| Message ID | orwpec3e5y.fsf@lxoliva.fsfla.org |
|---|---|
| State | New |
| Headers | show |
On 01/02/2017 10:28 PM, Alexandre Oliva wrote: > In stage2 of bootstrap-O1, the code that warns if sprintf might > overflow its output buffer cannot tell that an unsigned value narrowed > to 16 bits will fit in 4 bytes with %4x. > > I couldn't find a better way to avoid the warning at -O1 than growing > the buffer so that there's no doubt the output will fit. > > Regstrapped on x86_64-linux-gnu and i686-linux-gnu. Ok to install? > > for gcc/c-family/ChangeLog > > * c-pretty-print.c (pp_c_tree_decl_identifier): Grow static > buffer to avoid false-positive warning. Presumably this is an artifact of not running VRP at -O1 and thus we don't have a narrowed range from the masking operation. This isn't performance critical code so we *could* avoid the statically sized array. But I doubt it's worth the effort. OK for the trunk. jeff
On 01/03/2017 10:39 AM, Jeff Law wrote: > On 01/02/2017 10:28 PM, Alexandre Oliva wrote: >> In stage2 of bootstrap-O1, the code that warns if sprintf might >> overflow its output buffer cannot tell that an unsigned value narrowed >> to 16 bits will fit in 4 bytes with %4x. >> >> I couldn't find a better way to avoid the warning at -O1 than growing >> the buffer so that there's no doubt the output will fit. >> >> Regstrapped on x86_64-linux-gnu and i686-linux-gnu. Ok to install? >> >> for gcc/c-family/ChangeLog >> >> * c-pretty-print.c (pp_c_tree_decl_identifier): Grow static >> buffer to avoid false-positive warning. > Presumably this is an artifact of not running VRP at -O1 and thus we > don't have a narrowed range from the masking operation. > > This isn't performance critical code so we *could* avoid the statically > sized array. But I doubt it's worth the effort. The manual recommends to use a length modifier to constrain the length of output to that of a narrower type: sprintf (xname, "<U%4hx>", ((unsigned short)((uintptr_t)(t) & 0xffff))); This should work even without optimization. Martin
diff --git a/gcc/c-family/c-pretty-print.c b/gcc/c-family/c-pretty-print.c index c32d0a0..dc6856a 100644 --- a/gcc/c-family/c-pretty-print.c +++ b/gcc/c-family/c-pretty-print.c @@ -2375,7 +2375,8 @@ pp_c_tree_decl_identifier (c_pretty_printer *pp, tree t) name = IDENTIFIER_POINTER (DECL_NAME (t)); else { - static char xname[8]; + /* xname[8] would do, but at -O1 we can't tell it's enough. */ + static char xname[12]; sprintf (xname, "<U%4x>", ((unsigned)((uintptr_t)(t) & 0xffff))); name = xname; }