search

seL4 / microkit

Microkit - A simple operating system framework for the seL4 microkernel
Other
70 stars 37 forks source link

Omit assembler debug level to improve toolchain compatability #79

Closed nspin closed 7 months ago

nspin commented 8 months ago

More recent versions of aarch64-none-elf-as don't support passing a debug level to -g.

Specifically, GNU Binutils 2.40 (associated with GCC 12.3) doesn't support this.

Ivan-Velickovic commented 8 months ago

I guess the reason we pin a specific version of the toolchain is to avoid issues like this.

I'm not hesitant to upgrade the toolchain version if there's some specific reason for it, but the README does mention a specific toolchain version for a reason.

nspin commented 8 months ago

I noticed that the debug level parameter to -g in as is undocumented even in Binutils 2.35.1, the version included in the toolchain pinned in the Microkit README, which accepts the paramter. I took a quick look at as.c in Binutils 2.35.1 and Binutils 2.40, the version I was using that does not accept that parameter, along with the commit responsible for this change, which confirmed my suspicion that the debug level parameter doesn't actually do anything in the as version that does accept it.

So, there is no cost to dropping the debug level parameter to -g.

Ivan-Velickovic commented 8 months ago

I noticed that the debug level parameter to -g in as is undocumented even in Binutils 2.35.1, the version included in the toolchain pinned in the Microkit README, which accepts the paramter. I took a quick look at as.c in Binutils 2.35.1 and Binutils 2.40, the version I was using that does not accept that parameter, along with the commit responsible for this change, which confirmed my suspicion that the debug level parameter doesn't actually do anything in the as version that does accept it.

So, there is no cost to dropping the debug level parameter to -g.

Thanks for looking into it, I have come across this issue before and I did find documentation on it here https://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html (search for -glevel).

I know that the toolchain provided by ARM for GCC 12 and above does not allow specifying the level and for adding macOS support to the SDK we would need to upgrade the toolchain version anyways as the macOS ARM64 host toolchain is only available for 12 and above.

This kind of inconsistency between C compilers is quite... annoying. What I might do is take your patch and see if the hash of all the ELFs is the same, that way we'll know if specifying the level is doing anything.

nspin commented 8 months ago

GCC supports a debug level parameter, but the issue here is the assembler ($(TOOLCHAIN)-as) not supporting it.

Ivan-Velickovic commented 8 months ago

Ah my bad, I thought you were removing -g3 from GCC as well. Apologies.

Ivan-Velickovic commented 7 months ago

No difference in the binaries. Merged in this case because we don't have to do any special handling to get both the ARM provided toolchain and the Nix ARM toolchain working and I want to upgrade to GCC 12 soon anyways for macOS support.