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Re: [PATCH] avoid folding snprintf calls with bounds > INT_MAX (PR 87096)
Hi,
On Thu, 13 Dec 2018 at 19:14, Jeff Law <law@redhat.com> wrote:
>
> On 12/12/18 4:18 PM, Martin Sebor wrote:
> > POSIX requires snprintf to fail with EOVERFLOW when the specified
> > bound exceeds INT_MAX. This requirement conflicts with the C
> > requirements on valid calls to the function and isn't universally
> > implemented (e.g., Glibc doesn't seem to follow it, and GCC has
> > historically not paid heed to it either). Nevertheless, there
> > are implementations that do respect it (Solaris being one of
> > them), and it seems that GCC should make a tricky situation
> > even more treacherous for programmers by returning different
> > values from some calls to the function than the library would.
> > This is also what bug 87096 requests. The patch also adds
> > a warning that was missing from a subset of these troublesome
> > calls.
> >
> > The attached patch disables the snprintf constant folding and
> > range optimization for calls to it and other related bounded
> > functions when the bound is not known not to exceed INT_MAX.
> >
> > Tested on x86_64-linux.
> >
> > Martin
> >
> > gcc-87096.diff
> >
> > PR tree-optimization/87096 - Optimised snprintf is not POSIX conformant
> >
> > gcc/ChangeLog:
> >
> > PR rtl-optimization/87096
> > * gimple-ssa-sprintf.c (sprintf_dom_walker::handle_gimple_call): Avoid
> > folding calls whose bound may exceed INT_MAX. Diagnose bound ranges
> > that exceed the limit.
> >
> > gcc/testsuite/ChangeLog:
> >
> > PR tree-optimization/87096
> > * gcc.dg/tree-ssa/builtin-snprintf-4.c: New test.
This new test fails on arm (and other 32 bits targets according to
gcc-testresults)
FAIL: gcc.dg/tree-ssa/builtin-snprintf-4.c (test for warnings, line 106)
FAIL: gcc.dg/tree-ssa/builtin-snprintf-4.c (test for warnings, line 128)
FAIL: gcc.dg/tree-ssa/builtin-snprintf-4.c (test for warnings, line 74)
FAIL: gcc.dg/tree-ssa/builtin-snprintf-4.c (test for warnings, line 87)
FAIL: gcc.dg/tree-ssa/builtin-snprintf-4.c scan-tree-dump-times
optimized " = snprintf" 12
FAIL: gcc.dg/tree-ssa/builtin-snprintf-4.c scan-tree-dump-times
optimized " = vsnprintf" 12
Christophe
> OK
> jeff