linux-kernel - Re: [PATCH v5] gcov: Clang support

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Date:   Wed, 17 Apr 2019 16:21:39 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Tri Vo <trong@...roid.com>
Cc:     ghackmann@...roid.com, ndesaulniers@...gle.com,
        linux-kernel@...r.kernel.org, oberpar@...ux.ibm.com,
        Trilok Soni <tsoni@...cinc.com>,
        Prasad Sodagudi <psodagud@...cinc.com>,
        Daniel Mentz <danielmentz@...gle.com>,
        Petri Gynther <pgynther@...gle.com>
Subject: Re: [PATCH v5] gcov: Clang support

On Wed, 17 Apr 2019 15:53:28 -0700 Tri Vo <trong@...roid.com> wrote:

> LLVM uses profiling data that's deliberately similar to GCC, but has a very
> different way of exporting that data.  LLVM calls llvm_gcov_init() once per
> module, and provides a couple of callbacks that we can use to ask for more
> data.
> 
> We care about the "writeout" callback, which in turn calls back into
> compiler-rt/this module to dump all the gathered coverage data to disk:
> 
>    llvm_gcda_start_file()
>      llvm_gcda_emit_function()
>      llvm_gcda_emit_arcs()
>      llvm_gcda_emit_function()
>      llvm_gcda_emit_arcs()
>      [... repeats for each function ...]
>    llvm_gcda_summary_info()
>    llvm_gcda_end_file()
> 
> This design is much more stateless and unstructured than gcc's, and is
> intended to run at process exit.  This forces us to keep some local state
> about which module we're dealing with at the moment.  On the other hand, it
> also means we don't depend as much on how LLVM represents profiling data
> internally.
> 
> See LLVM's lib/Transforms/Instrumentation/GCOVProfiling.cpp for more
> details on how this works, particularly GCOVProfiler::emitProfileArcs(),
> GCOVProfiler::insertCounterWriteout(), and GCOVProfiler::insertFlush().

checkpatch speaketh truth.

Also, I'll change those Co-authored-by's to the documented Co-developed-by.


From: Andrew Morton <akpm@...ux-foundation.org>
Subject: gcov-clang-support-checkpatch-fixes

WARNING: Non-standard signature: Co-authored-by:
#31: 
Co-authored-by: Nick Desaulniers <ndesaulniers@...gle.com>

WARNING: Non-standard signature: Co-authored-by:
#32: 
Co-authored-by: Tri Vo <trong@...roid.com>

WARNING: Possible unnecessary 'out of memory' message
#158: FILE: kernel/gcov/clang.c:90:
+	if (!info) {
+		pr_warn_ratelimited("failed to allocate gcov info\n");

WARNING: Possible unnecessary 'out of memory' message
#193: FILE: kernel/gcov/clang.c:125:
+	if (!info) {
+		pr_warn_ratelimited("failed to allocate gcov function info for %s\n",

WARNING: line over 80 characters
#546: FILE: kernel/gcov/clang.c:478:
+			pos += store_gcov_u32(buffer, pos, fi_ptr->cfg_checksum);

total: 0 errors, 5 warnings, 663 lines checked

NOTE: For some of the reported defects, checkpatch may be able to
      mechanically convert to the typical style using --fix or --fix-inplace.

./patches/gcov-clang-support.patch has style problems, please review.

NOTE: If any of the errors are false positives, please report
      them to the maintainer, see CHECKPATCH in MAINTAINERS.

Please run checkpatch prior to sending patches

Cc: Daniel Mentz <danielmentz@...gle.com>
Cc: Greg Hackmann <ghackmann@...roid.com>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Peter Oberparleiter <oberpar@...ux.ibm.com>
Cc: Petri Gynther <pgynther@...gle.com>
Cc: Prasad Sodagudi <psodagud@...cinc.com>
Cc: Trilok Soni <tsoni@...cinc.com>
Cc: Tri Vo <trong@...roid.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 kernel/gcov/clang.c |    9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

--- a/kernel/gcov/clang.c~gcov-clang-support-checkpatch-fixes
+++ a/kernel/gcov/clang.c
@@ -86,10 +86,8 @@ void llvm_gcov_init(llvm_gcov_callback w
 {
 	struct gcov_info *info = kzalloc(sizeof(*info), GFP_KERNEL);
 
-	if (!info) {
-		pr_warn_ratelimited("failed to allocate gcov info\n");
+	if (!info)
 		return;
-	}
 
 	INIT_LIST_HEAD(&info->head);
 	INIT_LIST_HEAD(&info->functions);
@@ -121,11 +119,8 @@ void llvm_gcda_emit_function(u32 ident,
 {
 	struct gcov_fn_info *info = kzalloc(sizeof(*info), GFP_KERNEL);
 
-	if (!info) {
-		pr_warn_ratelimited("failed to allocate gcov function info for %s\n",
-				function_name ?: "UNKNOWN");
+	if (!info)
 		return;
-	}
 
 	INIT_LIST_HEAD(&info->head);
 	info->ident = ident;
_