[Question] What is the .bolt.org.text segment used for?

[zbetter]

Hi,

I noticed that the .bolt.org.text segment takes up half of the binary size, but the content of the .bolt.org.text segment already has an optimized edition in the .text and .text.cold segments. I tried to get rid of the .bolt.org.text segment with llvm-objcopy, but the binary won't run.. So what is the .bolt.org.text segment mainly used for?

Thanks!

[zbetter]

I tested a small test case and found that the .bolt.org.text section was consistent with the pre-optimized .text section, and the new .text section and the .text.cold section were not empty. But after I deleted the .text section, the program worked well. I don't know why.

[maksfb]

The answer depends on how you build the application and what BOLT flags you use. If you run in relocation mode (link with --emit-relocs), then .bolt.org.text wouldn't be used unless you also specify -lite. You can also add --use-old-text BOLT flag that will reuse the original section for the optimized code.

[getianao]

Hi, @maksfb. I have a similar question. Why not just remove .bolt.org.text segment if it won't be used. It can reduce the generated binary size.

[maksfb]

It should be possible to remove .bolt.org.text, but then to make the use of the created gap we would have to break the containing segment into two.