Declare __warn_memset_zero_len internally for newer gcc [bz #25399]
Commit Message
The __warn_memset_zero_len symbol, used to issue a linker warning
about zero length memset calls, is included in warning-nop.o only when
glibc is built with an older gcc, which is incorrect. When a program
calling memset with zero length is built with either gcc < 5.0 or with
clang (which advertises __GNUC__ as 4), it results in a link failure
due to not finding the symbol in libc_nonshared.a.
Fill in this gap by declaring __warn_memset_zero_len for newer gcc as
well so that it is always available in libc_nonshared.a for any
compiler to link against.
---
debug/warning-nop.c | 10 ++++++++++
string/bits/string_fortified.h | 6 ++++--
2 files changed, 14 insertions(+), 2 deletions(-)
Comments
* Siddhesh Poyarekar via Libc-alpha:
> The __warn_memset_zero_len symbol, used to issue a linker warning
> about zero length memset calls, is included in warning-nop.o only when
> glibc is built with an older gcc, which is incorrect. When a program
> calling memset with zero length is built with either gcc < 5.0 or with
> clang (which advertises __GNUC__ as 4), it results in a link failure
> due to not finding the symbol in libc_nonshared.a.
>
> Fill in this gap by declaring __warn_memset_zero_len for newer gcc as
> well so that it is always available in libc_nonshared.a for any
> compiler to link against.
Does Clang have its own warning for this?
An alternative would be to drop the warning from the glibc headers
because current compilers do not need it.
Thanks,
Florian
On Tue, Nov 03, 2020 at 04:05:11PM +0100, Florian Weimer wrote:
> * Siddhesh Poyarekar via Libc-alpha:
>
> > The __warn_memset_zero_len symbol, used to issue a linker warning
> > about zero length memset calls, is included in warning-nop.o only when
> > glibc is built with an older gcc, which is incorrect. When a program
> > calling memset with zero length is built with either gcc < 5.0 or with
> > clang (which advertises __GNUC__ as 4), it results in a link failure
> > due to not finding the symbol in libc_nonshared.a.
> >
> > Fill in this gap by declaring __warn_memset_zero_len for newer gcc as
> > well so that it is always available in libc_nonshared.a for any
> > compiler to link against.
>
> Does Clang have its own warning for this?
Clang has -Wmemset-transposed-args. The warning is emitted during smeantic
analysis, catching two patterns: 1. a size argument of 0 and 2. when the
constant argument is a sizeof
> An alternative would be to drop the warning from the glibc headers
> because current compilers do not need it.
>
> Thanks,
> Florian
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>
* Serge Guelton:
> On Tue, Nov 03, 2020 at 04:05:11PM +0100, Florian Weimer wrote:
>> * Siddhesh Poyarekar via Libc-alpha:
>>
>> > The __warn_memset_zero_len symbol, used to issue a linker warning
>> > about zero length memset calls, is included in warning-nop.o only when
>> > glibc is built with an older gcc, which is incorrect. When a program
>> > calling memset with zero length is built with either gcc < 5.0 or with
>> > clang (which advertises __GNUC__ as 4), it results in a link failure
>> > due to not finding the symbol in libc_nonshared.a.
>> >
>> > Fill in this gap by declaring __warn_memset_zero_len for newer gcc as
>> > well so that it is always available in libc_nonshared.a for any
>> > compiler to link against.
>>
>> Does Clang have its own warning for this?
>
> Clang has -Wmemset-transposed-args. The warning is emitted during smeantic
> analysis, catching two patterns: 1. a size argument of 0 and 2. when the
> constant argument is a sizeof
Is it enabled by -Wall?
