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authorZack Weinberg <zackw@panix.com>2018-02-10 11:58:35 -0500
committerZack Weinberg <zackw@panix.com>2018-12-25 05:57:54 -0500
commitda1907bb99bdd376e3b356c6501e88bfda74e3e8 (patch)
tree2207140a7fd45137338917866ab963b9fa70b1d7 /sysdeps/ieee754/ldbl-opt/nldbl-vwscanf.c
parent57b3ff8e1a4ca8118c5d9a47584e6e0ce6f7002f (diff)
downloadglibc-da1907bb99bdd376e3b356c6501e88bfda74e3e8.tar.gz
Use C99-compliant scanf under _GNU_SOURCE with modern compilers.zack/c99-compliant-scanf
The only difference between noncompliant and C99-compliant scanf is that the former accepts the archaic GNU extension '%as' (also %aS and %a[...]) meaning to allocate space for the input string with malloc. This extension conflicts with C99's use of %a as a format _type_ meaning to read a floating-point number; POSIX.1-2008 standardized equivalent functionality using the modifier letter 'm' instead (%ms, %mS, %m[...]). The extension was already disabled in most conformance modes: specifically, any mode that doesn't involve _GNU_SOURCE and _does_ involve either strict conformance to C99 or loose conformance to both C99 and POSIX.1-2001 would get the C99-compliant scanf. With compilers new enough to use -std=gnu11 instead of -std=gnu89, or equivalent, that includes the default mode. This patch tightens things up further: you now get C99-compliant scanf in all configurations except when _GNU_SOURCE is defined *and* __STDC_VERSION__ or __cplusplus (whichever is relevant) indicates C89/C++98. This leaves the old scanf available under e.g. -std=c89 -D_GNU_SOURCE, but removes it from e.g. -std=gnu11 -D_GNU_SOURCE (it was already not present under -std=gnu11 without -D_GNU_SOURCE) and from -std=gnu89 without -D_GNU_SOURCE. There needs to be an internal override so we can compile the noncompliant scanf itself. This is the same problem we had when we removed 'gets' from _GNU_SOURCE and it's dealt with the same way: there's a new __GLIBC_USE symbol, DEPRECATED_SCANF, which defaults to off under the appropriate conditions for external code, but can be overridden by individual files within stdio. We also run into problems with PLT bypass for internal uses of sscanf, because libc_hidden_proto uses __REDIRECT and so does the logic in stdio.h for choosing which implementation of scanf to use; __REDIRECT isn't transitive, so include/stdio.h needs to bridge the gap with a macro. As far as I can tell, sscanf is the only function in this family that's internally called by unrelated code. I'm open to better ideas if anyone has one. N.B. I would accept "internal code shouldn't call *scanf ever" as a better idea, but there are several internal uses and some of them are pretty complicated, I don't want to hold up this patch for that. On a related note, the interaction of the C99/not-C99 scanf redirect with the __LDBL_COMPAT scanf redirect was complicated, confusing, and possibly wrong. I tried to match the intent rather than the letter of the previous behavior. I do not have access to physical hardware for which __LDBL_COMPAT is relevant, so my ability to test it is limited. Careful review and maybe even some volunteer testing would be appreciated. Finally, there are several tests in stdio-common that use the extension. bug21 is a regression test for a crash, and still exercises the relevant code if changed to use %ms instead of %as. scanf14 through scanf17 are more complicated since they are actually testing the subtleties of the extension - under what circumstances is 'a' treated as a modifier letter, etc. My approach here is to duplicate scanf14.c and scanf16.c; the originals change to use %ms instead, the copies select precisely the right conformance mode to get %as with the old GNU