# NASM - The Netwide Assembler

## version 3.01

## Appendix A: List of Warning Classes

These are the warning classes currently defined by NASM for the purpose of enabling, disabling and promoting to error. See section 2.1.26 and section 8.14.

### A.1. Warning Classes

This list shows each warning class that can be enabled or disabled individually. Each warning containing a `-` character in the name can also be enabled or disabled as part of a group, named by removing one or more `-`–delimited suffixes.

#### A.1.1. Enabled by default

- `db-empty`: no operand for data declaration

  Warns about a `D`x declaration with no operands, producing no output. This is permitted, but often indicative of an error. See section 3.2.1.

- `ea-absolute`: absolute address cannot be RIP-relative

  Warns that an address that is inherently absolute cannot be generated with RIP-relative encoding using `REL`, see section 8.2.1.

- `ea-dispsize`: displacement size ignored on absolute address

  Warns that NASM does not support generating displacements for inherently absolute addresses that do not match the address size of the instruction.

- `float-overflow`: floating point overflow

  Warns about floating point underflow.

- `float-toolong`: too many digits in floating-point number

  Warns about too many digits in floating-point numbers.

- `forward`: forward reference may have unpredictable results

  Warns that a forward reference is used which may have unpredictable results, notably in a `RESB`–type pseudo-instruction. These would be critical expressions (see section 3.8) but are permitted in a handful of cases for compatibility with older versions of NASM. This warning should be treated as a severe programming error as the code could break at any time for any number of reasons.

- `implicit-abs-deprecated`: implicit DEFAULT ABS is deprecated

  Warns that in a future version of NASM, the 64-bit default addressing form is likely to change from `DEFAULT ABS` to `DEFAULT REL`. If absolute addressing is indeed intended, it is strongly recommended to specify `DEFAULT ABS` explicitly.

- `label-orphan`: labels alone on lines without trailing `:`

  Warns about source lines which contain no instruction but define a label without a trailing colon. This is most likely indicative of a typo, but is technically correct NASM syntax (see section 3.1.)

- `number-deprecated-hex`: $ prefix for hexadecimal is deprecated

  Warns that the `$` prefix for hexadecimal numbers is deprecated, due to the syntactic conflict with `$` used as a symbol escape prefix. This syntax may be disabled by default in a future version of NASM. Replace `$` with `0x` to ensure compatibility with future versions.

- `number-overflow`: numeric constant does not fit

  Covers warnings about numeric constants which don't fit in 64 bits.

- `obsolete-nop`: instruction obsolete and is a noop on the target CPU

  Warns for an instruction which has been removed from the architecture, but has been architecturally defined to be a noop for future CPUs.

- `obsolete-removed`: instruction obsolete and removed on the target CPU

  Warns for an instruction which has been removed from the architecture, and is no longer included in the CPU definition given in the `[CPU]` directive, for example `POP CS`, the opcode for which, `0Fh`, instead is an opcode prefix on CPUs newer than the first generation 8086.

- `obsolete-valid`: instruction obsolete but valid on the target CPU

  Warns for an instruction which has been removed from the architecture, but is still valid on the specific CPU given in the `CPU` directive. Code using these instructions is most likely not forward compatible.

- `other`: any warning not assigned to a specific warning class

  Specifies any warning not included in any specific warning class.

- `pp-else-elif`: `%elif` after `%else`

  Warns that an `%elif`–type directive was encountered after `%else` has already been encounted. As a result, the content of the `%elif` will never be expanded.

- `pp-else-else`: `%else` after `%else`

  Warns that a second `%else` clause was found for the same `%if` statement. The content of this `%else` clause will never be expanded.

- `pp-empty-braces`: empty `%{}` construct

  Warns that an empty `%{}` was encountered. This expands to a single `%` character, which is normally the `%` arithmetic operator.

