linux-kernel - [PATCH 1/2] gcov: re-fix clang-11+ support

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Date:   Wed,  7 Apr 2021 11:54:55 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Peter Oberparleiter <oberpar@...ux.ibm.com>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Fangrui Song <maskray@...gle.com>,
        Prasad Sodagudi <psodagud@...cinc.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        stable@...r.kernel.org
Subject: [PATCH 1/2] gcov: re-fix clang-11+ support

LLVM changed the expected function signature for
llvm_gcda_emit_function() in the clang-11 release.  Users of clang-11 or
newer may have noticed their kernels producing invalid coverage
information:

$ llvm-cov gcov -a -c -u -f -b <input>.gcda -- gcno=<input>.gcno
1 <func>: checksum mismatch, \
  (<lineno chksum A>, <cfg chksum B>) != (<lineno chksum A>, <cfg chksum C>)
2 Invalid .gcda File!
...

Fix up the function signatures so calling this function interprets its
parameters correctly and computes the correct cfg checksum. In
particular, in clang-11, the additional checksum is no longer optional.

Link: https://reviews.llvm.org/rG25544ce2df0daa4304c07e64b9c8b0f7df60c11d
Cc: stable@...r.kernel.org #5.4+
Reported-by: Prasad Sodagudi <psodagud@...cinc.com>
Tested-by: Prasad Sodagudi <psodagud@...cinc.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
 kernel/gcov/clang.c | 38 +++++++++++++++++++++++++++++++++-----
 1 file changed, 33 insertions(+), 5 deletions(-)

diff --git a/kernel/gcov/clang.c b/kernel/gcov/clang.c
index d41f5ecda9db..1747204541bf 100644
--- a/kernel/gcov/clang.c
+++ b/kernel/gcov/clang.c
@@ -69,7 +69,9 @@ struct gcov_fn_info {
 
 	u32 ident;
 	u32 checksum;
+#if CONFIG_CLANG_VERSION < 110000
 	u8 use_extra_checksum;
+#endif
 	u32 cfg_checksum;
 
 	u32 num_counters;
@@ -111,6 +113,7 @@ void llvm_gcda_start_file(const char *orig_filename, u32 version, u32 checksum)
 }
 EXPORT_SYMBOL(llvm_gcda_start_file);
 
+#if CONFIG_CLANG_VERSION < 110000
 void llvm_gcda_emit_function(u32 ident, u32 func_checksum,
 		u8 use_extra_checksum, u32 cfg_checksum)
 {
@@ -126,6 +129,21 @@ void llvm_gcda_emit_function(u32 ident, u32 func_checksum,
 	info->cfg_checksum = cfg_checksum;
 	list_add_tail(&info->head, &current_info->functions);
 }
+#else
+void llvm_gcda_emit_function(u32 ident, u32 func_checksum, u32 cfg_checksum)
+{
+	struct gcov_fn_info *info = kzalloc(sizeof(*info), GFP_KERNEL);
+
+	if (!info)
+		return;
+
+	INIT_LIST_HEAD(&info->head);
+	info->ident = ident;
+	info->checksum = func_checksum;
+	info->cfg_checksum = cfg_checksum;
+	list_add_tail(&info->head, &current_info->functions);
+}
+#endif
 EXPORT_SYMBOL(llvm_gcda_emit_function);
 
 void llvm_gcda_emit_arcs(u32 num_counters, u64 *counters)
@@ -256,11 +274,16 @@ int gcov_info_is_compatible(struct gcov_info *info1, struct gcov_info *info2)
 		!list_is_last(&fn_ptr2->head, &info2->functions)) {
 		if (fn_ptr1->checksum != fn_ptr2->checksum)
 			return false;
+#if CONFIG_CLANG_VERSION < 110000
 		if (fn_ptr1->use_extra_checksum != fn_ptr2->use_extra_checksum)
 			return false;
 		if (fn_ptr1->use_extra_checksum &&
 			fn_ptr1->cfg_checksum != fn_ptr2->cfg_checksum)
 			return false;
+#else
+		if (fn_ptr1->cfg_checksum != fn_ptr2->cfg_checksum)
+			return false;
+#endif
 		fn_ptr1 = list_next_entry(fn_ptr1, head);
 		fn_ptr2 = list_next_entry(fn_ptr2, head);
 	}
@@ -378,17 +401,22 @@ size_t convert_to_gcda(char *buffer, struct gcov_info *info)
 
 	list_for_each_entry(fi_ptr, &info->functions, head) {
 		u32 i;
-		u32 len = 2;
-
-		if (fi_ptr->use_extra_checksum)
-			len++;
 
 		pos += store_gcov_u32(buffer, pos, GCOV_TAG_FUNCTION);
-		pos += store_gcov_u32(buffer, pos, len);
+#if CONFIG_CLANG_VERSION < 110000
+		pos += store_gcov_u32(buffer, pos,
+			fi_ptr->use_extra_checksum ? 3 : 2);
+#else
+		pos += store_gcov_u32(buffer, pos, 3);
+#endif
 		pos += store_gcov_u32(buffer, pos, fi_ptr->ident);
 		pos += store_gcov_u32(buffer, pos, fi_ptr->checksum);
+#if CONFIG_CLANG_VERSION < 110000
 		if (fi_ptr->use_extra_checksum)
 			pos += store_gcov_u32(buffer, pos, fi_ptr->cfg_checksum);
+#else
+		pos += store_gcov_u32(buffer, pos, fi_ptr->cfg_checksum);
+#endif
 
 		pos += store_gcov_u32(buffer, pos, GCOV_TAG_COUNTER_BASE);
 		pos += store_gcov_u32(buffer, pos, fi_ptr->num_counters * 2);
-- 
2.31.1.295.g9ea45b61b8-goog