A question regarding the use of luaL_Buffer in Lua 5.4

[Marc Balmer <marc@...>]

I have a C program that uses two luaL_Buffer variables to build up content dynamically.  I init both, then I write something to buffer B, after that, buffer A gets filled by repeated calls to luaL_addchar, in the end I push both buffers and out them:

#include <stdio.h>
#include <stdlib.h>

#include <lua.h>
#include <lauxlib.h>

int
main(int argc, char *argv[])
{
        lua_State *L;
        luaL_Buffer A, B;
        int count, n;

        count = atoi(argv[1]);

        L = luaL_newstate();
        luaL_buffinit(L, &A);
        luaL_buffinit(L, &B);

        luaL_addstring(&B, "_ENV = ...\n");

        for (n = 0; n < count; n++)
                luaL_addchar(&A, 'N');
        luaL_addchar(&A, '\n');

        luaL_pushresult(&B);
        luaL_pushresult(&A);

        printf("Lua buffer A:\n");
        printf("%s\n", lua_tostring(L, -1));

        printf("Lua buffer B:\n");
        printf("%s\n", lua_tostring(L, -2)); /* this fails if count is >= 1024 */

        lua_close(L);
        return 0;
}

This works up to a certain number of calls to luaL_addchar(&A, 'N').  In my case, if count is 1024 or greater, I get a segmentation fault.

The real world code where this happens in the reader() function in https://github.com/arcapos/luatemplate/blob/master/reader.c where two buffers are used to build two parts of Lua source code.

The second call to luaL_pushresult() seems to somehow "destroy" what the first call to luaL_pushresult() did put on the stack.

It happens only on Lua 5.4, but not on Lua 5.3, apparently.

fwiw, I used a RHEL 8 system for testing.

Any ideas or suggestions?

- mb