On Wed, Jul 31, 2024 at 11:34:13PM +0200, Alice Ryhl wrote:
> > Please work harder to not have to duplicate stuff like this.
>
> I really didn't want to duplicate it, but it's very hard to find a
> performant alternative. Is there any way we could accept duplication
> only in the cases where an 'i' parameter is used? I don't have the
> choice of using a Rust helper for 'i' parameters.
>
> Perhaps one option could be to put the Rust code inside jump_label.h
> and have the header file evaluate to either C or Rust depending on the
> value of some #ifdefs?
>
> #ifndef RUST_ASM
> /* existing C code goes here */
> #endif
> #ifdef RUST_ASM
> // rust code goes here
> #endif
>
> That way the duplication is all in a single file. It would also avoid
> the need for duplicating the nop5 string, as the Rust case is still
> going through the C preprocessor and can use the existing #define.
I suppose that is slightly better, but ideally you generate the whole of
the Rust thing from the C version. After all, Clang can already parse
this.
That said, with the below patch, I think you should be able to reuse the
JUMP_TABLE_ENTRY macro like:
JUMP_TABLE_ENTRY({0}, {1}, {2} + {3})
> I'm also open to other alternatives. But I don't have infinite
> resources to drive major language changes.
Yes, well, you all picked this terrible language full well knowing it
hated C/C++ and had not a single effort put into integration with
existing code bases.
I find it very hard to care for the problems you've created for
yourself.
---
diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
index cbbef32517f0..6cff7bf5e779 100644
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -12,12 +12,12 @@
#include <linux/stringify.h>
#include <linux/types.h>
-#define JUMP_TABLE_ENTRY \
- ".pushsection __jump_table, \"aw\" \n\t" \
- _ASM_ALIGN "\n\t" \
- ".long 1b - . \n\t" \
- ".long %l[l_yes] - . \n\t" \
- _ASM_PTR "%c0 + %c1 - .\n\t" \
+#define JUMP_TABLE_ENTRY(l_yes, key, branch) \
+ ".pushsection __jump_table, \"aw\" \n\t" \
+ _ASM_ALIGN "\n\t" \
+ ".long 1b - . \n\t" \
+ ".long " __stringify(l_yes) "- . \n\t" \
+ _ASM_PTR " " __stringify(key) " + " __stringify(branch) " - . \n\t" \
".popsection \n\t"
#ifdef CONFIG_HAVE_JUMP_LABEL_HACK
@@ -26,7 +26,7 @@ static __always_inline bool arch_static_branch(struct static_key *key, bool bran
{
asm goto("1:"
"jmp %l[l_yes] # objtool NOPs this \n\t"
- JUMP_TABLE_ENTRY
+ JUMP_TABLE_ENTRY(%[l_yes], %c0, %c1)
: : "i" (key), "i" (2 | branch) : : l_yes);
return false;
@@ -40,7 +40,7 @@ static __always_inline bool arch_static_branch(struct static_key * const key, co
{
asm goto("1:"
".byte " __stringify(BYTES_NOP5) "\n\t"
- JUMP_TABLE_ENTRY
+ JUMP_TABLE_ENTRY(%[l_yes], %c0, %c1)
: : "i" (key), "i" (branch) : : l_yes);
return false;
@@ -54,7 +54,7 @@ static __always_inline bool arch_static_branch_jump(struct static_key * const ke
{
asm goto("1:"
"jmp %l[l_yes]\n\t"
- JUMP_TABLE_ENTRY
+ JUMP_TABLE_ENTRY(%[l_yes], %c0, %c1)
: : "i" (key), "i" (branch) : : l_yes);
return false;
