| Message ID | 20201127175738.1085417-3-jackmanb@google.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | BPF |
| Headers | show |
| Series | Atomics for eBPF | expand |
| Context | Check | Description |
|---|---|---|
| netdev/cover_letter | success | Link |
| netdev/fixes_present | success | Link |
| netdev/patch_count | success | Link |
| netdev/tree_selection | success | Clearly marked for bpf-next |
| netdev/subject_prefix | success | Link |
| netdev/source_inline | success | Was 0 now: 0 |
| netdev/verify_signedoff | success | Link |
| netdev/module_param | success | Was 0 now: 0 |
| netdev/build_32bit | success | Errors and warnings before: 0 this patch: 0 |
| netdev/kdoc | success | Errors and warnings before: 0 this patch: 0 |
| netdev/verify_fixes | success | Link |
| netdev/checkpatch | warning | WARNING: line length of 81 exceeds 80 columns |
| netdev/build_allmodconfig_warn | success | Errors and warnings before: 3 this patch: 3 |
| netdev/header_inline | success | Link |
| netdev/stable | success | Stable not CCed |
On Fri, Nov 27, 2020 at 05:57:27PM +0000, Brendan Jackman wrote: > The JIT case for encoding atomic ops is about to get more > complicated. In order to make the review & resulting code easier, > let's factor out some shared helpers. > > Signed-off-by: Brendan Jackman <jackmanb@google.com> > --- > arch/x86/net/bpf_jit_comp.c | 39 ++++++++++++++++++++++--------------- > 1 file changed, 23 insertions(+), 16 deletions(-) > > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c > index 94b17bd30e00..a839c1a54276 100644 > --- a/arch/x86/net/bpf_jit_comp.c > +++ b/arch/x86/net/bpf_jit_comp.c > @@ -702,6 +702,21 @@ static void emit_modrm_dstoff(u8 **pprog, u32 r1, u32 r2, int off) > *pprog = prog; > } > > +/* > + * Emit a REX byte if it will be necessary to address these registers What is "REX byte" ? May be rename it to maybe_emit_mod() ? > + */ > +static void maybe_emit_rex(u8 **pprog, u32 reg_rm, u32 reg_reg, bool wide) could you please keep original names as dst_reg/src_reg instead of reg_rm/reg_reg ? reg_reg reads really odd and reg_rm is equally puzzling unless the reader studied intel's manual. I didn't. All these new abbreviations are challenging for me. > +{ > + u8 *prog = *pprog; > + int cnt = 0; > + > + if (wide) what is 'wide' ? Why not to call it 'bool is_alu64' ? > + EMIT1(add_2mod(0x48, reg_rm, reg_reg)); > + else if (is_ereg(reg_rm) || is_ereg(reg_reg)) > + EMIT1(add_2mod(0x40, reg_rm, reg_reg)); > + *pprog = prog; > +}
On Sat, Nov 28, 2020 at 05:14:05PM -0800, Alexei Starovoitov wrote: > On Fri, Nov 27, 2020 at 05:57:27PM +0000, Brendan Jackman wrote: > > The JIT case for encoding atomic ops is about to get more > > complicated. In order to make the review & resulting code easier, > > let's factor out some shared helpers. > > > > Signed-off-by: Brendan Jackman <jackmanb@google.com> > > --- > > arch/x86/net/bpf_jit_comp.c | 39 ++++++++++++++++++++++--------------- > > 1 file changed, 23 insertions(+), 16 deletions(-) > > > > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c > > index 94b17bd30e00..a839c1a54276 100644 > > --- a/arch/x86/net/bpf_jit_comp.c > > +++ b/arch/x86/net/bpf_jit_comp.c > > @@ -702,6 +702,21 @@ static void emit_modrm_dstoff(u8 **pprog, u32 r1, u32 r2, int off) > > *pprog = prog; > > } > > > > +/* > > + * Emit a REX byte if it will be necessary to address these registers > > What is "REX byte" ? > May be rename it to maybe_emit_mod() ? Er, this is the REX prefix as described in https://wiki.osdev.org/X86-64_Instruction_Encoding#REX_prefix Would maybe_emit_mod be accurate? In my mind "mod" is a field in the ModR/M byte which comes _after_ the opcode. Before developing this patchset I knew almost nothing about x86, so maybe I'm missing something about the general terminology? > > + */ > > +static void maybe_emit_rex(u8 **pprog, u32 reg_rm, u32 reg_reg, bool wide) > > could you please keep original names as dst_reg/src_reg instead of reg_rm/reg_reg ? > reg_reg reads really odd and reg_rm is equally puzzling unless the reader studied > intel's manual. I didn't. All these new abbreviations are challenging for me. OK. I originally changed it to use the x86 names because in theory you could do: maybe_emit_rex(&prog, src_reg, dst_reg); so the names would look backwards when you jump into the function implementation. > > +{ > > + u8 *prog = *pprog; > > + int cnt = 0; > > + > > + if (wide) > > what is 'wide' ? Why not to call it 'bool is_alu64' ? Ack - there's precedent in the file for 'is64' so I'll go with that.
