Re: [PATCH] trace2: tolerate failed timestamp formatting

[Taylor Blau <ttaylorr@openai.com>]

On Wed, Jul 15, 2026 at 04:12:11PM +0000, Derrick Stolee via GitGitGadget wrote:
> This change removes all uses of xsnprintf() from the trace2/ directory.
> There are two uses of xstrdup() that could be considered for removal,
> but they only die() on out-of-memory errors instead of formatting
> issues. I chose to leave those in place for now.

I may be missing some Git for Windows context, but I dug into this a
little and I'm not sure 'gettimeofday()' is the culprit...

In my understanding Git for Windows's 'gettext.h' appears[1] to redirect
the 'vsnprintf()' inside 'xsnprintf()' to 'libintl_vsnprintf()'. In this
case, we have seven '%' placeholders. Gettext can store only six plus
its end marker inline, so parsing the seventh causes an allocation
before any timestamp values are read.

A failure there would produce the observed -1, after which 'xsnprintf()'
dies and trace2 can recurse.

I think that also explains why calling 'snprintf()' directly helps.
tr2_tbuf.c doesn't include gettext.h, so I think it bypasses libintl. If
I'm reading compat/mingw.c correctly, 'gettimeofday()' fills tv and
always returns zero [2], making the zero-initialization unrelated.

Would it make more sense to fix the xsnprintf()/libintl boundary and
treat Trace2 reentrancy separately? I still can't explain why the
allocation failed, so there may be another GfW-specific piece I’m
missing.

I think something like the following (untested) would prevent the
redirection to `libintl_vsnprintf()`:

--- 8< ---
diff --git a/wrapper.c b/wrapper.c
index 16f5a63fbb..2976d4e110 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -7,7 +7,14 @@
 #include "git-compat-util.h"
 #include "abspath.h"
 #include "parse.h"
+
+/*
+ * xsnprintf() only formats non-translated strings. On MinGW, avoid
+ * redirecting its vsnprintf() call to libintl's allocating replacement.
+ */
+#define _INTL_NO_DEFINE_MACRO_VSNPRINTF
 #include "gettext.h"
+#undef _INTL_NO_DEFINE_MACRO_VSNPRINTF
 #include "strbuf.h"
 #include "trace2.h"
--- >8 ---

Thanks,
Taylor

[1]: https://github.com/git-for-windows/git-sdk-64/blob/1351ad2fc39a1f74c56b2cc2b38107ec8df8eb40/mingw64/include/libintl.h#L731-L754
[2]: https://github.com/microsoft/git/blob/vfs-2.55.0/compat/mingw.c#L1609-L1618