Re: C99 %zu support (on MSVC) (was: [PATCH 4/6] builtin/stash: provide a way to export stashes to a ref)
From: Phillip Wood <hidden>
Date: 2022-03-18 16:28:39
Subsystem:
the rest · Maintainer:
Linus Torvalds
On 18/03/2022 13:34, Ævar Arnfjörð Bjarmason wrote:
On Wed, Mar 16 2022, brian m. carlson wrote:quoted
[[PGP Signed Part:Undecided]] On 2022-03-14 at 21:19:10, Phillip Wood wrote:quoted
Hi Brian and Ævar Firstly I think this is a useful feature to add to git stash, thanks for working on it BrianThanks. I'm glad folks other than me will find it useful.quoted
On 11/03/2022 02:08, Ævar Arnfjörð Bjarmason wrote:quoted
On Thu, Mar 10 2022, brian m. carlson wrote:quoted
+ size_t author_len, committer_len; + struct commit *this = NULL; + const char *orig_author = NULL, *orig_committer = NULL; + char *author = NULL, *committer = NULL; + const char *buffer = NULL; + unsigned long bufsize; + const char *p; + char *msg = NULL;These shouldn't be initialized unless they really need to..quoted
+ this = lookup_commit_reference(the_repository, &info->w_commit);..and some are clobbered right away here, so all of these should not be initializzed.This function got hoisted out of what would otherwise be duplicated code, and that's why they're all initialized (because we would otherwise have called free on an uninitialized value). I can remove the ones that aren't strictly needed.quoted
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+ buffer = get_commit_buffer(this, &bufsize); + orig_author = find_commit_header(buffer, "author", &author_len); + orig_committer = find_commit_header(buffer, "committer", &committer_len); + p = memmem(buffer, bufsize, "\n\n", 2);You could start searching from orig_committer rather than buffer but I'm sure it doesn't make any real difference. The sequencer does something similar to this to replay commits when rebasing - is there any scope for sharing code between the two?I can look into it. The amount of code that would be duplicated here is very minimal, so I'm okay with just adding a few lines here.quoted
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...since by doing so we hide genuine "uninitialized" warnings. E.g. "author_len" here isn't initialized, but is set by find_commit_header(), but if that line was removed we'd warn below, but not if it's initialized when the variables are declared..quoted
+ for (size_t i = 0;; i++, nitems++) {Do we need i and nitems?I can look into removing them.quoted
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+ char buf[32]; + int ret; + + if (nalloc <= i) { + size_t new = nalloc * 3 / 2 + 5; + items = xrealloc(items, new * sizeof(*items)); + nalloc = new;Can't we just use the usual ALLOC_GROW() pattern here?ALLOC_GROW_BY() zeros out the memory which would mean we could remove the memset() calls in the loops. I noticed in some other loops we know the size in advance and could use CALLOC_ARRAY().Yeah, I can switch to that. I was looking for that, but I was thinking of a function and not a macro, so I missed it.quoted
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+ } + snprintf(buf, sizeof(buf), "%zu", i);Aren't the %z formats unportable (even with our newly found reliance on more C99)? I vaguely recall trying them recently and the windows CI jobs erroring...According to [1] it has been available since at least 2015. It is certainly much nicer than casting every size_t to uintmax_t and having to use PRIuMAX.If we're relying on a new enough MSVC for C11, then it's much newer than 2015, so we should be fine. It's mandatory on POSIX systems.FWIW I dug into my logs and I ran into it with %zu (not %z), but that's what you're using. Sorry about being inaccurate, it seems %z's portability isn't the same as %z. I ran into it in mid-2021 in the GitHub CI, but those logs are deleted now (and I didn't re-push that specific OID): https://github.com/avar/git/runs/2298653913 Where it would emit output like: builtin/log.c: In function 'gen_message_id': 311 builtin/log.c:1047:29: error: unknown conversion type character 'z' in format [-Werror=format=] 312 1047 | strbuf_addf(&fmt, "%%s-%%0%zud.%%0%zud-%%s-%%s-%%s", tmp.len, tmp.len); This SO post, whose accuracy I can't verify, claims it is supported in VS 2013 or later, and that the way to check for it is with "_MSC_VER >= 1800": https://stackoverflow.com/questions/44382862/how-to-printf-a-size-t-without-warning-in-mingw-w64-gcc-7-1
Oh, so it is mingw that is the problem, not MSVC. Indeed using "%zu" (see the diff below) fails for the "win build" job[1] but the "win+VS build" succeeds[2]. mingw config.mak.uname to uses -D__MINGW_USE_ANSI_STDIO=0. Even if we could change that to =1 it would be insufficient as it does not affect the format specifiers allowed by __attribute__((format (printf, 3, 4))). I think to do that we would have to change "printf" to "__MINGW_PRINTF_FORMAT" for each attribute declaration[3]. In short unfortunately I don't think we can easily use "%zu" Best wishes Phillip
diff --git a/add-interactive.c b/add-interactive.c
index e1ab39cce3..1790ad6359 100644
--- a/add-interactive.c
+++ b/add-interactive.c@@ -193,9 +193,8 @@ static ssize_t find_unique(const char *string, struct prefix_item_list *list)
struct string_list_item *item;
if (list->items.nr != list->sorted.nr)
- BUG("prefix_item_list in inconsistent state (%"PRIuMAX
- " vs %"PRIuMAX")",
- (uintmax_t)list->items.nr, (uintmax_t)list->sorted.nr);
+ BUG("prefix_item_list in inconsistent state (%zu vs %zu)",
+ list->items.nr, list->sorted.nr);
if (index < 0)
item = list->sorted.items[-1 - index].util;
[1]
https://github.com/phillipwood/git/runs/5601840748?check_suite_focus=true
[2]
https://github.com/phillipwood/git/runs/5601840528?check_suite_focus=true
[3] https://sourceforge.net/p/mingw-w64/wiki2/gnu%20printf
So if we are going to use it and that's true (which would be great!) it
would IMO make sense to introduce it in some prep commit where we delete
e.g. "_MSC_VER>=1310" and other things you'll see in-tree if you look
through:
git grep _MSC_VER
I.e. to push out some canary commit for using that specific feature, and
along with it delete the old MSVC compatibility shims (which presumably
we can't use if we're going to hard depend on %zu).