[Nasm-devel] [PATCH 2/9] MPX: Adapt GAS's mib syntax with an index reg only

[Jin K. S. <jin...@in...>]

GAS uses *1 multiplier for explicitly marking an index register in mib operand.
e.g.) [rdx * 1 + 3] is equivalent to [3, rdx] in NASM's split EA format
So only for mib operands, this is encoded same as gas does.

Signed-off-by: Jin Kyu Song <jin...@in...>
---
 assemble.c      |   12 ++++++++++++
 test/mpx-64.asm |    8 ++++----
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/assemble.c b/assemble.c
index ddf0af7..2f35cd9 100644
--- a/assemble.c
+++ b/assemble.c
@@ -1205,6 +1205,18 @@ static int64_t calcsize(int32_t segment, int64_t offset, int bits,
                     opy->hinttype = EAH_NOTBASE;
                 }
 
+                /*
+                 * only for mib operands, make a single reg index [reg*1].
+                 * gas uses this form to explicitly denote index register.
+                 */
+                if ((temp->flags & IF_MIB) &&
+                    (opy->indexreg == -1 && opy->hintbase == opy->basereg &&
+                     opy->hinttype == EAH_NOTBASE)) {
+                    opy->indexreg = opy->basereg;
+                    opy->basereg  = -1;
+                    opy->scale    = 1;
+                }
+
                 if (process_ea(opy, &ea_data, bits,
                                rfield, rflags, ins) != eat) {
                     errfunc(ERR_NONFATAL, "invalid effective address");
diff --git a/test/mpx-64.asm b/test/mpx-64.asm
index 50cc4da..bc5e7d4 100644
--- a/test/mpx-64.asm
+++ b/test/mpx-64.asm
@@ -81,16 +81,16 @@ BITS 64
 	bndstx [rax+0x3], bnd0, rbx	; ICC-1
 	bndstx [rax+0x3], rbx, bnd0	; ICC-2
 
-	; GAS's confusing EA - rcx is base reg in NASM
-	bndstx [rcx*1], bnd2
-	; next 4 lines should be parsed same
+	; next 5 lines should be parsed same
 	bndstx [,rcx*1], bnd2		; NASM
 	bndstx [0,rcx*1], bnd2		; NASM
 	bndstx [0], bnd2, rcx		; ICC-1
 	bndstx [0], rcx, bnd2		; ICC-2
+	bndstx [rcx*1], bnd2		; GAS - rcx is encoded as index only when it is mib
 
-	bndstx [1*r12+3], bnd2		; GAS's confusing EA again
+	; next 3 lines should be parsed same
 	bndstx [3,1*r12], bnd2		; NASM
+	bndstx [1*r12+3], bnd2		; GAS
 	bndstx [3], r12, bnd2		; ICC
 
 	bndstx [r12+0x399], bnd3
-- 
1.7.9.5