- `pp-environment`: nonexistent environment variable

  Warns if a nonexistent environment variable is accessed using the `%!` preprocessor construct (see section 5.13.2.) Such environment variables are treated as empty (with this warning issued) starting in NASM 2.15; earlier versions of NASM would treat this as an error.

- `pp-macro-def-case-single`: single-line macro defined both case sensitive and insensitive

  Warns when a single-line macro is defined both case sensitive and case insensitive. The new macro definition will override (shadow) the original one, although the original macro is not deleted, and will be re-exposed if the new macro is deleted with `%undef`, or, if the original macro is the case insensitive one, the macro call is done with a different case.

- `pp-macro-def-greedy-single`: single-line macro

  Warns that a single-line macro is defined which would match a previously existing greedy definition. The new macro definition will override (shadow) the original one, although the original macro is not deleted, and will be re-exposed if the new macro is deleted with `%undef`, and will be invoked if called with a parameter count that does not match the new definition.

- `pp-macro-defaults`: macros with more default than optional parameters

  Warns when a macro has more default parameters than optional parameters. See section 5.5.5 for why one might want to disable this warning.

- `pp-macro-params-legacy`: improperly calling multi-line macro for legacy support

  Warns about multi-line macros being invoked with the wrong number of parameters, but for bug-compatibility with NASM versions older than 2.15, NASM tried to fix up the parameters to match the legacy behavior and call the macro anyway. This can happen in certain cases where there are empty arguments without braces, sometimes as a result of macro expansion.

  The legacy behavior is quite strange and highly context-dependent, and can be disabled with:

           %pragma preproc sane_empty_expansion true

  It is highly recommended to use this option in new code.

- `pp-macro-params-multi`: multi-line macro calls with wrong parameter count

  Warns about multi-line macros being invoked with the wrong number of parameters. See section 5.5.1 for an example of why you might want to disable this warning.

- `pp-macro-params-single`: single-line macro calls with wrong parameter count

  Warns about single-line macros being invoked with the wrong number of parameters.

- `pp-macro-redef-multi`: redefining multi-line macro

  Warns that a multi-line macro is being redefined, without first removing the old definition with `%unmacro`.

- `pp-open-braces`: unterminated `%{...}`

  Warns that a preprocessor parameter enclosed in braces `%{...}` lacks the terminating `}` character.

- `pp-open-brackets`: unterminated `%[...]`

  Warns that a preprocessor `%[...]` construct lacks the terminating `]` character.

- `pp-open-string`: unterminated string

  Warns that a quoted string without a closing quotation mark was encountered during preprocessing.

- `pp-rep-negative`: regative `%rep` count

  Warns about a negative count given to the `%rep` preprocessor directive.

- `pp-sel-range`: `%sel()` argument out of range

  Warns that the `%sel()` preprocessor function was passed a value less than 1 or larger than the number of available arguments.

- `pp-trailing`: trailing garbage ignored

  Warns that the preprocessor encountered additional text where no such text was expected. This can sometimes be the result of an incorrectly written expression, or arguments that are inadvertently separated.

- `prefix-bnd`: invalid `BND` prefix

  Warns about ineffective use of the `BND` prefix when the `JMP` instruction is converted to the `SHORT` form. This should be extremely rare since the short `JMP` only is applicable to jumps inside the same module, but if it is legitimate, it may be necessary to use `bnd jmp dword`.

- `prefix-hint-dropped`: invalid branch hint prefix dropped

  Warns that the `{PT`} (predict taken) or `{PN`} (predict not taken) branch prediction hint prefixes are specified on an instruction that does not take these prefixes. As these prefixes alias the segment override prefixes, this may be a very serious error, and therefore NASM will not generate these prefixes. To force these prefixes to be emitted, use `DS` or `CS`, instead, respectively.

- `prefix-hle`: invalid HLE prefix

  Warns about invalid use of the HLE `XACQUIRE` or `XRELEASE` prefixes.

