'Section type conflict' using clang++ for Win32

Question

I need help to port my embedded C++ code (running on an ARM processor) into a local machine (x86).

Some parts of the code run on a dedicated memory section (ROM), to spare some embedded RAM. This was achieved with the compiler feature attribute (( section )).

The same code doesn't build on my local PC (Win32) using clang/clang++ v.12. I run into several 'section type conflict' compilation errors.

I have a short sample code that reproduces the issue:

Constant.hpp

#pragma once

class Constant {
public:
    Constant(int val) { value = val; }
    int get() { return value; }
private:
    int value = 0;
};

Global.hpp

#pragma once
#include "Constant.hpp"

static Constant myConstant = Constant{3};
extern Constant * const pConstant __attribute__((__section__(".mySection1"))) = &myConstant;

Sum.hpp

#pragma once

struct Sum {
  Sum() = default;
  int calculate(int a, int b) __attribute__((__section__(".mySection1")));
};

main.cpp

#include <iostream>
#include "Global.hpp"
#include "Sum.hpp"

extern Constant * const pConstant;

int main(int argc, char **argv) {
    Sum * sum = new Sum();
    int result = sum->calculate(1, pConstant->get());
    std::cout << result << std::endl;
    return 0;
}

The compiler output is:

error: 'calculate' causes a section type conflict with 'pConstant'
  int calculate(int a, int b) __attribute__((__section__(".mySection1")));
      ^
.../Global.hpp:6:25: note: declared here
extern Constant * const pConstant __attribute__((__section__(".mySection1"))) = &myConstant;

If I use 2 different sections (.mySection1 for the variable and mySection2 for the method), the code builds and runs successfully. Disassembled code is below:

.../Sum.cpp.obj:     file format pe-i386

SYMBOL TABLE:
[  0](sec  1)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .text
AUX scnlen 0x2a nreloc 3 nlnno 0 checksum 0x7187c290 assoc 1 comdat 0
[  2](sec  2)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .data
AUX scnlen 0x0 nreloc 0 nlnno 0 checksum 0x0 assoc 2 comdat 0
[  4](sec  3)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .bss
AUX scnlen 0x4 nreloc 0 nlnno 0 checksum 0x0 assoc 3 comdat 0
[  6](sec  4)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .text
AUX scnlen 0x1f nreloc 0 nlnno 0 checksum 0x6ff4fbec assoc 4 comdat 2
[  8](sec  4)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x00000000 ??0Constant@@QAE@H@Z
[  9](sec  5)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .mySection2
AUX scnlen 0x2b nreloc 2 nlnno 0 checksum 0x56c90986 assoc 5 comdat 0
[ 11](sec  6)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .text
AUX scnlen 0x11 nreloc 0 nlnno 0 checksum 0x80cdff44 assoc 6 comdat 2
[ 13](sec  6)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x00000000 ?get@Constant@@QAEHXZ
[ 14](sec  7)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .mySection1
AUX scnlen 0x4 nreloc 1 nlnno 0 checksum 0x0 assoc 7 comdat 0
[ 16](sec  8)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .CRT$XCU
AUX scnlen 0x4 nreloc 1 nlnno 0 checksum 0x0 assoc 8 comdat 0
[ 18](sec  9)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .drectve
AUX scnlen 0x18 nreloc 0 nlnno 0 checksum 0x63557b96 assoc 9 comdat 0
[ 20](sec 10)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .debug$S
AUX scnlen 0x56c nreloc 23 nlnno 0 checksum 0xa675e8b1 assoc 10 comdat 0
[ 22](sec 13)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .debug$S
AUX scnlen 0x150 nreloc 9 nlnno 0 checksum 0xecc1ccc6 assoc 4 comdat 5
[ 24](sec 14)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .debug$S
AUX scnlen 0x11c nreloc 7 nlnno 0 checksum 0xefad5adf assoc 6 comdat 5
[ 26](sec 11)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .debug$T
AUX scnlen 0x3b0 nreloc 0 nlnno 0 checksum 0x954cd43c assoc 11 comdat 0
[ 28](sec 12)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .llvm_addrsig
AUX scnlen 0x4 nreloc 0 nlnno 0 checksum 0x9c7eb272 assoc 12 comdat 0
[ 30](sec -1)(fl 0x00)(ty   0)(scl   3) (nx 0) 0x00000001 @feat.00
[ 31](sec  1)(fl 0x00)(ty  20)(scl   3) (nx 0) 0x00000000 ??__EmyConstant@@YAXXZ
[ 32](sec  3)(fl 0x00)(ty   0)(scl   3) (nx 0) 0x00000000 _myConstant
[ 33](sec  5)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x00000000 ?calculate@Sum@@QAEHH@Z
[ 34](sec  1)(fl 0x00)(ty  20)(scl   3) (nx 0) 0x00000020 __GLOBAL__sub_I_Sum.cpp
[ 35](sec  7)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x00000000 ?pConstant@@3QAVConstant@@A
[ 36](sec -2)(fl 0x00)(ty   0)(scl 103) (nx 1) 0x00000000 Sum.cpp
File

I have the impression that clang for x86 doesn't allow to place constant variables and functions in the same section, but I couldn't find any x86/Win32 restriction on the clang compiler reference...

Any ideas?

Answer 1

The issue came from using a newer version of the arm compiler... Since arm compiler version 6.15, it is forbidden to mix code and data in the same memory section. See arm compiler changelog