(gcc.info) Profiling
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(gcc.info) Function Entry
(gcc.info) Stack and Calling
Generating Code for Profiling
-----------------------------
These macros will help you generate code for profiling.
`FUNCTION_PROFILER (FILE, LABELNO)'
A C statement or compound statement to output to FILE some
assembler code to call the profiling subroutine `mcount'. Before
calling, the assembler code must load the address of a counter
variable into a register where `mcount' expects to find the
address. The name of this variable is `LP' followed by the number
LABELNO, so you would generate the name using `LP%d' in a
`fprintf'.
The details of how the address should be passed to `mcount' are
determined by your operating system environment, not by GNU CC. To
figure them out, compile a small program for profiling using the
system's installed C compiler and look at the assembler code that
results.
`PROFILE_BEFORE_PROLOGUE'
Define this macro if the code for function profiling should come
before the function prologue. Normally, the profiling code comes
after.
`FUNCTION_BLOCK_PROFILER (FILE, LABELNO)'
A C statement or compound statement to output to FILE some
assembler code to initialize basic-block profiling for the current
object module. The global compile flag `profile_block_flag'
distinguishes two profile modes.
`profile_block_flag != 2'
Output code to call the subroutine `__bb_init_func' once per
object module, passing it as its sole argument the address of
a block allocated in the object module.
The name of the block is a local symbol made with this
statement:
ASM_GENERATE_INTERNAL_LABEL (BUFFER, "LPBX", 0);
Of course, since you are writing the definition of
`ASM_GENERATE_INTERNAL_LABEL' as well as that of this macro,
you can take a short cut in the definition of this macro and
use the name that you know will result.
The first word of this block is a flag which will be nonzero
if the object module has already been initialized. So test
this word first, and do not call `__bb_init_func' if the flag
is nonzero. BLOCK_OR_LABEL contains a unique number which
may be used to generate a label as a branch destination when
`__bb_init_func' will not be called.
Described in assembler language, the code to be output looks
like:
cmp (LPBX0),0
bne local_label
parameter1 <- LPBX0
call __bb_init_func
local_label:
`profile_block_flag == 2'
Output code to call the subroutine `__bb_init_trace_func' and
pass two parameters to it. The first parameter is the same as
for `__bb_init_func'. The second parameter is the number of
the first basic block of the function as given by
BLOCK_OR_LABEL. Note that `__bb_init_trace_func' has to be
called, even if the object module has been initialized
already.
Described in assembler language, the code to be output looks
like:
parameter1 <- LPBX0
parameter2 <- BLOCK_OR_LABEL
call __bb_init_trace_func
`BLOCK_PROFILER (FILE, BLOCKNO)'
A C statement or compound statement to output to FILE some
assembler code to increment the count associated with the basic
block number BLOCKNO. The global compile flag
`profile_block_flag' distinguishes two profile modes.
`profile_block_flag != 2'
Output code to increment the counter directly. Basic blocks
are numbered separately from zero within each compilation.
The count associated with block number BLOCKNO is at index
BLOCKNO in a vector of words; the name of this array is a
local symbol made with this statement:
ASM_GENERATE_INTERNAL_LABEL (BUFFER, "LPBX", 2);
Of course, since you are writing the definition of
`ASM_GENERATE_INTERNAL_LABEL' as well as that of this macro,
you can take a short cut in the definition of this macro and
use the name that you know will result.
Described in assembler language, the code to be output looks
like:
inc (LPBX2+4*BLOCKNO)
`profile_block_flag == 2'
Output code to initialize the global structure `__bb' and
call the function `__bb_trace_func', which will increment the
counter.
`__bb' consists of two words. In the first word, the current
basic block number, as given by BLOCKNO, has to be stored. In
the second word, the address of a block allocated in the
object module has to be stored. The address is given by the
label created with this statement:
ASM_GENERATE_INTERNAL_LABEL (BUFFER, "LPBX", 0);
Described in assembler language, the code to be output looks
like:
move BLOCKNO -> (__bb)
move LPBX0 -> (__bb+4)
call __bb_trace_func
`FUNCTION_BLOCK_PROFILER_EXIT (FILE)'
A C statement or compound statement to output to FILE assembler
code to call function `__bb_trace_ret'. The assembler code should
only be output if the global compile flag `profile_block_flag' ==
2. This macro has to be used at every place where code for
returning from a function is generated (e.g. `FUNCTION_EPILOGUE').
Although you have to write the definition of `FUNCTION_EPILOGUE'
as well, you have to define this macro to tell the compiler, that
the proper call to `__bb_trace_ret' is produced.
`MACHINE_STATE_SAVE (ID)'
A C statement or compound statement to save all registers, which
may be clobbered by a function call, including condition codes.
The `asm' statement will be mostly likely needed to handle this
task. Local labels in the assembler code can be concatenated with
the string ID, to obtain a unique lable name.
Registers or condition codes clobbered by `FUNCTION_PROLOGUE' or
`FUNCTION_EPILOGUE' must be saved in the macros
`FUNCTION_BLOCK_PROFILER', `FUNCTION_BLOCK_PROFILER_EXIT' and
`BLOCK_PROFILER' prior calling `__bb_init_trace_func',
`__bb_trace_ret' and `__bb_trace_func' respectively.
`MACHINE_STATE_RESTORE (ID)'
A C statement or compound statement to restore all registers,
including condition codes, saved by `MACHINE_STATE_SAVE'.
Registers or condition codes clobbered by `FUNCTION_PROLOGUE' or
`FUNCTION_EPILOGUE' must be restored in the macros
`FUNCTION_BLOCK_PROFILER', `FUNCTION_BLOCK_PROFILER_EXIT' and
`BLOCK_PROFILER' after calling `__bb_init_trace_func',
`__bb_trace_ret' and `__bb_trace_func' respectively.
`BLOCK_PROFILER_CODE'
A C function or functions which are needed in the library to
support block profiling.
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