Slave memory out of Bounds (Bugzilla #32)

[GerbilSoft]

status VERIFIED severity normal in component gens for ---
Reported in version r7.1 on platform i386
Assigned to: David Korth

On 2010-01-28 08:55:25 -0500, Paul Mc Quade wrote:

gens_core/mem/mem_s68k.asm:2772: warning: signed byte value exceeds bounds
gens_core/mem/mem_s68k.asm:2799: warning: signed byte value exceeds bounds
gens_core/mem/mem_s68k.asm:2848: warning: signed byte value exceeds bounds
gens_core/mem/mem_s68k.asm:3496: warning: signed byte value exceeds bounds
gens_core/mem/mem_s68k.asm:3514: warning: signed byte value exceeds bounds
gens_core/mem/mem_s68k.asm:3550: warning: signed byte value exceeds bounds

Its always a register overflow, like

.Reg_Vector_Adr:
and ax, 0xFFFE

(etc)

On 2010-01-28 18:54:40 -0500, David Korth wrote:

This isn't actually a bug. nasm seems a bit overzealous with regards to 16-bit instructions, and is trying to warn us that 0xFE will get sign-extended to 0xFFFFFFFE if a byte operand is used with a 32-bit register in 32-bit mode.

Example: Suppose you want to AND the value in eax with 0xFE.

Correct: and eax, 0xFE
Incorrect: and eax, byte 0xFE

The latter version will sign-extend the value to 0xFFFFFFFE instead of zero-extending it to 0x000000FE.

In the case of mem_s68k.asm, the ANDs are merely for masking out a single bit, so it isn't a problem. However, I may replace it with 32-bit register operations later on for performance purposes.