From 695d49c05d4d3db822830abaf45210f4a680d969 Mon Sep 17 00:00:00 2001 From: Kartik Agaram Date: Tue, 27 Nov 2018 21:22:36 -0800 Subject: 4791 --- subx/Readme.md | 27 ++++++++++++++------------- 1 file changed, 14 insertions(+), 13 deletions(-) (limited to 'subx') diff --git a/subx/Readme.md b/subx/Readme.md index 15e17219..39952d2d 100644 --- a/subx/Readme.md +++ b/subx/Readme.md @@ -145,11 +145,12 @@ There's a lot here, so let's unpack it piece by piece: * The addressing mode byte is used by all instructions that take an `rm32` operand according to `subx help opcodes`. (That's most instructions.) The - `rm32` operand shows how these instructions load one operand from memory. - That operand is encoded by the addressing mode byte and, optionally, the SIB - (scale, index, base) byte. The `rm32` operand is constructed like this: + `rm32` operand expresses how an instruction should load one 32-bit operand + from either a register or memory. It is configured by the addressing mode + byte and, optionally, the SIB (scale, index, base) byte as follows: - - if `mod` is 3: the contents of the register described by the `r/m` bits. + - if the `mod` (mode) field is 3: the `rm32` operand is the contents of the + register described by the `r/m` bits. - `000` (0) means register `EAX` - `001` (1) means register `ECX` - `010` (2) means register `EDX` @@ -162,17 +163,17 @@ There's a lot here, so let's unpack it piece by piece: - if `mod` is 0: `rm32` is the contents of the address provided in the register provided by `r/m`. That's `*r/m` in C syntax. - - if `mod` is 1: the contents of the address provided by adding the register - in `r/m` with the (1-byte) displacement. That's `*(r/m + disp8)` in C - syntax. + - if `mod` is 1: `rm32` is the contents of the address provided by adding + the register in `r/m` with the (1-byte) displacement. That's `*(r/m + + disp8)` in C syntax. - - if `mod` is 2: the contents of the address provided by adding the register - in `r/m` with the (4-byte) displacement. That's `*(r/m + disp32)` in C - syntax. + - if `mod` is 2: `rm32` is the contents of the address provided by adding + the register in `r/m` with the (4-byte) displacement. That's `*(r/m + + disp32)` in C syntax. - In the last 3 cases, one exception occurs when `r/m` contains `010` or 4. - Rather than encoding register ESP, '4' means the address is provided by a - SIB byte next: + In the last 3 cases, one exception occurs when the `r/m` field contains + `010` or 4. Rather than encoding register ESP, '4' means the address is + provided by a SIB byte next: ``` base * 2^scale + index -- cgit 1.4.1-2-gfad0 5.2&id=a1749411e61d20f701442c9c7e58464f4e0203b8'>account/compose.go

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