- `prefix-invalid`: invalid prefix for instruction

  Warns about an instruction which is only valid with certain combinations of prefixes. The prefix will still be generated as requested, but the result may be a completely different instruction or result in a `#UD` trap.

- `prefix-lock-error`: `LOCK` prefix on unlockable instruction

  Warns about `LOCK` prefixes specified on unlockable instructions.

- `prefix-lock-xchg`: superfluous `LOCK` prefix on `XCHG` instruction

  Warns about a `LOCK` prefix added to an `XCHG` instruction. The `XCHG` instruction is always locking, and so this prefix is not necessary; however, NASM will generate it if explicitly provided by the user, so this warning indicates that suboptimal code is being generated.

- `prefix-opsize`: invalid operand size prefix

  Warns that an operand prefix (`o16`, `o32`, `o64`, `osp`) invalid for the specified instruction has been specified. The operand prefix will be ignored by the assembler.

- `prefix-seg`: segment prefix ignored in 64-bit mode

  Warns that an `es`, `cs`, `ss` or `ds` segment override prefix has no effect in 64-bit mode. The prefix will still be generated as requested.

- `ptr`: non-NASM keyword used in other assemblers

  Warns about keywords used in other assemblers that might indicate a mistake in the source code. Currently only the MASM `PTR` keyword is recognized. If (limited) MASM compatibility is desired, the `%use masm` macro package is available, see section 7.5; however, carefully note the caveats listed.

- `regsize`: register size specification ignored

  Warns about a register with implicit size (such as `EAX`, which is always 32 bits) been given an explicit size specification which is inconsistent with the size of the named register, e.g. `WORD EAX`. `DWORD EAX` or `WORD AX` are permitted, and do not trigger this warning. Some registers which do not imply a specific size, such as `K0`, may need this specification unless the instruction itself implies the instruction size:

           KMOVW K0,[foo]          ; OK: KMOVW = 16 bits
           KMOV  WORD K0,[foo]     ; OK: WORD K0 = 16 bits
           KMOV  K0,WORD [foo]     ; OK: WORD [foo] = 16 bits
           KMOV  K0,[foo]          ; Error: unknown size

- `section-alignment-rounded`: section alignment rounded up

  Warn if a section alignment is specified which is not supported by the underlying object format, but can be rounded up to a supported value.

- `user`: `%warning` directives

  Controls output of `%warning` directives (see section 5.11).

- `warn-stack-empty`: warning stack empty

  A `[WARNING POP]` directive was executed when the warning stack is empty. This is treated as a `[WARNING *all]` directive.

- `zeroing`: `RES`x in initialized section becomes zero

  A `RES`x directive was used in a section which contains initialized data, and the output format does not support this. Instead, this will be replaced with explicit zero content, which may produce a large output file.

- `zext-reloc`: relocation zero-extended to match output format

  Warns that a relocation has been zero-extended due to limitations in the output format.

#### A.1.2. Enabled and promoted to error by default

- `directive-garbage-eol`: garbage after directive

  Text was found after a directive. This is a warning so it can be suppressed, because previous versions of NASM did not check for this condition.

- `label-redef-late`: label (re)defined during code generation

  The value of a label changed during the final, code-generation pass. This may be the result of strange use of the preprocessor. This is very likely to produce incorrect code and may end up being an unconditional error in a future version of NASM.

- `pp-macro-def-param-single`: single-line macro defined with and without parameters

  Warns if the same single-line macro is defined with and without parameters. The new macro definition will override (shadow) the original one, although the original macro is not deleted, and will be re-exposed if the new macro is deleted with `%undef`.

- `prefix-badmode-o64`: o64 prefix invalid in 16/32-bit mode

  Warns that an `a64` prefix was specified in 16- or 32-bit mode. If the error is demoted to a warning or suppressed, the prefix is ignored by the assembler, but is likely to trigger futher errors.

#### A.1.3. Disabled by default

- `float-denorm`: floating point denormal

  Warns about denormal floating point constants.