meaning, plus everything else they need (it's not as simple as saying -std=gnu89, unfortunately). scanf15 and scanf17 become simpler because they no longer need to avoid _GNU_SOURCE, and all of them no longer need diagnostic overrides. Yay! -- * include/features.h (__GLIBC_USE_DEPRECATED_SCANF): New __GLIBC_USE parameter. Only use deprecated scanf when __USE_GNU is defined and __STDC_VERSION__ is less than 199901L or __cplusplus is less than 201103L, whichever is relevant for the language being compiled. * libio/stdio.h, libio/bits/stdio-ldbl.h: Decide whether or not to redirect scanf, fscanf, sscanf, vscanf, vfscanf, and vsscanf to their __isoc99_ variants based only on __GLIBC_USE(DEPRECATED_SCANF). * wcsmbs/wchar.h: wcsmbs/bits/wchar-ldbl.h: Likewise for wscanf, fwscanf, swscanf, vwscanf, vfwscanf, and vswscanf. * libio/iovsscanf.c * libio/fwscanf.c * libio/iovswscanf.c * libio/swscanf.c * libio/vscanf.c * libio/vwscanf.c * libio/wscanf.c * stdio-common/fscanf.c * stdio-common/scanf.c * stdio-common/vfscanf.c * stdio-common/vfwscanf.c * sysdeps/ieee754/ldbl-opt/nldbl-compat.c * sysdeps/ieee754/ldbl-opt/nldbl-fscanf.c * sysdeps/ieee754/ldbl-opt/nldbl-fwscanf.c * sysdeps/ieee754/ldbl-opt/nldbl-iovfscanf.c * sysdeps/ieee754/ldbl-opt/nldbl-scanf.c * sysdeps/ieee754/ldbl-opt/nldbl-sscanf.c * sysdeps/ieee754/ldbl-opt/nldbl-swscanf.c * sysdeps/ieee754/ldbl-opt/nldbl-vfscanf.c * sysdeps/ieee754/ldbl-opt/nldbl-vfwscanf.c * sysdeps/ieee754/ldbl-opt/nldbl-vscanf.c * sysdeps/ieee754/ldbl-opt/nldbl-vsscanf.c * sysdeps/ieee754/ldbl-opt/nldbl-vswscanf.c * sysdeps/ieee754/ldbl-opt/nldbl-vwscanf.c * sysdeps/ieee754/ldbl-opt/nldbl-wscanf.c: Override __GLIBC_USE_DEPRECATED_SCANF to 1. * stdio-common/sscanf.c: Likewise. Remove ldbl_hidden_def for __sscanf. * stdio-common/isoc99_sscanf.c: Add libc_hidden_def for __isoc99_sscanf. * include/stdio.h: Provide libc_hidden_proto for __isoc99_sscanf, not sscanf. [!__GLIBC_USE(DEPRECATED_SCANF)]: Define sscanf as __isoc99_scanf with a preprocessor macro. * stdio-common/bug21.c, stdio-common/scanf14.c: Use %ms instead of %as, %mS instead of %aS, %m[] instead of %a[]; remove DIAG_IGNORE_NEEDS_COMMENT for -Wformat. * stdio-common/scanf16.c: Likewise. Add __attribute__((format(scanf))) to xscanf, xfscanf, xsscanf. * stdio-common/scanf14a.c: New copy of scanf14.c which still uses %as, %aS, %a[]. Use conformance mode -std=gnu89, _POSIX_C_SOURCE=199506L, _XOPEN_SOURCE=1, _XOPEN_SOURCE_EXTENDED=1, which will use the nonconformant scanf implementation. Remove DIAG_IGNORE_NEEDS_COMMENT for -Wformat. * stdio-common/scanf16a.c: New copy of scanf16.c which still uses %as, %aS, %a[]. Use conformance mode -std=gnu89, _POSIX_C_SOURCE=199506L, _XOPEN_SOURCE=1, _XOPEN_SOURCE_EXTENDED=1, _ISOC99_SOURCE=1, which will use the nonconformant scanf implementation. Add __attribute__((format(scanf))) to xscanf, xfscanf, xsscanf. * stdio-common/scanf15.c, stdio-common/scanf17.c: No need to override feature selection macros or provide definitions of u_char etc. * stdio-common/Makefile (tests): Add scanf14a and scanf16a. (CFLAGS-scanf15.c, CFLAGS-scanf17.c): Remove. (CFLAGS-scanf14a.c, CFLAGS-scanf16a.c): New.
Diffstat (limited to 'sysdeps/ieee754/ldbl-opt/nldbl-vwscanf.c')
-rw-r--r--sysdeps/ieee754/ldbl-opt/nldbl-vwscanf.c5
1 files changed, 5 insertions, 0 deletions
diff --git a/sysdeps/ieee754/ldbl-opt/nldbl-vwscanf.c b/sysdeps/ieee754/ldbl-opt/nldbl-vwscanf.c
index d39578ca4e..b3d0f1be18 100644
--- a/sysdeps/ieee754/ldbl-opt/nldbl-vwscanf.c
+++ b/sysdeps/ieee754/ldbl-opt/nldbl-vwscanf.c
@@ -1,3 +1,8 @@
+/* This file defines one of the deprecated scanf variants. */
+#include <features.h>
+#undef __GLIBC_USE_DEPRECATED_SCANF
+#define __GLIBC_USE_DEPRECATED_SCANF 1
+
#include "nldbl-compat.h"
int