Remove wrappers around inline -- static inline is used without
wrappers throughout the source code. We rely on the compiler or
linker to eliminate unused static functions.
Fix warnings flagged by the new warning option -Wunused-but-set-variable
that was added to GCC 4.6 and that is enabled by -Wunused and -Wall. The
option causes a warning whenever a local variable is assigned to but is
later unused. It also warns about meaningless pointer dereferences.
Bug#52261: 64 bit atomic operations do not work on Solaris i386
gcc in debug compilation
One of the various problems was that the source operand to
CMPXCHG8b was marked as a input/output operand, causing GCC
to use the EBX register as the destination register for the
CMPXCHG8b instruction. This could lead to crashes as the EBX
register is also implicitly used by the instruction, causing
the value to be potentially garbaged and a protection fault
once the value is used to access a position in memory.
Another problem was the lack of proper clobbers for the atomic
operations and, also, a discrepancy between the implementations
for the Compare and Set operation. The specific problems are
described and fixed by Kristian Nielsen patches:
Patch: 1
Fix bugs in my_atomic_cas*(val,cmp,new) that *cmp is accessed
after CAS succeds.
In the gcc builtin implementation, problem was that *cmp was
read again after atomic CAS to check if old *val == *cmp;
this fails if CAS is successful and another thread modifies
*cmp in-between.
In the x86-gcc implementation, problem was that *cmp was set
also in the case of successful CAS; this means there is a
window where it can clobber a value written by another thread
after successful CAS.
Patch 2:
Add a GCC asm "memory" clobber to primitives that imply a
memory barrier.
This signifies to GCC that any potentially aliased memory
must be flushed before the operation, and re-read after the
operation, so that read or modification in other threads of
such memory values will work as intended.
In effect, it makes these primitives work as memory barriers
for the compiler as well as the CPU. This is better and more
correct than adding "volatile" to variables.
strict aliasing violations.
Post-merge fix: include my_compiler.h before my_attribute.h
as the latter will undef __attribute__ if the compiler is not
GCC. Based on the compiler version, in my_compiler.h we know
for sure whether the aligned attribute is supported. Furthermore,
undefining attribute might cause bugs if some system header
uses it.
strict aliasing violations.
Another rather noisy violation of strict aliasing rules
is the spatial code which makes use of stack-based memory
(of type Geometry_buffer) to provide placement for Geometry
objects. Although a placement new is allowed to dynamically
change the type of a object, the object returned by the
new placement was being ignored and the original stack-based
object was being casted to the new type, thus violating strict
aliasing rules.
The solution is to reorganize the code so that the object
returned by the new placement is used instead of casting the
original object. Also, to ensure that the stack-based object
is properly aligned with respect to the objects it provides
placement for, a set of compiler-dependent macros and types
are introduced so that the alignment of objects can be inquired
and specified.
This change is for performance optimization.
Fixed the performance schema instrumentation interface as follows:
- simplified mysql_unlock_mutex()
- simplified mysql_unlock_rwlock()
- simplified mysql_cond_signal()
- simplified mysql_cond_broadcast()
Changed the get_thread_XXX_locker apis to have one extra parameter,
to provide memory to the instrumentation implementation.
This API change allows to use memory provided by the caller,
to avoid having to use thread local storage.
Using this extra parameter will be done in a separate fix,
this change is for the interface only.
Adjusted all the code and unit tests accordingly.
Although the C standard mandates that sprintf return the number
of bytes written, some very ancient systems (i.e. SunOS 4)
returned a pointer to the buffer instead. Since these systems
are not supported anymore and are hopefully long dead by now,
simply remove the portability wrapper that dealt with this
discrepancy. The autoconf check was causing trouble with GCC.
Essentially, the problem is that safemalloc is excruciatingly
slow as it checks all allocated blocks for overrun at each
memory management primitive, yielding a almost exponential
slowdown for the memory management functions (malloc, realloc,
free). The overrun check basically consists of verifying some
bytes of a block for certain magic keys, which catches some
simple forms of overrun. Another minor problem is violation
of aliasing rules and that its own internal list of blocks
is prone to corruption.
Another issue with safemalloc is rather the maintenance cost
as the tool has a significant impact on the server code.
Given the magnitude of memory debuggers available nowadays,
especially those that are provided with the platform malloc
implementation, maintenance of a in-house and largely obsolete
memory debugger becomes a burden that is not worth the effort
due to its slowness and lack of support for detecting more
common forms of heap corruption.
Since there are third-party tools that can provide the same
functionality at a lower or comparable performance cost, the
solution is to simply remove safemalloc. Third-party tools
can provide the same functionality at a lower or comparable
performance cost.
The removal of safemalloc also allows a simplification of the
malloc wrappers, removing quite a bit of kludge: redefinition
of my_malloc, my_free and the removal of the unused second
argument of my_free. Since free() always check whether the
supplied pointer is null, redudant checks are also removed.
Also, this patch adds unit testing for my_malloc and moves
my_realloc implementation into the same file as the other
memory allocation primitives.
The atomic operations implementation on 5.1 has a few problems,
which might cause tests to abort randomly. Since no code in 5.1
uses atomic operations, simply remove the code.
Apart strict-aliasing warnings, fix the remaining warnings
generated by GCC 4.4.4 -Wall and -Wextra flags.
One major source of warnings was the in-house function my_bcmp
which (unconventionally) took pointers to unsigned characters
as the byte sequences to be compared. Since my_bcmp and bcmp
are deprecated functions whose only difference with memcmp is
the return value, every use of the function is replaced with
memcmp as the special return value wasn't actually being used
by any caller.
There were also various other warnings, mostly due to type
mismatches, missing return values, missing prototypes, dead
code (unreachable) and ignored return values.
POSIX requires that a signal handler defined with sigaction()
is not reset on delivering a signal unless SA_NODEFER or
SA_RESETHAND is set. It is therefore unnecessary to redefine
the handler on signal delivery on platforms where sigaction()
is used without those flags.