On Tue, Dec 1, 2020 at 4:12 AM Brendan Jackman <jackmanb@google.com> wrote: > > On Sat, Nov 28, 2020 at 05:14:05PM -0800, Alexei Starovoitov wrote: > > On Fri, Nov 27, 2020 at 05:57:27PM +0000, Brendan Jackman wrote: > > > The JIT case for encoding atomic ops is about to get more > > > complicated. In order to make the review & resulting code easier, > > > let's factor out some shared helpers. > > > > > > Signed-off-by: Brendan Jackman <jackmanb@google.com> > > > --- > > > arch/x86/net/bpf_jit_comp.c | 39 ++++++++++++++++++++++--------------- > > > 1 file changed, 23 insertions(+), 16 deletions(-) > > > > > > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c > > > index 94b17bd30e00..a839c1a54276 100644 > > > --- a/arch/x86/net/bpf_jit_comp.c > > > +++ b/arch/x86/net/bpf_jit_comp.c > > > @@ -702,6 +702,21 @@ static void emit_modrm_dstoff(u8 **pprog, u32 r1, u32 r2, int off) > > > *pprog = prog; > > > } > > > > > > +/* > > > + * Emit a REX byte if it will be necessary to address these registers > > > > What is "REX byte" ? > > May be rename it to maybe_emit_mod() ? > > Er, this is the REX prefix as described in > https://wiki.osdev.org/X86-64_Instruction_Encoding#REX_prefix > > Would maybe_emit_mod be accurate? In my mind "mod" is a field in the > ModR/M byte which comes _after_ the opcode. Before developing this > patchset I knew almost nothing about x86, so maybe I'm missing something > about the general terminology? I wrote the JIT without looking into the manual and without studying the terminology. Why? Because it was not necessary. I still don't see a reason why that obscure terminology needs to be brought in into the code. 'mod' to me is a 'modifier'. Nothing to do with intel's modrm thing.
On Tue, Dec 01, 2020 at 09:48:36PM -0800, Alexei Starovoitov wrote: > On Tue, Dec 1, 2020 at 4:12 AM Brendan Jackman <jackmanb@google.com> wrote: > > > > On Sat, Nov 28, 2020 at 05:14:05PM -0800, Alexei Starovoitov wrote: > > > On Fri, Nov 27, 2020 at 05:57:27PM +0000, Brendan Jackman wrote: > > > > The JIT case for encoding atomic ops is about to get more > > > > complicated. In order to make the review & resulting code easier, > > > > let's factor out some shared helpers. > > > > > > > > Signed-off-by: Brendan Jackman <jackmanb@google.com> > > > > --- > > > > arch/x86/net/bpf_jit_comp.c | 39 ++++++++++++++++++++++--------------- > > > > 1 file changed, 23 insertions(+), 16 deletions(-) > > > > > > > > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c > > > > index 94b17bd30e00..a839c1a54276 100644 > > > > --- a/arch/x86/net/bpf_jit_comp.c > > > > +++ b/arch/x86/net/bpf_jit_comp.c > > > > @@ -702,6 +702,21 @@ static void emit_modrm_dstoff(u8 **pprog, u32 r1, u32 r2, int off) > > > > *pprog = prog; > > > > } > > > > > > > > +/* > > > > + * Emit a REX byte if it will be necessary to address these registers > > > > > > What is "REX byte" ? > > > May be rename it to maybe_emit_mod() ? > > > > Er, this is the REX prefix as described in > > https://wiki.osdev.org/X86-64_Instruction_Encoding#REX_prefix > > > > Would maybe_emit_mod be accurate? In my mind "mod" is a field in the > > ModR/M byte which comes _after_ the opcode. Before developing this > > patchset I knew almost nothing about x86, so maybe I'm missing something > > about the general terminology? > > I wrote the JIT without looking into the manual and without studying > the terminology. > Why? Because it was not necessary. I still don't see a reason why > that obscure terminology needs to be brought in into the code. > 'mod' to me is a 'modifier'. Nothing to do with intel's modrm thing. OK, calling it maybe_emit_mod(pprog, dst_reg, src_reg)
