It is 1 << 50 is the limit on heap. The following code doesn't compile:
package main
func main() {
var X [1 << 50]byte // type [1125899906842624]byte larger than address
space
_ = X
}
But with 1 << 50 - 1, it compiles:
package main
func main() {
var X [1 << 50 - 1]byte // runtime: out of memory: cannot allocate
1125899906842624-byte block (3997696 in use)
_ = X
}
It is weird that there are several different runtime error messages:
package main
func main() {
var X [1 << 46]byte // fatal error: runtime: out of memory
_ = X
}
package main
func main() {
var X [1 << 47]byte // runtime: out of memory: cannot allocate
140737488355328-byte block (3997696 in use)\nfatal error: out of memory
_ = X
}
So it looks there are at least 3 thresholds are set in the code.
On Friday, November 26, 2021 at 12:00:20 PM UTC+8 [email protected]
wrote:
> On Saturday, November 13, 2021 at 12:48:41 PM UTC-6 [email protected]
> wrote:
>
>> global variables are stored in there data section of the compiled binary,
>> the linker imposes a 2GB size limit
>> the array in main can be allocated at runtime, and given enough memory,
>> it could succeed
>>
>>
> Why does the linker impose a 2GB limit on .bss data but not heap memory?
> Is there a limit on heap variables?
>
>
>>
>> On Saturday, November 13, 2021 at 5:46:29 PM UTC [email protected]
>> wrote:
>>
>>> On a 64bit Mac, this code:
>>>
>>> package main
>>>
>>> var X [^uint(0)>>14]byte
>>> func main() {
>>> }
>>>
>>> produces a compile time error:
>>> main.X: symbol too large (1125899906842623 bytes > 2000000000 bytes)
>>>
>>> But this compiles and crashes at runtime.
>>>
>>> package main
>>>
>>> func main() {
>>> var X [^uint(0) >> 14]byte
>>> _ = X
>>> }
>>>
>>> runtime: out of memory: cannot allocate 1125899906842624-byte block
>>> (3997696 in use)
>>> fatal error: out of memory
>>>
>>> goroutine 1 [running]:
>>> runtime.throw({0x1061335, 0x11})
>>> /usr/local/go/src/runtime/panic.go:1198 +0x71 fp=0xc000042658
>>> sp=0xc000042628 pc=0x102b031
>>> runtime.(*mcache).allocLarge(0x100a734, 0x3ffffffffffff, 0x11, 0x1)
>>> /usr/local/go/src/runtime/mcache.go:229 +0x22e fp=0xc0000426b8
>>> sp=0xc000042658 pc=0x101086e
>>> runtime.mallocgc(0x3ffffffffffff, 0x1059300, 0x1)
>>> /usr/local/go/src/runtime/malloc.go:1082 +0x5c5 fp=0xc000042738
>>> sp=0xc0000426b8 pc=0x100a645
>>> runtime.newobject(0x1058a00)
>>> /usr/local/go/src/runtime/malloc.go:1228 +0x27 fp=0xc000042760
>>> sp=0xc000042738 pc=0x100aa87
>>> main.main()
>>> /Users/billmorgan/git/tmp/main.go:5 +0x25 fp=0xc000042780
>>> sp=0xc000042760 pc=0x1054c65
>>> runtime.main()
>>> /usr/local/go/src/runtime/proc.go:255 +0x227 fp=0xc0000427e0
>>> sp=0xc000042780 pc=0x102d6c7
>>> runtime.goexit()
>>> /usr/local/go/src/runtime/asm_amd64.s:1581 +0x1 fp=0xc0000427e8
>>> sp=0xc0000427e0 pc=0x1051fa1
>>>
>>>
>>> Why does the 2nd program succeed compilation of the same array that
>>> failed compilation in the 1st program?
>>>
>>> It was known ahead of time that the allocation would fail so I think the
>>> 2nd program should have failed to compile too.
>>>
>>>
>>>
>>>
>>>
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