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ARM: net: bpf: imm12 constant conversion 

Provide a version of the imm8m() function that the compiler can optimise
when used with a constant expression.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Russell King 2018-07-11 10:32:07 +01:00 committed by Daniel Borkmann
parent 96cced4e77
commit 1ca3b17b77
1 changed files with 49 additions and 1 deletions
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50
arch/arm/net/bpf_jit_32.c
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@ -236,10 +236,56 @@ static inline void emit(u32 inst, struct jit_ctx *ctx)
_emit(ARM_COND_AL, inst, ctx);
}
/*
* This is rather horrid, but necessary to convert an integer constant
* to an immediate operand for the opcodes, and be able to detect at
* build time whether the constant can't be converted (iow, usable in
* BUILD_BUG_ON()).
*/
#define imm12val(v, s) (rol32(v, (s)) | (s) << 7)
#define const_imm8m(x) \
({ int r; \
u32 v = (x); \
if (!(v & ~0x000000ff)) \
r = imm12val(v, 0); \
else if (!(v & ~0xc000003f)) \
r = imm12val(v, 2); \
else if (!(v & ~0xf000000f)) \
r = imm12val(v, 4); \
else if (!(v & ~0xfc000003)) \
r = imm12val(v, 6); \
else if (!(v & ~0xff000000)) \
r = imm12val(v, 8); \
else if (!(v & ~0x3fc00000)) \
r = imm12val(v, 10); \
else if (!(v & ~0x0ff00000)) \
r = imm12val(v, 12); \
else if (!(v & ~0x03fc0000)) \
r = imm12val(v, 14); \
else if (!(v & ~0x00ff0000)) \
r = imm12val(v, 16); \
else if (!(v & ~0x003fc000)) \
r = imm12val(v, 18); \
else if (!(v & ~0x000ff000)) \
r = imm12val(v, 20); \
else if (!(v & ~0x0003fc00)) \
r = imm12val(v, 22); \
else if (!(v & ~0x0000ff00)) \
r = imm12val(v, 24); \
else if (!(v & ~0x00003fc0)) \
r = imm12val(v, 26); \
else if (!(v & ~0x00000ff0)) \
r = imm12val(v, 28); \
else if (!(v & ~0x000003fc)) \
r = imm12val(v, 30); \
else \
r = -1; \
r; })
/*
* Checks if immediate value can be converted to imm12(12 bits) value.
*/
static int16_t imm8m(u32 x)
static int imm8m(u32 x)
{
u32 rot;
@ -249,6 +295,8 @@ static int16_t imm8m(u32 x)
return -1;
}
#define imm8m(x) (__builtin_constant_p(x) ? const_imm8m(x) : imm8m(x))
static u32 arm_bpf_ldst_imm12(u32 op, u8 rt, u8 rn, s16 imm12)
{
op |= rt << 12 | rn << 16;