-mmacosx-version-min influences packing behaviour with bitfields?
I'm seeing an odd behaviour where my bitfields are ended up in the padding:
struct Test
unsigned short a : 1;
unsigned short b : 15;
;
when compiled with -mmacosx-version-min=10.11 (or greater) in clang (tested 4.0.1 and Apple's 10.0.0), I get in https://github.com/arvidn/struct_layout:
struct ::Test [2 Bytes]
--- 2 Bytes padding ---
with -mmacosx-version-min=10.10 (or lower) I get:
struct ::Test [2 Bytes]
0: [unsigned short : 2] a -- cache-line 0
0: [unsigned short : 2] b
Anyone have any ideas what standard or rule I've violated?
Thanks!
c++ macos clang
asked Nov 13 '18 at 22:24
stevechanstevechan
163
add a comment |
I'm seeing an odd behaviour where my bitfields are ended up in the padding:
struct Test
unsigned short a : 1;
unsigned short b : 15;
;
when compiled with -mmacosx-version-min=10.11 (or greater) in clang (tested 4.0.1 and Apple's 10.0.0), I get in https://github.com/arvidn/struct_layout:
struct ::Test [2 Bytes]
--- 2 Bytes padding ---
with -mmacosx-version-min=10.10 (or lower) I get:
struct ::Test [2 Bytes]
0: [unsigned short : 2] a -- cache-line 0
0: [unsigned short : 2] b
Anyone have any ideas what standard or rule I've violated?
Thanks!
c++ macos clang
asked Nov 13 '18 at 22:24
stevechanstevechan
163
add a comment |
I'm seeing an odd behaviour where my bitfields are ended up in the padding:
struct Test
unsigned short a : 1;
unsigned short b : 15;
;
when compiled with -mmacosx-version-min=10.11 (or greater) in clang (tested 4.0.1 and Apple's 10.0.0), I get in https://github.com/arvidn/struct_layout:
struct ::Test [2 Bytes]
--- 2 Bytes padding ---
with -mmacosx-version-min=10.10 (or lower) I get:
struct ::Test [2 Bytes]
0: [unsigned short : 2] a -- cache-line 0
0: [unsigned short : 2] b
Anyone have any ideas what standard or rule I've violated?
Thanks!
c++ macos clang
asked Nov 13 '18 at 22:24
stevechanstevechan
163
I'm seeing an odd behaviour where my bitfields are ended up in the padding:
struct Test
unsigned short a : 1;
unsigned short b : 15;
;
when compiled with -mmacosx-version-min=10.11 (or greater) in clang (tested 4.0.1 and Apple's 10.0.0), I get in https://github.com/arvidn/struct_layout:
struct ::Test [2 Bytes]
--- 2 Bytes padding ---
with -mmacosx-version-min=10.10 (or lower) I get:
struct ::Test [2 Bytes]
0: [unsigned short : 2] a -- cache-line 0
0: [unsigned short : 2] b
Anyone have any ideas what standard or rule I've violated?
Thanks!
c++ macos clang
c++ macos clang
asked Nov 13 '18 at 22:24
stevechanstevechan
163
asked Nov 13 '18 at 22:24
stevechanstevechan
163
edited Nov 13 '18 at 22:42
stevechan
asked Nov 13 '18 at 22:24
stevechanstevechan
163
asked Nov 13 '18 at 22:24
stevechanstevechan
163
asked Nov 13 '18 at 22:24
stevechanstevechan
163
163
add a comment |
add a comment |
1 Answer
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It seems that the struct_layout tool you're using relies on DWARF debugging information. The differences you're seeing do not reflect a difference in data layout, only in the available debugging info.
Using -mmacosx-version-min=10.10 limits the version of DWARF used to version 2, because that's all that macOS 10.10's tools will understand. I expect that you would get similar results by specifying -gdwarf-2.
answered Nov 14 '18 at 0:09
Ken ThomasesKen Thomases
69.9k669106
Thanks, LLDB from VS Code was giving me the same issues, but it's probably because due to an older version of it being packaged with its C++ extensions.
– stevechan
Nov 14 '18 at 2:22
add a comment |
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1 Answer
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1 Answer
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It seems that the struct_layout tool you're using relies on DWARF debugging information. The differences you're seeing do not reflect a difference in data layout, only in the available debugging info.
Using -mmacosx-version-min=10.10 limits the version of DWARF used to version 2, because that's all that macOS 10.10's tools will understand. I expect that you would get similar results by specifying -gdwarf-2.
answered Nov 14 '18 at 0:09
Ken ThomasesKen Thomases
69.9k669106
Thanks, LLDB from VS Code was giving me the same issues, but it's probably because due to an older version of it being packaged with its C++ extensions.
– stevechan
Nov 14 '18 at 2:22
add a comment |
It seems that the struct_layout tool you're using relies on DWARF debugging information. The differences you're seeing do not reflect a difference in data layout, only in the available debugging info.
Using -mmacosx-version-min=10.10 limits the version of DWARF used to version 2, because that's all that macOS 10.10's tools will understand. I expect that you would get similar results by specifying -gdwarf-2.
answered Nov 14 '18 at 0:09
Ken ThomasesKen Thomases
69.9k669106
Thanks, LLDB from VS Code was giving me the same issues, but it's probably because due to an older version of it being packaged with its C++ extensions.
– stevechan
Nov 14 '18 at 2:22
add a comment |
It seems that the struct_layout tool you're using relies on DWARF debugging information. The differences you're seeing do not reflect a difference in data layout, only in the available debugging info.
Using -mmacosx-version-min=10.10 limits the version of DWARF used to version 2, because that's all that macOS 10.10's tools will understand. I expect that you would get similar results by specifying -gdwarf-2.
answered Nov 14 '18 at 0:09
Ken ThomasesKen Thomases
69.9k669106
It seems that the struct_layout tool you're using relies on DWARF debugging information. The differences you're seeing do not reflect a difference in data layout, only in the available debugging info.
Using -mmacosx-version-min=10.10 limits the version of DWARF used to version 2, because that's all that macOS 10.10's tools will understand. I expect that you would get similar results by specifying -gdwarf-2.
answered Nov 14 '18 at 0:09
Ken ThomasesKen Thomases
69.9k669106
answered Nov 14 '18 at 0:09
Ken ThomasesKen Thomases
69.9k669106
answered Nov 14 '18 at 0:09
Ken ThomasesKen Thomases
69.9k669106
answered Nov 14 '18 at 0:09
Ken ThomasesKen Thomases
69.9k669106
69.9k669106
Thanks, LLDB from VS Code was giving me the same issues, but it's probably because due to an older version of it being packaged with its C++ extensions.
– stevechan
Nov 14 '18 at 2:22
add a comment |
Thanks, LLDB from VS Code was giving me the same issues, but it's probably because due to an older version of it being packaged with its C++ extensions.
– stevechan
Nov 14 '18 at 2:22
Thanks, LLDB from VS Code was giving me the same issues, but it's probably because due to an older version of it being packaged with its C++ extensions.
– stevechan
Nov 14 '18 at 2:22
Thanks, LLDB from VS Code was giving me the same issues, but it's probably because due to an older version of it being packaged with its C++ extensions.
– stevechan
Nov 14 '18 at 2:22
add a comment |
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