-g- Produce debugging information in the operating system's native format
(stabs, COFF, XCOFF, or DWARF). GDB can work with this debugging
information.
On most systems that use stabs format, -g enables use of extra
debugging information that only GDB can use; this extra information
makes debugging work better in GDB but will probably make other debuggers
crash or
refuse to read the program. If you want to control for certain whether
to generate the extra information, use -gstabs+, -gstabs,
-gxcoff+, -gxcoff, or -gvms (see below).
Unlike most other C compilers, GCC allows you to use -g with
-O. The shortcuts taken by optimized code may occasionally
produce surprising results: some variables you declared may not exist
at all; flow of control may briefly move where you did not expect it;
some statements may not be executed because they compute constant
results or their values were already at hand; some statements may
execute in different places because they were moved out of loops.
Nevertheless it proves possible to debug optimized output. This makes
it reasonable to use the optimizer for programs that might have bugs.
The following options are useful when GCC is generated with the
capability for more than one debugging format.
-ggdb- Produce debugging information for use by GDB. This means to use the
most expressive format available (DWARF 2, stabs, or the native format
if neither of those are supported), including GDB extensions if at all
possible.
-gstabs- Produce debugging information in stabs format (if that is supported),
without GDB extensions. This is the format used by DBX on most BSD
systems. On MIPS, Alpha and System V Release 4 systems this option
produces stabs debugging output which is not understood by DBX or SDB.
On System V Release 4 systems this option requires the GNU assembler.
-feliminate-unused-debug-symbols- Produce debugging information in stabs format (if that is supported),
for only symbols that are actually used.
-gstabs+- Produce debugging information in stabs format (if that is supported),
using GNU extensions understood only by the GNU debugger (GDB). The
use of these extensions is likely to make other debuggers crash or
refuse to read the program.
-gcoff- Produce debugging information in COFF format (if that is supported).
This is the format used by SDB on most System V systems prior to
System V Release 4.
-gxcoff- Produce debugging information in XCOFF format (if that is supported).
This is the format used by the DBX debugger on IBM RS/6000 systems.
-gxcoff+- Produce debugging information in XCOFF format (if that is supported),
using GNU extensions understood only by the GNU debugger (GDB). The
use of these extensions is likely to make other debuggers crash or
refuse to read the program, and may cause assemblers other than the GNU
assembler (GAS) to fail with an error.
-gdwarf-2- Produce debugging information in DWARF version 2 format (if that is
supported). This is the format used by DBX on IRIX 6.
-gvms- Produce debugging information in VMS debug format (if that is
supported). This is the format used by DEBUG on VMS systems.
-glevel-ggdblevel-gstabslevel-gcofflevel-gxcofflevel-gvmslevel- Request debugging information and also use level to specify how
much information. The default level is 2.
Level 1 produces minimal information, enough for making backtraces in
parts of the program that you don't plan to debug. This includes
descriptions of functions and external variables, but no information
about local variables and no line numbers.
Level 3 includes extra information, such as all the macro definitions
present in the program. Some debuggers support macro expansion when
you use -g3.
Note that in order to avoid confusion between DWARF1 debug level 2,
and DWARF2 -gdwarf-2 does not accept a concatenated debug
level. Instead use an additional -glevel option to
change the debug level for DWARF2.
-feliminate-dwarf2-dups- Compress DWARF2 debugging information by eliminating duplicated
information about each symbol. This option only makes sense when
generating DWARF2 debugging information with -gdwarf-2.
-p- Generate extra code to write profile information suitable for the
analysis program prof. You must use this option when compiling
the source files you want data about, and you must also use it when
linking.
-pg- Generate extra code to write profile information suitable for the
analysis program gprof. You must use this option when compiling
the source files you want data about, and you must also use it when
linking.
-Q- Makes the compiler print out each function name as it is compiled, and
print some statistics about each pass when it finishes.
-ftime-report- Makes the compiler print some statistics about the time consumed by each
pass when it finishes.
