Hi Steven, On Tue, Jan 07, 2025 at 08:32:14AM -0500, Steven Rostedt wrote: > From: Steven Rostedt <rostedt@xxxxxxxxxxx> > > The mcount_loc section holds the addresses of the functions that get > patched by ftrace when enabling function callbacks. It can contain tens of > thousands of entries. These addresses must be sorted. If they are not > sorted at compile time, they are sorted at boot. Sorting at boot does take > some time and does have a small impact on boot overhead. > > x86 and arm32 have the addresses in the mcount_loc section of the ELF > file. But for arm64, the section just contains zeros. The .rela.dyn > Elf_Rela section holds the addresses and they get patched at boot during > the relocation phase. > > In order to sort these addresses, the Elf_Rela needs to be updated instead > of the location in the binary that holds the mcount_loc section. Have the > sorttable code, allocate an array to hold the function addresses, load the > addresses from the Elf_Rela entries, sort them, then put them back in > order into the Elf_rela entries so that they will be sorted at boot up > without having to sort them during boot up. > > Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx> > --- > > Note, this is based on top of my sorttable clean up code: > > https://lore.kernel.org/linux-trace-kernel/20250105162211.971039541@xxxxxxxxxxx/ > git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git sorttable/for-next > > I tested this on a arm64 VM (running on x86 host), with > CONFIG_FTRACE_SORT_STARTUP_TEST enabled, which verifies the mcount entries > are sorted at boot up. > > I wonder if this will also work for s390? But I do not know s390 Elf layout. Thanks for the hint! We look into this, but it might take some time.
