leandrof/linux
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

ARM: assembler: add optimized ldr/str macros to load variables from memory

Browse Source 
We will be adding variable loads to various hot paths, so it makes sense
to add a helper macro that can load variables from asm code without the
use of literal pool entries. On v7 or later, we can simply use MOVW/MOVT
pairs, but on earlier cores, this requires a bit of hackery to emit a
instruction sequence that implements this using a sequence of ADD/LDR
instructions.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Tested-by: Marc Zyngier <maz@kernel.org>
Tested-by: Vladimir Murzin <vladimir.murzin@arm.com> # ARMv7M
This commit is contained in:
Ard Biesheuvel
2021-11-26 19:37:27 +01:00
parent 1fa8c4b195
commit 4e918ab13e
3 changed files with 43 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

45
arch/arm/include/asm/assembler.h
View File

@@ -568,12 +568,12 @@ THUMB( orr \reg , \reg , #PSR_T_BIT )
/*
* mov_l - move a constant value or [relocated] address into a register
*/
.macro mov_l, dst:req, imm:req
.macro mov_l, dst:req, imm:req, cond
.if __LINUX_ARM_ARCH__ < 7
ldr \dst, =\imm
ldr\cond \dst, =\imm
.else
movw \dst, #:lower16:\imm
movt \dst, #:upper16:\imm
movw\cond \dst, #:lower16:\imm
movt\cond \dst, #:upper16:\imm
.endif
.endm
@@ -611,6 +611,43 @@ THUMB( orr \reg , \reg , #PSR_T_BIT )
__adldst_l str, \src, \sym, \tmp, \cond
.endm
.macro __ldst_va, op, reg, tmp, sym, cond
#if __LINUX_ARM_ARCH__ >= 7 || \
(defined(MODULE) && defined(CONFIG_ARM_MODULE_PLTS)) || \
(defined(CONFIG_LD_IS_LLD) && CONFIG_LLD_VERSION < 140000)
mov_l \tmp, \sym, \cond
\op\cond \reg, [\tmp]
#else
/*
* Avoid a literal load, by emitting a sequence of ADD/LDR instructions
* with the appropriate relocations. The combined sequence has a range
* of -/+ 256 MiB, which should be sufficient for the core kernel and
* for modules loaded into the module region.
*/
.globl \sym
.reloc .L0_\@, R_ARM_ALU_PC_G0_NC, \sym
.reloc .L1_\@, R_ARM_ALU_PC_G1_NC, \sym
.reloc .L2_\@, R_ARM_LDR_PC_G2, \sym
.L0_\@: sub\cond \tmp, pc, #8
.L1_\@: sub\cond \tmp, \tmp, #4
.L2_\@: \op\cond \reg, [\tmp, #0]
#endif
.endm
/*
* ldr_va - load a 32-bit word from the virtual address of \sym
*/
.macro ldr_va, rd:req, sym:req, cond
__ldst_va ldr, \rd, \rd, \sym, \cond
.endm
/*
* str_va - store a 32-bit word to the virtual address of \sym
*/
.macro str_va, rn:req, sym:req, tmp:req, cond
__ldst_va str, \rn, \tmp, \sym, \cond
.endm
/*
* rev_l - byte-swap a 32-bit value
*