Why PlatON wasm vm supports memory malloc functions

[MaggieNgWu]

Hi, guys

I was wondering why PlotON VM supply functions of "malloc" and "free" memory.

"malloc":  &exec.FunctionImport{Execute: envMalloc, GasCost: envMallocGasCost},
"free":    &exec.FunctionImport{Execute: envFree, GasCost: envFreeGasCost},
"calloc":  &exec.FunctionImport{Execute: envCalloc, GasCost: envCallocGasCost},
"realloc": &exec.FunctionImport{Execute: envRealloc, GasCost: envReallocGasCost},

This struct seems like defined by PlatON. As I have known, memory in WAVM is a byte array, used by program to store string and other values. The memory can be managed by WAVM. So, why PlatON would like to define this Memory structure and supply "malloc" function for smart contracts?

type Memory struct {
	Memory []byte
	Start  int //start position for malloc
	Size   int //memory size for malloc
	tree   []int
}

[woda0109]

Efficient use of memory, reusing destructed memory.

[MaggieNgWu]

What is the mechanism of the memory use?/ How PlatON manage wavm memory?
(We can use Chinese if you like)

[jiangshangqifeng]

The question you mentioned is more detailed and may not be clearly described in a few words. Do you have any problems during the specific application development process? You can send a look at the specific problems you have encountered. thx @MaggieNgWu

[MaggieNgWu]

Let's make it simple. In which case, a smart contract wasm code would call "malloc" function?

[jiangshangqifeng]

you can use ‘malloc' as you need
I suggest you debug the code and see the details ：）

[MaggieNgWu]

Would you please make an example?