Hacking Lua for debug information
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- Subject: Hacking Lua for debug information
- From: Florian Hester <florian@...>
- Date: 2012年3月18日 02:08:07 +0100
Hello,
I am trying to create a debug function which shows what is currently on
the stack, since it is a debug function and wont end up in a release
build, i decided to dive in to the guts of Lua.
See here, my testing program for the debug function simple_dump:
#include <stdio.h>
#include <stdlib.h>
#include <lua.h>
#include <lualib.h>
#include <lauxlib.h>
#ifdef LUA_GUTS
#include <lapi.h>
#endif
int simple_dump(lua_State* L)
{
int top = lua_gettop(L);
printf("%d stack items.\n", top);
for (int i = 1; i <= top; i++)
{
#ifdef LUA_GUTS
TValue* p = L->ci->func + i;
int type = ttypenv(p);
#else
const void* p = lua_topointer(L, i);
int type = lua_type(L, i);
#endif
printf("pointer: %p", p);
switch(type)
{
case LUA_TSTRING:
printf("\tstr value: %s", lua_tostring(L, i));
break;
case LUA_TNUMBER:
printf("\tnr value: %f", lua_tonumber(L, i));
break;
#ifdef LUA_GUTS
default:
printf("\tgc pointer: %p", p->value_.gc);
break;
#endif
}
printf("\n");
}
return 0;
}
int main(int argc, char* argv[])
{
puts("Lua 5.2 debug test.");
lua_State* L = luaL_newstate();
lua_pushcfunction(L, simple_dump);
lua_newtable(L);
lua_newtable(L);
lua_pushvalue(L, -1);
lua_pushstring(L, "Foo");
lua_pushnumber(L, 5.2);
lua_pushnumber(L, -3.223);
lua_pushvalue(L, -3);
lua_pushnumber(L, 10.8233);
lua_pushstring(L, "Bar");
lua_newtable(L);
lua_newtable(L);
lua_call(L, lua_gettop(L) - 1, 0);
lua_close(L);
}
On 64 bit Linux, with GCC 4.6.3, and compiled as:
gcc main.c -g -DLUA_GUTS -std=c99 -o main -I/opt/lua52/src
/opt/lua52/src/liblua.a -lm
The ouput:
Lua 5.2 debug test.
11 stack items.
pointer: 0x23f41a0 gc pointer: 0x23f3fe0
pointer: 0x23f41b0 gc pointer: 0x23f4030
pointer: 0x23f41c0 gc pointer: 0x23f4030
pointer: 0x23f41d0 str value: Foo
pointer: 0x23f41e0 nr value: 5.200000
pointer: 0x23f41f0 nr value: -3.223000
pointer: 0x23f4200 str value: Foo
pointer: 0x23f4210 nr value: 10.823300
pointer: 0x23f4220 str value: Bar
pointer: 0x23f4230 gc pointer: 0x23f40e0
pointer: 0x23f4240 gc pointer: 0x23f4130
Looks okay so far.
But since the software that is going use this debugging function is
cross platform, it should also work on Windows.
On 64 bit Windows 7, with GCC 4.6.2 (MinGW 32 bit), and compiled as:
gcc -g -std=c99 -DLUA_GUTS -ID:\software\lua-5.2.0\src main.c -o
main.exe D:\software\lua-5.2.0\src\liblua.a
The output (run from GDB):
Starting program: d:\code\c\luatest\main.exe
[New Thread 1052.0x1004]
Lua 5.2 debug test.
11 stack items.
pointer: 003e4230 gc pointer: 003e4140
pointer: 003e4240 gc pointer: 003e37b0
pointer: 003e4250 gc pointer: 39581062
pointer: 003e4260 gc pointer: 93dd97f6
pointer: 003e4270 gc pointer: 003e41a8
pointer: 003e4280 gc pointer: baadf00d
pointer: 003e4290 gc pointer: baadf00d
pointer: 003e42a0 gc pointer: baadf00d
pointer: 003e42b0 gc pointer: baadf00d
pointer: 003e42c0 gc pointer: baadf00d
pointer: 003e42d0 gc pointer: baadf00d
[Inferior 1 (process 1052) exited normally]
Wait, what? how can this be? The first item and the last item are both a
table (different instances), but why is the last table's gc pointer
NULL? And why is the type not found for the string and number values?
What is going on here?
Lua seems to work just fine otherwise. There is no reason for me to
believe Lua is corrupted somehow other then the above output.
Also without LUA_GUTS defined, i get the right output according to Lua
documentation on both platforms.
So, am i doing something which i simply should not be doing, debugging
or otherwise, or is there truly something screwy going on?
- Florian