On Sun, 7 Mar 2021 13:31:11 +0100 Pali Rohár <p...@kernel.org> wrote:
> On Sunday 07 March 2021 13:26:36 Marek Behun wrote: > > On Sun, 7 Mar 2021 06:02:16 +0100 > > Marek Vasut <ma...@denx.de> wrote: > > > > > On 3/7/21 5:58 AM, Marek Behun wrote: > > > > On Sun, 7 Mar 2021 05:46:24 +0100 > > > > Marek Vasut <ma...@denx.de> wrote: > > > > > > > >> On 3/7/21 5:25 AM, Marek Behún wrote: > > > >>> When compiling with LTO, the compiler fails with an error saying that > > > >>> `crc_table` causes a section type conflict with `efi_var_buf`. > > > >>> > > > >>> This is because both are declared to be in the same section (via macro > > > >>> `__efi_runtime_data`), but one is const while the other is not. > > > >>> > > > >>> Make this variable non-const in order to fix this. > > > >> > > > >> This does not look right, the crc32 array is constant. > > > >> Maybe what you want to do instead if create some __efi_constant_data > > > >> section ? > > > > > > > > Yes, this was the easier solution, and maybe is not ideal. > > > > > > > > I thought it would not be much of a problem since this array can be > > > > nonconstant (generated after boot) if CONFIG_DYNAMIC_CRC_TABLE is > > > > enabled. > > > > > > > > Anyway I don't much understand the EFI code so I wanted to poke into it > > > > as little as possible. > > > > > > Isn't the compiler capable of better optimization on constant stuff ? > > > That's pretty much what prompted my suggestion to add separate section. > > > > Yes, but > > - for this case I don't think the compiler actually can do any > > significat optimizations when declaring the table const, since it has > > to access > > tab[(crc ^ (x)) & 255] > > I tried with arm compiler just now, with -O2 and -Os, and it > > generated the same code either way > > - when using LTO, the compiler theoretically should be able to deduce > > that the table is never written to > > > > But if people insist on declaring the table const, I will look into > > this... > > If you try to overwrite a const variable from the same code unit then > compiler throw an error. So declaring read-only variable as a const > could prevent people to unintentionally overwrite read-only variable. > And detect possible bad code. OK it seems all linker scripts also mention .rodata.efi_runtime*, not just .data.efi_runtime*. I shall put it into the .rodata.efi_runtime section. Marek
