gcc, define alloca(size) to be __builtin_alloca(size). > > > > musl people don't do that. > > They just go ahead define it, if any other header file requires > > alloca, they will include alloca.h > > > >> So, even if <alloca.h> is #included after regex.c:66, it wouldn't > >> be a problem. Since I don't have access to a musl based system, > >> I don't know what that system header is doing. > > > > 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. But, I think they're picky when come to C-correctly and POSIX-correctly. Does C or POSIX define alloca(3) at all? And, I /think/ they'll likely ignore this one, [musl-faq] says: Assuming that including one header will cause symbols from another unrelated header to be exposed. This is an application bug, and fixing it is as simple as adding the missing #include directives. I guess they meant, if we have `alloca` defined, we must have included `alloca.h` somewhere. > >> However, I said *even if* above, because I don't see why it is trying > >> to #include <alloca.h> in the first place! ;-) > > > > I looked into my system again. The inclusion chain is: > > > > compat/regex/regex.c:77 > > `-> compat/regex/regex_internal.h:26 > > `-> /usr/include/stdlib.h:138 [*1*] > > > > [*1*]: https://git.musl-libc.org/cgit/musl/tree/include/stdlib.h#n137 > > > > I don't know why _GNU_SOURCE and/or _BSD_SOURCE is defined. > > ... and this explains the main cause. Hmm, as you say, why are > one (or both) of those pp variables set. :( Okay, I tracked it down. compat/regex/regex.c:63 `-> /usr/include/limits.h:4 `-> /usr/include/features.h:15 https://git.musl-libc.org/cgit/musl/tree/include/features.h?id=8e452abae67db445fb6c3e37cd566c4788c2e8f3#n14 musl defined `_BSD_SOURCE` if none of those below macro was defined: - _BSD_SOURCE - _POSIX_SOURCE - _XOPEN_SOURCE - _GNU_SOURCE - __STRICT_ANSI__ I don't think we have any business to define which one of those macros should be defined in the compat code. > > [snip] > >> BTW, why are you compiling with NO_REGEX set anyway? > > > > Because I use musl-libc, and musl-libc doesn't have StartEnd > > Ah, OK. ;-) > > Well, even if the musl project accepted a PR and provided a fix, that > will not help you in the short term! :D > > Hmm, whatever patch you decide to send (even the original one) I think > you need to add an explanation of the problem to the commit message, > including why the patch provides a solution. (You don't have to type > a novel - see commit bd8f005583 :-P ). > > I haven't thought about this too much, but some options: > > - iff the musl library sets some kind of identifying pp variable > (_MUSL_LIBC_ or somesuch - I haven't looked), then you could > make the '#include <alloca.h>' conditional on that variable. > This has the benefit of making it obvious to people reading the > code that this is specific to musl-libc. musl's wiki's faq [musl-wiki-faq]: Q: Why is there no __MUSL__ macro? > - you could simply remove that '#ifdef GAWK' block completely (Lines > 64->67). We set GAWK and NO_MBSUPPORT unconditionally in the Makefile > so that it compiles (see commit a997bf423d), but these particular > lines simply reflect the gawk projects dislike of alloca (along with > the desire to catch any attempts to add new calls which are not protected > by HAVE_ALLOCA). Given that we are very unlikely to add new calls ... > > - change the conditional on this block to (totally untested, just typing > into my email client) '#if defined(GAWK) && defined(HAVE_ALLOCA)'. > This should work, but it does disable the 'catch any attempts to add > new _unintentional_ calls' aspect of that block; so you may as well > remove it ... I'll go with your patch in the next email. <1a0c2b25-e283-9936-1fa2-ce51df1404dc@xxxxxxxxxxxxxxxxxxxx> [musl-faq]: https://www.musl-libc.org/faq.html [musl-wiki-faq]: https://wiki.musl-libc.org/faq.html -- Danh
