Using clang the following code:
```
__asm__ __volatile__ (
	".ifndef _.stapsdt.base\n"                                     \
	".pushsection .stapsdt.base,\"aG\",\"progbits\", .stapsdt.base, comdat\n" \
	".weak _.stapsdt.base\n"                                       \
	".hidden _.stapsdt.base\n"                                     \
	"_.stapsdt.base: .space 1\n"                                   \
	".size _.stapsdt.base,1\n"                                     \
	".popsection\n"                                                \
	".endif"
);
```
adds the allocated section to elf file:
```
$ clang source/sdt_expanded.c -ocsdt
$ readelf -x .stapsdt.base csdt

Hex dump of section '.stapsdt.base':
  0x000aa442 00                                  .

```
I translated this code to ldc:
```
__asm (
	.ifndef _.stapsdt.base
	.pushsection .stapsdt.base,\"aG\",\"progbits\", .stapsdt.base, comdat
	.weak _.stapsdt.base
	.hidden _.stapsdt.base
	_.stapsdt.base: .space 1
	.size _.stapsdt.base,1
	.popsection
	.endif`, ""
);
```
but ldc (1.18) do not add the section without any error.
```
$ dub --compiler=ldc2
$ readelf -x .stapsdt.base usdt
readelf: Warning: Section '.stapsdt.base' was not dumped because it does not exist!
```

If I make the section non allocated (removing `a` from \"aG\") then the section is added.
```
$ readelf -x .stapsdt.base usdt

Hex dump of section '.stapsdt.base':
  0x00000000 00                                  .
```
But this section needs to be allocated.

Is it a bug or I misuse something? Is there way to work around it?

On Tuesday, 5 November 2019 at 09:49:35 UTC, drug wrote:
> Is it a bug or I misuse something? Is there way to work around it?

I assume you're looking for module-level assembly, not contained in a function; that's what we lower DMD-style asm to, but isn't supported for __asm AFAIK.

Anyway, I recommend comparing the generated assembly by clang (`-S` IIRC) and LDC (-output-s) to figure out the difference.

On 11/5/19 2:13 PM, kinke wrote:
> On Tuesday, 5 November 2019 at 09:49:35 UTC, drug wrote:
>> Is it a bug or I misuse something? Is there way to work around it?
> 
> I assume you're looking for module-level assembly, not contained in a function; that's what we lower DMD-style asm to, but isn't supported for __asm AFAIK.
> 
> Anyway, I recommend comparing the generated assembly by clang (`-S` IIRC) and LDC (-output-s) to figure out the difference.

Thanks for hint! Output of clang and ldc is identical

clang:
```
  #NO_APP
  #APP
  .section	.stapsdt.base,"aG",@progbits,.stapsdt.base,comdat
  .weak	_.stapsdt.base
  .hidden	_.stapsdt.base
_.stapsdt.base:
  .zero	1
  .size	_.stapsdt.base, 1
  .text
```
ldc
```
  .section	.stapsdt.base,"aG",@progbits,.stapsdt.base,comdat
  .weak	_.stapsdt.base
  .hidden	_.stapsdt.base
_.stapsdt.base:
  .zero	1
  .size	_.stapsdt.base, 1
```

Moreover, if I remove 'a' from "aG" the section appears in the binary. So I guess the generated assembly is correct and the problem is in another place.
How can I compile .s file? I tried
```
clang app.s -L/path/to/ldc/lib/ -ldruntime-ldc -lphobos2-ldc -Wl,pie -o app2
```
but I get
```
app.s:33187:2: error: unknown section type
        .hidden DW.ref._d_eh_personality
```

On Tuesday, 5 November 2019 at 12:20:14 UTC, drug wrote:
> How can I compile .s file?

The .s file is just the textual representation of the .o object file, so compiling it shouldn't be necessary.

> So I guess the generated assembly is correct and the problem is in another place.

