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@xxxxxxxxxx> > > --- > > 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.