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 94b17bd30e00..a839c1a54276 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -702,6 +702,21 @@ static void emit_modrm_dstoff(u8 **pprog, u32 r1, u32 r2, int off) *pprog = prog; } +/* + * Emit a REX byte if it will be necessary to address these registers + */ +static void maybe_emit_rex(u8 **pprog, u32 reg_rm, u32 reg_reg, bool wide) +{ + u8 *prog = *pprog; + int cnt = 0; + + if (wide) + EMIT1(add_2mod(0x48, reg_rm, reg_reg)); + else if (is_ereg(reg_rm) || is_ereg(reg_reg)) + EMIT1(add_2mod(0x40, reg_rm, reg_reg)); + *pprog = prog; +} + /* LDX: dst_reg = *(u8*)(src_reg + off) */ static void emit_ldx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off) { @@ -854,10 +869,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, case BPF_OR: b2 = 0x09; break; case BPF_XOR: b2 = 0x31; break; } - if (BPF_CLASS(insn->code) == BPF_ALU64) - EMIT1(add_2mod(0x48, dst_reg, src_reg)); - else if (is_ereg(dst_reg) || is_ereg(src_reg)) - EMIT1(add_2mod(0x40, dst_reg, src_reg)); + maybe_emit_rex(&prog, dst_reg, src_reg, + BPF_CLASS(insn->code) == BPF_ALU64); EMIT2(b2, add_2reg(0xC0, dst_reg, src_reg)); break; @@ -1301,20 +1314,16 @@ xadd: emit_modrm_dstoff(&prog, dst_reg, src_reg, insn->off); case BPF_JMP32 | BPF_JSGE | BPF_X: case BPF_JMP32 | BPF_JSLE | BPF_X: /* cmp dst_reg, src_reg */ - if (BPF_CLASS(insn->code) == BPF_JMP) - EMIT1(add_2mod(0x48, dst_reg, src_reg)); - else if (is_ereg(dst_reg) || is_ereg(src_reg)) - EMIT1(add_2mod(0x40, dst_reg, src_reg)); + maybe_emit_rex(&prog, dst_reg, src_reg, + BPF_CLASS(insn->code) == BPF_JMP); EMIT2(0x39, add_2reg(0xC0, dst_reg, src_reg)); goto emit_cond_jmp; case BPF_JMP | BPF_JSET | BPF_X: case BPF_JMP32 | BPF_JSET | BPF_X: /* test dst_reg, src_reg */ - if (BPF_CLASS(insn->code) == BPF_JMP) - EMIT1(add_2mod(0x48, dst_reg, src_reg)); - else if (is_ereg(dst_reg) || is_ereg(src_reg)) - EMIT1(add_2mod(0x40, dst_reg, src_reg)); + maybe_emit_rex(&prog, dst_reg, src_reg, + BPF_CLASS(insn->code) == BPF_JMP); EMIT2(0x85, add_2reg(0xC0, dst_reg, src_reg)); goto emit_cond_jmp; @@ -1350,10 +1359,8 @@ xadd: emit_modrm_dstoff(&prog, dst_reg, src_reg, insn->off); case BPF_JMP32 | BPF_JSLE | BPF_K: /* test dst_reg, dst_reg to save one extra byte */ if (imm32 == 0) { - if (BPF_CLASS(insn->code) == BPF_JMP) - EMIT1(add_2mod(0x48, dst_reg, dst_reg)); - else if (is_ereg(dst_reg)) - EMIT1(add_2mod(0x40, dst_reg, dst_reg)); + maybe_emit_rex(&prog, dst_reg, dst_reg, + BPF_CLASS(insn->code) == BPF_JMP); EMIT2(0x85, add_2reg(0xC0, dst_reg, dst_reg)); goto emit_cond_jmp; }
The JIT case for encoding atomic ops is about to get more complicated. In order to make the review & resulting code easier, let's factor out some shared helpers. Signed-off-by: Brendan Jackman <jackmanb@google.com> --- arch/x86/net/bpf_jit_comp.c | 39 ++++++++++++++++++++++--------------- 1 file changed, 23 insertions(+), 16 deletions(-)