| Message ID | 3194055.aeNJFYEL58@fomalhaut |
|---|---|
| State | New |
| Headers | show |
| Series | Fix bogus -Wstringop-overflow warning | expand |
On 10/13/22 06:06, Eric Botcazou via Gcc-patches wrote: > Hi, > > if you compile the attached testcase with -O2 -fno-inline -Wall, you get: > > In function 'process_array3': > cc1: warning: 'process_array4' accessing 4 bytes in a region of size 3 [- > Wstringop-overflow=] > cc1: note: referencing argument 1 of type 'char[4]' > t.c:6:6: note: in a call to function 'process_array4' > 6 | void process_array4 (char a[4], int n) > | ^~~~~~~~~~~~~~ > cc1: warning: 'process_array4' accessing 4 bytes in a region of size 3 [- > Wstringop-overflow=] > cc1: note: referencing argument 1 of type 'char[4]' > t.c:6:6: note: in a call to function 'process_array4' > > That's because the ICF IPA pass has identified the two functions and turned > process_array3 into a wrapper of process_array4. This looks sensible to me > given that the only difference between them is an "access" attribute on their > type describing the access size of the parameter and the "access" attribute > does not affect type identity (struct attribute_spec.affects_type_identity). > > Hence the proposed fix, tested on x86-64/Linux, OK for the mainline? > > > 2022-10-13 Eric Botcazou <ebotcazou@adacore.com> > > * gimple-ssa-warn-access.cc (pass_waccess::check_call): Return > early for calls made from thunks. > > > 2022-10-13 Eric Botcazou <ebotcazou@adacore.com> > > * gcc.dg/Wstringop-overflow-89.c: New test. Not a fan as it could potentially hide a real issue, but I don't really have a better solution. I pondered suggesting "access" affect type identity, but the cases where that's really important are probably better handled by the "fn spec" attribute, leaving "access" strictly impacting diagnostics. OK jeff
> Not a fan as it could potentially hide a real issue, but I don't really > have a better solution. Thanks. > I pondered suggesting "access" affect type identity, but the cases where > that's really important are probably better handled by the "fn spec" > attribute, leaving "access" strictly impacting diagnostics. I can expand a bit here, because I tried to change the "access" attribute that way and this badly breaks the C compiler, for example: int foo (int n, char m[1][n]); int foo (int n, char m[1][n]) {} no longer compiles with an error about different function types.
On Fri, Oct 14, 2022 at 12:54 AM Eric Botcazou via Gcc-patches <gcc-patches@gcc.gnu.org> wrote: > > > Not a fan as it could potentially hide a real issue, but I don't really > > have a better solution. > > Thanks. > > > I pondered suggesting "access" affect type identity, but the cases where > > that's really important are probably better handled by the "fn spec" > > attribute, leaving "access" strictly impacting diagnostics. > > I can expand a bit here, because I tried to change the "access" attribute that > way and this badly breaks the C compiler, for example: > > int foo (int n, char m[1][n]); > > int foo (int n, char m[1][n]) {} > > no longer compiles with an error about different function types. Note in discussion with IPA folks we agreed that IPA cloning that modifies arguments either has to remove access attributes, adjust them or refrain from cloning. Martin - has anything been done to this respect? I suppose there's also a way to figure if a clone has arguments changed in any way? Thanks, Richard. > -- > Eric Botcazou > >
On 10/14/22 08:12, Richard Biener wrote: > On Fri, Oct 14, 2022 at 12:54 AM Eric Botcazou via Gcc-patches > <gcc-patches@gcc.gnu.org> wrote: >> >>> Not a fan as it could potentially hide a real issue, but I don't really >>> have a better solution. >> >> Thanks. >> >>> I pondered suggesting "access" affect type identity, but the cases where >>> that's really important are probably better handled by the "fn spec" >>> attribute, leaving "access" strictly impacting diagnostics. >> >> I can expand a bit here, because I tried to change the "access" attribute that >> way and this badly breaks the C compiler, for example: >> >> int foo (int n, char m[1][n]); >> >> int foo (int n, char m[1][n]) {} >> >> no longer compiles with an error about different function types. > > Note in discussion with IPA folks we agreed that IPA cloning that modifies > arguments either has to remove access attributes, adjust them or refrain > from cloning. > > Martin - has anything been done to this respect? I think it's more for Martin Jambor who's the IPA specialist when it comes to parameter manipulation. Martin > > I suppose there's also a way to figure if a clone has arguments > changed in any way? > > Thanks, > Richard. > >> -- >> Eric Botcazou >> >>