- `float-underflow`: floating point underflow

  Warns about floating point underflow (a nonzero constant rounded to zero.)

- `label-redef`: label redefined to an identical value

  Warns if a label is defined more than once, but the value is identical. It is an unconditional error to define the same label more than once to different values.

- `phase`: phase error during stabilization

  Warns about symbols having changed values during the second-to-last assembly pass. This is not inherently fatal, but may be a source of bugs.

- `pragma-bad`: malformed `%pragma`

  Warns about a malformed or otherwise unparsable `%pragma` directive.

- `pragma-empty`: empty `%pragma` directive

  Warns about a `%pragma` directive containing nothing. This is treated identically to `%pragma ignore` except for this optional warning.

- `pragma-na`: `%pragma` not applicable to this compilation

  Warns about a `%pragma` directive which is not applicable to this particular assembly session. This is not yet implemented.

- `pragma-unknown`: unknown `%pragma` facility or directive

  Warns about an unknown `%pragma` directive. This is not yet implemented for most cases.

- `reloc-abs-byte`: 8-bit absolute section-crossing relocation

  Warns that an 8-bit absolute relocation that could not be resolved at assembly time was generated in the output format.

  This is usually normal, but may not be handled by all possible target environments

- `reloc-abs-dword`: 32-bit absolute section-crossing relocation

  Warns that a 32-bit absolute relocation that could not be resolved at assembly time was generated in the output format.

  This is usually normal, but may not be handled by all possible target environments

- `reloc-abs-qword`: 64-bit absolute section-crossing relocation

  Warns that a 64-bit absolute relocation that could not be resolved at assembly time was generated in the output format.

  This is usually normal, but may not be handled by all possible target environments

- `reloc-abs-word`: 16-bit absolute section-crossing relocation

  Warns that a 16-bit absolute relocation that could not be resolved at assembly time was generated in the output format.

  This is usually normal, but may not be handled by all possible target environments

- `reloc-rel-byte`: 8-bit relative section-crossing relocation

  Warns that an 8-bit relative relocation that could not be resolved at assembly time was generated in the output format.

  This is usually normal, but may not be handled by all possible target environments

- `reloc-rel-dword`: 32-bit relative section-crossing relocation

  Warns that a 32-bit relative relocation that could not be resolved at assembly time was generated in the output format.

  This is usually normal, but may not be handled by all possible target environments

- `reloc-rel-qword`: 64-bit relative section-crossing relocation

  Warns that an 64-bit relative relocation that could not be resolved at assembly time was generated in the output format.

  This is usually normal, but may not be handled by all possible target environments

- `reloc-rel-word`: 16-bit relative section-crossing relocation

  Warns that a 16-bit relative relocation that could not be resolved at assembly time was generated in the output format.

  This is usually normal, but may not be handled by all possible target environments

- `unknown-warning`: unknown warning in `-W`/`-w` or warning directive

  Warns about a `-w` or `-W` option or a `[WARNING]` directive that contains an unknown warning name or is otherwise not possible to process.

### A.2. Warning Class Groups

Warning class groups are aliases for all warning classes with a common prefix. This list shows the warnings that are currently included in specific warning groups.

- `all`: all possible warnings

  `all` is an group alias for all warning classes. Thus, `-w+all` enables all available warnings, and `-w-all` disables warnings entirely (since NASM 2.13).

