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Date: Tue, 17 Apr 2012 21:57:16 +0200
From: Sam Ravnborg <sam@...nborg.org>
To: David Miller <davem@...emloft.net>
Cc: netdev@...r.kernel.org, sparclinux@...r.kernel.org
Subject: Re: [PATCH] net: filter: Just In Time compiler for sparc
Hi David.
I am glad to see sparc32 covered as well as sparc64 - but you knew that.
A few nits below.
I did not find the time to walk through it so I understood
the functionality. But I guess netdev's will do so.
I hope you had some fun doing this work - it does not look simple!
Sam
> diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
> index db4e821..9f9afd9 100644
> --- a/arch/sparc/Kconfig
> +++ b/arch/sparc/Kconfig
> @@ -30,6 +30,7 @@ config SPARC
> select USE_GENERIC_SMP_HELPERS if SMP
> select GENERIC_PCI_IOMAP
> select HAVE_NMI_WATCHDOG if SPARC64
> + select HAVE_BPF_JIT
If we sorted this block of select then the chances
for merge conflict would be smaller.
But this is not this patch to do so.
> +#define r_TMP G1
> +#define r_TMP2 G2
> +#define r_OFF G3
> +#else
> +#define r_SKB %o0
> +#define r_A %o1
> +#define r_X %o2
> +#define r_saved_O7 %o3
> +#define r_HEADLEN %o4
> +#define r_SKB_DATA %o5
> +#define r_TMP %g1
> +#define r_TMP2 %g2
> +#define r_OFF %g3
> +#endif
Nice helpers - they made it easier for me to follow the assembler.
r_SKB is not used in assembler?
> +++ b/arch/sparc/net/bpf_jit_asm.S
> @@ -0,0 +1,199 @@
> +#include <asm/ptrace.h>
> +
> +#include "bpf_jit.h"
> +
> +#ifdef CONFIG_SPARC64
> +#define SAVE_SZ 176
> +#define SCRATCH_OFF STACK_BIAS + 128
> +#define BE_PTR(label) be,pn %xcc, label
> +#else
> +#define SAVE_SZ 96
> +#define SCRATCH_OFF 72
> +#define BE_PTR(label) be label
> +#endif
Is it coincidentally that SAVE_SZ has same value as BASE_STACKFRAME?
>From my quick browse of the code I think this is two distinct things,
but if not we should move the definition to the header file and use the same.
> +bpf_error:
> + jmpl r_saved_O7 + 8, %g0
> + clr %o0
I wondered about this - because this is the only reference to %03 aka r_saved_O7
And then the + 8 also puzzeled me.
A small comment would be nice.
> diff --git a/arch/sparc/net/bpf_jit_comp.c b/arch/sparc/net/bpf_jit_comp.c
> new file mode 100644
> index 0000000..86349ca
> --- /dev/null
> +++ b/arch/sparc/net/bpf_jit_comp.c
> @@ -0,0 +1,785 @@
> +#include <linux/moduleloader.h>
> +#include <linux/workqueue.h>
> +#include <linux/netdevice.h>
> +#include <linux/filter.h>
> +#include <linux/cache.h>
> +
> +#include <asm/cacheflush.h>
> +#include <asm/ptrace.h>
> +
> +#include "bpf_jit.h"
> +
> +int bpf_jit_enable __read_mostly;
> +
> +/* assembly code in arch/sparc/net/bpf_jit_asm.S */
> +extern u32 bpf_jit_load_word[];
> +extern u32 bpf_jit_load_half[];
> +extern u32 bpf_jit_load_byte[];
> +extern u32 bpf_jit_load_byte_msh[];
> +extern u32 bpf_jit_load_word_positive_offset[];
> +extern u32 bpf_jit_load_half_positive_offset[];
> +extern u32 bpf_jit_load_byte_positive_offset[];
> +extern u32 bpf_jit_load_byte_msh_positive_offset[];
> +extern u32 bpf_jit_load_word_negative_offset[];
> +extern u32 bpf_jit_load_half_negative_offset[];
> +extern u32 bpf_jit_load_byte_negative_offset[];
> +extern u32 bpf_jit_load_byte_msh_negative_offset[];
I know this is from assembler files - but I hate externs in .c files.
sparse did not complain though.
