Pass callbacks to git by address

ISO C has no conversion between a function pointer and void *, so the
callbacks handed through git's data pointers and the write found by
dlsym stopped the pedantic half of a DEVELOPER=1 build.

5 files changed, 20 insertions, 8 deletions

diff --git a/source/cgit.mk b/source/cgit.mkindex 4109930..6e17737 100644--- a/source/cgit.mk+++ b/source/cgit.mk@@ -34,7 +34,7 @@ $(CGIT_BUILD)/VERSION: force-version  # Pinned so a compiler moving its default, as GCC 15 did to gnu23, cannot # change what the sources mean. The GNU dialect because git's headers use GNU-# extensions and dlsym needs a non-conforming cast. Git keeps its own choice.+# extensions. Git keeps its own choice. CGIT_STD ?= gnu17  # CGIT_CFLAGS is tracked separately so that changing it does not force a rebuild
diff --git a/source/cgit.mk b/source/cgit.mk
index 4109930..6e17737 100644
--- a/source/cgit.mk
+++ b/source/cgit.mk
@@ -34,7 +34,7 @@ $(CGIT_BUILD)/VERSION: force-version
 
 # Pinned so a compiler moving its default, as GCC 15 did to gnu23, cannot
 # change what the sources mean. The GNU dialect because git's headers use GNU
-# extensions and dlsym needs a non-conforming cast. Git keeps its own choice.
+# extensions. Git keeps its own choice.
 CGIT_STD ?= gnu17
 
 # CGIT_CFLAGS is tracked separately so that changing it does not force a rebuild
diff --git a/source/filter.c b/source/filter.cindex 3ffd077..5f96cc0 100644--- a/source/filter.c+++ b/source/filter.c@@ -150,9 +150,14 @@ static struct cgit_filter *current_write_filter = NULL;  void cgit_init_filters(void) {-	libc_write = dlsym(RTLD_NEXT, "write");-	if (!libc_write)+	void *symbol = dlsym(RTLD_NEXT, "write");++	if (!symbol) 		die("Unable to find libc's write function");+	// ISO C cannot convert an object pointer to a function pointer, while+	// POSIX guarantees the two share a representation, so the bytes are+	// copied across instead.+	memcpy(&libc_write, &symbol, sizeof(libc_write)); }  /*
diff --git a/source/filter.c b/source/filter.c
index 3ffd077..5f96cc0 100644
--- a/source/filter.c
+++ b/source/filter.c
@@ -150,9 +150,14 @@ static struct cgit_filter *current_write_filter = NULL;
 
 void cgit_init_filters(void)
 {
-	libc_write = dlsym(RTLD_NEXT, "write");
-	if (!libc_write)
+	void *symbol = dlsym(RTLD_NEXT, "write");
+
+	if (!symbol)
 		die("Unable to find libc's write function");
+	// ISO C cannot convert an object pointer to a function pointer, while
+	// POSIX guarantees the two share a representation, so the bytes are
+	// copied across instead.
+	memcpy(&libc_write, &symbol, sizeof(libc_write));
 }
 
 /*
diff --git a/source/shared.c b/source/shared.cindex a6a5106..af848f6 100644--- a/source/shared.c+++ b/source/shared.c@@ -123,7 +123,7 @@ static void release_mmfile(mmfile_t *file, const struct object_id *oid)  */ static int emit_line(void *priv, mmbuffer_t *mb, int nbuf) {-	linediff_fn emit = (linediff_fn)priv;+	linediff_fn emit = *(linediff_fn *)priv; 	int i;  	for (i = 0; i < nbuf; i++) {@@ -372,7 +372,7 @@ int cgit_refs_cb(const struct reference *ref, void *cb_data)  void cgit_diff_tree_cb(struct diff_queue_struct *q, struct diff_options *options, void *data) {-	filepair_fn fn = (filepair_fn)data;+	filepair_fn fn = *(filepair_fn *)data; 	int i;  	for (i = 0; i < q->nr; i++) {@@ -443,7 +443,7 @@ int cgit_diff_files(const struct object_id *old_oid, const struct object_id *new 	emit_params.ctxlen = context > 0 ? context : DEFAULT_DIFF_CONTEXT; 	emit_params.flags = XDL_EMIT_FUNCNAMES; 	emit_cb.out_line = emit_line;-	emit_cb.priv = fn;+	emit_cb.priv = &fn; 	xdl_diff(&old_file, &new_file, &diff_params, &emit_params, &emit_cb); 	release_mmfile(&old_file, old_oid); 	release_mmfile(&new_file, new_oid);@@ -477,7 +477,7 @@ void cgit_diff_tree(const struct object_id *old_oid, const struct object_id *new 	if (ignorews) 		DIFF_XDL_SET(&opt, IGNORE_WHITESPACE); 	opt.format_callback = cgit_diff_tree_cb;-	opt.format_callback_data = fn;+	opt.format_callback_data = &fn; 	if (prefix) 		cgit_diff_limit_path(&opt, prefix); 	diff_setup_done(&opt);
diff --git a/source/shared.c b/source/shared.c
index a6a5106..af848f6 100644
--- a/source/shared.c
+++ b/source/shared.c
@@ -123,7 +123,7 @@ static void release_mmfile(mmfile_t *file, const struct object_id *oid)
  */
 static int emit_line(void *priv, mmbuffer_t *mb, int nbuf)
 {
-	linediff_fn emit = (linediff_fn)priv;
+	linediff_fn emit = *(linediff_fn *)priv;
 	int i;
 