- `ea`: group alias for:

           ea-absolute
           ea-dispsize

- `float`: group alias for:

           float-denorm
           float-overflow
           float-toolong
           float-underflow

- `label`: group alias for:

           label-orphan
           label-redef
           label-redef-late

- `number`: group alias for:

           number-deprecated-hex
           number-overflow

- `obsolete`: group alias for:

           obsolete-nop
           obsolete-removed
           obsolete-valid

- `pp`: group alias for:

           pp-else-elif
           pp-else-else
           pp-empty-braces
           pp-environment
           pp-macro-def-case-single
           pp-macro-def-greedy-single
           pp-macro-def-param-single
           pp-macro-defaults
           pp-macro-params-legacy
           pp-macro-params-multi
           pp-macro-params-single
           pp-macro-redef-multi
           pp-open-braces
           pp-open-brackets
           pp-open-string
           pp-rep-negative
           pp-sel-range
           pp-trailing

- `pp-else`: group alias for:

           pp-else-elif
           pp-else-else

- `pp-macro`: group alias for:

           pp-macro-def-case-single
           pp-macro-def-greedy-single
           pp-macro-def-param-single
           pp-macro-defaults
           pp-macro-params-legacy
           pp-macro-params-multi
           pp-macro-params-single
           pp-macro-redef-multi

- `pp-macro-def`: group alias for:

           pp-macro-def-case-single
           pp-macro-def-greedy-single
           pp-macro-def-param-single

- `pp-macro-params`: group alias for:

           pp-macro-params-legacy
           pp-macro-params-multi
           pp-macro-params-single

- `pp-open`: group alias for:

           pp-open-braces
           pp-open-brackets
           pp-open-string

- `pragma`: group alias for:

           pragma-bad
           pragma-empty
           pragma-na
           pragma-unknown

- `prefix`: group alias for:

           prefix-badmode-o64
           prefix-bnd
           prefix-hint-dropped
           prefix-hle
           prefix-invalid
           prefix-lock-error
           prefix-lock-xchg
           prefix-opsize
           prefix-seg

- `prefix-lock`: group alias for:

           prefix-lock-error
           prefix-lock-xchg

- `reloc`: group alias for:

           reloc-abs-byte
           reloc-abs-dword
           reloc-abs-qword
           reloc-abs-word
           reloc-rel-byte
           reloc-rel-dword
           reloc-rel-qword
           reloc-rel-word

- `reloc-abs`: group alias for:

           reloc-abs-byte
           reloc-abs-dword
           reloc-abs-qword
           reloc-abs-word

- `reloc-rel`: group alias for:

           reloc-rel-byte
           reloc-rel-dword
           reloc-rel-qword
           reloc-rel-word

### A.3. Warning Class Aliases for Backward Compatiblity

These aliases are defined for compatibility with earlier versions of NASM.

- `bad-pragma`: malformed `%pragma`

  Alias for `pragma-bad`.

- `bnd`: invalid `BND` prefix

  Alias for `prefix-bnd`.

- `environment`: nonexistent environment variable

  Alias for `pp-environment`.

- `hle`: invalid HLE prefix

  Alias for `prefix-hle`.

- `lock`: `LOCK` prefix on unlockable instruction

  Alias for `prefix-lock-error`.

- `macro-def-case-single`: single-line macro defined both case sensitive and insensitive

  Alias for `pp-macro-def-case-single`.

- `macro-def-greedy-single`: single-line macro

  Alias for `pp-macro-def-greedy-single`.

- `macro-def-param-single`: single-line macro defined with and without parameters

  Alias for `pp-macro-def-param-single`.

- `macro-defaults`: macros with more default than optional parameters

  Alias for `pp-macro-defaults`.

- `macro-params-legacy`: improperly calling multi-line macro for legacy support

  Alias for `pp-macro-params-legacy`.

- `macro-params-multi`: multi-line macro calls with wrong parameter count

  Alias for `pp-macro-params-multi`.

- `macro-params-single`: single-line macro calls with wrong parameter count

  Alias for `pp-macro-params-single`.

- `negative-rep`: regative `%rep` count

  Alias for `pp-rep-negative`.

- `not-my-pragma`: `%pragma` not applicable to this compilation

  Alias for `pragma-na`.

- `orphan-labels`: labels alone on lines without trailing `:`

  Alias for `label-orphan`.

- `unknown-pragma`: unknown `%pragma` facility or directive

  Alias for `pragma-unknown`.