[3pt] Demangling of C symbols inside memprof

[veod32]

Product: Tarantool
Since: 2.10
Root document: https://www.tarantool.io/en/doc/latest/book/app_server/luajit_memprof/
Dev issue: tarantool/tarantool#5813
SME: @ igormunkin , @ Buristan

Details

We can use the Dl_info and dladdr() functions to provide the name of the <*.so> file and the name of the C function, where the allocation event occurred. It's better than just a raw C address that shows nothing.

[mkokryashkin]

Resolver

Consider the following chunks of code:

// hello.c
#include "lua.h"
#include "lauxlib.h"

static int say_hello(lua_State *L) {
    lua_pushstring(L, "Hello, world!");
    return 1;
}

static const struct luaL_Reg functions [] = {
    {"say_hello", say_hello},
    {NULL, NULL}
};

int luaopen_hello(lua_State *L) {
    luaL_register(L, "hello", functions);
    return 1;
}

-- test.lua
package.cpath = "./?.so"
require "hello"
misc.memprof.start('memprof.test')
for i=1, 1e5 do hello.say_hello() end
misc.memprof.stop()

After the considered patchset application, memprof reports this:

ALLOCATIONS
INTERNAL: 20 events     +427859 bytes   -0 bytes
say_hello:0x7fb48ce6d119: 1 events      +29 bytes       -0 bytes

REALLOCATIONS
INTERNAL: 1 events      +128 bytes      -256 bytes

DEALLOCATIONS
INTERNAL: 49 events     +0 bytes        -428427 bytes
        Overrides:
                INTERNAL


HEAP SUMMARY:
INTERNAL holds 1548 bytes: 20 allocs, 14 frees
say_hello:0x7fb48ce6d119 holds 29 bytes: 1 allocs, 0 frees

instead of that:

ALLOCATIONS
INTERNAL: 20 events     +427859 bytes   -0 bytes
CFUNC:0x7fb48ce6d119: 1 events      +29 bytes       -0 bytes

REALLOCATIONS
INTERNAL: 1 events      +128 bytes      -256 bytes

DEALLOCATIONS
INTERNAL: 49 events     +0 bytes        -428427 bytes
        Overrides:
                INTERNAL


HEAP SUMMARY:
INTERNAL holds 1548 bytes: 20 allocs, 14 frees
CFUNC:0x7fb48ce6d119 holds 29 bytes: 1 allocs, 0 frees

If a new library was loaded during the memprof runtime, and an
allocation occured in one of its functions, then that function's name is guaranteed
to be resolved.