Monday, March 28, 2022

[SOLVED] Obtaining current GCC exception model

Issue

g++ is built using either the DWARF2, sjlj or seh exception model. rel="noreferrer">MinGW-builds provide various builds of g++ that have different exception models. I would like to be able to determine from the gcc toolchain what exception model is being used. Is there a g++ argument that will dump the default exception model of the compiler?


Solution

Edit: Originally, I was testing for the configuration flags that are described in g++ -v. As Jonathon Wakely points out in the comments, this is not a good thing to do.

An inspection way to do it is to compile to assembly:

struct S { ~S(); };
void bar();
void foo() {
  S s;
  bar();
}

The result of g++ -S <filename> -o output.s have the following exception references in them:

MinGW-4.8.1-x86-posix-sjlj:

.def    ___gxx_personality_sj0; .scl    2;  .type   32; .endef
.def    __Unwind_SjLj_Register; .scl    2;  .type   32; .endef
.def    __Unwind_SjLj_Unregister;   .scl    2;  .type   32; .endef
.def    __Unwind_SjLj_Resume;   .scl    2;  .type   32; .endef

MinGW-4.8.1-x86-posix-dwarf:

.def    ___gxx_personality_v0;  .scl    2;  .type   32; .endef
.def    __Unwind_Resume;    .scl    2;  .type   32; .endef

MinGW-4.8.1-x64-win32-sjlj:

.def    __gxx_personality_sj0;  .scl    2;  .type   32; .endef
.def    _Unwind_SjLj_Register;  .scl    2;  .type   32; .endef
.def    _Unwind_SjLj_Unregister;    .scl    2;  .type   32; .endef
.def    _Unwind_SjLj_Resume;    .scl    2;  .type   32; .endef

MinGW-4.8.1-x64-posix-seh:

.def    __gxx_personality_seh0; .scl    2;  .type   32; .endef
.def    _Unwind_Resume; .scl    2;  .type   32; .endef

MinGW-4.8.1-x64-posix-sjlj:

.def    __gxx_personality_sj0;  .scl    2;  .type   32; .endef
.def    _Unwind_SjLj_Register;  .scl    2;  .type   32; .endef
.def    _Unwind_SjLj_Unregister;    .scl    2;  .type   32; .endef
.def    _Unwind_SjLj_Resume;    .scl    2;  .type   32; .endef

FC17-g++-4.7.2-x64:

.cfi_personality 0x3,__gxx_personality_v0
.globl  __gxx_personality_v0
call    _Unwind_Resume

Looks like we should search for __gxx_personality_([a-z])(0-9]+) and then compare the first capture group to:

  • v = dwarf
  • seh = seh
  • sj = sjlj


Answered By - Matt Clarkson
Answer Checked By - David Goodson (WPSolving Volunteer)
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