-fmem-report- Makes the compiler print some statistics about permanent memory
allocation when it finishes.
-fprofile-arcs- Add code so that program flow arcs are instrumented. During
execution the program records how many times each branch and call is
executed and how many times it is taken or returns. When the compiled
program exits it saves this data to a file called
auxname.gcda for each source file. The data may be used for
profile-directed optimizations (-fbranch-probabilities), or for
test coverage analysis (-ftest-coverage). Each object file's
auxname is generated from the name of the output file, if
explicitly specified and it is not the final executable, otherwise it is
the basename of the source file. In both cases any suffix is removed
(e.g. foo.gcda for input file dir/foo.c, or
dir/foo.gcda for output file specified as -o dir/foo.o).
- Compile the source files with -fprofile-arcs plus optimization
and code generation options. For test coverage analysis, use the
additional -ftest-coverage option. You do not need to profile
every source file in a program.
- Link your object files with -lgcov or -fprofile-arcs
(the latter implies the former).
- Run the program on a representative workload to generate the arc profile
information. This may be repeated any number of times. You can run
concurrent instances of your program, and provided that the file system
supports locking, the data files will be correctly updated. Also
fork calls are detected and correctly handled (double counting
will not happen).
- For profile-directed optimizations, compile the source files again with
the same optimization and code generation options plus
-fbranch-probabilities (see Options that Control Optimization).
- For test coverage analysis, use gcov to produce human readable
information from the .gcno and .gcda files. Refer to the
gcov documentation for further information.
With -fprofile-arcs, for each function of your program GCC
creates a program flow graph, then finds a spanning tree for the graph.
Only arcs that are not on the spanning tree have to be instrumented: the
compiler adds code to count the number of times that these arcs are
executed. When an arc is the only exit or only entrance to a block, the
instrumentation code can be added to the block; otherwise, a new basic
block must be created to hold the instrumentation code.
-ftest-coverage- Produce a notes file that the gcov code-coverage utility
(see gcov—a Test Coverage Program) can use to
show program coverage. Each source file's note file is called
auxname.gcno. Refer to the -fprofile-arcs option
above for a description of auxname and instructions on how to
generate test coverage data. Coverage data will match the source files
more closely, if you do not optimize.
-dletters- Says to make debugging dumps during compilation at times specified by
letters. This is used for debugging the compiler. The file names
for most of the dumps are made by appending a pass number and a word to
the dumpname. dumpname is generated from the name of the
output file, if explicitly specified and it is not an executable,
otherwise it is the basename of the source file. In both cases any
suffix is removed (e.g. foo.01.rtl or foo.02.sibling).
Here are the possible letters for use in letters, and their
meanings:
- `A'
- Annotate the assembler output with miscellaneous debugging information.
- `b'
- Dump after computing branch probabilities, to file.12.bp.
- `B'
- Dump after block reordering, to file.31.bbro.
- `c'
- Dump after instruction combination, to the file file.20.combine.
- `C'
- Dump after the first if conversion, to the file file.14.ce1.
Also dump after the second if conversion, to the file file.21.ce2.
- `d'
- Dump after branch target load optimization, to to file.32.btl.
Also dump after delayed branch scheduling, to file.36.dbr.
- `D'
- Dump all macro definitions, at the end of preprocessing, in addition to
normal output.
- `E'
- Dump after the third if conversion, to file.30.ce3.
- `f'
- Dump after control and data flow analysis, to file.11.cfg.
Also dump after life analysis, to file.19.life.
- `F'
- Dump after purging
ADDRESSOF codes, to file.07.addressof.
- `g'
- Dump after global register allocation, to file.25.greg.
- `G'
- Dump after GCSE, to file.08.gcse.
Also dump after jump bypassing and control flow optimizations, to
file.10.bypass.
- `h'
- Dump after finalization of EH handling code, to file.03.eh.
