[tarantool-patches] Re: [PATCH 3/3] Show names of Lua functions in backtraces

[Konstantin Osipov]

* Georgy Kirichenko <georgy at tarantool.org> [18/09/22 00:21]:
> Trace corresponding Lua state as well as normal C stack frames while
> fiber backtracing. This might be useful for debugging purposes.
> 
> Fixes: #3538
> ---
>  src/lua/fiber.c         | 86 +++++++++++++++++++++++++++++++++++------
>  test/app/fiber.result   | 33 ++++++++++++++++
>  test/app/fiber.test.lua | 12 ++++++
>  3 files changed, 120 insertions(+), 11 deletions(-)
> 
> diff --git a/src/lua/fiber.c b/src/lua/fiber.c
> index 147add89b..289d240f6 100644
> --- a/src/lua/fiber.c
> +++ b/src/lua/fiber.c
> @@ -178,20 +178,79 @@ lbox_fiber_id(struct lua_State *L)
>  	return 1;
>  }
>  
> +/**
> + * Lua fiber traceback context.
> + */
> +struct lua_fiber_tb_ctx {
> +	/* Lua stack to push values. */
> +	struct lua_State *L;
> +	/* Lua stack to trace. */
> +	struct lua_State *R;
> +	/* Current Lua frame. */
> +	int lua_frame;
> +	/* Count of traced frames (both C and Lua). */
> +	int tb_frame;
> +};
> +
>  #ifdef ENABLE_BACKTRACE
> -static int
> -fiber_backtrace_cb(int frameno, void *frameret, const char *func, size_t offset, void *cb_ctx)
> +static void
> +dump_lua_frame(struct lua_State *L, lua_Debug *ar, int tb_frame, int lua_frame)
>  {
>  	char buf[512];
> -	int l = snprintf(buf, sizeof(buf), "#%-2d %p in ", frameno, frameret);
> -	if (func)
> -		snprintf(buf + l, sizeof(buf) - l, "%s+%zu", func, offset);
> -	else
> -		snprintf(buf + l, sizeof(buf) - l, "?");
> -	struct lua_State *L = (struct lua_State*)cb_ctx;
> -	lua_pushnumber(L, frameno + 1);
> +	snprintf(buf, sizeof(buf), "LUA:#%d %s in %s at line %i",
> +		 lua_frame + 1,
> +		 ar->name != NULL ? ar->name : "(unnamed)",
> +		 ar->source, ar->currentline);

I have only a stupid comment, and it's about formatting. I think
we should not change the formatting of C frames, it should be left
without a prefix.

> +	lua_pushnumber(L, tb_frame);
>  	lua_pushstring(L, buf);
>  	lua_settable(L, -3);
> +}
> +
> +static int
> +fiber_backtrace_cb(int frameno, void *frameret, const char *func, size_t offset, void *cb_ctx)
> +{
> +	struct lua_fiber_tb_ctx *tb_ctx = (struct lua_fiber_tb_ctx *)cb_ctx;
> +	struct lua_State *L = tb_ctx->L;
> +	if (strstr(func, "lj_BC_FUNCC") == func) {
> +		// LUA code.
> +		lua_Debug ar;
> +		while (tb_ctx->R && lua_getstack(tb_ctx->R, tb_ctx->lua_frame, &ar) > 0) {
> +			// Skip all C-frames.

Please use C style comments.

> +			lua_getinfo(tb_ctx->R, "Sln", &ar);
> +			if (*ar.what != 'C')
> +				break;
> +			if (ar.name != NULL) {
> +				// Dump frame if it is a built-in call
> +				tb_ctx->tb_frame++;
> +				dump_lua_frame(L, &ar, tb_ctx->tb_frame,
> +					       tb_ctx->lua_frame);
> +			}
> +			tb_ctx->lua_frame++;
> +		}
> +		while (tb_ctx->R && lua_getstack(tb_ctx->R, tb_ctx->lua_frame, &ar) > 0) {
> +			// Trace Lua frames.
> +			lua_getinfo(tb_ctx->R, "Sln", &ar);
> +			if (*ar.what == 'C') {
> +				break;
> +			}
> +			tb_ctx->tb_frame++;
> +			dump_lua_frame(L, &ar, tb_ctx->tb_frame,
> +				       tb_ctx->lua_frame);
> +			tb_ctx->lua_frame++;
> +		}
> +	} else {
> +		char buf[512];
> +		int l = snprintf(buf, sizeof(buf), "C:#%d %p in ",
> +				 frameno + 1, frameret);
> +		if (func)
> +			snprintf(buf + l, sizeof(buf) - l, "%s+%zu", func, offset);
> +		else
> +			snprintf(buf + l, sizeof(buf) - l, "?");
> +		tb_ctx->tb_frame++;
> +		lua_pushnumber(L, tb_ctx->tb_frame);
> +		lua_pushstring(L, buf);
> +		lua_settable(L, -3);
> +	}
>  	return 0;
>  }
>  #endif
> @@ -229,10 +288,15 @@ lbox_fiber_statof(struct fiber *f, void *cb_ctx, bool backtrace)
>  
>  	if (backtrace) {
>  #ifdef ENABLE_BACKTRACE
> +		struct lua_fiber_tb_ctx tb_ctx;
> +		tb_ctx.L = L;
> +		tb_ctx.R = f->storage.lua.stack;
> +		tb_ctx.lua_frame = 0;
> +		tb_ctx.tb_frame = 0;
>  		lua_pushstring(L, "backtrace");
>  		lua_newtable(L);
> -		if (f != fiber())
> -			backtrace_foreach(fiber_backtrace_cb, &f->ctx, L);
> +		backtrace_foreach(fiber_backtrace_cb,
> +				  f != fiber() ? &f->ctx : NULL, &tb_ctx);
>  		lua_settable(L, -3);
>  #endif /* ENABLE_BACKTRACE */
>  	}

-- 
Konstantin Osipov, Moscow, Russia, +7 903 626 22 32
http://tarantool.io - www.twitter.com/kostja_osipov