Hello, On Fri, Oct 14 2022, Martin Liška wrote: > On 10/14/22 08:12, Richard Biener wrote: >> On Fri, Oct 14, 2022 at 12:54 AM Eric Botcazou via Gcc-patches >> <gcc-patches@gcc.gnu.org> wrote: >>> >>>> Not a fan as it could potentially hide a real issue, but I don't really >>>> have a better solution. >>> >>> Thanks. >>> >>>> I pondered suggesting "access" affect type identity, but the cases where >>>> that's really important are probably better handled by the "fn spec" >>>> attribute, leaving "access" strictly impacting diagnostics. >>> >>> I can expand a bit here, because I tried to change the "access" attribute that >>> way and this badly breaks the C compiler, for example: >>> >>> int foo (int n, char m[1][n]); >>> >>> int foo (int n, char m[1][n]) {} >>> >>> no longer compiles with an error about different function types. >> >> Note in discussion with IPA folks we agreed that IPA cloning that modifies >> arguments either has to remove access attributes, adjust them or refrain >> from cloning. >> >> Martin - has anything been done to this respect? > > I think it's more for Martin Jambor who's the IPA specialist when it comes > to parameter manipulation. > They are being dropped since 2af63f0f53a Adjusting them accordingly is an item buried quite deep in my TODO list. >> >> I suppose there's also a way to figure if a clone has arguments >> changed in any way? Look whether clone_info::get (node) exists and its param_adjustments is non-NULL. In theory the param_adjustments could contain description of the very same signature the original function has but in practice it does not currently happen and is unlikely to happen ever. Martin
diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc index 04aa849a4b1..59a70530600 100644 --- a/gcc/gimple-ssa-warn-access.cc +++ b/gcc/gimple-ssa-warn-access.cc @@ -4291,14 +4291,18 @@ pass_waccess::check_pointer_uses (gimple *stmt, tree ptr, void pass_waccess::check_call (gcall *stmt) { - if (gimple_call_builtin_p (stmt, BUILT_IN_NORMAL)) - check_builtin (stmt); + /* Skip special calls generated by the compiler. */ + if (gimple_call_from_thunk_p (stmt)) + return; /* .ASAN_MARK doesn't access any vars, only modifies shadow memory. */ if (gimple_call_internal_p (stmt) && gimple_call_internal_fn (stmt) == IFN_ASAN_MARK) return; + if (gimple_call_builtin_p (stmt, BUILT_IN_NORMAL)) + check_builtin (stmt); + if (!m_early_checks_p) if (tree callee = gimple_call_fndecl (stmt)) {
Hi, if you compile the attached testcase with -O2 -fno-inline -Wall, you get: In function 'process_array3': cc1: warning: 'process_array4' accessing 4 bytes in a region of size 3 [- Wstringop-overflow=] cc1: note: referencing argument 1 of type 'char[4]' t.c:6:6: note: in a call to function 'process_array4' 6 | void process_array4 (char a[4], int n) | ^~~~~~~~~~~~~~ cc1: warning: 'process_array4' accessing 4 bytes in a region of size 3 [- Wstringop-overflow=] cc1: note: referencing argument 1 of type 'char[4]' t.c:6:6: note: in a call to function 'process_array4' That's because the ICF IPA pass has identified the two functions and turned process_array3 into a wrapper of process_array4. This looks sensible to me given that the only difference between them is an "access" attribute on their type describing the access size of the parameter and the "access" attribute does not affect type identity (struct attribute_spec.affects_type_identity). Hence the proposed fix, tested on x86-64/Linux, OK for the mainline? 2022-10-13 Eric Botcazou <ebotcazou@adacore.com> * gimple-ssa-warn-access.cc (pass_waccess::check_call): Return early for calls made from thunks. 2022-10-13 Eric Botcazou <ebotcazou@adacore.com> * gcc.dg/Wstringop-overflow-89.c: New test.