- `i'
- Dump after sibling call optimizations, to file.02.sibling.
- `j'
- Dump after the first jump optimization, to file.04.jump.
- `k'
- Dump after conversion from registers to stack, to file.34.stack.
- `l'
- Dump after local register allocation, to file.24.lreg.
- `L'
- Dump after loop optimization passes, to file.09.loop and
file.16.loop2.
- `M'
- Dump after performing the machine dependent reorganization pass, to
file.35.mach.
- `n'
- Dump after register renumbering, to file.29.rnreg.
- `N'
- Dump after the register move pass, to file.22.regmove.
- `o'
- Dump after post-reload optimizations, to file.26.postreload.
- `r'
- Dump after RTL generation, to file.01.rtl.
- `R'
- Dump after the second scheduling pass, to file.33.sched2.
- `s'
- Dump after CSE (including the jump optimization that sometimes follows
CSE), to file.06.cse.
- `S'
- Dump after the first scheduling pass, to file.23.sched.
- `t'
- Dump after the second CSE pass (including the jump optimization that
sometimes follows CSE), to file.18.cse2.
- `T'
- Dump after running tracer, to file.15.tracer.
- `u'
- Dump after null pointer elimination pass to file.05.null.
- `U'
- Dump callgraph and unit-at-a-time optimization file.00.unit.
- `V'
- Dump after the value profile transformations, to file.13.vpt.
- `w'
- Dump after the second flow pass, to file.27.flow2.
- `z'
- Dump after the peephole pass, to file.28.peephole2.
- `Z'
- Dump after constructing the web, to file.17.web.
- `a'
- Produce all the dumps listed above.
- `H'
- Produce a core dump whenever an error occurs.
- `m'
- Print statistics on memory usage, at the end of the run, to
standard error.
- `p'
- Annotate the assembler output with a comment indicating which
pattern and alternative was used. The length of each instruction is
also printed.
- `P'
- Dump the RTL in the assembler output as a comment before each instruction.
Also turns on -dp annotation.
- `v'
- For each of the other indicated dump files (except for
file.01.rtl), dump a representation of the control flow graph
suitable for viewing with VCG to file.pass.vcg.
- `x'
- Just generate RTL for a function instead of compiling it. Usually used
with `r'.
- `y'
- Dump debugging information during parsing, to standard error.
-fdump-unnumbered- When doing debugging dumps (see -d option above), suppress instruction
numbers and line number note output. This makes it more feasible to
use diff on debugging dumps for compiler invocations with different
options, in particular with and without -g.
-fdump-translation-unit (C and C++ only)-fdump-translation-unit-options (C and C++ only)- Dump a representation of the tree structure for the entire translation
unit to a file. The file name is made by appending .tu to the
source file name. If the `-options' form is used, options
controls the details of the dump as described for the
-fdump-tree options.
-fdump-class-hierarchy (C++ only)-fdump-class-hierarchy-options (C++ only)- Dump a representation of each class's hierarchy and virtual function
table layout to a file. The file name is made by appending .class
to the source file name. If the `-options' form is used,
options controls the details of the dump as described for the
-fdump-tree options.
-fdump-tree-switch (C++ only)-fdump-tree-switch-options (C++ only)- Control the dumping at various stages of processing the intermediate
language tree to a file. The file name is generated by appending a switch
specific suffix to the source file name. If the `-options'
form is used, options is a list of `-' separated options that
control the details of the dump. Not all options are applicable to all
dumps, those which are not meaningful will be ignored. The following
options are available
- `address'
- Print the address of each node. Usually this is not meaningful as it
changes according to the environment and source file. Its primary use
is for tying up a dump file with a debug environment.
- `slim'
- Inhibit dumping of members of a scope or body of a function merely
because that scope has been reached. Only dump such items when they
are directly reachable by some other path.
- `all'
- Turn on all options.
The following tree dumps are possible:
- `original'
- Dump before any tree based optimization, to file.original.