Thanks,
Florian
On Tue, Nov 03, 2020 at 05:05:54PM +0100, Florian Weimer wrote:
> * Serge Guelton:
>
> > On Tue, Nov 03, 2020 at 04:05:11PM +0100, Florian Weimer wrote:
> >> * Siddhesh Poyarekar via Libc-alpha:
> >>
> >> > The __warn_memset_zero_len symbol, used to issue a linker warning
> >> > about zero length memset calls, is included in warning-nop.o only when
> >> > glibc is built with an older gcc, which is incorrect. When a program
> >> > calling memset with zero length is built with either gcc < 5.0 or with
> >> > clang (which advertises __GNUC__ as 4), it results in a link failure
> >> > due to not finding the symbol in libc_nonshared.a.
> >> >
> >> > Fill in this gap by declaring __warn_memset_zero_len for newer gcc as
> >> > well so that it is always available in libc_nonshared.a for any
> >> > compiler to link against.
> >>
> >> Does Clang have its own warning for this?
> >
> > Clang has -Wmemset-transposed-args. The warning is emitted during smeantic
> > analysis, catching two patterns: 1. a size argument of 0 and 2. when the
> > constant argument is a sizeof
>
> Is it enabled by -Wall?
Yes
On 11/3/20 8:35 PM, Florian Weimer via Libc-alpha wrote:
> An alternative would be to drop the warning from the glibc headers
> because current compilers do not need it.
This would mean dropping this check for situations where one is building
against a newer glibc with gcc < 5.0. I don't know how common this use
case is.
Siddhesh
* Serge Guelton:
> On Tue, Nov 03, 2020 at 05:05:54PM +0100, Florian Weimer wrote:
>> * Serge Guelton:
>>
>> > On Tue, Nov 03, 2020 at 04:05:11PM +0100, Florian Weimer wrote:
>> >> * Siddhesh Poyarekar via Libc-alpha:
>> >>
>> >> > The __warn_memset_zero_len symbol, used to issue a linker warning
>> >> > about zero length memset calls, is included in warning-nop.o only when
>> >> > glibc is built with an older gcc, which is incorrect. When a program
>> >> > calling memset with zero length is built with either gcc < 5.0 or with
>> >> > clang (which advertises __GNUC__ as 4), it results in a link failure
>> >> > due to not finding the symbol in libc_nonshared.a.
>> >> >
>> >> > Fill in this gap by declaring __warn_memset_zero_len for newer gcc as
>> >> > well so that it is always available in libc_nonshared.a for any
>> >> > compiler to link against.
>> >>
>> >> Does Clang have its own warning for this?
>> >
>> > Clang has -Wmemset-transposed-args. The warning is emitted during smeantic
>> > analysis, catching two patterns: 1. a size argument of 0 and 2. when the
>> > constant argument is a sizeof
>>
>> Is it enabled by -Wall?
>
> Yes
Then I don't think we need the manual warning in the glibc headers.
Thanks,
Florian
@@ -68,3 +68,13 @@ nop (void)
#define __builtin_object_size(bos, level) 0
#include <string.h>
+
+/* The public string_fortify.h header (included via string.h above) declares
+ __warn_memset_zero_len only when it is built with GCC < 5.0 or a non-gcc
+ compiler where compiler support for zero length memset warning may not be
+ available. Internally however we need to ensure that __warn_memset_zero_len
+ is always available when using older gcc or other compilers to link against
+ glibc. */
+#if __GNUC_PREREQ (5,0)
+__warndecl (__warn_memset_zero_len, __WARN_MEMSET_ZERO_LEN_MSG);
+#endif
@@ -22,9 +22,11 @@
# error "Never use <bits/string_fortified.h> directly; include <string.h> instead."
#endif
+#define __WARN_MEMSET_ZERO_LEN_MSG \
+ "memset used with constant zero length parameter; this could be due to transposed parameters"
+
#if !__GNUC_PREREQ (5,0)
-__warndecl (__warn_memset_zero_len,
- "memset used with constant zero length parameter; this could be due to transposed parameters");
+__warndecl (__warn_memset_zero_len, __WARN_MEMSET_ZERO_LEN_MSG);
#endif
__fortify_function void *