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s390/current: Implement current with inline assembly

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Implement current with an inline assembly, which makes use of the
ALTERNATIVE macro, to read current from lowcore. Provide an alternative
instruction with a different offset in case lowcore is relocated.

This replaces sequences of two instructions with one instruction.

Before:
 100076:       a5 1e 00 00             llilh   %r1,0
 10007a:       e3 40 13 40 00 04       lg      %r4,832(%r1)

After:
 100076:       e3 10 03 40 00 04       lg      %r1,832

Kernel image size change:
add/remove: 3/17 grow/shrink: 166/2204 up/down: 7122/-24594 (-17472)

Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
This commit is contained in:
Heiko Carstens 2025-03-10 10:33:39 +01:00 committed by Vasily Gorbik
parent 430693c836
commit 65c07e91cc
1 changed files with 17 additions and 1 deletions
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18
arch/s390/include/asm/current.h
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@ -11,9 +11,25 @@
#define _S390_CURRENT_H
#include <asm/lowcore.h>
#include <asm/machine.h>
struct task_struct;
#define current ((struct task_struct *const)get_lowcore()->current_task)
static __always_inline struct task_struct *get_current(void)
{
unsigned long ptr, lc_current;
lc_current = offsetof(struct lowcore, current_task);
asm_inline(
ALTERNATIVE(" lg %[ptr],%[offzero](%%r0)\n",
" lg %[ptr],%[offalt](%%r0)\n",
ALT_FEATURE(MFEATURE_LOWCORE))
: [ptr] "=d" (ptr)
: [offzero] "i" (lc_current),
[offalt] "i" (lc_current + LOWCORE_ALT_ADDRESS));
return (struct task_struct *)ptr;
}
#define current get_current()
#endif /* !(_S390_CURRENT_H) */