On Wed, 2022-10-05 at 16:32 +1100, Benjamin Gray wrote:
> Inserts a direct branch to the stub target when possible, replacing
> the
> mtctr/btctr sequence.
>
> The load into r12 could potentially be skipped too, but that change
> would need to refactor the arguments to indicate that the address
> does not have a separate local entry point.
>
> This helps the static call implementation, where modules calling
> their
> own trampolines are called through this stub and the trampoline is
> easily within range of a direct branch.
>
> Signed-off-by: Benjamin Gray <bg...@linux.ibm.com>
I'm not well versed in this code but nothing stands out as problematic
and it makes sense.
Reviewed-by: Andrew Donnellan <a...@linux.ibm.com>
> ---
> arch/powerpc/kernel/module_64.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/arch/powerpc/kernel/module_64.c
> b/arch/powerpc/kernel/module_64.c
> index 4d816f7785b4..13ce7a4d8a8d 100644
> --- a/arch/powerpc/kernel/module_64.c
> +++ b/arch/powerpc/kernel/module_64.c
> @@ -141,6 +141,12 @@ static u32 ppc64_stub_insns[] = {
> PPC_RAW_BCTR(),
> };
>
> +#ifdef CONFIG_PPC64_ELF_ABI_V1
> +#define PPC64_STUB_MTCTR_OFFSET 5
> +#else
> +#define PPC64_STUB_MTCTR_OFFSET 4
> +#endif
> +
> /* Count how many different 24-bit relocations (different symbol,
> different addend) */
> static unsigned int count_relocs(const Elf64_Rela *rela, unsigned
> int num)
> @@ -426,6 +432,7 @@ static inline int create_stub(const Elf64_Shdr
> *sechdrs,
> struct module *me,
> const char *name)
> {
> + int err;
> long reladdr;
> func_desc_t desc;
> int i;
> @@ -439,6 +446,11 @@ static inline int create_stub(const Elf64_Shdr
> *sechdrs,
> return 0;
> }
>
> + /* Replace indirect branch sequence with direct branch where
> possible */
> + err = patch_branch(&entry->jump[PPC64_STUB_MTCTR_OFFSET],
> addr, 0);
> + if (err && err != -ERANGE)
> + return 0;
> +
> /* Stub uses address relative to r2. */
> reladdr = (unsigned long)entry - my_r2(sechdrs, me);
> if (reladdr > 0x7FFFFFFF || reladdr < -(0x80000000L)) {
--
Andrew Donnellan OzLabs, ADL Canberra
a...@linux.ibm.com IBM Australia Limited
