Support systems without qsort_r

qsort_r is a non-standard glibc extension and turns out to be the only
thing that prevents drgn from working on a musl system. "Fix" the use of
qsort_r by switching it to qsort with a thread local variable for the
parameter.

Tested in a clean chroot install of musl voidlinux.

Signed-off-by: Boris Burkov <boris@bur.io>

libdrgn/dwarf_info.c

@@ -7411,11 +7411,12 @@ static void drgn_debug_info_cache_sh_addr(struct drgn_module *module,
 	}
 }
 
-static int drgn_dwarf_fde_compar(const void *_a, const void *_b, void *arg)
+static _Thread_local struct drgn_dwarf_cie *drgn_dwarf_fde_compar_cies;
+static int drgn_dwarf_fde_compar(const void *_a, const void *_b)
 {
 	const struct drgn_dwarf_fde *a = _a;
 	const struct drgn_dwarf_fde *b = _b;
-	const struct drgn_dwarf_cie *cies = arg;
+	const struct drgn_dwarf_cie *cies = drgn_dwarf_fde_compar_cies;
 	if (a->initial_location < b->initial_location)
 		return -1;
 	else if (a->initial_location > b->initial_location)
@@ -7453,8 +7454,9 @@ drgn_debug_info_parse_frames(struct drgn_module *module)
 	 * Sort FDEs and remove duplicates, preferring .debug_frame over
 	 * .eh_frame.
 	 */
-	qsort_r(fdes.data, fdes.size, sizeof(fdes.data[0]),
-		drgn_dwarf_fde_compar, cies.data);
+	drgn_dwarf_fde_compar_cies = cies.data;
+	qsort(fdes.data, fdes.size, sizeof(fdes.data[0]),
+	      drgn_dwarf_fde_compar);
 	if (fdes.size > 0) {
 		size_t src = 1, dst = 1;
 		for (; src < fdes.size; src++) {

libdrgn/orc_info.c

@@ -32,9 +32,10 @@ static inline uint64_t drgn_raw_orc_pc(struct drgn_module *module, size_t i)
 	return module->orc.pc_base + UINT64_C(4) * i + offset;
 }
 
-static int compare_orc_entries(const void *a, const void *b, void *arg)
+static _Thread_local struct drgn_module *compare_orc_entries_module;
+static int compare_orc_entries(const void *a, const void *b)
 {
-	struct drgn_module *module = arg;
+	struct drgn_module *module = compare_orc_entries_module;
 	size_t index_a = *(size_t *)a;
 	size_t index_b = *(size_t *)b;
 
@@ -203,17 +204,17 @@ static struct drgn_error *drgn_debug_info_parse_orc(struct drgn_module *module)
 	for (size_t i = 0; i < num_entries; i++)
 		indices[i] = i;
 
+	compare_orc_entries_module = module;
 	/*
 	 * Sort the ORC entries for binary search. Since Linux kernel commit
 	 * f14bf6a350df ("x86/unwind/orc: Remove boot-time ORC unwind tables
 	 * sorting") (in v5.6), this is already sorted for vmlinux, so only sort
 	 * it if necessary.
 	 */
 	for (size_t i = 1; i < num_entries; i++) {
-		if (compare_orc_entries(&indices[i - 1], &indices[i],
-					module) > 0) {
-			qsort_r(indices, num_entries, sizeof(indices[0]),
-				compare_orc_entries, module);
+		if (compare_orc_entries(&indices[i - 1], &indices[i]) > 0) {
+			qsort(indices, num_entries, sizeof(indices[0]),
+			      compare_orc_entries);
 			break;
 		}
 	}