 	for (i = 0; i < nbuf; i++) {
@@ -372,7 +372,7 @@ int cgit_refs_cb(const struct reference *ref, void *cb_data)
 
 void cgit_diff_tree_cb(struct diff_queue_struct *q, struct diff_options *options, void *data)
 {
-	filepair_fn fn = (filepair_fn)data;
+	filepair_fn fn = *(filepair_fn *)data;
 	int i;
 
 	for (i = 0; i < q->nr; i++) {
@@ -443,7 +443,7 @@ int cgit_diff_files(const struct object_id *old_oid, const struct object_id *new
 	emit_params.ctxlen = context > 0 ? context : DEFAULT_DIFF_CONTEXT;
 	emit_params.flags = XDL_EMIT_FUNCNAMES;
 	emit_cb.out_line = emit_line;
-	emit_cb.priv = fn;
+	emit_cb.priv = &fn;
 	xdl_diff(&old_file, &new_file, &diff_params, &emit_params, &emit_cb);
 	release_mmfile(&old_file, old_oid);
 	release_mmfile(&new_file, new_oid);
@@ -477,7 +477,7 @@ void cgit_diff_tree(const struct object_id *old_oid, const struct object_id *new
 	if (ignorews)
 		DIFF_XDL_SET(&opt, IGNORE_WHITESPACE);
 	opt.format_callback = cgit_diff_tree_cb;
-	opt.format_callback_data = fn;
+	opt.format_callback_data = &fn;
 	if (prefix)
 		cgit_diff_limit_path(&opt, prefix);
 	diff_setup_done(&opt);
diff --git a/source/shared.h b/source/shared.hindex 129cfb7..46324a1 100644--- a/source/shared.h+++ b/source/shared.h@@ -48,6 +48,11 @@ extern int cgit_refs_cb(const struct reference *ref, void *cb_data); extern void cgit_free_commitinfo(struct commitinfo *info); extern void cgit_free_taginfo(struct taginfo *info); +/*+ * A diff format callback that hands each filepair to the filepair_fn data+ * points at. ISO C has no conversion between a function pointer and void *,+ * so the function travels by address.+ */ extern void cgit_diff_tree_cb(struct diff_queue_struct *q, struct diff_options *options, void *data);  /*
diff --git a/source/shared.h b/source/shared.h
index 129cfb7..46324a1 100644
--- a/source/shared.h
+++ b/source/shared.h
@@ -48,6 +48,11 @@ extern int cgit_refs_cb(const struct reference *ref, void *cb_data);
 extern void cgit_free_commitinfo(struct commitinfo *info);
 extern void cgit_free_taginfo(struct taginfo *info);
 
+/*
+ * A diff format callback that hands each filepair to the filepair_fn data
+ * points at. ISO C has no conversion between a function pointer and void *,
+ * so the function travels by address.
+ */
 extern void cgit_diff_tree_cb(struct diff_queue_struct *q, struct diff_options *options, void *data);
 
 /*
diff --git a/source/ui-log.c b/source/ui-log.cindex 9f21114..d23fcd4 100644--- a/source/ui-log.c+++ b/source/ui-log.c@@ -93,6 +93,8 @@ static void follow_path(struct diff_filepair *pair)  */ static int should_show(struct commit *commit, struct rev_info *revs) {+	// Static, because the walk keeps the address in its diff options.+	static filepair_fn follow = follow_path; 	struct commit_list *parents = commit->parents; 	struct commit *parent; 	int found = 0, saved_fmt;@@ -128,7 +130,7 @@ static int should_show(struct commit *commit, struct rev_info *revs) 	saved_fmt = revs->diffopt.output_format; 	revs->diffopt.output_format = DIFF_FORMAT_CALLBACK; 	revs->diffopt.format_callback = cgit_diff_tree_cb;-	revs->diffopt.format_callback_data = follow_path;+	revs->diffopt.format_callback_data = &follow; 	revs->diffopt.no_free = 1; 	diff_flush(&revs->diffopt); 	revs->diffopt.output_format = saved_fmt;
diff --git a/source/ui-log.c b/source/ui-log.c
index 9f21114..d23fcd4 100644
--- a/source/ui-log.c
+++ b/source/ui-log.c
@@ -93,6 +93,8 @@ static void follow_path(struct diff_filepair *pair)
  */
 static int should_show(struct commit *commit, struct rev_info *revs)
 {
+	// Static, because the walk keeps the address in its diff options.
+	static filepair_fn follow = follow_path;
 	struct commit_list *parents = commit->parents;
 	struct commit *parent;
 	int found = 0, saved_fmt;
@@ -128,7 +130,7 @@ static int should_show(struct commit *commit, struct rev_info *revs)
 	saved_fmt = revs->diffopt.output_format;
 	revs->diffopt.output_format = DIFF_FORMAT_CALLBACK;
 	revs->diffopt.format_callback = cgit_diff_tree_cb;
-	revs->diffopt.format_callback_data = follow_path;
+	revs->diffopt.format_callback_data = &follow;
 	revs->diffopt.no_free = 1;
 	diff_flush(&revs->diffopt);
 	revs->diffopt.output_format = saved_fmt;