> +#define CONDN COND (0x0)
> +#define CONDE COND (0x1)
> +#define CONDLE COND (0x2)
> +#define CONDL COND (0x3)
> +#define CONDLEU COND (0x4)
> +#define CONDCS COND (0x5)
> +#define CONDNEG COND (0x6)
> +#define CONDVC COND (0x7)
> +#define CONDA COND (0x8)
> +#define CONDNE COND (0x9)
> +#define CONDG COND (0xa)
> +#define CONDGE COND (0xb)
> +#define CONDGU COND (0xc)
> +#define CONDCC COND (0xd)
> +#define CONDPOS COND (0xe)
> +#define CONDVS COND (0xf)
The added space between COND and (0x..) looks strange to me.
> +} while (0)
> +
> + /* Emit
> + *
> + * OP r_A, r_X, r_A
> + */
My vim marks the mixed spaces/tabs before OP with red.
> +do { \
Mixed spaces and tabs (vim is again red here)
> + if (K) { \
> + unsigned int _insn = OPCODE; \
> + _insn |= RS1(r_A) | RD(r_A); \
> + if (is_simm13(K)) { \
> + *prog++ = _insn | IMMED | S13(K); \
> + } else { \
> + emit_set_const(K, r_TMP); \
> + *prog++ = _insn | RS2(r_TMP); \
> + } \
Mixed spaces and tabs.
> +#define emit_loadptr(BASE, STRUCT, FIELD, DEST) \
> +do { unsigned int _off = offsetof(STRUCT, FIELD); \
> + BUILD_BUG_ON(FIELD_SIZEOF(STRUCT, FIELD) != sizeof(void *)); \
> + *prog++ = LDPTRI | RS1(BASE) | S13(_off) | RD(DEST); \
> +} while(0)
^
Missing space. Repeats in the following macros.
> #define emit_read_y(REG) *prog++ = RD_Y | RD(REG);
> #define emit_write_y(REG) *prog++ = WR_Y | IMMED | RS1(REG) | S13(0);
Mixed spaces and tabs, (The above is pasted).
> + proglen = 0;
> + prog = temp;
> +
> + /* Prologue */
> + if (seen_or_pass0) {
> + if (seen_or_pass0 & SEEN_MEM) {
> + unsigned int sz = BASE_STACKFRAME;
> + sz += BPF_MEMWORDS * sizeof(u32);
> + emit_alloc_stack(sz);
> + }
> +
> + /* Make sure we dont leek kernel memory. */
> + if (seen_or_pass0 & SEEN_XREG)
> + emit_clear(r_X);
> +
> + /* If this filter needs to access skb data,
> + * load %o4 and %o4 with:
> + * %o4 = skb->len - skb->data_len
> + * %o5 = skb->data
We have nice menonics for o4 and o5 (r_HEADLEN, r_SKB_DATA),
but I assume you follow the registers easier.
> + * And also back up %o7 into r_saved_O7 so we can
> + * invoke the stubs using 'call'.
> + */
> + if (seen_or_pass0 & SEEN_DATAREF) {
> + emit_load32(r_SKB, struct sk_buff, len, r_HEADLEN);
> + emit_load32(r_SKB, struct sk_buff, data_len, r_TMP);
> + emit_sub(r_HEADLEN, r_TMP, r_HEADLEN);
> + emit_loadptr(r_SKB, struct sk_buff, data, r_SKB_DATA);
> + }
> + }
> + emit_reg_move(O7, r_saved_O7);
I want to say that I have seen this use of saved_O7 - but it did not help me.
> +#ifdef CONFIG_SPARC32
> + emit_branch(BE, t_offset + 20);
> +#else
> + emit_branch(BE, t_offset + 8);
> +#endif
What are these magic 8 and 20?
> + emit_nop(); /* delay slot */
> + } else {
> + emit_branch_off(BNE, 16);
> + emit_nop();
> +#ifdef CONFIG_SPARC32
> + emit_jump(cleanup_addr + 20);
> +#else
> + emit_jump(cleanup_addr + 8);
> +#endif
Here they are again.
> + emit_clear(r_A);
> + }
> + emit_write_y(G0);
> +#ifdef CONFIG_SPARC32
> + emit_nop();
> + emit_nop();
> + emit_nop();
> +#endif
Why these nops? Comment?
--
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