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parisc: Switch user access functions to signal errors in r29 instead of r8

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Use register r29 instead of register r8 to signal faults when accessing
user memory. In case of faults, the fixup routine will store -EFAULT in
this register.

This change saves up to 752 bytes on a 32bit kernel, partly because the
compiler doesn't need to save and restore the old r8 value on the stack.

bloat-o-meter results for usage with r29 register:
add/remove: 0/0 grow/shrink: 23/86 up/down: 228/-980 (-752)

bloat-o-meter results for usage with r28 register:
add/remove: 0/0 grow/shrink: 28/83 up/down: 296/-956 (-660)

Signed-off-by: Helge Deller <deller@gmx.de>
This commit is contained in:
Helge Deller 2021-12-23 21:46:35 +01:00
parent 9e9d4b460f
commit 4b9d2a731c
2 changed files with 11 additions and 7 deletions
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12
arch/parisc/include/asm/uaccess.h
View file

@ -53,15 +53,18 @@ struct exception_table_entry {
/*
* ASM_EXCEPTIONTABLE_ENTRY_EFAULT() creates a special exception table entry
* (with lowest bit set) for which the fault handler in fixup_exception() will
* load -EFAULT into %r8 for a read or write fault, and zeroes the target
* load -EFAULT into %r29 for a read or write fault, and zeroes the target
* register in case of a read fault in get_user().
*/
#define ASM_EXCEPTIONTABLE_REG 29
#define ASM_EXCEPTIONTABLE_VAR(__variable) \
register long __variable __asm__ ("r29") = 0
#define ASM_EXCEPTIONTABLE_ENTRY_EFAULT( fault_addr, except_addr )\
ASM_EXCEPTIONTABLE_ENTRY( fault_addr, except_addr + 1)
#define __get_user_internal(sr, val, ptr) \
({ \
register long __gu_err __asm__ ("r8") = 0; \
ASM_EXCEPTIONTABLE_VAR(__gu_err); \
\
switch (sizeof(*(ptr))) { \
case 1: __get_user_asm(sr, val, "ldb", ptr); break; \
@ -131,7 +134,7 @@ struct exception_table_entry {
#define __put_user_internal(sr, x, ptr) \
({ \
register long __pu_err __asm__ ("r8") = 0; \
ASM_EXCEPTIONTABLE_VAR(__pu_err); \
__typeof__(*(ptr)) __x = (__typeof__(*(ptr)))(x); \
\
switch (sizeof(*(ptr))) { \
@ -168,7 +171,8 @@ struct exception_table_entry {
* gcc knows about, so there are no aliasing issues. These macros must
* also be aware that fixups are executed in the context of the fault,
* and any registers used there must be listed as clobbers.
* r8 is already listed as err.
* The register holding the possible EFAULT error (ASM_EXCEPTIONTABLE_REG)
* is already listed as input and output register.
*/
#define __put_user_asm(sr, stx, x, ptr) \

6
arch/parisc/mm/fault.c
View file

@ -148,11 +148,11 @@ int fixup_exception(struct pt_regs *regs)
* Fix up get_user() and put_user().
* ASM_EXCEPTIONTABLE_ENTRY_EFAULT() sets the least-significant
* bit in the relative address of the fixup routine to indicate
* that %r8 should be loaded with -EFAULT to report a userspace
* access error.
* that gr[ASM_EXCEPTIONTABLE_REG] should be loaded with
* -EFAULT to report a userspace access error.
*/
if (fix->fixup & 1) {
regs->gr[8] = -EFAULT;
regs->gr[ASM_EXCEPTIONTABLE_REG] = -EFAULT;
/* zero target register for get_user() */
if (parisc_acctyp(0, regs->iir) == VM_READ) {