Re: [PATCH] gcov: fix clang-11+ support

[Nathan Chancellor <nathan@kernel.org>]

On Fri, Mar 12, 2021 at 11:21:39AM -0800, Nick Desaulniers wrote:
> LLVM changed the expected function signatures for llvm_gcda_start_file()
> and llvm_gcda_emit_function() in the clang-11 release. Users of clang-11
> or newer may have noticed their kernels failing to boot due to a panic
> when enabling CONFIG_GCOV_KERNEL=y +CONFIG_GCOV_PROFILE_ALL=y.  Fix up
> the function signatures so calling these functions doesn't panic the
> kernel.
> 
> When we drop clang-10 support from the kernel, we should carefully
> update the original implementations to try to preserve git blame,
> deleting these implementations.
> 
> Link: https://reviews.llvm.org/rGcdd683b516d147925212724b09ec6fb792a40041
> Link: https://reviews.llvm.org/rG13a633b438b6500ecad9e4f936ebadf3411d0f44
> Cc: Fangrui Song <maskray@google.com>
> Reported-by: Prasad Sodagudi<psodagud@quicinc.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>

I can reproduce the panic (as a boot hang) in QEMU before this patch and
it is resolved after it so:

Tested-by: Nathan Chancellor <nathan@kernel.org>

However, the duplication hurts :( would it potentially be better to just
do the full update to clang-11+ and require it for CONFIG_GCOV_KERNEL?

    depends on CC_IS_GCC || CLANG_VERSION >= 110000?

> ---
>  kernel/gcov/clang.c | 69 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 69 insertions(+)
> 
> diff --git a/kernel/gcov/clang.c b/kernel/gcov/clang.c
> index c94b820a1b62..20e6760ec05d 100644
> --- a/kernel/gcov/clang.c
> +++ b/kernel/gcov/clang.c
> @@ -75,7 +75,9 @@ struct gcov_fn_info {
>  
>  	u32 num_counters;
>  	u64 *counters;
> +#if __clang_major__ < 11
>  	const char *function_name;
> +#endif
>  };
>  
>  static struct gcov_info *current_info;
> @@ -105,6 +107,7 @@ void llvm_gcov_init(llvm_gcov_callback writeout, llvm_gcov_callback flush)
>  }
>  EXPORT_SYMBOL(llvm_gcov_init);
>  
> +#if __clang_major__ < 11
>  void llvm_gcda_start_file(const char *orig_filename, const char version[4],
>  		u32 checksum)
>  {
> @@ -113,7 +116,17 @@ void llvm_gcda_start_file(const char *orig_filename, const char version[4],
>  	current_info->checksum = checksum;
>  }
>  EXPORT_SYMBOL(llvm_gcda_start_file);
> +#else
> +void llvm_gcda_start_file(const char *orig_filename, u32 version, u32 checksum)
> +{
> +	current_info->filename = orig_filename;
> +	current_info->version = version;
> +	current_info->checksum = checksum;
> +}
> +EXPORT_SYMBOL(llvm_gcda_start_file);
> +#endif
>  
> +#if __clang_major__ < 11
>  void llvm_gcda_emit_function(u32 ident, const char *function_name,
>  		u32 func_checksum, u8 use_extra_checksum, u32 cfg_checksum)
>  {
> @@ -133,6 +146,24 @@ void llvm_gcda_emit_function(u32 ident, const char *function_name,
>  	list_add_tail(&info->head, &current_info->functions);
>  }
>  EXPORT_SYMBOL(llvm_gcda_emit_function);
> +#else
> +void llvm_gcda_emit_function(u32 ident, u32 func_checksum,
> +		u8 use_extra_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->use_extra_checksum = use_extra_checksum;
> +	info->cfg_checksum = cfg_checksum;
> +	list_add_tail(&info->head, &current_info->functions);
> +}
> +EXPORT_SYMBOL(llvm_gcda_emit_function);
> +#endif
>  
>  void llvm_gcda_emit_arcs(u32 num_counters, u64 *counters)
>  {
> @@ -295,6 +326,7 @@ void gcov_info_add(struct gcov_info *dst, struct gcov_info *src)
>  	}
>  }
>  
> +#if __clang_major__ < 11
>  static struct gcov_fn_info *gcov_fn_info_dup(struct gcov_fn_info *fn)
>  {
>  	size_t cv_size; /* counter values size */
> @@ -322,6 +354,28 @@ static struct gcov_fn_info *gcov_fn_info_dup(struct gcov_fn_info *fn)
>  	kfree(fn_dup);
>  	return NULL;
>  }
> +#else
> +static struct gcov_fn_info *gcov_fn_info_dup(struct gcov_fn_info *fn)
> +{
> +	size_t cv_size; /* counter values size */
> +	struct gcov_fn_info *fn_dup = kmemdup(fn, sizeof(*fn),
> +			GFP_KERNEL);
> +	if (!fn_dup)
> +		return NULL;
> +	INIT_LIST_HEAD(&fn_dup->head);
> +
> +	cv_size = fn->num_counters * sizeof(fn->counters[0]);
> +	fn_dup->counters = vmalloc(cv_size);
> +	if (!fn_dup->counters) {
> +		kfree(fn_dup);
> +		return NULL;
> +	}
> +
> +	memcpy(fn_dup->counters, fn->counters, cv_size);
> +
> +	return fn_dup;
> +}
> +#endif
>  
>  /**
>   * gcov_info_dup - duplicate profiling data set
> @@ -362,6 +416,7 @@ struct gcov_info *gcov_info_dup(struct gcov_info *info)
>   * gcov_info_free - release memory for profiling data set duplicate
>   * @info: profiling data set duplicate to free
>   */
> +#if __clang_major__ < 11
>  void gcov_info_free(struct gcov_info *info)
>  {
>  	struct gcov_fn_info *fn, *tmp;
> @@ -375,6 +430,20 @@ void gcov_info_free(struct gcov_info *info)
>  	kfree(info->filename);
>  	kfree(info);
>  }
> +#else
> +void gcov_info_free(struct gcov_info *info)
> +{
> +	struct gcov_fn_info *fn, *tmp;
> +
> +	list_for_each_entry_safe(fn, tmp, &info->functions, head) {
> +		vfree(fn->counters);
> +		list_del(&fn->head);
> +		kfree(fn);
> +	}
> +	kfree(info->filename);
> +	kfree(info);
> +}
> +#endif
>  
>  #define ITER_STRIDE	PAGE_SIZE
>  
> 
> base-commit: f78d76e72a4671ea52d12752d92077788b4f5d50
> -- 
> 2.31.0.rc2.261.g7f71774620-goog
>