- `optimized'
- Dump after all tree based optimization, to file.optimized.
- `inlined'
- Dump after function inlining, to file.inlined.
-frandom-seed=string- This option provides a seed that GCC uses when it would otherwise use
random numbers. It is used to generate certain symbol names
that have to be different in every compiled file. It is also used to
place unique stamps in coverage data files and the object files that
produce them. You can use the -frandom-seed option to produce
reproducibly identical object files.
The string should be different for every file you compile.
-fsched-verbose=n- On targets that use instruction scheduling, this option controls the
amount of debugging output the scheduler prints. This information is
written to standard error, unless -dS or -dR is
specified, in which case it is output to the usual dump
listing file, .sched or .sched2 respectively. However
for n greater than nine, the output is always printed to standard
error.
For n greater than zero, -fsched-verbose outputs the
same information as -dRS. For n greater than one, it
also output basic block probabilities, detailed ready list information
and unit/insn info. For n greater than two, it includes RTL
at abort point, control-flow and regions info. And for n over
four, -fsched-verbose also includes dependence info.
-save-temps- Store the usual “temporary” intermediate files permanently; place them
in the current directory and name them based on the source file. Thus,
compiling foo.c with `-c -save-temps' would produce files
foo.i and foo.s, as well as foo.o. This creates a
preprocessed foo.i output file even though the compiler now
normally uses an integrated preprocessor.
-time- Report the CPU time taken by each subprocess in the compilation
sequence. For C source files, this is the compiler proper and assembler
(plus the linker if linking is done). The output looks like this:
# cc1 0.12 0.01
# as 0.00 0.01
The first number on each line is the “user time,” that is time spent
executing the program itself. The second number is “system time,”
time spent executing operating system routines on behalf of the program.
Both numbers are in seconds.
-print-file-name=library- Print the full absolute name of the library file library that
would be used when linking—and don't do anything else. With this
option, GCC does not compile or link anything; it just prints the
file name.
-print-multi-directory- Print the directory name corresponding to the multilib selected by any
other switches present in the command line. This directory is supposed
to exist in GCC_EXEC_PREFIX.
-print-multi-lib- Print the mapping from multilib directory names to compiler switches
that enable them. The directory name is separated from the switches by
`;', and each switch starts with an `@' instead of the
`-', without spaces between multiple switches. This is supposed to
ease shell-processing.
-print-prog-name=program- Like -print-file-name, but searches for a program such as `cpp'.
-print-libgcc-file-name- Same as -print-file-name=libgcc.a.
This is useful when you use -nostdlib or -nodefaultlibs
but you do want to link with libgcc.a. You can do
gcc -nostdlib files... `gcc -print-libgcc-file-name`
-print-search-dirs- Print the name of the configured installation directory and a list of
program and library directories gcc will search—and don't do anything else.
This is useful when gcc prints the error message
`installation problem, cannot exec cpp0: No such file or directory'.
To resolve this you either need to put cpp0 and the other compiler
components where gcc expects to find them, or you can set the environment
variable GCC_EXEC_PREFIX to the directory where you installed them.
Don't forget the trailing '/'.
See Environment Variables.
-dumpmachine- Print the compiler's target machine (for example,
`i686-pc-linux-gnu')—and don't do anything else.
-dumpversion- Print the compiler version (for example, `3.0')—and don't do
anything else.
-dumpspecs- Print the compiler's built-in specs—and don't do anything else. (This
is used when GCC itself is being built.) See Spec Files.
-feliminate-unused-debug-types- Normally, when producing DWARF2 output, GCC will emit debugging
information for all types declared in a compilation
unit, regardless of whether or not they are actually used
in that compilation unit. Sometimes this is useful, such as
if, in the debugger, you want to cast a value to a type that is
not actually used in your program (but is declared). More often,
however, this results in a significant amount of wasted space.
With this option, GCC will avoid producing debug symbol output
for types that are nowhere used in the source file being compiled.