Re: [PATCH] maint.mk: add a syntax-check rule to ensure tightly-scoped symbols

[Pádraig Brady]

On 17/05/11 15:08, Jim Meyering wrote:
> Pádraig Brady wrote:
>> On 09/05/11 11:44, Jim Meyering wrote:
>>> I've been using a precursor of this rule in coreutils for many years,
>>
>>> so finally have made it general enough so that the same
>>
>> The above change is giving a false positive on my 32 linux laptop,
>> where it flags  __i686.get_pc_thunk.bx from src/libstdbuf_so-libstdbuf.o
>> The following fix auto excludes any symbols starting with an underscore.
>> Maybe I should do this only for double underscores?
>>
>> pb-laptop:~/git/coreutils$ diff gnulib/top/maint.mk maint.mk
>> --- gnulib/top/maint.mk 2011-05-14 09:30:58.000000000 +0000
>> +++ maint.mk    2011-05-17 12:45:56.000000000 +0000
>> @@ -1397,7 +1397,7 @@
>>           perl -lne '$(_gl_TS_function_match)'                          \
>>                   -e 'and print $$1' $$hdr;                             \
>>         ) | sort -u | sed 's/^/^/;s/$$/$$/' > $$t;                      \
>> -       nm -e *.$(OBJEXT) | sed -n 's/.* T //p' | grep -Ev -f $$t       \
>> +       nm -e *.$(OBJEXT) | sed -n 's/.* T \([^_]\)/\1/p' | grep -Ev -f $$t \
>>           && { echo the above functions should have static scope >&2;   \
>>                exit 1; } || : ;                                         \
>>         ( printf '^%s$$\n' $(_gl_TS_unmarked_extern_vars);              \
> 
> Hi Pádraig,
> I did hesitate as I removed the filter that ignored
> any name with a leading underscore.  But since I didn't
> see any such symbol actually being removed in testing
> I chose to omit the filter.
> 
> I'm reluctant to ignore all of them... what if someone accidentally
> declares e.g., int _foo () { ... }
> (omitting the "static")?  I wouldn't want to fail to warn about that,
> just because their function name starts with "_".
> 
> Two alternatives:
> 
>   - rather than hard-coding *.$(OBJEXT), use something like this:
>       _gl_TS_function_objects ?= *.$(OBJEXT)
>     and override it in coreutils to $(filter-out ...) that one
>     offending .o file.

A bit hacky, and exludes that whole module from the check.

> 
>   - in coreutils, add __i686.get_pc_thunk.bx or maybe just '^__i686.*$$'
>     to the list of _gl_TS_unmarked_extern_functions

A bit specific/fragile.

Given '^__.*' names are reserved by the compiler,
perhaps the happy medium is to to allow single underscores,
but exclude double underscores, with something like:

--- gnulib/top/maint.mk 2011-05-14 09:30:58.000000000 +0000
+++ maint.mk    2011-05-17 14:25:15.000000000 +0000
@@ -1362,14 +1362,15 @@
 # Most functions should have static scope.
 # Any that don't must be marked with `extern', but `main'
 # and `usage' are exceptions: they're always extern, but
-# do not need to be marked.
-_gl_TS_unmarked_extern_functions ?= main usage
+# do not need to be marked.  Symbols starting with `__'
+# are reserved by the compiler, so exclude those also.
+_gl_TS_unmarked_extern_functions ?= main usage __.*
 _gl_TS_function_match ?= \
   /^(?:extern|XTERN) +(?:void|(?:struct |const |enum )?\S+) +\**(\S+) +\(/

 # The second nm|grep checks for file-scope variables with `extern' scope.
 # Without gnulib's progname module, you might put program_name here.
-_gl_TS_unmarked_extern_vars ?=
+_gl_TS_unmarked_extern_vars ?= __.*

 # NOTE: the _match variables are perl expressions -- not mere regular
 # expressions -- so that you can extend them to match other patterns