Mark Rutland <mark.rutl...@arm.com> writes:
> On Thu, Jan 27, 2022 at 07:46:01AM -0500, Steven Rostedt wrote:
>> On Thu, 27 Jan 2022 12:27:04 +0000
>> Mark Rutland <mark.rutl...@arm.com> wrote:
>>
>> > Ah, so those non-ELF relocations for the mcount_loc table just mean "apply
>> > the
>> > KASLR offset here", which is equivalent for all entries.
>> >
>> > That makes sense, thanks!
>>
>> And this is why we were having such a hard time understanding each other ;-)
>
> ;)
>
> With that in mind, I think that we understand that the build-time sort works
> for:
>
> * arch/x86, becuase the non-ELF relocations for mcount_loc happen to be
> equivalent.
>
> * arch/arm, because there's no dynamic relocaiton and the mcount_loc entries
> have been finalized prior to sorting.
>
> ... but doesn't work for anyone else (including arm64) because the ELF
> relocations are not equivalent, and need special care that is not yet
> implemented.
For s390 my idea is to just skip the addresses between __start_mcount_loc
and __stop_mcount_loc, because for these addresses we know that they are
64 bits wide, so we just need to add the KASLR offset.
I'm thinking about something like this:
diff --git a/arch/s390/boot/compressed/decompressor.h
b/arch/s390/boot/compressed/decompressor.h
index f75cc31a77dd..015d7e2e94ef 100644
--- a/arch/s390/boot/compressed/decompressor.h
+++ b/arch/s390/boot/compressed/decompressor.h
@@ -25,6 +25,8 @@ struct vmlinux_info {
unsigned long rela_dyn_start;
unsigned long rela_dyn_end;
unsigned long amode31_size;
+ unsigned long start_mcount_loc;
+ unsigned long stop_mcount_loc;
};
/* Symbols defined by linker scripts */
diff --git a/arch/s390/boot/startup.c b/arch/s390/boot/startup.c
index 1aa11a8f57dd..7bb0d88db5c6 100644
--- a/arch/s390/boot/startup.c
+++ b/arch/s390/boot/startup.c
@@ -88,6 +88,11 @@ static void handle_relocs(unsigned long offset)
dynsym = (Elf64_Sym *) vmlinux.dynsym_start;
for (rela = rela_start; rela < rela_end; rela++) {
loc = rela->r_offset + offset;
+ if ((loc >= vmlinux.start_mcount_loc) &&
+ (loc < vmlinux.stop_mcount_loc)) {
+ (*(unsigned long *)loc) += offset;
+ continue;
+ }
val = rela->r_addend;
r_sym = ELF64_R_SYM(rela->r_info);
if (r_sym) {
@@ -232,6 +237,8 @@ static void offset_vmlinux_info(unsigned long offset)
vmlinux.rela_dyn_start += offset;
vmlinux.rela_dyn_end += offset;
vmlinux.dynsym_start += offset;
+ vmlinux.start_mcount_loc += offset;
+ vmlinux.stop_mcount_loc += offset;
}
static unsigned long reserve_amode31(unsigned long safe_addr)
diff --git a/arch/s390/kernel/vmlinux.lds.S b/arch/s390/kernel/vmlinux.lds.S
index 42c43521878f..51c773405608 100644
--- a/arch/s390/kernel/vmlinux.lds.S
+++ b/arch/s390/kernel/vmlinux.lds.S
@@ -213,6 +213,8 @@ SECTIONS
QUAD(__rela_dyn_start) /*
rela_dyn_start */
QUAD(__rela_dyn_end) /* rela_dyn_end
*/
QUAD(_eamode31 - _samode31) /* amode31_size
*/
+ QUAD(__start_mcount_loc)
+ QUAD(__stop_mcount_loc)
} :NONE
/* Debugging sections. */
Not sure whether that would also work on power, and also not sure
whether i missed something thinking about that. Maybe it doesn't even
work. ;-)
