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665280aeaf
This patch changes the interface and behaviour of VG_(demangle) and VG_(maybe_Z_demangle). Instead of copying the demangled name into a fixed sized buffer that is passed in from the caller (HChar *buf, Int n_buf), the demangling functions will now return a pointer to the full-length demangled name (HChar **result). It is the caller's responsiblilty to make a copy if needed. This change in function parameters ripples upward - first: to get_sym_name - then to the convenience wrappers - VG_(get_fnname) - VG_(get_fnname_w_offset) - VG_(get_fnname_if_entry) - VG_(get_fnname_raw) - VG_(get_fnname_no_cxx_demangle) - VG_(get_datasym_and_offset) The changes in foComplete then forces the arguments of - VG_(get_objname) to be changed as well There are some issues regarding the ownership and persistence of character strings to consider. In general, the returned character string is owned by "somebody else" which means the caller must not free it. Also, the caller must not modify the returned string as it possibly points to read only memory. Additionally, the returned string is not necessarily persistent. Here are the scenarios: - the returned string is a demangled function name in which case the memory holding the string will be freed when the demangler is called again. - the returned string hangs off of a DebugInfo structure in which case it will be freed when the DebugInfo is discarded - the returned string hangs off of a segment in the address space manager in which case it may be overwritten when the segment is merged with another segment So the rule of thunb here is: if in doubt strdup the string. git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14664
=============================================================================
Notes about performance benchmarks
=============================================================================
For each benchmark, here is a brief description and notes about its
strengths and weaknesses.
-----------------------------------------------------------------------------
Artificial stress tests
-----------------------------------------------------------------------------
bigcode1, bigcode2:
- Description: Executes a lot of (nonsensical) code.
- Strengths: Demonstrates the cost of translation which is a large part
of runtime, particularly on larger programs.
- Weaknesses: Highly artificial.
heap:
- Description: Does a lot of heap allocation and deallocation, and has a lot
of heap blocks live while doing so.
- Strengths: Stress test for an important sub-system; bug #105039 showed
that inefficiencies in heap allocation can make a big
difference to programs that allocate a lot.
- Weaknesses: Highly artificial -- allocation pattern is not real, and only
a few different size allocations are used.
sarp:
- Description: Does a lot of stack allocation and deallocation.
- Strengths: Tests for a specific performance bug that existed in 3.1.0 and
all earlier versions.
- Weaknesses: Highly artificial.
-----------------------------------------------------------------------------
Real programs
-----------------------------------------------------------------------------
bz2:
- Description: Burrows-Wheeler compression and decompression.
- Strengths: A real, widely used program, very similar to the 256.bzip2
SPEC2000 benchmark. Not dominated by any code, the hottest
55 blocks account for only 90% of execution. Has lots of
short blocks and stresses the memory system hard.
- Weaknesses: None, really, it's a good benchmark.
fbench:
- Description: Does some ray-tracing.
- Strengths: Moderately realistic program.
- Weaknesses: Dominated by sin and cos, which are not widely used, and are
hardware-supported on x86 but not on other platforms such as
PPC.
ffbench:
- Description: Does a Fast Fourier Transform (FFT).
- Strengths: Tests common FP ops (mostly adding and multiplying array
elements), FFT is a very important operation.
- Weaknesses: Dominated by the inner loop, which is quite long and flatters
Valgrind due to the small dispatcher overhead.
tinycc:
- Description: A very small and fast C compiler. A munged version of
Fabrice Bellard's TinyCC compiling itself multiple times.
- Strengths: A real program, lots of code (top 100 blocks only account for
47% of execution), involves large irregular data structures
(presumably, since it's a compiler). Does lots of
malloc/free calls and so changes that make a big improvement
to perf/heap typically cause a small improvement.
- Weaknesses None, really, it's a good benchmark.