-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+ or -gstabs
(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.
-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.
(Other debug formats, such as -gcoff, are not supported in
Darwin or Mac OS X.)
-glevel-ggdblevel-gstabslevel-
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, neither -gdwarf nor -gdwarf-2 accept
a concatenated debug level. Instead use an additional -glevel
option to change the debug level for DWARF1 or 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- Instrument arcs during compilation to generate coverage data or
for profile-directed block ordering. During execution the program
records how many times each branch is executed and how many times it is
taken. When the compiled program exits it saves this data to a file
called auxname.da for each source file. 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.da
for input file dir/foo.c, or dir/foo.da for output file
specified as -o dir/foo.o).
For profile-directed block ordering, compile the program with
-fprofile-arcs plus optimization and code generation options,
generate the arc profile information by running the program on a
selected workload, and then compile the program again with the same
optimization and code generation options plus
-fbranch-probabilities (see Options that Control Optimization).
The other use of -fprofile-arcs is for use with gcov,
when it is used with the -ftest-coverage option.
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- Create data files for the gcov code-coverage utility
(see gcov—a Test Coverage Program). See
-fprofile-arcs option above for a description of auxname.
- auxname
.bb - A mapping from basic blocks to line numbers, which gcov uses to
associate basic block execution counts with line numbers.
- auxname
.bbg - A list of all arcs in the program flow graph. This allows gcov
to reconstruct the program flow graph, so that it can compute all basic
block and arc execution counts from the information in the
auxname.da file.
Use -ftest-coverage with -fprofile-arcs; the latter
option adds instrumentation to the program, which then writes
execution counts to another data file:
- auxname
.da - Runtime arc execution counts, used in conjunction with the arc
information in the file auxname.bbg.
Coverage data will map better to the source files if
-ftest-coverage is used without optimization.
-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.00.rtl or foo.01.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.14.bp.
- B
- Dump after block reordering, to file.32.bbro.
- c
- Dump after instruction combination, to the file file.19.combine.
- C
- Dump after the first if conversion, to the file file.15.ce1.
- d
- Dump after delayed branch scheduling, to file.34.dbr.
- D
- Dump all macro definitions, at the end of preprocessing, in addition to
normal output.
- e
- Dump after SSA optimizations, to file.04.ssa and
file.07.ussa.
- E
- Dump after the second if conversion, to file.29.ce3.
- f
- Dump after life analysis, to file.18.life.
- F
- Dump after purging
ADDRESSOF codes, to file.10.addressof.
- g
- Dump after global register allocation, to file.24.greg.
- h
- Dump after finalization of EH handling code, to file.02.eh.
- k
- Dump after reg-to-stack conversion, to file.31.stack.
- o
- Dump after post-reload optimizations, to file.25.postreload.
- G
- Dump after GCSE, to file.11.gcse.
- i
- Dump after sibling call optimizations, to file.01.sibling.
- j
- Dump after the first jump optimization, to file.03.jump.
- k
- Dump after conversion from registers to stack, to file.31.stack.
- l
- Dump after local register allocation, to file.23.lreg.
- L
- Dump after loop optimization, to file.12.loop.
- M
- Dump after performing the machine dependent reorganization pass, to
file.33.mach.
- n
- Dump after register renumbering, to file.28.rnreg.
- N
- Dump after the register move pass, to file.21.regmove.
- r
- Dump after RTL generation, to file.00.rtl.
- R
- Dump after the second scheduling pass, to file.30.sched2.
- s
- Dump after CSE (including the jump optimization that sometimes follows
CSE), to file.09.cse.
- S
- Dump after the first scheduling pass, to file.22.sched.
- t
- Dump after the second CSE pass (including the jump optimization that
sometimes follows CSE), to file.17.cse2.
- u
- Dump after null pointer elimination pass to file.08.null.
- w
- Dump after the second flow pass, to file.26.flow2.
- X
- Dump after SSA dead code elimination, to file.06.ssadce.
- z
- Dump after the peephole pass, to file.27.peephole2.
- a
- Produce all the dumps listed above.
- 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.00.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.
-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.
-fsave-repository=location- Creates separate symbol repository at location for given input
header file. Separate repository contains only debugging symbols in
stabs format.
-grepository- Instructs compiler to use separate symbol repository with debugging
symbols. Compiler searches for such repositories in include paths.
-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.