[PATCH] Fix stxr_c on i386

[Paolo Bonzini-2]

Alban Bedel wrote:

> Hi all,
>
> I'm using lightning in a small JIT compiler and I found a little bug.
> To store a char on i386 the source register must be 8bit, so when the
> source is in ESI or EDI it must be moved to another register.
> But currently lightning unconditionaly use EAX, this obviously can lead
> to broken code if eax is used in the argument. Like this:
>
> stxr_c eax, ebx, esi => push eax
>                         mov esi, eax
>                         mov al, (eax, ebx)
>                         pop eax
>
> Attached is a patch that fix this.

Applied, thanks!!

Paolo


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[Alban Bedel]

Hi all,

I'm using lightning in a small JIT compiler and I found a little bug.
To store a char on i386 the source register must be 8bit, so when the
source is in ESI or EDI it must be moved to another register.
But currently lightning unconditionaly use EAX, this obviously can lead
to broken code if eax is used in the argument. Like this:

stxr_c eax, ebx, esi => push eax
                        mov esi, eax
                        mov al, (eax, ebx)
                        pop eax

Attached is a patch that fix this.

        Albeu

[i386_stxr_c.diff]

---

diff --git a/lightning/i386/core-32.h b/lightning/i386/core-32.h
index 48153e6..09e7f5f 100644
--- a/lightning/i386/core-32.h
+++ b/lightning/i386/core-32.h
@@ -117,7 +117,12 @@ struct jit_local_state {
 #define jit_movbrm(rs, dd, db, di, ds)                                                \
         (jit_check8(rs)                                                         \
                 ? MOVBrm(jit_reg8(rs), dd, db, di, ds)                          \
-                : jit_replace(_EBX, rs, _EAX, MOVBrm(_AL, dd, db, di, ds)))
+                : jit_replace(_EBX, rs,                                         \
+                              ((dd != _EAX && db != _EAX) ? _EAX :              \
+                              ((dd != _ECX && db != _ECX) ? _ECX : _EDX)),      \
+                              MOVBrm(((dd != _EAX && db != _EAX) ? _AL :        \
+                                     ((dd != _ECX && db != _ECX) ? _CL : _DL)), \
+                                     dd, db, di, ds)))
 
 #define jit_ldi_c(d, is)                MOVSBLmr((is), 0,    0,    0, (d))
 #define jit_ldxi_c(d, rs, is)           MOVSBLmr((is), (rs), 0,    0, (d))

---

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