I'd look at the surrounding assembly as well, probably easiest when wrapping your inline asm in a trivial `extern(C++) void foo() { ... }` (no other functions, and using -betterC) for direct comparability with clang's output.

On 11/5/19 7:55 PM, kinke wrote:
> On Tuesday, 5 November 2019 at 12:20:14 UTC, drug wrote:
>> How can I compile .s file?
> 
> The .s file is just the textual representation of the .o object file, so compiling it shouldn't be necessary.

Ah, I see, thanks

> 
>> So I guess the generated assembly is correct and the problem is in another place.
> 
> I'd look at the surrounding assembly as well, probably easiest when wrapping your inline asm in a trivial `extern(C++) void foo() { ... }` (no other functions, and using -betterC) for direct comparability with clang's output.

I try to add support for SystemTap userland probes in D. They shall be `injectable` in any place in your source.
I took a look at the surrounding assembly and as I understood considering my low skill the problem was in this section definition:
```
.section	".linker-options","e",@llvm_linker_options
```
clang complained about the code after this line no matter what code it was. I read the documentation about section directive https://sourceware.org/binutils/docs/as/Section.html but didn't see anything wrong

On 11/5/19 7:55 PM, kinke wrote:
> On Tuesday, 5 November 2019 at 12:20:14 UTC, drug wrote:
>> How can I compile .s file?
> 
> The .s file is just the textual representation of the .o object file, so compiling it shouldn't be necessary.
> 
>> So I guess the generated assembly is correct and the problem is in another place.
> 
> I'd look at the surrounding assembly as well, probably easiest when wrapping your inline asm in a trivial `extern(C++) void foo() { ... }` (no other functions, and using -betterC) for direct comparability with clang's output.

I found that if I compile sources to object file by means of ldc2 and then link it using clang then the resulting binary has this section.
```
ldc2 source/app.d source/sdt.d -c -ofsdt.o
clang sdt.o -osdt
```
if I use ldc2 for everything:
```
ldc2 source/app.d source/sdt.d -of sdt
```
The resulting binary has no the section.

What can be the reason of this?

On Thursday, 7 November 2019 at 14:58:24 UTC, drug wrote:
> What can be the reason of this?

--gc-sections applied by LDC by default - use -disable-linker-strip-dead to keep unreferenced sections.

On 11/7/19 6:20 PM, kinke wrote:
> On Thursday, 7 November 2019 at 14:58:24 UTC, drug wrote:
>> What can be the reason of this?
> 
> --gc-sections applied by LDC by default - use -disable-linker-strip-dead to keep unreferenced sections.

Thank you very much! It works now.

What is the best way to create a reference to this section to prevent its stripping?

On 2019-11-08, drug wrote:
>On 11/7/19 6:20 PM, kinke wrote:
>>On Thursday, 7 November 2019 at 14:58:24 UTC, drug wrote:
>>>What can be the reason of this?
>>
>>--gc-sections applied by LDC by default - use -disable-linker-strip-dead to keep unreferenced sections.
>
>Thank you very much! It works now.
>
>What is the best way to create a reference to this section to prevent its stripping?

Use the .reloc directive and an R_*_NONE (no-op) relocation to reference
the section from a known-live section (e.g. main). As an example:

import ldc.llvmasm;

void foo() {
  __asm!void(
    `.pushsection .stapsdt.base,"aG",%progbits,.stapsdt.base,comdat
     .weak _.stapsdt.base
     .hidden _.stapsdt.base
     _.stapsdt.base: .space 1
     .size _.stapsdt.base,1
     .popsection`, ""
  );
}

void main() {
  __asm!void(".reloc 0, R_X86_64_NONE, .stapsdt.base", "");
}

This works with GNU ld, gold and lld, and it does not require
-disable-linker-strip-dead. Parsing R_*_NONE requires llvm 9 or newer.
I added .reloc for x86/ARM/AArch64/PowerPC in May 2019. R_MIPS_NONE
worked even before that time.